Regular Friday tea meetings & Other talks

October 2017:

October 27: TBD - Rebecca Davies

October 20: TBDMing-Yi Lin

October 13:   Kinematic and structural evolution of star-forming galaxies at 1.4≤z≤3.8 with MOSDEF & CANDELS  - Dr. Sedona Price

I will present preliminary results on the kinematics and masses of star-forming galaxies at “cosmic noon” (z~1.5-3) using the MOSDEF (MOSFIRE Deep Evolution Field) Survey. Using the MOSDEF observations together with CANDELS imaging and multiband photometry, we examine how masses, structures, and inferred dark matter fractions vary across the galaxy population and over time.     

October 6: No Talk

September 2017:

September 29:  Flame: A Flexible Data Reduction Pipeline for Near-Infrared and Optical Spectroscopy - Dr. Sirio Belli

Flame is a pipeline for reducing spectroscopic observations obtained with multi-slit near-infrared and optical instruments. Because of its flexible design, Flame can be easily applied to data obtained with a wide variety of spectrographs. I will illustrate the pipeline by showing an example of data reduction for a near-infrared instrument (LUCI at the Large Binocular Telescope) and an optical one (LRIS at the Keck telescope).

 September 22: SHINING: A Survey of Far-Infrared Fine-Structure Lines, from Resolved Star-Forming Galaxies and Active Galactic Nuclei to Ultraluminous Infrared Galaxies - Dr. Rodrigo Herrera-Camus


July 2017:

July 14: No Talk - Start of Summer Break

July 7: Dusty spirals triggered by shadows in protoplanetary disks - Dr. Nicolás Cuello (PUC)

Spirals waves form in protoplanetary disks (PPDs) around young stars due to different physical mechanisms: planet torques, gravitational perturbations and illumination effects. Although recent near-infrared and sub-millimetric observations revealed astonishing spiral-shaped features in PPDs, there is an active discussion to understand how they formed. Regardless of their origin, spirals are characterized by a local increase in pressure, which translates into radial and azimuthal asymmetries in the gas and in the dust distribution. In this work, we focus on the spirals formed in the gaseous phase due to shadows cast at fixed disk locations, as in Montesinos et al. 2016. During this talk, we will discuss how these spirals affect dust dynamics and planet formation in the disk. Also, we will show what are the observational signatures of the dusty spirals obtained. Finally, we will show how ALMA could observe them at millimetric wavelengths.

June 2017:

June 30: Twelve years of spectroscopic monitoring in the Galactic Center: the closest look at S-stars near the black hole - Dr. Mariam Habibi

I will present our study of young S-stars wiythin a distance of 0.04 pc from the supermassive black hole in the center of our Galaxy. Given how inhospitable the region is for star formation, their presence is more puzzling the younger we estimate their ages. By co-adding the result of 12 years (2004-2016) of high resolution spectroscopy within the central arcsecond, we have obtained high signal to noise H- and K-band spectra of eight stars orbiting the central supermassive black hole. Using deep H-band spectra, we show that these stars must be high surface gravity (dwarf) stars. We compare these deep spectra to detailed model atmospheres to infer the stellar parameters. The inferred masses lie within 8--14$M_\odot$. We derive an age of $6.6^{+3.4 }_{-4.7}$ Myr for the star S2, which is compatible with the age of the clockwise rotating young stellar disk in the GC. We estimate the age of all other studied S-stars to be less than 15 Myr, which are compatible with the age of S2 within the uncertainties. The relatively low ages for all S-stars we have investigated favor a scenario in which the stars formed in a local disk rather than the field-binary-disruption scenario throughout a longer period of time.


June 23: No talk

June 16: Holiday

June 9: Update on Outflows Projects - Dr. Eckhard Sturm

June 2: The Physical State of the Cold Gas and Star Formation Process in Nearby Galaxies - Dr. Andreas Schruba

A key challenge for current star formation studies is to link the detailed view of the star formation process within individual Galactic molecular clouds to the kpc-scale and galaxy-wide trends described by extragalactic work. I will highlight recent progress in observing the cold gas in nearby galaxies, focussing on new results from large programs at millimeter and radio wavelengths to observe the overall atomic and molecular gas reservoir in galaxies at cloud-scale resolution, and to probe the gas at higher densities with multi-line spectroscopy. The picture that emerges from these studies is that the conversion of cold gas into young stars depends on galactic environment: gas at a particular density does not appear to form stars in a universal way.

May 2017:

May 26: Impact of Faraday effects on polarisation  - Alejandra Jimenez Rosales

At the centre of our galaxy lies a supermassive black hole, Sagittarius A* (Sgr A*). Mm-VLBI observations made with the Event Horizon Telescope (EHT) have spatially resolved a linear polarisation fraction (LPF).
The present work studies the impact of Faraday effects (rotation and conversion) on the measured LPF. Considering a model with accretion from a magnetised disk onto a black hole, we post-process GRMHD simulations tied to the observed sub-millimetre flux observed in Sgr A* and perform a fully relativistic radiative transfer calculation of the emitted synchrotron radiation. We obtain polarised images and, by comparing the scrambled vs. the coherent, we characterise their degree of change, which we call the ‘correlation length’ of the image. We show how measurements of the polarised correlation length could constrain the strength of these effects, and, consequentially, plasma properties like electron temperature and magnetic energy fraction

May 19: JWST-MIRI: getting ready for launch - Dr. Ewine van Dishoeck

This talk will give a brief overview of the JWST project and the MIRI instrument in particular. Preparations for GTO, GO and Early Release Science (ERS) science are in full swing and galactic science plans will be discussed.

May 12: KMOS-3D reveals Halpha emission in high-redshift quiescent galaxies  - Dr. Sirio Belli

I will present a study of emission lines in the quiescent galaxies targeted by the KMOS-3D survey. We detect line emission in about 20% of the 120 quiescent galaxies observed. Nine of these objects have low [NII]/Halpha ratio, consistent with low-level star formation activity. The presence of satellites and the low inferred gas metallicity suggest that these quiescent galaxies are accreting fresh gas from minor mergers or gas inflows. Finally, by analizing the spatially resolved emission lines we find evidence for rotation in about half of the nine targets. This rare population represents an important link between gas-poor quiescent galaxies and their progenitors, the star-forming massive disks.

May 5:
How the role of environment in fuelling AGN depends on the host galaxy  - Dr. Ric Davies

I will show that the fraction of local AGN in S0 hosts decreases strongly as a function of galaxy group size or halo mass; but that this is not the case for AGN in spiral hosts (which, because most AGN are found in spiral galaxies, dilutes the signature of environmental dependence for the population as a whole). The difference is due to the source of gas and so should also impact the AGN luminosity function, duty cycle, and obscuration. Indeed, there is a significant difference in the luminosity function for AGN in spiral and S0 galaxies, and tentative evidence for some difference in the fraction of obscured AGN. 

April 2017:

April 28: The detection of Sgr A* in the far infrared HERSCHEL/PACS 2012 March Campaign - Sebastiano von Fellenberg

Following a dedicated reduction process, a significant increase of flux could be measured during one night in March 2012. I will present the reduction steps necessary to remove artifacts and systematics present in the standard pipeline product. 

April 21: 
Gas dynamics and extended x-ray emission from the Galactic Centre - Dr. Jorge Cuadra (PUC)

Abstract: I will present numerical models of the gas dynamics in the inner parsec of the Galactic centre. We follow the gas from its origin as stellar winds of around 30 observed young massive stars, until it is either captured by the central black hole, or leaves the region. I will show how comparing the simulations with recent Chandra observations  confirms the origin of the gas in stellar winds, and constrains the properties of Sgr A* outflows during the last few hundred years.

April 14: Holiday

April 7: No talk

March 2017:

March 24: Spatially resolved star formation at z=1: molecular gas & stars - Magdalena Lippa

Cosmic star formation went through a peak close to redshift z=1 and since then has been decreasing. While there are many observational studies which analyze the ionized gas in star-forming galaxies in great detail at this epoch, spatially resolved molecular studies are still rather rare. In the work presented here I perform a respective analysis on sub-galactic scales looking at the main players of star formation: molecular gas and stars. The sample of five massive star-forming galaxies taken from the PHIBSS surveys shows clumpy morphologies in both these components. The light of the bulk stellar component in the centers of galaxies retrieved from SED fitting of rest-frame UV/optical photometry is highly extincted. Bright clumps off these centers show star-forming regions with comparably low visual extinction. These are findings already reported in literature. But what abou the gas? Imaging spectroscopy performed by the IRAM interferometer reveals that the molecular gas is rotating and turbulent at the same time as already shown for the ionized gas at similar redshifts. Dynamical modeling can help to get a handle on intrinsic properties measured by the kinematics such as dynamical mass and intrinsic velocity dispersion. However, constraining the various parameters of such models, especially galaxy orientation, can be a science on its own. For this reason I would like to share and discuss my findings with you.

March 17: Infalling clouds onto massive black hole binaries - Felipe Garrido (PUC)

Gas accretion is thought to be important for the dynamical evolution of massive black hole binaries, although the mechanisms that drive material to the galactic nuclei are poorly constrained. One plausible source of the gaseous fuel is clumps of gas formed due to turbulence and gravitational instabilities in the interstellar medium that later fall towards and interact with the binary. In this context, I present a suite of SPH simulations to study the evolution of turbulent gas clouds as they infall towards equal-mass, circular MBH binaries. I study the formation of gaseous structures and their dynamics, as well as the the feeding rate onto the MBHs depending on the different configurations, and show that some of the variabilities can have implications in the observability of these systems. I additionally study the dynamical evolution of the binary orbit during the interaction with different clouds and show that is dominated by the exchange of angular momentum through gas accretion during the first stages of the interaction for all orbital configurations. Building on these results, I construct a simple model for evolving a MBHB interacting with a sequence of clouds, which are randomly drawn from reasonable populations with different levels of anisotropy. In this scenario the binary efficiently evolves down to the gravitational wave regime, overcoming the "final parsec".

March 10: The Evolution of the Tully-Fisher Relation between z~2.3 and z~0.9 with KMOS^3D - Hannah Übler

We investigate the stellar mass and baryonic mass Tully-Fisher relations (TFRs) of massive star-forming disk galaxies at redshift z~2.3 and z~0.9 as part of the KMOS^3D integral field spectroscopy survey. Our spatially resolved data allow reliable modelling of individual galaxies, including the effect of pressure support on the inferred gravitational potential. At fixed circular velocity, we find higher baryonic masses and similar stellar masses at z~2.3 as compared to z~0.9. Together with the decreasing gas-to-stellar mass ratios with decreasing redshift, this implies that the contribution of dark matter to the dynamical mass at the galaxy scale increases towards lower redshift. A comparison to local relations reveals a negative evolution of the stellar and baryonic TFR zero-points from z=0 to z~0.9, but a positive evolution of the baryonic TFR zero-point from z~0.9 to z~2.3. We discuss a toy model of disk galaxy evolution to explain the observed, non-monotonic TFR evolution, taking into account the empirically motivated redshift dependencies of galactic gas fractions, and of the relative amount of baryons to dark matter on the galaxy and halo scales.


March 3: CN Fluxes and Rings in Plotoplanetary Rings - Paolo Cazzoletti

The bright emission of the CN molecule has been readily  observed in protoplanetary disk in the last 20 years with single dish observations. With the advent of modern interferometers, we are now able  to spatially resolve CN emission, which often shows ring-like structures. We investigate if such structures are due to the morphology  of the disk itself or if they are instead an intrinsic feature of the  emission of CN. With the help of the 2D thermochemical code DALI, we run  a set of disk models for different stellar spectra, masses and physical structures, and by using a chemical network accounting for the most  relevant CN reactions. We find that ring-shaped emission is a common feature of all the models we adopted: the highest abundance is found in the outer regions, the column density always peaks at 50-70 AU, and the  emission profile follows the column density. Higher mass disks therefore generally show brighter CN. We also find a strong dependence of the ring
brightness and location on the UV field, and in general that higher UV fluxes on the disk result in brighter and larger rings. This is for example what happens when the UV radiation impinging on the disk increases because of a higher disk flaring. These trends are due to the fact that the main path for the formation of CN relies on the existence in the disk of excited H2* molecules, which is formed through FUV pumping of the H2 molecules. The strong bond between FUV flux and CN emission and morphology could therefore provide critical information on the physical structure of the disk and on the distribution of dust grains (which affects the UV penetration), and could help to break some degeneracies in the SED fitting. Recent observations of other PDR tracers such as C2H and C3H2 also show a ring-shaped emission which is likely related to dust settling and to C and O depletion. A comparison between these molecules and CN will be made.

