Regular Friday tea meetings & Other talks


The full 2018 schedule can be found here

September 2018:

September 21: Next generation disk dynamics modeling -- Sedona Price

I will present an overview of Dysmalpy, an updated implementation of the disk modeling code DYSMAL. I will cover the available modeling options, show some example model fits, and touch on the ongoing/future options to be implemented. 

September 14: No Talk -- MPE Science Day this week

August - Sep 7: Summer Break

July 2018:

July 27: Galactic Winds at Cosmic Noon -- Natascha M. Förster Schreiber 

I will present the latest results from our studies of the demographics and properties of galactic outflows at z ~ 1 - 3, based on the KMOS^3D and SINS/zC-SINF IFU surveys. 

July 20: 
GeMS/GSAOI, Calibration of the optical distortion for an MCAO-fed imager -- Vincent Garrel

GeMS, the Gemini Multi-Conjugate Adaptive Optics (MCAO) System, is the first multi-sodium based Laser Guide Star (LGS) Adaptive Optics (AO) system used for astronomy. It delivers a uniform, close to diffraction- limited Near-Infrared (NIR) image over an extended FoV of 2arcminutes. The compensated images routinely show PSF in the K-band with Strehl Ratios (SR) in the 20% range and Full-Width Half Maximum (FWHM) less than 90 mas over a field of view of 85x85 arcsecond of the instrument GSAOI, Gemini South Adaptive Optics Imager. Due to the particular configuration of the pair, the optical distortion display a complex pattern and a fast temporal evolution, limiting its astrometric performance. I review the past and current effort to measure, model and provide a correction solution to astronomers.

July 13: No Talk - IR BBQ

July 6:  Interferometry in Astronomy - The GRAVITY Metrology System and Galaxy Evolution with the IRAM Interferometer -- Magdalena Lippa

Interferometry is a powerful tool in astronomy used for sky observations with increased spatial resolution and sensitivity. In my dissertation, I demonstrate these and other capabilities of interferometry using two leading world-class representatives of both the radio and optical regime, namely the IRAM interferometer and the GRAVITY instrument at the VLTI. GRAVITY observes two sky objects simultaneously at wavelengths of 2 µm. Measuring the differential optical path difference (dOPD) between both signals for pairs of telescopes provides the intrinsic phase of the science object as well as its angular separation to the reference target, known as phase-referenced imaging and narrow-angle astrometry. For this purpose, the internal dOPDs in the instrument and observatory need to be measured with nanometer accuracy. The laser metrology traces all the light paths from the GRAVITY spectrometers back to the telescopes.

The IRAM interferometer provided a first large statistical census of the molecular gas in distant galaxies at the peak of cosmic star formation. On this basis, I studied spatially resolved molecular gas in a small sample of galaxies. I compared the morphology of the molecular gas with the structures of stellar continuum, stellar mass and star-formation rate. Furthermore, I extracted the kinematics of the molecular gas. While similar studies are frequently done for the ionized-gas component on large statistical samples, the corresponding analysis of molecular gas is still rather rare.

June 2018:

June 29: The ALMA, MUSE, and SINFONI view of the circumnuclear region around the luminous AGN in NGC 5728  -- Taro Shimizu

AGN feedback seems to be a necessary ingredient in models of galaxy evolution to reproduce the population we observe today. Without AGN feedback, star formation in simulated galaxies runs wild and results in a large population of blue, star forming galaxies at z=0 while the addition of energy from an AGN successfully moderates the growth of galaxies and shuts down star formation. However, while successful in simulations, observations of AGN feedback in nature currently are limited and debate occurs over the precise physical processes that govern AGN feedback. In this talk, I will detail my recent work on a powerful local AGN in NGC 5728 for which I have combined observations from ALMA, MUSE, and SINFONI to study the circumnuclear region in depth. I will discuss the energetics and kinematics revealed from these observations that show evidence for a complex interplay between an AGN driven outflow and nuclear ring of star formation and what this suggests for the overall effect of AGN feedback in this singular galaxy.

