The full 2023 schedule can be found here

March 2023

March 3: Is it a Black hole?-- Diogo Ribeiro

Monitoring the few central parsecs of our galaxy over the last few decades has given us precise insight into the nature of the mysterious compact massive object SgrA*. Remarkably, the observed behavior of matter and light around this object matches to astonishing accuracy that of the predicted one by the Theory of General Relativity - We seem to have a Black hole at the heart of our galaxy. However, the ever more precise observations allow us to test this hypothesis to unmatched precision. In tomorrow's tea talk, I'll review some of my recent work toward this goal.

February 2023

February 10: CO and CI mapping in nearby galaxies, their traced ISM properties, stellar feedback and conversion factors, and clues to high redshift galaxies -- Daizhong Liu

I would like to present my latest works about high-J CO and CI mapping in nearby galaxies and shed some light on the CO dissociation and CI enrichment by stellar feedback in starburst environment, and link these local results to our high-redshift studies. This local galaxy work is based on the ALMA CO(4-3) and [CI](3P1-3P0) mapping, archival lower-J CO mapping, and new PHANGS-JWST near-/mid-infrared imaging within the PHANGS collaboration. My radiative transfer modeling including the effect of varying gas temperature, density and CI/CO abundance ratio reveals that there are trends in the temperature, density and CI abundance along with the bar-driven gas flow motions within a nearby galaxy center (r < 1 kpc). These trends agree with the scenario of strong stellar feedback heating up the gas and dissociating the CO into CI on the way. The high CO dissociation in starburst environments also makes the ideally constant CI-to-H2 conversion factor varying with the CI abundances. I further show a preliminary work on understanding the conversion factor of CO and [CI] lines in an analytical way. The analysis shows that these conversion factors strongly depend on a good knowledge of the gas temperature and density conditions and the CO or CI abundances.

February 3: Beam Compressor Differential Delay Line -- Jonas Sauter and Patrick Wessely

GRAVITY Wide comprises an upgrade of the existing beam compressors to incorporate the current PRIMA Differential Delay Line (DDL) functionality. This will save five optical reflections in the science-target beam and consequently increase the optical throughput. We build up a BCDDL mock-up system comprising the metrology beam path, the underlying hardware, and the controlling real-time system. We were able to derive a functional system that can correct differential optical path differences in the order of 10 nm.
In the talk we will present the status of the BCDDL mock-up and give a short introduction to its hardware design and control architecture.

December 2022

December 16: Probing the inner planet-forming zones of disks with mid-infrared spectroscopy -- Giulio Bettoni

Protoplanetary disks are the rotating structures of dust and gas in which planets are formed. In the past decade, ALMA has allowed studying the cold dust and gas of the outer part of disks. The inner region within 10 AU plays a crucial role in the evolution of the entire disk and planet formation but can only be marginally probed by ALMA. In contrast, infrared spectroscopy is a powerful tool to study the warm gas emitting from the inner disk. Thanks to new state-of-the-art facilities such as the VLT-CRIRES+ and JWST-MIRI instruments, it is now possible to significantly improve our understanding of the inner regions of disks.

In this talk, I will discuss how ground-based high-resolution and space-based medium-resolution spectrometers can probe the physical and chemical structure of the inner disk. I will present my work on the CRIRES+ Science Verification observations of the SCrA binary system as an example of how the kinematics and the physical structure of the inner disk can be studied.  I will also present the first JWST mid-infrared detection of abundant carbonaceous molecules in the disk of a very low-mass star, highlighting how JWST-MIRI will help constrain the chemical composition of the inner disk and the processes that are occurring in the terrestrial planet-forming zones.

December 2: First on-sky results of ERIS at VLT -- Kateryna Kravchenko

ERIS is a new adaptive optics instrument installed at the Cassegrain focus of the VLT-UT4 telescope at the Paranal Observatory. ERIS consists of two near-infrared instruments: SPIFFIER, an integral field spectrograph covering J to K bands, and NIX, an imager covering J to M bands. ERIS has an adaptive optics system able to work with both LGS and NGS. The AIV phase of ERIS at Paranal was completed in winter 2021-2022, followed by several commissioning runs in 2022. In this talk I will present the first results of the on-sky performance of ERIS during its commissioning and preliminary scientific results.