Febuary 2017:

February 24: The on-sky performance of the CIAO wavefront sensors and implications for GRAVITY performance - Dr. Casey Deen

I will give a brief overview of the CIAO wavefront sensors which currently inhabit the Coudé rooms of the Unit Telescopes on Cerro Paranal.  I will discuss the results of the commissioning activities for the CIAO units, standalone performance on sky, and the performance of GRAVITY when fed by CIAO.

February 17: Sub-milliarcsecond Optical Interferometry of HMXBs with VLTI/GRAVITY: The cases of BP Cru and SS 433 - Idel Waisberg

GRAVITY has opened a new window in the study of High-mass X-ray Binary (HMXB) systems by allowing spectral differential interferometry at high resolution for fainter targets. In this talk, I will present the results for two of these systems: BP Cru and SS 433. The first one consists of a slowly-rotating neutron star accreting from its blue hypergiant companion. Interferometry shows evidence for a distorted stellar wind and a long-predicted accretion stream. The second one consists of a compact object (most likely a black hole) accreting super-critically from its companion, with super-Eddington outflow in the form of accretion disk winds and collimated relativistic jets that show remarkable optical line emission. GRAVITY has allowed to spatially resolve the optical jet lines in this system for the first time, as well as the circumstellar wind environment probed by the stationary lines. I will conclude with the potential of upcoming multi-instrument observation plans for these objects.

February 10: A Massive Binary System can Feed Sgr A* - Diego Calderón (PUC, Chile)

The enigmatic G2 cloud just passed pericentre around the Galactic Centre super-massive black hole, Sgr A*. Despite all theoretical and observational efforts, its nature remains unclear. If purely gaseous, it is possible to explain it as a gas clump formed in a colliding wind binary. Here we study the hypothesis of G2 being one of such clumps ejected from the massive binary IRS 16SW. 

February 3: The interplay between dust and gas in protoplanetary disks - Dr. Stefano Facchini

The high sensitivity and angular resolution of ALMA are providing new insights on the typical properties of protoplanetary disks. A key parameter governing the secular evolution of disks is their outer radius. Interestingly, ALMA observations confirm earlier indications that there is a clear difference between the dust and gas radial extents. The origin of this difference is still debated, with both radial drift of the dust and optical depth effects suggested in the literature. In thermo-chemical models of protoplanetary disks, the dust properties are usually prescribed by simple parametrisations. In this work, the feedback of more realistic dust particle distributions onto the gas chemistry and molecular emissivity is investigated, with a particular focus on CO isotopologues. We take into account how dust surface area and density influence the disk thermal structure, molecular abundances and excitation. We show that the difference of dust and gas radial sizes is largely due to differences in the optical depth of CO lines and millimeter continuum, without the need to invoke radial drift. The effect of radial drift is primarily visible in the sharp outer edge of the continuum intensity profile. The gas outer radius probed by 12CO emission can easily differ by a factor of 2 between the models for a turbulent α ranging between typical values, with the ratio of the CO and mm radius increasing with turbulence. Grain growth and settling concur in thermally decoupling the gas and dust components, due to the low collision rate with large grains. As a result, the gas can be much colder than the dust at intermediate heights, reducing the CO excitation and emission, especially for low turbulence values. Interestingly, the low thermal coupling is expected to arise also in the dust cavity of large transition disks, or in the dust gaps recently observed at high angular resolution. A proper treatment of the thermal structure is fundamental to infer the properties of the purported planets invoked in some of these systems.

January 2017

January 27: Canceled - Dr. Annemieke Janssen

January 20: No Talk

January 13: The Post-Pericenter Evolution of G2 - Philipp Plewa 

We report on the evolution of G2 in the immediate aftermath of its recent pericenter passage, revealed by deep observations obtained in 2015 and 2016 using SINFONI and NACO at the VLT. Putting these new data sets in the context of our previous observations allows us to draw the most comprehensive picture of G2 to date and establish a number of key observational facts. On this basis we discuss the unique opportunity of using G2 as a probe of the inner accretion zone around Sgr A*, as well as implications for the nature, origin and fate of G2. 

January 6: No talk - Winter break

December 2016

December 23 & 30: No talk - Winter break

December 16: An Update on Monitoring Stellar Orbits in the Galactic Center - Dr. Stefan Gillessen 

Using 25 years of data from uninterrupted monitoring of stellar orbits in the Galactic Center, we present an update of the main results from this unique data set: A measurement of mass of and distance to Sgr A*. Our progress is not only due to the eight year increase in time base, but also due to the improved definition of the coordinate system. The star S2 continues to yield the best constraints on the mass of and distance to Sgr A*; the statistical errors of 0.13×10^6 M_sun and 0.12 kpc have halved compared to the previous study. The S2 orbit fit is robust and does not need any prior information. Using coordinate system priors, also the star S1 yields tight constraints on mass and distance. For a combined orbit fit, we use 17 stars, which yields our current best estimates for mass and distance: M = 4.28±0.10|stat. ±0.21|sys ×106 M_sun and R0 = 8.32±0.07|stat. ±0.14|sys kpc. These numbers are in agreement with the recent determination of R0 from the statistical cluster parallax. The positions of the mass, of the near-infrared flares from Sgr A* and of the radio source Sgr A* agree to within 1 mas. In total, we have determined orbits for 40 stars so far, a sample which consists of 32 stars with randomly oriented orbits and a thermal eccentricity distribution, plus eight stars for which we can explicitly show that they are members of the clockwise disk of young stars, and which have lower eccentricity orbits.

December 16: No talk

December 2:   The Spatial Distribution of Star Formation in Galaxies: Observing the Emergence of Galactic structure   Dr. Erica Nelson 

Imaging surveys with HST and kinematic surveys with KMOS have demonstrated that the structure of many galaxies is emerging at z~1. Key to understanding this process is a high resolution measurement of the distribution of star formation within galaxies. In this talk, I will describe my PhD thesis work studying the emergence of galactic structure using the spatial distribution of star formation in galaxies. This work uses WFC3 grism capability on HST which provides Hα maps of all galaxies at 0.7<z<1.5 in its field of view. Using Hα maps for 2676 galaxies, I will show where star formation is distributed in galaxies across the star formation - mass plane (the main sequence) placing constraints on both the mechanisms for enhancing and quenching star formation as well as on how the structure of galaxies is built.

November 2016

November 25:  The Connection Between Star Formation and AGN Activity in the Local Universe - Dr. Taro Shimizu 

Most theoretical models and cosmological simulations rely on some form of AGN feedback to slow or stop star formation in massive  galaxies and reproduce the local stellar mass function. I will present my work focusing on a Herschel survey of a relatively unbiased sample of  AGN at z~0 where I measured the star-forming properties using the  far-infrared SED. I find that while a comparison to a mass-matched sample of non-AGN galaxies indicates higher SFRs, AGN host galaxies seem to prefer a region on the SFR-stellar mass diagram in transition between the star-forming and quenched populations. I will further discuss the differences between Type 1 and Type 2 AGN and our recent VLA 22 GHz survey to try and spatially resolve the circumnuclear star formation and test the FIR-radio correlation.

November 18: Advanced Deconvolution of SINFONI Spectral Data Cubes   -  Stefan Schmalzl 

I present advanced techniques for spectral image deconvolution conducted in my master thesis. I worked on a deconvolution approach called Myopic deconvolution which tries to approximate the object as well as the PSF simultaneously. The focus lies on a mathematical formulation via linear algebra, embedded in a Maximum Likelihood or Maximum a Posteriori framework with different priors on the object and the PSF. As a result, deconvolution becomes an optimization problem which could be evaluated by a very efficient scaled gradient projection method. 

November 11: No Tea talk

November 4: No Tea Talk - Ringberg Galaxy Evolution Meeting

October 2016

October 28: ASTE CO(3-2) survey for nearby merging galaxies & ALMA band 3 line survey towards late stage merging galaxy NGC3256 - Tomonari Michiyama (NAOJ, SOKENDAI)

I review the Michiyama et al. 2016 (, which investigate the relation between the CO(3–2) luminosity and the far Infrared luminosity a sample of 29 early stage and 31 late stage merging galaxies, and 28 nearby isolated spiral galaxies. We find that normal isolated spiral galaxies and merging galaxies have different slopes (α) in the log ′CO(3−2)-logLFIR plane (α ∼ 0.79 for spirals and ∼ 1.12 for mergers). Comparing our results with sub-kpc scale local star formation and global star-burst activity in the high-z Universe, we find deviations from the linear relationship in the logL′CO(3−2)-logLFIR plane for the late stage mergers and high-z star forming galaxies. 

If I have time, I quickly introduce our recent  ALMA Cycle 3 results of molecular line survey towards a late stage merging galaxy NGC3256. We have detected 24 molecules at 2” angular resolution, which is high enough to resolve the double nuclei.

October 21: Pulse Profiles from Spinning Neutron Stars - Dr. Michael Bauböck

I will discuss efforts to model pulse profiles arising from hotspots on spinning neutron stars. These pulse profiles provide one of the most promising avenues for measuring neutron-star properties and constraining the equation of state of cold nuclear matter. I will describe current and future work to understand the physical effects that influence pulse profile shapes.  

October 14: Gaussian Processes for Bayesian Parameter Estimation - Philipp Plewa

Noise matters but is never known exactly, so we have to model it. In this whiteboard talk I will introduce the fundamentals of Gaussian Processes, which make it possible to model real world (correlated) noise in many situations.

October 7: The Kinematics of High-Redshift Quiescent Galaxies - Dr. Sirio Belli

I will present the recent results of a deep spectroscopic survey of quiescent galaxies at 1 < z < 2.5 carried out at Keck using the LRIS and MOSFIRE instruments. I will discuss the galaxy kinematics focusing in particular on the importance of rotational support for early quiescent galaxies, and the implications for galaxy evolution models.


Summer Break - No talks

July 2016

July 29: No talk - Start of Summer Break

July 22: A brief description of new results on the dynamics and chemistry of galactic and extragalactic ISM - Dr. Thomas Bisbas

In this tea talk I will present results of four different on-going projects examining the dynamics and chemistry of ISM. I will discuss about the role played by cosmic rays in tracing H2 gas in galaxies and I will show new 3D simulations of how CO is effectively converted to CI and CII by increasing the cosmic-ray ionization rate while the H2 molecule remains unaffected. I will present newly published ACA observations of NGC253 comparing CO(1-0) versus CI(1-0) ratio emissions and how they compare with the corresponding Milky Way values. I will further go through an extended study of CII emission from different environments and try to tackle the long standing question "where does your CII emission come from?". Finally I will show results of the StarBench code-comparison project on expanding HII regions and I will present a new analytical equation that describes the entire D-type phase with an error of less than 1% at all times when compared to high-resolution simulations. 

July 15: Mrk 231: The Nearest Laboratory to Study Quasar Feedback in Action, Slim Accretion Disks, but not Binary Black Holes - Prof. Sylvain Veilleux (University of Maryland) 

At a distance of only 178 Mpc, Mrk 231 is the nearest quasar known. In recent years, Mrk 231 has become the archetype of galactic-scale quasar-driven winds. These outflow events are purported to self-regulate the growth of the black hole (BH) and spheroidal component of the galaxy and explain the relatively tight BH-spheroid mass relation. In this presentation, I will first summarize the latest evidence for quasar feedback in action in this system. Next, I will present new ultraviolet HST spectra suggesting that Mrk 231 is also the nearest example of weak-lined "wind-dominated" quasars with high Eddington ratios and geometrically thick ("slim") accretion disks. I will argue that these data are inconsistent with the recently proposed binary black hole model. 