June 22: (Another) Update on Galactic Center Observations -- Oliver Pfuhl

June 15: QFitsView: unde venis - quo vadis? -- Thomas Ott and Alex Agudo

A new shiny improved expanded upgraded version of QFitsView and dpuser will be released in the very near future. In this presentation we demonstrate some of the new features. We will also remind the audience of some not commonly known aspects of QFitsView.

June 7: What can we learn from GRAVITY astrometry of Sgr A* flares? -- Michael Bauböck 

The precision of GRAVITY is continuing to improve and approach the ~10s of Î¼as scale. This opens the possibility to obtain multiple astrometric measurements during a single infrared flare, allowing for a measurement of the possible motion of the source. This motion along with the corresponding lightcurve of the flare encodes information about both the accretion flow as well as the black hole itself. Measuring these properties depends on accurate models of the relativistic motion of material near the black hole as well as the lensing of photons as they escape to a distant observer. I will discuss our efforts to model the expected motion during IR flares and the degree to which we can expect to constrain the properties of Sgr A* using GRAVITY.

May 2018:

May 26:  Late-Type Stars around the Central Black Hole --  Maryam Habibi

Observations show a relative paucity of red giant stars within the central 0.5 pc in the Galactic Center (GC). By co-adding spectroscopic observation within 10 years, I identify five new late-type stars within the central 1 arcsecond 2 (0.02 pc× 0.2 pc) of the Galaxy. This finding increase the number of late-type stars to 21, of which I construct deep spectra of 15 stars. Ten of these stars are K0-K3III-type stars (T eff ∼ 4100 − 4600 K) consistent with 3-10 Gyr isochrones. The brightest late-type star in this region is a K3III star with 30 Rsun ,
providing a clue to stellar interactions proposed to remove the brightest giants in the region. Expanding the spectral-type-classification in the vicinity of Sgr A* down to 17.5 mag,
I re-address the search for the predicted stellar cusp around the Milky Way's central black hole. My preliminary results shows that the radial density distribution of this late-type stellar ‘‘cusp'’ follows a power law of exponent ~0.3 which is shallower than initially theoretically-predicted and steeper than previously suggested in observations. I also report on identifying the first five warm giants (G2-G8III) in this region, among which the star S20 is the warmest late-type star (G2III, T eff = 5550±54 K) detected in the central arcsecond, with a strong Brγ line and weak CO bandheads, only detectable in its combined spectrum with an S/N> 100.

May 18:  Unveiling the origin of gaps in protoplanetary disks via CO observations --  Stefano Facchini

High angular resolution observations of protoplanetary disks are showing a variety of sub-structures, where gaps and rings in particular seem to be a common feature shared by many systems. Until now, such structures have been detected in continuum, both in the (sub-)mm and in NIR scattered light maps, tracing the distribution of dust particles. A variety of models has been invoked to interpret the observations, ranging from embedded protoplanets to dust opacity variations at condensation fronts, and many other physical mechanisms. In this talk, I will show how observations of molecular lines with ALMA can distinguish between different scenarios. In the planetary hypothesis, simultaneous observations of thermal continuum and molecular lines can be used to infer the mass of the planets carving the observed gaps.

May 11:  No Talk (day after holiday)

May 4: Where do the spirals come from? A multi-wavelength, high-resolution study of HD135344b -- Paolo Cazzoletti

Recent observations of protoplanetary disks in both optical/near-infrared scattered light and (sub-)mm continuum emission have revealed complex structures such as spirals, rings and vortices in micron- sized and mm-sized respectively. Planets are often invoked as an explanation, but the number of planets and their location are degenerate, and the same system can often be explained by more than one scenario. Moreover, most of the time simulations are only able to reproduce the structures observed in one wavelength at the time, missing the information provided by differently sized dust grains. In fact, no clear connection between the structures observed in scattered light and mm has so far been found. HD135344B is a bright transition disk showing perfectly symmetrical spiral arms at near-IR and asymmetric structures at mm-wavelengths at the same time, and an ideal candidate to look for this missing connection. We present new 0.06” resolution ALMA Cycle 4 and 5 observations of this object in Band 3 (3 mm) and Band 4 (2 mm). A combination of these optically thin observations with our previous data at shorter wavelengths will allow a study the spectral index and the dust properties inside the asymmetry through a multi-wavelength analysis, and thus to determine whether or not dust is being trapped inside a massive vortex. Ultimately, we will be able to test whether the asymmetric structure is massive enough to launch the spiral arms observed at near-IR and if a single, massive inner planet is sufficient to explain micron and mm wavelength observations simultaneously, as proposed in van der Marel, Cazzoletti et al. 2016. 