November 2022

November 25: The science of scientific writing -- Stefan Gillessen

November 18: An update on SgrA* Flares in Astrometrie & Polarization  -- Felix Widmann

November 4: The Universe and I - musings about the usefulness of astronomy -- Eckhard Sturm

As part of my work I often have to justify the value of astronomy for humankind. Often in an economic context or in terms of technology return. Be it in reports to funding agencies (e.g. DLR), talking to politicians (and other decision makers), or in public talks in schools, in the Volkshochschule (adult education centers), or at parties. I have collected (more or less) usefull arguments that I want to share and discuss with you.

October 2022

October 14: Overview of Galactic Center observations with GRAVITY in 2022 -- Antonia Drescher

In this tea talk I will give an overview of Galactic Center observations with GRAVITY that we had this year. I will start with explaining the motivation for the observations and present the questions that we’re trying to answer. With the main goals for this year of catching a flare, which is hot gas that orbits Sgr A*’s event horizon, tracing the orbits of stars with pericenters that just happened or are soon to come, and deep imaging to search for unknown faint stars, we monitored Sgr A* over a period of 7 months, from March to September 2022. I will show results obtained from imaging with CLEAN, discuss which of the above mentioned goals we could achieve, which difficulties we faced this year, and where we stand with the analysis of the data.
 

October 7: Verification of MICADO Cold Optics -- Federico Biondi

Even if the MICADO team is facing the fourth Final Design Review, the project has already entered the MAIT phase. Consortium partners are getting ready for the integration of the sub-systems and are finalizing and procuring the equipment for the test setups. The complexity of the instrument and the strict requirements demand for a solid test campaign for components and sub-systems. Besides being the PI institute for MICADO, MPE is also responsible for its cryostat and de-rotator, for the focal plane and detector positioning mechanisms, and for the Cold Optics. In this talk I will describe the tests foreseen for the Cold Optics, giving some details on the relation between the requirements to validate and the planning and construction of the proper setup and equipment.

September 2022

Septemper 23: "Hitting Two Objects with One Instrument": Constraining the BLR size and SMBH mass of Mrk1239 and IC4329A with GRAVITY -- Daryl Santos

GRAVITY, the second-generation Very Large Telescope Interferometer (VLTI) instrument, recently paved the way for BH mass measurements by resolving the broad-line region (BLR) via spectro-astrometry, a technique where photocenter offsets of individual velocity channels are observed, providing BLR size measurements of high precision (about an order of 10 µas) and BH mass estimates. In this talk, I will discuss the current progress of our analyses of GRAVITY interferometric spectra of Mrk1239 and IC4329A, two of type 1 active galactic nuclei (AGNs) observed through our Large Program. We reveal the BLR of these objects to be ~135 μas (0.055 pc) and ~40 μas (0.013 pc) offset from their continuum photocenter via model-independent reconstruction of photocenters of the spectral channels of the Brγ, respectively. However, only the photocenters of IC4329A showed a significant (~5.3σ) clear velocity gradient that is almost perpendicular to its offset. We marginally resolved the BLR of Mrk1239 (IC4329A), thus providing a 3σ upper limit of log Θ_BLR (ld)= 2.12 (1.55) for the BLR radius which is consistent with the BLR radius-luminosity relation of nearby AGNs derived from reverberation mapping campaigns. Our dynamical modeling also indicates 3σ upper limits of log M_BH/M_⊙ = 8.23 (8.36) for the BH mass, which are also consistent with the standard MBH-σ* relation for early-type galaxies.

Septemper 9: Introduction of new group members

The specific angular momentum of ETGs --  Claudia Pulsoni

    Mass and angular momentum (AM) are key parameters to understand galaxies. Their co-evolution establishes a tight relation between the stellar specific AM (j*) and the total stellar mass (M*) for disk galaxies. The case of massive early type galaxies (ETGs) is far less explored, as a large fraction of their AM is distributed at large radii where stellar spectroscopy is unfeasible. 

    In this talk, I present results for 32 nearby ETGs based on 2D kinematics out to a mean 6 effective radii with planetary nebulae (PNe) as kinematic tracers of the stellar halos and integral field spectroscopy in the central regions. We estimate projection effects and correct for the limited radial coverage of the PN data using simulated ETGs from IllustrisTNG. The results show that, once j* is integrated out to large radii, ETGs have systematically lower j* than spiral galaxies with similar M*. Their j* is not “hidden” in the outskirts but must be lost during their evolution or distributed among the hot gas component and the satellite galaxies that have not yet merged with the central. 