July 8: No talk

July 1: No talk - Fachbeirat

June 2016

June 24:  Structure and Evolution of Protoplanetary Disks - Paolo Cazzoletti

A large diversity of exoplanetary systems has been found, but it is still unclear what drives this diversity. Planets are formed in disks around young stars, but the sensitivity and resolution of pre-ALMA data have allowed only a handful of disks to be characterized, usually only in the dust. ALMA has opened up the possibility to survey hundreds of disks in both the gas and dust, and to also spatially resolve them. From initial ALMA surveys (e.g. in the Lupus cloud), it is already clear that gas and dust have very different distributions and also evolve differently. Morphologies also depend on the tracer: CO generally shows smooth distributions, CN shows ring-like structures and dust emission often shows very asymmetric structures. During my PhD I will focus on the different gas and dust structures, looking for possible connections and common origins. I worked on the modelling of CN emission, showing that a ring-like emission is an intrinsic feature of this molecule. In addition to this, I worked on ALMA Band 7 data of the HD135344B system, looking for a connection between the spiral arms observed in scattered light and the mm-sized dust distribution.

June 17: Practice Talks - New seminar room 

June 10: Evidence for a large trans-Kuiper-Belt planet? - Dr. Thomas Müller  

Computer simulations and observations of distant objects in our solar system indicate the presence of another, so far undiscovered planet.  I'll present a closer look at the trans-Neptunian region, the indications for a gravitational influence of planet IX, and possibilities to find it (or not). 

June 3: A single HII region model of strong interstellar scattering towards the Galactic Center - Egid Sicheneder

Free electrons along the line of sight broaden the radio image of Sgr A*. For a long time, this strong interstellar scattering was thought to be local to the Galactic Center, explaining the absence of pulsars (Cordes+2002). The observation of radio pulses from a recently detected magnetar near Sgr A* contradicts this explanation (Spitler+2014). We show that a single HII region 1.5-3.5 kpc away from Earth, with ne ~ 100-200 cm-3, R ~ 3-5 pc, can explain the observed angular broadening and pulse time delay. For a magnetic field strength of 10-45 μG, the rotation measure, previously thought to come from hot gas in the Galactic center, can instead originate in a cloud along the line of sight. Furthermore, we predict that sources within ~10 pc should be scattered by this HII region, while other known GC pulsars at larger separations > 20 pc should not.

May 2016

May 27: No talk

May 20: Thick Disks, and an Outflow, of Dense Gas in the Nuclei of Nearby Seyfert Galaxies - Ming-Yi Lin

We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report arcsec resolution observations of HCN(1-0) and HCO+(1-0) for 3 objects. In NGC3079 the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H13CN reveals the continuum absorption profile, with a peak close to the galaxy’s systemic velocity that traces disk rotation, and a second feature with a blue wing extending to −350 km/s that most likely traces a nuclear outflow. The morphological and spectral properties of the emission lines allow us to constrain the dense gas dynamics. We combine our kinematic analysis for these 3 objects, with a previous comparable analysis of 4 other objects, to create a sample of 8 Seyferts. In 7 of these, the emission line kinematics imply thick disk structures on radial scales of ~100 pc, suggesting such structures are a common occurrence. We find a relation between the circumnuclear L_HCN and M_dyn that can be explained by a gas fraction of 10% and a conversion factor αHCN ~ 10 between gas mass and HCN luminosity. Finally, adopting a different perspective to probe the physical properties of the gas around AGN, we report on an analysis of molecular line ratios which indicates that the clouds in this region are not self-gravitating.

May 13: Science discussion with Prof. C. Martin (Caltech)

May 6: No talk

April 2016

April 29:  The ISM at High Resolution in Local Galaxies - Dr. Andreas Schruba

State-of-the-art instruments like, ALMA, NOEMA, JVLA, and VLT/MUSE are revolutionizing our view on the ISM structure and star formation process in nearby galaxies. I will showcase  our ongoing observational efforts to obtain high physical resolution mapping and sensitive spectroscopy across the nearby galaxy population. These observations supersede previous single-dish surveys by more than an order of magnitude in resolution and sensitivity and allow for the first time to systematically study the physical state of the ISM, its dependence on local environments, and influence on the star formation process at the scales of individual molecular clouds. We see a strong dependence of the cloud-scale ISM properties (surface density, turbulent line width, and apparent gravitational boundedness) on environment. New, sensitive spectroscopy of faint high dipole moment lines (HCN, HCO+, HNC, CS) across large areas also reveals strong, physically driven dependences of gas density on environment. Finally, these changing physical conditions seem to define the ability of the gas to form stars. I will highlight our efforts to extract the underlying physical drivers for the variations and showcase how these provide stringent tests for theories of star formation.

April 22:  Blue Compact Dwarf Galaxies (BCDs): Can of Worms or Pandora Box - Dr. Vanessa Doublier Pritchard 

First a quick reminder: BCDs are star busting dwarf galaxies: i.e. they are:1- low mass (DM haloes < 10^9.5 Msol) 2- very gas rich (Mstar/Mgas< 0.1) 3- the champion of star formation rate "efficiencies" (10^-10 < sSFR < 10^-8/yr, as a comparison current sSFR for Arp 220 is ~2x10^-8 /yr), 4- they still manage to appear as young" with z<20% solar, 5- very low dust content, BUT very bright PDRs finally 6- always a significant fraction of the stellar mass made of pre- (or very soon  after post-) re-ionisation stars. But, lets face it, these Blue Compact Dwarf galaxies are either  ignored/dismissed or making astronomers/physicists' life very hard when one gives it a go at understanding their properties in details. They  don't behave like normal galaxies: they refuse to be "too small to not  fail" re-ionisation shutdown, make a mess of fundamental relations and refuse to be either young or old. In this small talk, I will mostly lay down some questions and propose  some leads to answer them. I will focus on metallicity and why the  fundamental importance of this observable needs to be assessed, on dust-molecular gas contents and why this is a quick-sand subject and finally address some troubling matters about modelisations both at large scales and at small scales. Finally, I will stress and hope to impress  upon the real need to bridge a gap between extra-galactic and galactic  research to tackle the faint/low-mass end of the galaxy luminosity/mass distribution.

April 15: No talk

April 8:   Tracing high-z galaxy kinematics from turbulent disks to quenched spheroids .- Dr. Emily Wisnioski 

The representative selection and depth of the KMOS3D Survey, an integral field survey of over 600 galaxies at z=0.7-2.7 using KMOS at the VLT, has allowed us to study in unprecedented detail rare galaxies at z>1 that may be in the process of quenching. The short timescales associated with the quenching process make it difficult to catch galaxies in the act of shutting down their star formation. Compact star-forming galaxies, making-up ~7% of our sample, are selected to have properties aligned with already quenched galaxies at the same or lower redshifts, e.g. stellar mass, density, and sizes, but forming stars at rates 2-10x higher. We measure resolved kinematics of ~30 of these galaxies within the KMOS3D survey. Our results - the first resolved spectral data of such objects - show that compact star-forming galaxies are rotationally-dominated systems, providing strong evidence that recently quenched galaxies at these epochs are likely to be "fast rotators". The majority of compact star-forming galaxies show evidence that they host an active galactic nuclei indicative of secular quenching processes.

April 1:   Lifecycle of interstellar grains in numerical simulations of GMC evolution .- Dr. Svitlana Zhukovska (MPA)

I will present a three-dimensional model of dust evolution based on numerical hydrodynamic simulations of the giant molecular clouds in a Milky Way-like galaxy. Our approach includes destruction by interstellar shocks and dust mass growth through gas-grain interactions in the ISM. The observed local trends of element abundances with density are used to constrain the model of dust growth. I will discuss the physical conditions under which most of dust mass grows, time spent by grains in various environments and dust lifetimes inferred from the modelling of dust evolution. I will also present the dust and gas column density maps derived from their final spatial distribution in the numerical simulations.

March 2016

March 25: Holiday

March 18: No talk

March 11: Falling outer rotation curves of star-forming galaxies at 0.7 < z < 2.6 probed with KMOS-3D and SINS/zc-SINF.   - Philipp Lang

The rotation curves of star-forming galaxies at high redshift are currently well probed in their inner parts through deep IFU kinematics, while their extended shapes reaching to the outer faint levels of the disk are still largely unconstrained. I will present the results of a project  examining the unexplored outer rotation curves of star-forming galaxies at high redshift, exploiting the deep H-alpha IFU kinematic data from the  SINS/zc-SINF and KMOS-3D surveys. Through stacking the signal of ~100 massive galaxies at 0.7 < z < 2.6, a representative rotation curve out to  several effective radii can be constrained. The stacked rotation curve exhibits a turnover with a significant decrease in rotation velocity in  the outer regions, significantly strengthening the tantalizing evidence previously hinted at in a handful only of individual disks among the sample with the deepest data. These results are in good agreement with recent studies demonstrating that star-forming disks at high redshift are strongly baryon-dominated; the steep falloff of the outer rotation curve further indicates a significant level of pressure support at large radii, with important implications on the outer disk structure of massive
high-redshift galaxies. 

March 4: Where is the torus? - Leonard Burtscher

Mid-IR interferometry at the VLTI has resolved parsec-scale dusty structures in about 30 AGNs by now. We know they are composed of two distinct components and in a few well-resolved cases the dominant component is seen to be elongated in the direction of the narrow-line region -- quite in contrast to what is expected for the torus of the unified scheme. In a recent study ( we systematically constrained the detectability and prevalence of elongations in the entire sample. Is polar elongated mid-IR emission the end of the simple torus picture?

February 2016

February 26:  ISM day (MPA)

February 19: No talk

February 12: SPIFFI upgrade - Liz George and Dominik Gräff 

In January our group upgraded the VLT-Instrument SPIFFI, which is part of SINFONI. We want to deliver you an insight into this upgrade by talking about our work on Paranal - about the things we wanted to change in SPIFFI and the things we actually changed; about problems that occurred while the upgrade and how we solved them; and finally about commissioning and the new performance of SPIFFI. 

February 5: ALMA reveals rapid formation of a dense core for massive galaxies at z~2 - Ken-ichi Tadaki

At z~2, massive quiescent galaxies are extremely compact with a dense core while the majority of star-forming galaxies have more extended stellar disks. Here, a simple question is how the dense core is formed. I will present high-resolution (0.16"~1.3kpc) ALMA observations at 870 um for 25 massive galaxies on the star formation main sequence at z~2, and compare the  spatial distribution of the rest-frame far-infrared emission with stellar mass maps derived from spatially resolved stellar population modeling. The high-resolution ALMA data reveal that the dust continuum emission is mostly radiated from single region close to the galaxy center and its half light radius is more compact by a factor of 2-3 than the rest-frame optical light and stellar component. The extremely compact starburst can build up a dense core within a few hundred Myr. We may be witnessing an evolutionary pathway from extended star-forming disks to compact galaxies.

January 2016

January 29: Broad [CII] and CO(1-0) line wings as tracers of molecular outflows - Annemieke Janssen

We study a sample of 22 local (z < 0.1) ULIRGs, of which 16 are known to have molecular outflows as traced by blue-shifted OH absorption (at 119 um). Most objects in the sample also have broad [CII] wings, and for these objects the FWHM of the [CII] component correlates well with the blue-shifted OH velocity. Moreover, the outflow masses derived from [CII] and OH 119 are similar. This means that one might use [CII] broad wings as a tracer of molecular outflows. We furthermore want to know whether there is an equally good correlation with CO(1-0). I will present the ALMA data we got on 4 objects in the sample, and discuss some difficulties with the data reduction / interpretation. 

January 22: Practical MCMC - Philipp Plewa

I will start by briefly introducing the basic principles of parameter estimation and model selection from a Bayesian perspective. Then I will explain step by step how to use two popular implementations of different MCMC algorithms (emcee and MultiNest) to solve one particular example problem.