April 2018:

April 27: Star Formation Driven Outflows at z~2.3 with the SINS-AO survey  -- Rebecca Davies

Star formation driven outflows are believed to play an important role in regulating the conversion of gas to stars,  particularly in galaxies below the Schechter mass. However, the relationship between the presence and velocity of outflows and the rate and concentration of star formation in galaxies is a topic of ongoing debate. We utilise the excellent spatial resolution of the SINFONI data from the SINS-AO survey to investigate the relationship between star formation activity and outflow properties on scales of 1-2 kpc in a sample of 25 galaxies at z~2.3. We find that outflows can be driven only when the local star formation surface density exceeds ~0.8 Msun/yr/kpc^2, and that the outflow velocity is positively correlated with the star formation surface density. The fastest outflows have velocities comparable to the galaxy escape  velocities, indicating that some of the outflowing material may penetrate into the galaxy halos. However, the mass loading factors are relatively low (0.1-0.3), suggesting that the ionized gas phase may constitute only a small fraction of the total mass in these outflows.     

April 20: Multiple Star Systems in the Orion Nebula -- Martina Karl

This work presents an interferometric study of the massive binary fraction in the Orion Trapezium Cluster with the novel GRAVITY instrument. It is the most comprehensive and most sensitive interferometric survey of the Trapezium Cluster to date. The resolution and sensitivity of GRAVITY allows resolving companions on scales of 2–200 milliarcseconds with a magnitude as faint as 10.6 mag (K-band), which corresponds to ∼1–100 AU and stellar masses as low as 1.6 M⊙ at the distance of Orion. We observed a total of 16 stars of mainly OB spectral type. We found four previously unknown companions for θ1 Ori B, θ2 Ori B, θ2 Ori C and NU Ori. We confirmed four more companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We redefined the orbit of the eccentric high mass binary θ1 Ori C and we were able to derive a new orbit for θ1 Ori D. We found a system mass of 21.7 M⊙ and a period of 53 days. Together with previously detected other companions seen in spectroscopy or direct imaging, eleven of the 16 high mass stars are multiple systems. We obtained a total number of 22 companions. The companion fraction of the early B and O stars in our sample was about 2, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints towards a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also did not find a substantial population of twin binaries. The observed distribution of mass ratios declined steeply with mass, and like the direct star counts, indicates that our companions follow a more normal initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but found no clear preference for core accretion or competitive accretion.         

April 13: Image-To-Image Transformations with Generative Adversarial Networks -- Philipp Plewa

Recently, Stark et al. (https://arxiv.org/abs/1803.08925) have demonstrated a new approach for robust subtraction of AGN light from SDSS images of quasar host galaxies, using a generative adversarial network (GAN). I will briefly explain the main ideas behind this approach, and show how a similarly constructed GAN (https://github.com/pmplewa/GCGAN) can be successfully employed to either subtract point sources from near-infrared images of the Galactic Center, to reveal the structure of gas filaments spread throughout the region, or to subtract the background emission and sharpen the images, to mitigate source confusion. For these tasks, the GAN requires neither a source catalog, nor a particularly accurate model of the point spread function, in contrast to other techniques. At the start of the talk, I will also present an overview of my other recent work on the Galactic Center, in one-slide summaries, focusing on the modeling of astrometric confusion noise (http://doi.org/10.1093/mnras/sty512), efficient photometric stellar classification (http://doi.org/10.1093/mnras/sty511), and the correction of image distortion (http://doi.org/10.3847/2515-5172/aab3df).