In-Situ Formation of the Intra-Cluster Light at High Redshift  --  Capucine Barfety

    The Intra-Cluster Light (ICL) traces one of the key components of galaxy clusters. Centred around the core of the cluster, this diffuse halo of light made up of unbound stars is by its very nature a challenge to identify and study. As of today, studies find that the ICL assemble mostly below z=1, through tidal interactions between cluster members, with little evidence of significant ICL above z=1. In this project, I focused on measuring the amount of stellar mass unbound to any galaxy sitting in the core of a disrupted starbursting cluster at z=1.71; using near-infrared high-resolution imaging from the Hubble Space Telescope. I estimate that between (2.2 ± 0.5) × 10^10 M⊙ and (6.6 ± 1.2) × 10^10 M⊙ - depending on the data processing method - of stellar mass has already formed in the area. In addition, these stars are co-spatial with a large molecular gas reservoir (~1 × 10^11 M⊙), a large star formation rate (~860 M⊙/year), and X-ray emissions consistent with the presence of a cooling flow. All these elements combined together point towards in-situ formation of a substantial portion (10-21%) of the ICL in this cluster.

How did I get here?  --  Diogo Ribeiro

    Coming from the westernmost capital in Europe Diogo is one of the new PhD students recently arrived to the IR-GC. Back in Lisbon, Diogo worked at the GRIT group with Professor Vítor Cardoso and Miguel Zilhão on how ultralight bosonic dark matter can shape the evolution of binary systems of black holes.

    Moving to Garching, his work will focus on how the ever more precise data from the galactic center can be used to test GR to new limits. In this short talk he will tell you a bit about himself, his previous work, and his expectations for the years to come.

From Rome to Garching: my scientific interests  --  Matteo Bordoni

    I am a new PhD student in the Galactic Center (GC) group coming from Rome, Italy. I graduated in Astrophysics at "La Sapienza" University in Rome and worked with Prof. Roberto Capuzzo Dolcetta on theoretical aspects related to the orbital precession of S-stars in the GC and on the possibility of measuring the spin of Sgr A* through the detection of deeper S-stars. I am really excited to be here in Garching, having the unique possibility of working with the GRAVITY data and with the top scientists in the field.

July 2022

July 22: Shapes, transformations, and a pinch of gentle feedback -- Junkai Zhang and Stijn Wuyts (University of Bath)

3D shapes of galaxies encode crucial information on their formation process.  In this duo presentation, we start out by characterizing the intrinsic shapes of quiescent galaxies, across a range in mass, redshift, environment and surface brightness profiles.  A comparison to TNG simulated galaxies points at enhanced ex-situ stellar mass fractions as a source of their 3D shape transformation, but also reveals a shortcoming of cosmological simulations, namely in producing thin stellar structures.  We then turn to observations of star-forming galaxies, where the combination of projected axial ratios, galaxy sizes and SED shapes informs us on their dust attenuation, dust content and star/dust geometry.  We address the puzzle to reconcile inferences on dust properties from far-infrared observations on the one hand, and from attenuation estimates and their inclination dependence on the other hand.  Using TNG50, we ask ourselves the question what galaxy obervables -within the context of the simulation- are predictive of future bulge growth.  Finally, time permitting, we will summarize lessons learned from analyzing ionized and neutral gas winds observed among a large sample of normal nearby galaxies, selected from the MaNGA imaging spectroscopic survey.

July 15: Two stacking analyses of lensed galaxies -- Jean-Baptiste Jolly

In this tea talk I will present two stacking analyses of lensed galaxies behind galaxy clusters, from the ALMA Lensing Cluster Survey (ALCS). In the first (Jolly et al. 2021) we studied the [CII] emission line from 52 faint galaxies at z~6. More specifically we looked into the relationship between the stacked [CII] line luminosity and the average SFR of our sample, and compared it to local relationship. In the second analysis --still underway-- we performed continuum stacking of all the galaxies at z>1 in the 33 galaxy clusters observed in the ALCS. From these we derived dust mass evolution as well as comoving dust mass density evolution, from z=1 to z>5. I will finally briefly introduce the novel "symmetric-stacking" method and discuss its potential impact on future stacking analyses.