January 15: Molecular Cloud Structure and the Star Formation Process at Low Metallicity - Andreas Schruba

Stars from in cold, dense clouds of molecular gas. However, our understanding of the physical processes that control molecular cloud and star formation remains limited, especially at low metallicity. I will present ALMA CO observations of the 1/5-solar metallicity Local Group dwarf galaxy NGC 6822 that resolve four star-forming complexes at 2 parsec resolution -- unprecedented for extragalactic observations. The CO-bright clumps are small and have a low filling factor across the galaxy but share similar properties as Galactic clouds of equal size except of somewhat lower CO surface brightness. These CO clumps exist inside larger atomic-molecular complexes with masses similar to Galactic giant molecular clouds. Using dust to trace H2, we infer CO-to-H2 conversion factors ~3 times Galactic but with strong variations tracking the region's evolutionary state. The SFR-to-H2 ratio of these regions is quite high (~1/100Myr) but models of cloud evolution suggest that this measurement is biased by our focus on visible star-forming regions and may be in agreement with typical global star formation efficiencies of ~1/0.5Gyr also found for other dwarf galaxies.

January 8: The first rotation curve for a quiescent galaxy at high redshift - Sirio Belli

While surveys like KMOS-3D are finally measuring the rotation for hundreds of gas-rich galaxies at high redshift, the kinematics of gas-poor quiescent galaxies are still largely unknown, because of the intrinsic difficulty in measuring spatially-resolved absorption lines. One way to obtain the required high signal-to-noise ratio and spatial resolution is by taking advantage of strong gravitational lensing. However, most lensed galaxies are star-forming, and it is extremely rare to find high-redshift quiescent galaxies that happen to be strongly lensed. I will present the discovery and observation of one such rare system: a massive quiescent galaxy at z=2.6 that is multiply imaged by a foreground cluster. We obtained near-infrared spectra using Keck and Magellan, and we measured a significant amount of rotation. This is the first such measurement at z>1, and has important implications for models of galaxy quenching and evolution.

December 2015

December 18: Proper motions outside of the Galactic Center - Tobias Fritz, University of Virginia

December 11: IR RETREAT

December 4: Spectral study of S-stars in the Galactic center - Maryam Habibi

The presence of young massive stars in the vicinity of the supermassive black hole, Sgr A*, is puzzling given how inhospitable the region is for star formation. I present the result of 11 years (2004-2015) of high resolution spectroscopy within the central arc second of the Galactic center. By coadding the 50-100 hours of spectra we have obtained high signal/noise (50-400) spectra in H- and K-band for a sample of 8 stars orbiting the central super massive black hole. We use these data to derive improved radial velocities and therefore improved 3d stellar orbits. Our deep spectra combined with model atmospheres can be used to constrain their stellar properties in order to investigate their true nature as massive stars.

November 2015

November 27: The impact of environment on the evolution of protoplanetary discs: external photoevaporation and tidal encounters - Stefano Facchini

There is observational evidence that the environment of star forming regions can significantly affect the evolution of protostellar and protoplanetary discs. On one hand, the energetic radiation permeating young associations can drive photoevaporative winds from the discs' outer regions. On the other hand, gravitational interactions between stars within the cluster are expected to strongly perturb and affect the discs. Firstly, I will show that new hydrodynamical models indicate that the mass loss rates due to photoevaporation are high enough to affect the global evolution of protoplanetary discs, and thus limit their planet formation potential, even in moderate environments. Secondly, I will show recent observations at multiple frequencies of the RW Aur system. This peculiar binary system is very likely undergoing a tidal encounter caused be the secondary star, and it is the best candidate up to date to test well known theoretical models of star-disc interactions. We will see that these interactions not only affect the large scale structure of discs, but can have a significant impact in shaping the properties of their inner regions.

November 20: Tracing H2 in galactic and extragalactic systems using CI as a proxy - Thomas Bisbas

Molecular hydrogen is the most fundamental species in the Universe making up ~70% of its total baryonic non-stellar mass. Owing to
its quantum mechanical properties however, H2 is not readily observable by radiotelescopes and CO has been widely used as its tracer. During the last 5 years there is a growing evidence that the `traditional' CO-to-H2 method may not be accurate or even applicable to extragalactic studies. In this talk we will discuss the utility of CI in tracing H2 in the Universe focusing on the newly discovered effect of CO-destruction due to cosmic rays. CI appears to be a powerful tracer for extragalactic studies and CI-to-H2 methods become popular in the community particularly since ALMA open its eyes. 

November 13: The ionized gas in nearby galaxies as traced by the [NII] 122 and 205 um transitions - Rodrigo Herrera-Camus

The [NII] 122 and 205 um transitions are powerful tracers of the ionized gas in the ISM: (1) the [NII] 122/205 line ratio can be used to measure the electron density of the low-excitation, ionized gas, and (2) the intensity of these lines is directly related to the flux of ionizing photons, probing the most recent star formation activity. The study of these applications in nearby galaxies is specially relevant now that ALMA can observe both [NII] transitions at z>2. In this talk I will present Herschel observations of these pair of [NII] far-infrared lines in 21 nearby galaxies selected from the KINGFISH and Beyond the Peak samples. I will discuss the reliability of the [NII] lines as star formation tracers, and how the electron density of the ionized gas is related to other relevant ISM properties (e.g., radiation field strength, star formation activity, dust temperature, etc).

A more detailed abstract can be found here:

November 6: no talk

October 2015

October 30: Molecular gas in distant cluster galaxies and Eddington-limited star formation in compact mergers. - Gregory Rudnick, University of Kansas

I will present updates on two projects.  
The first project involves extremely deep CO(1-0) observations of molecular gas in star-forming galaxies residing in a z=1.62 proto-cluster.  These galaxies are massive, have high gas fractions, and long gas consumption timescales and they lie off the Genzel+15 scaling relations.  They are also surprisingly compact, which may yield information about the stability of their molecular gas.  I will discuss these results, what role they might play in motivating blind CO surveys, and the implication for the future star formation history of these cluster galaxies.
I will also present results from a project focussing on compact galaxies at z~0.6 that appear in the optical as very blue post-starbursts.  These galaxies are driving very fast winds, with speeds of up to 2000 km/s and, surprisingly, appear to host highly obscured star formation that has sufficient energetics to drive large multi-phase outflows without the need for an AGN.  This star formation is nearly at the galaxy-wide Eddington-limited for star formation and may indicate the final blowout of these galaxies.  I will discuss the characteristics of this enigmatic population and our current efforts to understand them.

October 23: The FIR emitting region in local galaxies and QSOs: Size and scaling relations - Dieter Lutz

October 16: First Results From the IGRINS Infrared Spectrograph - Daniel Jaffe (University of Texas) and Casey Deen (MPIA)

IGRINS, the Immersion Grating Infrared Spectrograph has a resolving power of 40,000 and covers the entire H and K bands, 1.4-2.5 microns in a single exposure.
The instrument has no moving parts.  It has just completed its first year of observations on the McDonald Observatory 2.7m telescope. On the 2.7m, it has ~70% of the instantaneous S/N of CRIRES on the VLT while having 30 times the spectral grasp.  We report on some of the outstanding first year results in studies of young stellar objects, stars, and the interstellar medium.

October 9: The ionizing radiation in star-forming galaxies - Lisa Kewley, ANU

October 2: Implications of X-ray population studies for the torus geometry and the SMBH accretion history - Johannes Buchner, PUC, Chile

In my PhD at the high-energy group in MPE I have spent much effort developing a consistent Bayesian spectral analysis and luminosity function methodology that can robustly constrain AGN demographics while incorporating all sources of uncertainties. I will discuss results from such X-ray studies working on the demography of AGN: their space density, the fraction of obscured and Compton-thick AGN, their evolution with redshift and luminosity.
From the luminosity-dependence of the obscured fraction, and its evolution, we can draw strong conclusions on how the torus is maintained. I also discuss whether the discovered Compton-thick population (38+-7%) is sufficient to explain the locally determined SMBH density.

August-September 2015: summer break

July 2015

July 24: GMC Populations of Nearby Galaxies - Annie Hughes, Toulouse

The observed ~kpc scaling relations between molecular gas and star formation in galaxies must ultimately be due to highly localised star formation activity that is occurring within individual giant molecular clouds (GMCs). In this talk, I will summarise what we have learnt about the dynamical properties and evolution of GMCs from recent high resolution surveys of CO emission in nearby galaxies (M51, NGC628, LMC), which provide a unique view of the relationship between star-forming clouds and their host galaxy. I will also present some of our ongoing work to characterise the connection between molecular gas and star formation on cloud- to galactic scales in these systems.

July 17: CAS bbq - no talk

July 10: Establishing super- and sub-Chandrasekhar limiting mass white dwarfs to explain peculiar type Ia supernovae - Upasana Das, Indian Institute of Science

Type Ia supernovae (SNeIa), a key to unravel the evolutionary history of the universe, are extremely bright thermonuclear explosions. They are believed to be triggered in carbon-oxygen white dwarfs having mass close to their maximum possible value of about 1.44 solar mass, which is known as the famous Chandrasekhar limit. However, observations of several peculiar, highly over- and under-luminous SNeIa do not conform to this conventional picture and argue for exploding masses widely different from the Chandrasekhar limit. The over-luminous SNeIa seem to invoke super-Chandrasekhar white dwarf progenitors, having mass 2.1-2.8 solar mass. While, the under-luminous SNeIa seem to favor sub-Chandrasekhar explosion scenarios. In our venture to obtain a fundamental basis behind the formation of such super-Chandrasekhar white dwarfs, we have exploited the enormous potential of magnetic fields, which can affect the structure and properties of the underlying white dwarf in a variety of ways. We have progressed from a simplistic to more rigorous and self-consistent models. In this talk I will try to give a brief overview of our results, with emphasis on the latest results obtained from an extensive GRMHD numerical formulation, whereby we have constructed stable equilibrium models of strongly magnetized, static, non-spherical white dwarfs. Very interestingly, our study establishes that strongly magnetized white dwarfs can be significantly super-Chandrasekhar, having mass 1.7-3.4 solar mass, irrespective of the nature of origin of the underlying magnetic effect. On a different note, we have also explored the effect of modification to Einstein’s gravity in white dwarfs, for the first time in the literature to the best of our knowledge. I will try to briefly motivate how this can lead to significantly super- as well as sub-Chandrasekhar limiting mass white dwarfs, determined by a single model parameter. Explosions of these white dwarfs can explain both the peculiar, over- and under-luminous SNeIa respectively, thus unifying these two apparently disjoint sub-classes of SNeIa.

July 3: The HIX galaxy survey - How spirals accrete gas and form stars - Katharina Lutz, Swinburne

When comparing the gas content of galaxies with their current star formation rate, it has been found that the gas consumption time scale is much smaller than the age of galaxies. This discrepancy leads to the conclusion that galaxies need to replenish their gas reservoirs to sustain star formation. In order to investigate this process of gas replenishment in more detail we target galaxies that contain at least 2.5 times more atomic hydrogen (HI) than expected from their optical properties using scaling relations. For this set of galaxies, we are building a rich data set consisting of deep HI interferometry (Australia Telescope Compact Array), optical integral field spectroscopy (WiFeS spectrograph on the SSO 2.3m telescope), deep imaging (DECam) and publicly available photometry from GALEX (ultraviolet), WISE (infrared) and DSS-II (optical). This data set will enable us to distinguish between multiple scenarios that might lead to an excess in HI content, among them a phase of elevated gas accretion, minor mergers or an inefficient conversion of gas into stars. In a next step it allows us to investigate the respective scenario in more detail. In my talk I will first introduce the survey, then compare the HI excess galaxies to the general galaxy population with respect to star formation and stellar mass and finally present first results of the more detailed analysis of the ATCA HI data combined with the optical IFU spectroscopy.