April 6: X-Shooting SS 433 I. Baryonic Jet Energetics  -- Idel Waisberg

The X-ray binary SS 433 is the only known steady super-Eddington accretor in the Galaxy. It is also the first microquasar discovered, though the rapidly moving hydrogen and helium optical emission lines from its relativistic (0.26c), baryonic jets. Being the only known source of its kind, the conditions of the optical emitting gas in the jets and its heating mechanism are still an open question, and are thought to be related to radiative instabilities in the jet and its interaction with the surrounding disk wind outflow. I will present the first XSHOOTER observations of SS 433, which were a spin-off of our GRAVITY observations last summer. We use the up to twenty jet lines of hydrogen and helium per epoch to constrain the temperature, density and optical depth of the jet gas using the spectral synthesis code Cloudy. Doing so at different epochs allows us to study the evolution of the optical emitting gas as it travels through its surrounding medium. 

March 2018:

March 30: No Talk -- Good Friday

March 23: Structuring Molecular Gas from GMC to Galaxy Scale -- Andreas Schruba

March 16: Everything You Always Wanted To Know About Galaxy Quenching (But Were Afraid To Ask)  -- Sirio Belli

The physical mechanism responsible for shutting off star formation in galaxies (i.e., quenching) represents one of the most important open questions in the field of galaxy formation and evolution. In this talk I will review the physical processes that could be responsible for quenching, discussing the theoretical and observational evidence, with a focus on the quenching of massive galaxies in the early universe. 

March 9: 
MicroJy Radio Sources and Cosmic Evolution -- Dr. Bill Cotton (NRAO)

Counts of sources at cosmological distances as a function of flux density have long been used to infer the cosmic evolution of various classes of objects.  Counts of faint radio sources offer an extinction free measure of the high mass star formation in galaxies as well as AGNs.  Inspired by the ARCADE-2 CMB balloon experiment which detected an unexplained low frequency component which was postulated to be a previously unknown population of extragalactic sources, we began a series of deep surveys using the VLA at 2-4 GHz. The "confusion limited" technique allows measuring populations below the image noise and revealed the expected turnover in the counts of star forming galaxies but no hint of a new faint population to explain the ARCADE-2 data.  The source counts differed from some previous deep radio surveys which we postulate is due to incorrect corrections for source size. Our results are consistent with the same steep luminosity evolution for both AGNs and star forming galaxies. Using images made with different VLA configurations we have determined that the median size of 10-100 microJy sources is 0.3" and that this population is dominated by star forming galaxies at z~1; the effective size of the star forming region is ~1 kpc.  A strong correlation between radio and near IR flux densities suggests that when star formation is active, the rate is proportional to the total mass of the galaxy.

March 2:  Ionized and molecular kinematics of a z~1.4 galaxy -- Hannah Übler

February 2018:

February 23: TBD

February 16: Update on Galactic Center science -- Stefan Gillessen

February 9: Special talk: Results from a Joint IFU-Interferometric Survey: Molecular Gas in Nearby Galaxies through the EDGE-CALIFA Survey  - Dyas Utomo (Ohio State University)

Over the past few decades, increasingly powerful optical surveys of galaxies have been used to study the process of structure formation in the Universe. In particular, spectroscopic surveys have revealed clear trends in star formation, metal enrichment, stellar populations, and nuclear activity. However, large-scale spectroscopic surveys mostly neglect the internal structure of galaxies, which is the key to their evolution. An era of integral field unit (IFU) spectroscopy (e.g. CALIFA survey) is now upon us, providing simultaneous spectral and spatial coverage and resolution. These data allow us to map gas and stellar metallicities, ionized gas and stellar dynamics, star formation rates (SFRs), stellar mass densities, and ages. Coupling with the imaging spectroscopy of molecular gas from millimeter interferometers (e.g. EDGE survey), it offers a new window for studying baryon cycle in local galaxies. In this talk, I will presents the recent results and progress of the EDGE-CALIFA survey, especially the molecular gas-star formation relation, the comparison between CO and H-alpha rotation curve, and the local ISM properties at the supernovae sites.

