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 6Mergers 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 30HOLIDAY

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 16no tea talk

May 9Feeding 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 2Unveiling 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

March 7: DOUBLE FEATURE

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 31Reconciling 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 17A 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.

 
loading content