June 2015

June 26: Where is Sgr A* (precisely) - Philipp Plewa

Near-infrared observations of stellar orbits at the Galactic Center provide conclusive evidence for a massive black hole associated with the compact radio source Sgr A*. In this talk I will explain how to construct a precise and stable (infrared) astrometric reference frame for these observations, in which (radio-)Sgr A* is localized to within a factor five better than previously. This improvement is mainly the result of modeling and correcting optical distortion in the NACO imager, but also other methods that unlock a new level of high-precision astrometry using our existing, decade-spanning data set. A further improvement will follow future observations and facilitate the detection of relativistic orbital effects. More immediately, we will be able to measure the orbits of even more stars and make refined estimates of the black hole’s mass and distance.

June 19: Obscuring gas and dust structures in nearby galactic nuclei - Marc Schartmann, Swinburne

A summary of our recent and ongoing work on the distribution of gas and dust in the nuclei of nearby galaxies will be given. 
I will focus on our latest work and present time-resolved images and spectral energy distributions (SEDs) of geometrically thick obscuring structures which are thought to enshroud the central engines of nearby Seyfert nuclei. The 3D dust continuum radiative transfer simulations are based on the radiation-driven dynamical model for the central obscurer by Wada (2012). When comparing the results to high spatial resolution SEDs as well as observed relations for nearby Seyfert galaxies, we find that a model which comprises of a clear three-component structure gives the best comparison with the data: a thin disc with spiral and filamentary high density features, a surrounding fluffy component (the obscurer) and a low density outflow along the rotation axis. Strong differences are found depending on wavelength: whereas the mid-infrared images are dominated by the elongated appearance of the outflow cone (reminiscent of recent interferometric observations), the long wavelength emission is mainly given by the cold and dense disc component. I will end my talk by giving a short outlook on our preliminary work on understanding the distribution and dynamics of gas and dust in a sample of nearby radio galaxies.

June 12: no talk

June 5: no talk

May 2015

May 29: ([CII]) intensity mapping - Dieter Lutz

Given a recent surge of papers discussing the potential of [CII] and CO intensity mapping of the high-z universe up to reionisation, I plan to give a journal-club like overview of those works.

May 22: no talk

May 15: A new view of the torus: a story of optical obscuration and x-ray absorption - Ric Davies

May 8: no talk

May 1: holiday

April 2015

April 24: The Nature of [CII] emission in Lensed Dusty Star-forming Galaxies from the SPT survey - Bitten Gullberg, ESO

ALMA spectroscopy (cycle 0 and 1) of point sources from the South Pole Telescope survey has uncovered a population of high-redshift (z = 2-5.7), strongly lensed dusty star-forming galaxies (DSFGs). This has resulted in an unbiased redshift distribution for DSFGs peaking for z~3.5, i.e. higher than previously believed of z~2.5, and doubled the number of sources at z > 4. In this talk I will present the latest result from our fine-structure line survey of 20 DSFGs. Comparing [CII] velocity profiles (APEX and Herschel) with CO velocity profiles from ALMA reveals consistent velocity profiles, suggesting little differential lensing between these species. 
Combining the [CII] detections with low-J CO detections (ATCA), we find [CII]/CO(1--0) luminosity ratios of 5200+/-1800, and argue that this line ratio is best described by [CII] and CO emitting gas with higher [CII] than CO excitation temperature,  high CO optical depth (tau>>1), and low to moderate [CII] optical depth (tau<1). The geometric structure of photodissociation regions (PDRs) allows for such conditions.

April 17: no talk

April 10: The role of disk instabilities and galaxy interactions in triggering AGN activity - Marco Gatti, Rome

At present, it has become widely accepted that Active Galactic Nuclei (AGN) are powered by short and repetitive accretion episodes onto Super Massive Black Holes (SMBHs) and that their evolution is tightly correlated with that of their host galaxies. However, understanding what triggers AGN activity producing at the same time the observed co-evolution remains one of the long-standing questions in astrophysics. A detailed statistical study about the role of different AGN triggering mechanisms can be performed using a state-of-the-art semi analytic model (SAM) for galaxy formation. In this talk I will discuss the effects of assuming different mechanisms for triggering AGN activity on several AGN and host galaxy properties (e.g. AGN luminosity function, Eddington ratio distribution, AGN 2PCF, host galaxy SSFRs). Two accretion modes will be considered: a first mode where AGN activity is triggered by disk instabilities in isolated galaxies, and a second mode where the mass inflow onto the central SMBH is induced by galaxy mergers and fly-by events (interacti

April 1: Graph theory and Molecular Gas Clusters - Dario Colombo, University of Alberta

In the present Universe, all stars born in cold clouds of molecular gas which inner and outer physical phenomena play a key role to set the star formation capabilities of the galaxies. The study of a molecular-dominated spiral galaxy as M51 has underlined the importance of the ISM clump characterization to provide fundamental insight within the physics involved into the process of star formation. In the same way, however, it challenged the performance of the most advanced cloud identification method to date, indicating the need for new, more powerful tools. 

Some of the limitations of commonly used algorithms can be overcome by considering the cloud segmentation problem in the broad framework of the graph theory.  Additionally, the clustering analysis provides a natural and robust mathematical description of the molecular ISM discrete features that might be viewed as “Molecular Gas Clusters”.

In particular, the algorithm we designed (SCIMES - Spectral Clustering for Molecular Emission Segmentation) applies the spectral clustering approach to look for relevant objects within topological graphs of emission (dendrograms) from star-forming clouds. SCIMES appears especially useful for the cloud identification within complex molecular emission data cubes since, in contrast to other algorithms, it does not over-divide structures, faithfully reproducing the work of the human eyes.

Moreover, SCIMES introduces a new philosophy in the identification of the molecular clouds, where virtually every property of the molecular emission might be used for the ISM segmentation. This may be helpful for distinguishing between the dominant physical mechanisms responsible for the formation of those molecular clusters.

March 2015

March 27: updates on LUCI - Peter Buschkamp

March 20: Astrophysical Levi Flights - Re'em Sari, the Hebrew University of Jerusalem

Levy flights are a form of random walk, where the step size is drawn from a distribution with infinite second moment. They appear quite ubiquitously in nature, like in the motion of Spider Monkeys or Albatrosses in their search for food, as well as in the stock market. We discuss their implication to astrophysical situations including eccentricity of planetesimals, eccentricities of binaries, formation of the Oort Cloud, collisional spins of asteroids, and perhaps astrometry and photometry of IR sources in the galactic center.

March 13: The incidence of kpc-scale outflows and conditions for star formation in luminous unobscured QSOs - Bernd Husemann, ESO

I will highlight the advantages to study the QSO-host galaxy connection with optical IFU
spectroscopy based on more than 50 luminous radio-quiet unobscured QSO (z<0.3). In particular I
will highlight the difficulty and our solution to deal with the beam smearing of the bright nucleus.
We find a much lower incidence of large-scale outflows which is in contradiction with
recent studies of luminous unobscured and obscured QSOs. Part of this can be explained by
ignoring seeing. We also find that our QSO host galaxies are consistent with conditions
for star formation in normal galaxies on the star forming main sequence.
Interestingly, we recover a correlation between bolometric AGN luminosity and molecular gas
mass for disc-dominated host, while elliptical hosts have a higher bolometric AGN luminosity
at a given gas mass. At the end I am going to briefly introduce the Close AGN Reference Survey (CARS)
which is a spatially-resolved multi-wavelength survey of ~40 luminous broad-line AGN at
0.01<z<0.06 with VLT-MUSE combined with other facilities.

March 6: proposal writing workshop

February 2015

February 27: What drives the intense star formation of high-z, massive, star-forming galaxies? - Matthieu Béthermin, ESO

Deep Spitzer and Herschel surveys revealed the important contribution of ULIRGs (SFR>100 Msun/yr)
to the star formation history at z>2. Standard theoretical models and numerical simulations cannot
reproduce their high number density easily. This intense star formation could be explained by
large gas reservoirs fed by a strong accretion of cold gas or by a higher star formation efficiency
caused by major mergers? I will present results from statistical advocating for that the first hypothesis.

Using a stacking analysis of mid-IR-to-mm data, we measured the evolution of the dust and gas content
of massive galaxies up to z=4. In average, they lie on the sequence of local spirals in the integrated
Schmidt-Kennicutt diagram, and their high SFR is explained by their large gas fraction (~60% at z=4).
The extreme starbursts (defined as being 10 times above the main-sequence) have similar gas fractions,
but much higher star-formation efficiencies.

The clustering of these objects provides interesting insights about the nature of their host dark matter
structures and the origin of these gas reservoirs. Both ~3x1010 Msun starbursts and main-sequence galaxies
are hosted in dark matter halos of few 1012 Msun. The accretion of baryons on these halos is sufficient
to refill the gas consumed by the star formation in main-sequence galaxies, but not in starbursts that
can maintain their SFR only during <100 Myr. The most massive (>1011 Msun) main-sequence galaxies are
hosted by group mass halos (>1013 Msun), progenitors of today’s clusters.

I will finally discuss the selection biases induced by the galaxy surveys using the Béthermin et al. (2012)
model of galaxy evolution. I will especially focus on the South Pole Telescope (SPT) sample of lensed
high-redshift galaxies. This sample is expected to contain mainly z~3.5 gas-rich main-sequence galaxies,
and opens interesting opportunity to study in detail the physics of these objects.

February 20: The HI and H2 content and sub-mm emission of galaxies over cosmic time: a semi-analytic and semi-empirical approach - Gergely Popping, ESO

The star-formation activity of our Universe increased from early epochs (z~6), peaked around z=2, and then decreased by an order of magnitude until present age. To fully appreciate the physical origin of the star-formation activity of our Universe we need to focus on the gas content of galaxies over cosmic time. The most recent versions of cosmological models of galaxy formation explicitly include the detailed tracking of the atomic and molecular hydrogen content of galaxies and make predictions for the sub-mm line emission from galaxies. New semi-empirical approaches provide data-driven predictions for the atomic and molecular gas content of galaxies. I will discuss the predictions made by these different types of models for the HI and H2 content and sub-mm line emission of galaxies. These predictions include a weak evolution in the HI content and HI mass function of galaxies, strong evolution in the H2 content of galaxies, the weak evolution in the cosmic density of HI,  CO SLEDs of galaxies over cosmic time, and predictions for CO luminosity functions. I will compare these predictions to current observational samples, discuss future observing strategies, and will also demonstrate how the combination of cosmological and semi- empirical models can help to reveal caveats in our understanding of galaxy formation.

February 13: no talk

February 6: The Galactic Center cloud G2 and its gas streamer - Oliver Pfuhl

I will discuss the latest observations of of the gas cloud G2 in the Galactic Center, from late 2013 and 2014. The cloud has reached its minimum distance to the MBH at 1950 Schwarzschild radii in July 2014. At this point roughly half of the gas is found at the redshifted, pre-pericenter side of the orbit, while the other half is at the post-pericenter, blueshifted side. Last years deep observations revealed a long stream of gas, which is following the path of G2. Furthermore we (re-)discovered a precursor cloud, named  G1. This cloud was first described a decade ago based on L′-band images when it was spatially almost coincident with Sgr A∗. The orientation of the G1 orbit in the three angles is almost identical to that of G2, although at somewhat lower eccentricity and smaller semi-major axis. We could show that the observed astrometric positions and radial velocities of G1 are compatible with the G2 orbit, assuming that (1) G1 was originally on the G2 orbit preceding G2 by 13 yr, and (2) a simple drag force acted on it during pericenter passage. Taken together with the previously described tail of G2, which we detect in recombination line emission and thermal broadband emission, we propose that G2 may be a bright knot in a much more extensive gas streamer. This matches purely gaseous models for G2, such as a stellar wind clump or the tidal debris from a partial disruption of a star.

January 2015

January 30: Does the Dense Gas Mass set the Star Formation Rate of a Galaxy? - Andreas Schruba

Stars form in the dense interstellar medium. Observations of HCN, a tracer of dense gas, in Milky Way cloud cores and entire (U)LIRG galaxies suggest a constant ratio of current star formation rate to HCN intensity which is interpreted by a density threshold for star formation with fixed star formation efficiency. I summarize results of a recent survey of HCN emission utilizing the IRAM 30m that targets the little-explored regime of normal star-forming disk galaxies. While our observations confirm the common picture that the dense gas fraction increases towards the galaxy centers, they reveal systematic variations in the SFR-to-HCN ratio. Under the assumption of a constant HCN-to-dense gas conversion factor these observation are not conform with the "density threshold" model. However, our knowledge on this conversion factors is still poor. Therefore, we analyze the range of (variable) conversion factors which are required for the density threshold model to hold. We also analyze another popular model of star formation in which the properties of entire molecular clouds regulate the star formation efficiency which can match our observations more naturally.