June 2022

June 3: MeerKAT, rotation measure and the cosmic magnetism -- Feng Gao

In this tea talk I will first give a brief introduction on MeerKAT, its observing capability and latest updates. Then I will switch the focus onto the science topic I’m interested, namely the cosmic magnetism, explaining why we care about magnetic field and why radio interferometer is the best tool to measure it. Finally I will report on the latest development of a new rotation measure synthesis algorithm I’m working on and how we can push the limit for solid rotation measure to fainter targets. 

May 2022

May 13: The Accretion Rate-Disk Mass Relationship in Intermediate-Mass Stars -- Sierra Grant

The accretion rate-disk mass relationship connects the evolution of protoplanetary disks at the star-disk connection to the outer disk mass reservoir. This relationship has long been predicted and has been seen observationally in recent years, teaching us how disks evolve with time. However, most observational efforts have been biased towards low-mass stars. On the other hand, more massive stars have lacked the extensive (sub-)millimeter observations needed to determine the disk masses. In this talk I will present the accretion rate-disk mass relationship for a sample of intermediate-mass stars, highlighting how these objects differ from their low-mass counterparts and what may be driving those differences. I will also discuss a bias in the intermediate-mass sample and how that limits our understanding of late-stage disk evolution around these objects. 

April 2022

April 29: An Observational Overview of Protoplanetary Disks -- Sierra Grant and Guillaume Bourdarot

In this special tea talk, we will give an introduction on our current knowledge of protoplanetary disks by presenting the observations at multiple scales (from a few stellar radii to hundreds of AU) and multiple wavelengths (near-IR, mid-IR, and submillimeter wavelengths). We highlight the complementarity between techniques probing the same scales at different wavelength (e.g., CRIRES+, GRAVITY, ALMA/NOEMA). In particular, we emphasize the unique capability of CRIRES+ and GRAVITY to probe the inner 10 AU of protoplanetary disks. Throughout the talk use on disk, HD 100546, as an example for which an extensive dataset is available to use for a multi-wavelength analysis.

April 8: Imaging with G^R -- Felix Mang

In this talk I will mainly focus on the imaging results of the first observing campaign in 2022. Additionally, I will introduce you further into the code of G^R and give you an update on my current work.

I analyzed various pointings by imaging them and by determining the positions of their corresponding sources. Besides minor deviations from the expected star positions in the SgrA* pointing, S300 in the West pointing showed a considerable offset to predictions. Moreover I will lay out my strategy to obtain unbiased position estimates of known stars in addition to deep images.

April 1: The first year of the MPE-UdeC Partner group -- Rodrigo Herrera-Camus

I will present a summary of the work done by our Partner Group during its first year of existence. First I will highlight the results from the Master thesis of two recently graduated students that used NOEMA observations to study the ISM properties of a massive, star-forming galaxy at z=2 (MD94), and one star-forming galaxy at z=7.2 (GN108036). Finally, I will present the main results of our kinematic analysis of the main-sequence galaxy HZ4 at z=5.5 (Herrera-Camus et al. 2022), and I will introduce the ALMA Large Program CRISTAL for which we are starting to get the first data products.

March 2022

March 25: JWST: new adventures in galaxy and AGN evolution -- Daizhong Liu and Jinyi Shangguan

The James Webb Space Telescope (JWST) has just made breathtaking (calibration) observations and will soon be conducting science observations in the mid of this year. It's more than twice better angular resolution than HST, orders of magnitude better sensitivity than Spitzer, unprecedented coverage of ~1–28μm, and large amount of early-release-science and treasury surveys will greatly benefit the high-z community and significantly push the high-z galaxy and AGN evolution fields forward. In this Special Tea Talk, we will briefly and selectively summarize the expected key scientific breakthroughs of JWST cycle 1 high-z galaxy and AGN evolution programs, and illustrate how we can prepare for and benefit from the upcoming surveys for our group. 