February 2: CubeSats: an opportunity for astronomy, or just a toy for grown up? - Sylvestre Lacour

PicSat is a nanosatellite that was integrated by, and is operated by, the Paris observatory (no space agency, no big consortium). Its goal is to observe the transit of the giant planet beta Pictoris, expected to happen in 2018. After only three years of development, the satellite has been put into a 505 km Sun sunchronous orbit in January 2018 (PSLV C-40). I will present the project, and hopefully, we can discuss if the technology can be useful for our projects here. I’ll also talk about gravitational wave, if we have time.

January 2018:

January 26: Spectro-Interferometric Signatures of the Broad Line Regions in Active Galactic Nuclei - Raphael Stock

The sensitivity of GRAVITY allows ten microarcsecond precision spectro-astrometry (referencing spectral lines to the continuum), opening up the possibility to spatially resolve the broad line region (BLR) of AGNs for the first time. We develop a flexible phenomenological model of the BLR based on collections of optically thin, orbiting clouds. Comparing the model with GRAVITY data provides constraints on BLR structure and dynamics, as well as an independent method for measuring black hole mass.

January 19: No talk

January 12: Zooming in on planet-forming zones of disks around young stars - Ewine F. van Dishoeck

Protoplanetary disks are the birthplaces of planets but the spatial resolution at long wavelengths has so far been insufficient to resolve the critical 5-30 AU region. The Atacama Large Millimeter/submillimeter Array (ALMA) now allows us to zoom in to nearby disks and determine the physical and chemical structure associated with planet formation. This talk will provide examples of recent work on observations and models of protoplanetary disks in various stages of evolution. Surveys of large numbers of disks such as performed for Lupus provide insight into typical masses and sizes, revealing surprisingly weak gas emission. Does this imply low disk masses or is carbon missing?

December 2017:

December 22: Start of Winter Break

December 15: Accretion physics and Sgr A* - Dr. Jason Dexter

Let's talk about accretion onto Sgr A* and what we might learn in the next few years. Ideally this would be in the form of a group discussion, so please come prepared with questions at any level about accretion disks and jets, the Galactic center, Sgr A*, black holes, variability/flares, interferometry/GRAVITY, or related topics.

December 8: The natural emergence of the SFR-H2 surface density relation in galaxy simulations - Dr. Alessandro Lupi (IAP)

Recent developments of numerical techniques and sub-grid modelling have allowed to investigate in more detail the galaxy properties and the effect of star formation (SF), and stellar and AGN feedback, on the host evolution. In particular, several groups have started to employ H2-based SF prescriptions in numerical simulations, motivated by the observational evidence of a linear correlation between the star formation (SF) rate and the molecular hydrogen (H2) surface densities in nearby star-forming galaxies. However, recent theoretical studies have revealed a lack of causal connection between H2 and SF, suggesting that the formation of H2 could be controlled by SF and not vice versa. I will present a new sub-grid model, implemented in the meshless code GIZMO, to follow the formation and dissociation of H2, via the chemistry package KROME, including gas and dust shielding, self-shielding of molecular gas, SF, supernova feedback, and extragalactic and local stellar radiation (modelled both as a sub-grid model and with on-the-fly radiative transfer calculations).
I will discuss the results of a suite of simulations of an isolated gas-rich galaxy at z=3, showing how it can naturally reproduce at the same time the Schmidt-Kennicutt law for total gas (HI+H2) the SF-H2 correlation, without any a priori dependence of SF on the H2 abundance. I will finally present, as one possible application of the model, a study of the the kinematics and dynamics of molecular gas in high-redshift quasars.

December 1: Update on NOEMA - Prof. Reinhard Genzel

November 2017:

November 24: No talk

Novermber 17: No talk - Ringberg IR Group Retreat

October 2017:

October 27: BAT AGN prefer circumnuclear star formation - Dr. Dieter Lutz

October 20: Local Luminous AGN with Matched Analogs (LLAMA): Nuclear stellar properties of Swift BAT AGN and matched inactive galaxies - Dr. Ming-Yi Lin

In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.

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 (http://ads.nao.ac.jp/doi/10.1093/pasj/psw087), 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.

August/September

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 (http://arxiv.org/abs/1602.05592) 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: http://www.mpe.mpg.de/~rhc/images/NII_abstract.jpg

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.

 
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