January 23: Test and Characterization of the GRAVITY Laser Metrology Injection - Johannes Weber (Master's thesis defense)

We investigated the laser metrology injection of GRAVITY, a second generation four-way beam combiner instrument for the ESO Very Large Telescope Interferometer (VLTI). This has been characterized in previous studies, but interference effects within the detector have limited the accuracy of these measurements to several ten nm. The goal of my master thesis, to develop a new technique to overcome these fringing effects and to characterize the metrology injection was achieved with a Fizeau-type interferometer, which allows separating the interference from the metrology injection and the detector fringing in Fourier domain. We will demonstrate that we can overcome residual errors from spectral leakage and thermal induced camera motion with an optimized data analysis, resulting in a closure phase accuracy of better than 1 nm. Subsequently we will present the results of the stability and sensitivity tests of the two different metrology injection designs and present our new model for the laser power induced path length variations. Finally we will draw conclusions concerning GRAVITY's metrology injection.

January 16: Does the NGC 1068 CO line SED constrain the amount/position of the X-ray obscuring gas? - Annemieke Janssen

NGC 1068 is  a nearby, compton thick, Seyfert 2  galaxy, so the AGN is obscured from our view by a gas column of 10^24 cm ^-2 or more. This obscuring gas can lie anywhere between a fraction of a parsec and tens of parsecs away from the AGN. Depending on its position and its total column density, the gas may be molecular and could possibly be observed in high J CO lines.

We observed NGC 1068 with PACS and retrieved the CO line SED up to J=30, while a deeper observation of CO(40-39) resulted in an upper limit of 2e-17 Wm^-2. We use the CO SED and an XDR code developed in our group by Simon Bruderer, to find the answer to 2 questions:
1) Does the upper limit on CO(40-39) constrain the position, density and amount of the X-ray obscuring gas?
2) Could the 'Highly Excited component' (which peaks around J=25) be attributed to the X-ray obscuring gas?

January 9: no talk

December 2014

December 26: HOLIDAY

December 19: no talk, enjoy the holidays!

December 12: Fast Stars and Fast Lives: G2 and the Fastest Stars in the Universe - James Guillochon, ITC (CfA, Harvard)

Orbiting about our galaxy's central black hole are many tightly-bound stars that move at great velocities. Occasionally, these stars pass close enough to the central black hole to lose mass, with larger stars being more prone to mass loss. I will first summarize the results of a paper published earlier this year suggesting that the G2 cloud could have formed through the partial disruption of a red giant star, and the status of the search for the object that was disrupted. The second part of my talk will focus on what would happen to the central cluster surrounding our galaxy's black hole if it were to merge with another black hole. I will argue that this process occurs regularly in the Universe when galaxies merge, and that this leads to the production of an unbound population of stars that can move at speeds in excess of a few tenths of the speed of light.

December 5: no talk, budget meeting

November 2014

November 28: MINI-RETREAT

November 21: Analytic models for deriving flows onto supermassive black holes in disc galaxies - Kambiz Fathi, Stockholm University

I will present a set of new results demonstrating how analytic dynamical models can be used to predict gas flows at galactic scales and in the circumnuclear regions of disc galaxies, down to the vicinity of supermassive black holes. The quantitative agreement between the models and observations of the multi-phase interstellar medium confirms that we are indeed able to follow gas from kpc scales down the resolution limit of state-of-the-art ALMA observations. I will further discuss how our tools could be used to gain further insight on observed kinematic features in more distant galaxies.

November 14: The variation in molecular gas depletion time among nearby galaxies: II the impact of galaxy internal structures - Mei-Ling Huang, MPA

We combine three data sets of nearby galaxies, including HERACLES, ATLAS3D, and COLD GASS surveys to study the impact of galaxy structure such as the bulge, arm, bar and ring on molecular gas depletion time (t_dep) on kiloparsec and global scales. Molecular gas is traced by CO line emission and star formation rate (SFR) is derived by the combination of far-ultraviolet and mid-infrared data either at 22 or 24 micron. We improve on previous studies of the COLD GASS and ATLAS3D samples by matching the apertures for CO and SFR measurements as closely as possible. The contribution of old stars to the mid-infrared emission from the early-type galaxies in ATLAS3D is corrected using K-band emission measured from 2MASS images.

Our results show that at a given value of the specific SFR (sSFR), the bulge region has reduced molecular gas depletion time than the disk region. Using a subset of COLD GASS galaxies whose discs are fully covered by the IRAM beam, we also find that the integrated H2 depletion time declines as the bulge-to-disc ratio of the galaxy increases. The depletion time in spiral arms is on average shorter than outside arms. In addition, the t_dep versus sSFR relation for the disks of galaxies with spiral arms is displaced to lower t_dep at fixed sSFR compared to galaxies without spiral arms. In contrast, the grids from galaxies with bars and rings have reduced t_dep at a given sSFR.

November 7: KVN, KaVA, and the Jets of AGN - Sascha Trippe, Seoul National University

At radio frequencies, active galactic nuclei (AGN) are dominated by collimated outflows - jets - that span hundreds of kiloparsecs. Jets play a crucial role in the energy budget of AGN and influence the evolution of their host galaxies. Despite their importance, the physics of jets, especially the mechanisms of launching and collimation, are only crudely understood. I present recent interferometric observations with the Korean VLBI Network (KVN) and KaVA, a combination of KVN with the Japanese VERA array. KVN is able to observe a target simultaneously at 22, 43, 86, and 129 GHz in dual polarization, making it ideal for studying the plasma physics of AGN jets. KaVA complements KVN via high-angular resolution observations at 22 and 43 GHz. With these capabilities, we have been able to trace the flux distributions, spectral index evolution, and linear polarization in the central parsecs of eight radio-bright AGN.

October 2014

October 31: The Structure of Quasar Accretion Disks - Jason Dexter

Despite its widespread use in interpreting observations of AGN for ~40 years, standard accretion disk theory cannot explain a number of independent optical/UV observations. I will discuss the major problems and a couple of possible (but speculative) solutions.

October 24: High-redshift disks with a central starburst - Ken-ichi Tadaki

Most massive galaxies are thought to grow inside-out: dense, compact cores form first and then gradually puff up probably through minor mergers. The formation mechanism of the compact cores (nuggets) is poorly understood. Recently, it is suggested that high-redshift clumpy disks can evolve into compact nuggets through the dissipative shrinkage as well as major mergers. Our Subaru NB survey has identified some candidates of the transition population which are clumpy galaxies with central starburst. I will talk about this result and future plans with ALMA, JVLA and NB+AO.

October 17: Planet formation and atmospheric mass loss - Re'em Sari, the Hebrew University of Jerusalem

October 10: The excitation of near-IR/mid-IR molecular lines in protoplanetary disks - Simon Bruderer

October 3: HOLIDAY

September 2014

September 26: Hot Jupiters, their cooling and their inflated sizes - Re'em Sari, the Hebrew University of Jerusalem

Some hot jupiters display larger radii and smaller densities than expected.  We lay out an analytic model for the cooling of such planets. The extreme illumination from the host star creates a thick isothermal layer in their envelopes, which slows down their convective cooling, but not sufficiently. We show how energy deposition deep in their envelope, even with lower power than that of the star, makes this isothermal layer thicker, farther slowing their cooling, potentially explaining their inflated sizes.

September 12: Understanding the ISM of nearby galaxies through IR spectral lines - Kevin Croxall, Ohio State University

Observations of the ISM in nearby galaxies is vital to connect in-depth studies of individual clouds in the Milky Way and the globally integrated measurements of more distant galaxies.  Indeed, to understand galaxies we must first understand the physical mechanisms that regulate and drive their evolution.   In order to characterize the ISM in these present-day galaxies and understand the physical processes linking the ISM with star formation, we have undertaken a large survey of 61 nearby galaxies with the Herschel space telescope selected to span a wide range of galaxy properties and environments found in the local universe.  I will give an overview of the KINGFISH survey, with a focus on spectral line imaging of the principle atomic cooling lines, [OI] 63μm, [OIII] 88 μm, [NII] 122,205 μm, and [CII] 158 μm, and the forthcoming spectral atlas.  Specifically, I will focus on how these data allow us to trace cooling and heating mechanisms and the physical conditions of the ISM.   

August 2014

Monday, August 11: Proper motions in the halo of the Milky Way - Tobias Fritz

Objects in the halo of the Milky Way like globular clusters, dwarf galaxies and tidal streams are useful to answer questions regarding the halo. On the one hand they themselves constitute the main baryonic component of the halo and are therefore important to understand galaxy formation in the nearly undisturbed outskirts of galaxies. On the other hand, they are the best tracers of the dark matter there. Especially for the second question full phase space information is important. While radial velocities are available for most objects, proper motions are missing for most.
I will present our current and future efforts to add proper motions. Firstly, I will show my very recent proper motion measurements for the globular cluster Palomar 5. I have achieved an accuracy of 0.18 mas/yr with a 15 year baseline using SDSS and LBT/LBC.  Secondly, I will introduce our 143 h large program at Gemini South which starts in September. By using MCAO we achieve high precision from the ground in only two years. We target 15 different objects.

July 2014

July 25: Sgr A*: intermittent accretion and outflows - Jorge Cuadra, Universidad Católica de Chile

We present numerical models of the gas dynamics in the inner parsec of the Galactic centre. We follow the gas from its origin as stellar winds of several observed young massive stars, until it is either captured by the central black hole, or leaves the system. Unlike our previous models, we include the expected outflow from the inner accretion flow. We find that the outflow perturbs the gas dynamics near the Bondi radius and the black hole capture rate significantly, and that these effects persist for longer than the outflow. Accretion rate estimates that do not account for feedback outflows over-predict not only the accretion rate onto the black hole but also the capture rate at the Bondi radius itself. Finally, the steady- state assumption under which non-radiative flows have been routinely studied in the literature may have to be abandoned if accretion feedback is bursty in nature.

July 18: Tucker Jones, UC Santa Barbara

I will discuss recent and ongoing work aimed at detailed characterization of typical star forming galaxies at redshifts z~2. The focus will be on galaxies with properties similar to those expected for Milky Way-like progenitors (with stellar masses of 1e9-1e10 Msun at z=2), and particularly on gravitationally lensed galaxies for which high quality spectroscopic data can be obtained inexpensively. Deep Hubble imaging and grism spectra are currently being taken for large samples via the Frontier Fields initiative and the GLASS survey, which together characterize the stellar and nebular properties with exquisite spatial resolution. I will present initial results from these efforts and prospects for the full survey. I will also describe our recent Keck campaign to obtain rest-frame UV spectroscopy, which reveals detailed information about the interstellar and outflowing gas as well as the stellar metallicity. Results from these surveys support a coherent picture of galaxy evolution along the "main sequence" in which star formation predominantly occurs in clumpy turbulent disks with sub-solar metallicity, and is regulated by outflows of metal-enriched gas.

July 11: KMOS3D: The Evolution of Resolved Kinematics from z=2.7 to z=0.7 - Emily Wisnioski

We present the first years data from the KMOS^3D Survey, a new integral field survey of over 600 galaxies at 0.7<z<2.7 using KMOS at the VLT. The KMOS^3D Survey utilises synergies with multi-wavelength ground and space-based surveys to trace the evolution of spatially-resolved kinematics and star formation from a homogeneous sample over 5 Gyrs of cosmic history. Targets, drawn from a mass-selected parent sample derived from the 3D-HST survey, cover the star formation-stellar mass (M_*) plane and rest-frame (U-V)-M_* plane uniformly. We detect Halpha emission for 191 M_*>10^10 Msun galaxies at z=0.7-1.1 and z=1.9-2.7 with KMOS. Within the sample, galaxies on the `main sequence' (MS) of star-forming galaxies - including lower mass and compact objects - are well described by ordered rotation.Our high quality KMOS data confirm the elevated velocity dispersion reported in previous IFS studies at z~0.7. Combined with existing results spanning z~0-3, the evolution follows an approximate (1+z) evolution that can be described mainly by the co-evolution of gas fractions and specific star formation rates, consistent with a dynamic equilibrium of gas flow into and out of galaxies.

July 4: Evidence for Wide-Spread AGN Driven Outflows in the Most Massive z~1-2 Star Forming Galaxies - Reinhard Genzel

In this study we follow up on our previous detection of nuclear ionized outflows in the most massive (log(M*/Msun) >= 10.9) z~1-3 star-forming galaxies (Forster Schreiber et al.), by increasing the sample size by a factor of six (to 44 galaxies above log(M*/Msun) >= 10.9) from a combination of the SINS/zC-SINF, LUCI, GNIRS, and KMOS^3D spectroscopic surveys. We find a fairly sharp onset of the incidence of broad nuclear emission (FWHM in the Ha, [NII], and [SII] lines ~ 450-5300 km/s), with large [NII]/Ha ratios, above log(M*/Msun) ~ 10.9, with 66+/-15% of the galaxies in this mass range exhibiting this component. Broad nuclear components near and above the Schechter mass are similarly prevalent above and below the main sequence of star-forming galaxies, and at z~1 and ~2. The line ratios of the nuclear component are fit by excitation from active galactic nuclei (AGN), or by a combination of shocks and photoionization. The incidence of the most massive galaxies with broad nuclear components is at least as large as that of AGNs identified by X-ray, optical, infrared or radio indicators. The mass loading of the nuclear outflows is near unity. Our findings provide compelling evidence for powerful, high-duty cycle, AGN-driven outflows near the Schechter mass, and acting across the peak of cosmic galaxy formation.

June 2014

June 27: Dynamical constraints on the mass budget in early star-forming disks - Stijn Wuyts

With KMOS^3D, we are mapping the velocity fields of a large and homogeneous sample of galaxies at redshifts z~1 and z~2.  For the same galaxies, a wealth of multi-wavelength imaging information is available, from the UV to the far-IR, including high-resolution ACS+WFC3 maps from HST.  Exploiting stellar mass maps based thereupon, and applying state-of-the-art gas scaling relations, I will address how the velocity curves observed with KMOS compare to expectations based on the multi-wavelength imagery.  I will further discuss how this analysis sheds light on the mass budget in early disks.

June 20: no talk - Albrechts' goodbye party

June 13: IGRINS- A Next-Generation R=40,000 Spectrograph for the Near-IR - Dan Jaffe, University of Texas

IGRINS, the immersion grating infrared spectrograph has high spectral resolution and an extraordinarily broad spectral grasp.  The instrument incorporates several new technical innovations including a silicon immersion echelle, H and K band VPH cross-dispersers, and a "build to print" optomechanical design.  We report on the results of two commissioning runs where we have taken sample observations of interstellar, stellar, and planetary targets. We will also outline some of the major science projects we will carry out with IGRINS in the next few years.

June 6: Mergers and Interactions in the Local Universe - Trevor Mendel, MPE/OPINAS

I'll talk about ongoing pair studies in the local Universe.  I'll discuss the role of dynamical interactions in triggering star formation, AGN activity, and, ultimately, morphological transformation.  This work is possible thanks to the enormous spectroscopic samples available in the SDSS and other local surveys;  I'll discuss the prospects of extending similar studies to z > 1, in particular using our ongoing KMOS GTO surveys.

May 2014


May 23: Metallicity evolution at 0.8 < z < 2.6 from LUCI, SINS and KMOS3D - Eva Wuyts

We present the correlations between stellar mass, star formation rate (SFR) and gas-phase metallicity estimated from the [NII]/Ha flux ratio for a sample of 222 galaxies at 0.8 < z < 2.6 and log(M*/Msun)=9.0-11.5 observed with LUCI at the LBT, and SINFONI and KMOS at the VLT. This sample provides the first analysis of the mass-metallicity relation (MZR) over an extended redshift range using consistent sample selection, data analysis techniques and strong-line metallicity indicator. We find a constant slope at the low-mass end of the MZR, which is however significantly steeper than seen in the local Universe. We can fully describe the redshift evolution of the high-z MZR through the evolution of the characteristic turnover mass where the relation begins to flatten at the asymptotic metallicity.
At fixed redshift, our data do not show a correlation between metallicity and SFR, which disagrees with the 0.2-0.3~dex offset in [N~II]/Ha predicted by the "fundamental relation'' between stellar mass, SFR and metallicity proposed by Mannucci et al. (2010). However, the MZR evolution towards lower metallicities at earlier times does agree within the uncertainties with their prediction. This suggests that the physical processes responsible for the spread in SFR at fixed redshifts are to some degree distinct from the physics driving the overall evolution in cosmic SFR, and correlate differently with galaxy abundance.

May 16: no tea talk

May 9: Feeding and Feedback in Nearby AGN - Allan Schnorr Müller

I will discuss the feeding and feedback in a small sample of nearby AGNs, observed with the GMOS integral field unit on the GEMINI telescopes at a spatial resolution of ~100 pc and a spectral resolution of ~50 km/s.  We observe gas inflows along nuclear spirals and filaments, with velocities ranging from 50 to 100km/s and mass flow rates from 0.1 to 1 Msun/yr. These rates are 2-3 orders of magnitude larger than the mass accretion rate to the supermassive black hole. Outflow velocities range from 50km/s to 200km/s and outflow rates from 0.5 to 1Msun/yr.

May 2: Unveiling the Infrared Properties of Optically-Selected Galaxies or: How I Learned to Stop Worrying and Love Statistical Methods - Marco Viero, Caltech/Stanford

Far-infrared/Submillimeter wavelengths provide a unique window into obscured star formation at high redshifts, with the full ensemble of dusty star-forming galaxies combining to make up the Cosmic Infrared Background (CIB). However, source confusion - a noise floor which is present in maps where the PSF is large enough to contain multiple sources - makes identifying individual sources and relating them to their optical counterparts incredibly challenging. Given these limitations, I will outline (relatively simple) methods designed to *statistically* make this connection, and I will present latest results from HerMES on the evolving infrared properties of optical/NIR-selected galaxies, including their redshift distributions, clustering properties, temperatures, and luminosity densities. I will show how these properties are intimately tied to their host galaxy stellar mass and redshift, and then summarize their implications for galaxy evolution and cosmology. I will finish by presenting HeLMS and HerS, two new Hershel surveys in the SDSS Stripe 82 which were designed to leverage the rich set of ancillary data in the stripe to better answer these and other exciting questions.

April 2014

April 25: Populations of Young Stellar Objects in Nearby Molecular Clouds - Tien-Hao Hsieh, National Tsing-Hua University, Taiwan

We develop a new method to identify YSOs from star-forming regions using the photometry data from Spitzer’s c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying the statistical properties, such as Star Formation Rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle for identifying YSOs comes from background galaxies with similar SEDs to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in Color-Color Diagrams (CCDs) and Color-Magnitude Diagrams (CMDs), those criteria may exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in multi-dimensional (Multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sources from molecular clouds to Spitzer’s SWIRE data, which have negligible amount of YSOs, we can naturally identify YSO candidates locating outside of the galaxy populated regions in the Multi-D space. In the five c2d-surveyed clouds, we select 322 new YSO candidates (YSOc), miss/exclude 33 YSOc compared to Evans et al.(2009) and result in 1313 YSOc in total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stages remain unchanged. Comparing to theories Krumholz & McKee(2005), our derived SFR suggests that star formation in large scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify 7 new Very Low Luminosity Objects (VeLLOs, Lint < 0.1L⊙).

We have used the Wide-field Infrared Camera (WIRCam) on the Canada France Hawaii Tele- scope (CFHT) to observe 20 faintest Low Luminosity Objects (LLOs, Lint < 0.2L⊙) identified by Dunham et al. (2008), which are believed to be Young Stellar Objects (YSOs) in extremely early stage. We obtained Ks band images which trace the scattered light from the dusty cone swept by the outflows, thus our observations explore the existence of outflow in extremely early stage of star formation. Outflow signatures are clearly detected toward 9 objects. By comparing the observing images with that of radiation transfer model, we estimate their opening angles that may be important indicator of the evolutionary status.

April 18: Holiday

April 11: What I did before I came to MPE, or The South Pole Telescope Temperature and Polarization Experiments - Liz George

The South Pole Telescope is a 10 meter millimeter-wavelength telescope located at the geographic South Pole. The facility has housed two cyrogenic bolometeric experiments, which have been used to conduct large surveys of the millimeter sky in temperature and polarization. I will describe the two instruments and surveys, and present our recent detection of lensing B-modes in the Cosmic Microwave Background in the broader context of CMB polarization measurements.

April 4: Bulge Growth and Quenching since z = 2.5 in CANDELS/3D-HST - Philipp Lang

Exploiting the deep high-resolution imaging of all 5 CANDELS fields, and accurate redshift information provided by 3D-HST, we investigate the relation between structure and stellar populations for a
mass-selected sample of 6764 galaxies above 10^10 Msun, spanning the redshift range 0.5 < z < 2.5. For the first time, we fit 2-dimensional models comprising a single Sersic fit and two-component (i.e., bulge + disk) decompositions not only to the H-band light distributions, but also to the stellar mass maps reconstructed from resolved stellar population modeling. We confirm that the increased bulge prominence among quiescent galaxies, as reported previously based on rest-optical observations, remains in place when considering the distributions of stellar mass. Moreover, we observe an increase of the typical Sersic index and bulge-to-total ratio (with median B/T reaching 40-50%) among star-forming galaxies above 10^11 Msun. Given that quenching for these most massive systems is likely to be imminent, our findings suggest that significant bulge growth precedes a departure from the star-forming main sequence. We demonstrate that the bulge mass (and ideally knowledge of the bulge and total mass) is a more reliable predictor of the star-forming versus quiescent state of a galaxy than the total stellar mass. The same trends are predicted by the state-of-the-art semi-analytic model by Somerville et al. In the latter, bulges and black holes grow hand in hand through merging and/or disk instabilities, and AGN-feedback shuts off star formation. Further observations will be required to pin down star formation quenching mechanisms, but our results imply they must be internal to the galaxies and closely associated with bulge growth.

March 2014

March 28: Spatially resolved molecular inflow and outflow: where do Seyferts get their gas? - Ric Davies

March 21: Global Gas Content vs. Evolutionary State at Low Redshift - Andrew Baker, Rutgers University

The ratio of a galaxy's global molecular and atomic gas masses has long been known to depend on its Hubble type and whether or not it is engaged in a major merger.  Close examination of a sample of local galaxies has now revealed an additional, intricate relationship between this ratio and the blueness of a galaxy's center relative to its outskirts-- a metric thought to reflect a system's recent interaction history.  I will introduce this relationship and suggest possible explanations for why different sorts of galaxies lie where they do in a new two-dimensional "fueling diagram" (Stark et al. 2013, ApJ, 769, 82)

March 14: no tea talk - ESO 3D2014 conference


1. Infrared Spectral Mapping of the Superwind in M82 - Pedro Beirao, IPAC

At a distance of about 3 Mpc, M82 affords an unparalleled opportunity to study a dusty outflow in great detail. By mapping the M82 outflow with Spitzer-IRS we can determine the physical properties and the structure of the dust and molecular gas swept up in the outflow, especially the small dust grains and the molecular hydrogen. I will present spectral maps built from the observations, using the PAH 11.3/7.7 and 6.2/7.7, [NeIII]/[NeII], H2/PAH, H2/[NeII], and PAH/[NeII] line ratios, and also H2 excitation diagrams. I will discuss the properties of the ionized gas, PAHs and the H2 emission, and the origin of H2 emission comparing our maps to X-ray images and using shock excitation models.

2. Gas flows (In&Out) around galaxies in the era of 3D spectroscopy - Nicolas Bouché, IRAP

We live in a golden era for integral field spectroscopy (IFS) available on 8m class telescopes, with SINFONI, KMOS and MUSE at the VLT. I will highlight some recent results on gas outflows and accretion around galaxies that rely on IFS. These results will serve to illustrate a new tool designed to go beyond traditional methods to extract physical properties from IFS data in low-SNR regime and without AO.

February 2014

February 28: AGN accretion history from Herschel - Ivan Delvecchio, University of Bologna

Constraining the evolution of active galactic nuclei (AGN) across the cosmic time is essential to shed light on the formation and evolution of galaxies. Several studies, mostly X-ray based, have significantly improved our knowledge on the supermassive black hole (SMBH) growth. I will present recent and consistent estimates on the AGN evolution from an infrared perspective, as obtained from Herschel data. In the framework of the PACS Evolutionary Probe (PEP) project, we study a sample of ~4400 Herschel-PACS selected galaxies within the GOODS-South and the COSMOS fields. Starting from the rich multi-wavelength photometric data-sets available in both fields, we perform a broad-band Spectral Energy Distribution (SED) decomposition to disentangle the possible AGN contribution from that related to the host galaxy. We find that 37 per cent of our sample shows signatures of nuclear activity at the 99 per cent confidence level. The probability to reveal AGN activity does increase as a function of both infrared (1-1000) luminosity and redshift, becoming about 80 per cent for the brightest (L 1-1000 > 10^12 L_sun) infrared galaxies at z>1. Finally, we reconstruct the AGN bolometric luminosity function and the SMBH growth rate up to z~3, also well reproducing the observed local BH mass density with consistent values of the BH radiative efficiency (~0.07).

February 21: Reducing fiber noise in high resolution spectroscopy and measuring the reflectivity and focussing properties of the Cherenkov telescopes MAGIC - Hanna Kellermann

February 14: Gravitational Waves and Black Hole Binaries from Galactic Nuclei - Hyung Mok Lee, Seoul National University

Gravitational waves predicted by the general relativity almost 100 years ago have been implicated indirectly only by astrophysical observations such as the orbital evolution of binary pulsars. The advanced detectors of gravitational waves will become operational in a few years and they are expected to make direct detection of gravitational wave signal coming from merging of binaries composed of neutron stars or stellar mass black holes from external galaxies. Current estimates of the expected rate of merger event of neutron star or black hole binaries are based on very limited number of observed binary pulsars with careful considerations on the observational biases, stellar evolution, including binary phases, and dynamics of dense star clusters. Therefore these estimations vary several orders of magnitude depending on assumed parameters and models. We concentrate on the expected rates of the black hole binaries originated from galactic nuclei star clusters (NC) purely based on the dynamical considerations. The NCs with central supermassive black holes (SMBHs) are modeled stars representing the stellar mass BHs together with the additional potential due to the central black hole and bulge in the N-body simulations.  In such an environment, binaries are predominantly formed by the gravitational radiation (GR) as a result of close encounters. Most of the binaries have very eccentric orbits (1-e ~10^-4) with very small presenter distances. The merging time after the formation of the binary is much shorter than any other dynamically relevant time scales. They will produce waveforms quite different from the ones with circularized orbits as they remain eccentric when they enter the aLIGO/Virgo bands. We find that the overall formation rates for BH-BH binaries per NC is 10^-10 per year for the Milky-Way-like galaxies, corresponding to order of 0.2 to 2 events per year within the  aLIGO/Virgo horizons.  However, several factors such as the dynamical evolution of the cluster, the variance of the number density of stars and the mass range of MBH give uncertainties by a large factor (up to a factor of ~100).

February 7: Probing the velocity dispersions of neutral gas in the ISM of nearby galaxies - Anahi Caldu-Primo, MPIA

With the advent of new instruments, it has been possible to gather a better understanding of the gas motions in nearby galaxies. Recent studies have provided evidence of the differentiation of the molecular gas in two phases: one that is associated with the dense gas linked to star formation, and an additional more diffuse component. This latter component has a higher velocity dispersion than the first one.

I will first show the results of a study in which we compare the line widths of CO (a common tracer for the molecular gas phase) and HI in a sample of 12 nearby galaxies. We look at the dependance of line widths with different physical parameters, like galactocentric distance or star formation rate surface density. We measure comparable line widths for both tracers, and propose a possible interpretation based on the existence of a high-velocity dispersion molecular gas component.

We pursue this idea further by comparing high–quality interferometric and single–dish imaging in NGC 4736 and NGC 5055. Our analysis shows that the single–dish line widths are indeed higher by ~20% than the ones based on the interferometric observations. This finding can be explained by the presence of a diffuse molecular gas component that is being missed by the interferometric observations.

January 2014

January 31: Reconciling the star-forming properties of Active Galaxies near and far - David Rosario

Our Herschel PEP studies of star-formation in distant AGN have revealed some interesting relationships, which I will briefly review in this talk. I will then move to an attempt to understand these same relationships in local populations of AGN using currently available deep far-IR data in the SDSS/Stripe82. In a work in progress, I show that some of the most massive and powerful star-forming galaxies tend to host AGN, though a wide range in SF properties is found. I show evidence that earlier methods of estimating the SFR in AGN may be systematically in error. Finally, with sufficient care to account for survey biases, I show that the SF trends for local AGN do indeed follow our earlier studies in detail.

January 24: Probing the ISM Properties of Galaxies through their FIR Fine-Structure Lines: The SHINING View - Javier Gracia Carpio

Fine-structure lines in the FIR are important probes of the physical conditions of the interstellar medium in galaxies. In this talk I will present the main results from the observation of these lines by our Herschel guaranteed time key program SHINING. We used the PACS spectrometer to study the FIR properties of a sample of more than 100 galaxies that includes local starbursts, Seyfert galaxies, low-metallicity systems, and infrared luminous galaxies at low and high redshift. We find that the ratio between the FIR luminosity and the molecular gas mass, Lfir/Mmol, is a much better proxy for the relative brightness of the fine-structure lines than Lfir alone. Systems with intense star formation tend to have weaker lines relative to their FIR continuum, than less active star-forming galaxies. These line deficits are found both in local and high-z galaxies, and are probably a consequence of their more intense interstellar radiation fields. Recently we have been able to extend our analysis to kpc and sub-kpc scales by resolving with Herschel the spatial emission in local galaxies. We find low line to continuum ratios in regions with high FIR surface densities and warm dust temperatures. Only the most compact and obscured regions in some local HII galaxies present line deficits as strong as those found globally in luminous and ultraluminous infrared galaxies.

January 17: A Keplerian Disk around a Class 0 source: ALMA observations of VLA1623A - Nadia Murillo

Rotationally supported disks are critical in the star formation process, for accretion in the early stage and planet formation in the later stages. The questions of when they form and what factors influence or hinder their formation have been studied but are largely unanswered. Observations of early-stage Young Stellar Objects (YSOs) are needed to probe disk formation. VLA1623 is a triple non-coeval protostellar system whose Class 0 component, VLA1623A, shows a disk-like structure in continuum with signatures of rotation in line emission. ALMA Cycle 0 Early Science 1.3 mm continuum and C18O (2-1) observations in the extended configuration are presented and used to perform an analysis of the disk-like structure using position-velocity (PV) diagrams and thin disk modeling with the addition of foreground absorption. Our study of the line emission shows that the disk out to 180 AU is rotationally supported, with the rotation described well by Keplerian rotation out to at least 150 AU, and the central source mass is ~0.2 M⊙ for an inclination of 55°. Pure infall and conserved angular momentum rotation models are ruled out. We find VLA1623A to have the youngest Keplerian disk yet observed, demonstrating that disk formation can occur very early.

December 2013

December 13: Possible evidence for the disappearance of the AGN torus at low luminosities - Leonard Burtscher

Theoretical studies suggest that low-luminosity AGNs are not able to sustain an obscuring torus. This holds both for tori that originate in an outflowing (wind) structure and for ones that are part of the accretion flow. So far, however, there is little evidence for a dependance of torus properties on AGN luminosity. Instead it seems that relations such as the mid-IR X-Ray correlation are unchanged down to about 10^41 erg/s. We compiled a large (> 50 sources) sample of IFU data for AGNs that span a wide range in luminosities around the expected threshold. The sources are nearby so that we are sensitive to the dilution of the stellar features on small spatial scales. With this sample, we study the dilution of the stellar light, traced by the near-infrared CO absorption features, by the non-stellar continuum as a function of radius and find a change in the properties of the diluting continuum that happens very close to the expected threshold luminosity. We will discuss whether this supports predictions that the torus disappears at low luminosities.

December 6: Dynamics and structures of the ISM around AGNs - Keiichi Wada

I am going to talk about recent progress in our on-going radiation-hydrodynamic simulations of the ISM on pc-10 pc scales around AGNs. We found that non-steady, non-uniform outflows are often formed, and as a result the nucleus is covered over wide solid angles.

November 2013

November 29: Not another narrow-angle astrometric interferometer? - Yitping Kok

Ever since the successful high-precision narrow-angle astrometric prototype observations of binary stars with optical long baseline interferometry (OLBI) more than two decades ago, the OLBI community has been putting significant effort to replicate the success by building similar astrometric instruments at stellar interferometers for similar and different scientific goals. The ASTRA facility at the Keck Interferometer, the PRIMA facility at the VLTI and the GRAVITY instrument we are currently assembling in the next building are examples of such effort. This talk will describe similar effort at the Sydney University Stellar Interferometer (SUSI). The main scientific goal of the recently installed astrometric instrument at SUSI is to carry out Jupiter-mass exoplanet search around bright binary stars. This talk will describe the interferometric methodology adopted and the observational strategy carried out at SUSI. Initial results and challenges going forward will also be discussed.

November 20: Accretion and stellar mass growth in low mass galaxies - Katharina Lutz - Master thesis defense

We combine deep long-slit optical spectra, atomic and molecular gas measurements, as well as public SDSS and GALEX imaging for a sample of 30 galaxies in the mass range 9.0 < log M⋆/M⊙ < 10.0. These galaxies are the first observed as part of a new survey whose goal is to study the formation histories of low mass galaxies, and the role of gas accretion and star formation efficiency in regulating their growth. This new survey, COLD GASS 2, builds upon the results of the GASS and COLD GASS surveys which targeted massive galaxies (log M⋆/M⊙ > 10.0). In this thesis, we use the long-slit optical spectra for 27 low mass galaxies to study the radial variation of key quantities such as metallicity, star formation surface density and stellar age, and correlate these variations with global galaxy properties. The results are combined with the COLD GASS sample to probe the full stellar mass range between 10^9 and 10^11.5 M⊙ . Our analysis reveals a mass threshold of log M⋆ ≈ 10.5, above and below which the stellar mass growth of galaxies appears to proceed differently. While high mass galaxies show clear signs of growing inside-out, the low mass galaxies appear to be forming stars throughout their disk, despite displaying significant radial metallicity variations. A simple closed-box chemical model is unable to reproduce all our observations, indicating that significant exchange of material with the intergalactic medium must be taking place, likely through both inflows and outflows.

November 8: The ALMA view of one of the nearest starburst galaxies - Alberto D. Bolatto

Department of Astronomy and Joint Space Institute, University of Maryland, Visiting Humboldt Fellow at MPIA-Heidelberg

In the context of galaxy evolution, it is particularly interesting to understand better the mechanisms that regulate starburst activity in galaxies. In this talk I will present an analysis of the molecular ISM properties in the prototypical circumnuclear starburst galaxy, NGC 253, derived from ALMA observations. I will discuss the evidence for a molecular superwind, our measurements of the mass loss rate, and the possible gas entraining mechanisms. I will show our measurement of the properties of giant molecular clouds in the starburst, in an effort to better understand the conditions in the starburst. Finally, I will present and discuss some of the spectroscopic complexity we see in the data. This extremely rich spectroscopy, a common feature in many ALMA datasets, opens new windows for the study of physical conditions in extragalactic systems.