March 4: The Data Reduction Pipeline for the MICADO Instrument -- Yixian Cao

As an integral part of the MICADO project, the MICADO data reduction pipeline is designed to provide data products ready for scientific analysis and instrument health monitoring from the raw data produced by the instrument. The pipeline supports all the four observation modes offered by MICADO: standard imaging, astrometric imaging, high contrast imaging, and slit spectroscopy. The pipeline software will be implemented in the ESO software framework, using the Common Pipeline Library and the High-level Data Reduction Library developed by ESO. For a successful implementation, the pipeline should timely and robustly produce processed data that meets quality requirements of each observation mode. To achieve this goal, simulated data and instrument test data will be used for the pipeline testing. I will summarize the scope and overall design of the pipeline software, present key algorithms for astrometric calibration, and give an overview about the current status of the development.

February 2022

February 25: Massive high-z disk kinematics under the microscope of strong lensing: Low dark matter fraction and inside-out quenching in the massive galactic disk of J0901 at z=2.259 -- Daizhong Liu

It is well-known that massive galaxies have the mass-quenching mechanism leading to the color bimodality seen in the present Universe. However, how the mass-quenching happens in massive star-forming galaxies (SFGs) at high-z are still not well understood. Here we study a unique case of a strongly-lensed z=2.259 SFG, J0901, which happens to be one of the most massive (log(M*/M☉)≥11.0) SFGs at Cosmic Noon (z~1–3) and harboring a mild AGN-driven outflow. Our new CO(3–2) imaging with ALMA probes an extended, ring-like cold molecular gas distribution and its kinematics out to ~5 kpc (~1.5 times the disk effective radius R_e), at a best delensed resolution of ~600 pc. Together with an even better resolved inner rotation curve, and a lower resolution outer profile from the AO-assisted and seeing-limited SINFONI/VLT data, respectively, we find that J0901 has a high baryon surface density and low dark matter mass fraction within R_e, strongly confirming the lower-resolution trends in ~100 unlensed massive SFGs. Our high-resolution data further reveals a large gas instability (Toomre’s Q ≪ 1) in its molecular gas ring, implying a rapid completion timescale of the ongoing inside-out quenching within about five orbital times. Finally, I will present an outlook for key future observations and coding development, e.g., with ALMA, ERIS and JWST, and multi-tracer fitting, which are crucially needed to reduce the uncertainties and constrain the rotation curve and dark matter beyond 1.5 R_e in this unique exemplar of massive SFGs with inside-out quenching caught in the act. 

February 18: Different methods to resolve AGN broad line region -- Jinyi Shangguan

To resolve the broad line region (BLR) of active galactic nuclei (AGNs) is almost the only method to measure the supermassive black hole mass in the distant Universe. In this tea talk, I will summarize four different methods that are able to constrain the geometry and kinematics of the BLR. The reverberation mapping and GRAVITY interferometry techniques have been extensively discussed in our group. I would like to summarize the main physical challenges that we currently encounter. They motivates us to look for other techniques to constrain the BLR structure. I will introduce what can be learned from spectropolarimetry and microlensing of lensed quasar. Some ideas of synergies of GRAVITY(+) observations with these methods will be discussed.

February 11: Globular Cluster Formation as a case of Overcooling -- Alvio Renzini

Observations, especially HST photometry and VLT spectroscopy, have revealed an extreme complexity of the stellar content of globular clusters, with multiple populations being characterized by different chemical compositions resulting from different degrees of CNO cycling, proton-capture processing and helium enrichment. Thus, all globular clusters formed, not in a single, but in a series of star formation episodes, with different complexity from one cluster to another. How this did happen, what kind of stars produced the nuclearly-processed material and which kind of environment gave birth to globular clusters are all highly debated issues with no consensus having emerged so far.
 
In a recent paper (Renzini, Marino & Milone, submitted), driven by observational findings, we select massive interactive binaries as the most suitable among the existing candidates for producing the chemical patterns typical of multiple populations. To avoid supernova contamination we are further driven to endorse the notion that above a critical mass stars fail to produce supernova events, but rather sink into black holes without ejecting much energy and heavy metals. This assumption has the attractive implication of suppressing star formation feedback for some 5–10 million years, leading to runaway star formation, analogous to overcooling that in absence of feedback would have turned most baryons into stars in the early Universe. Under such conditions, multiple episodes of stars formation, incorporating binary star ejecta from previous episodes, appear to be unavoidable, thus accounting for the ubiquity of the multiple population phenomenon in globular clusters. If this is the way globular clusters formed, such delayed supernova feedback may play a role in other star formation circumstances, such as the formation of nuclear star clusters and giant clumps in high redshift galaxies.

February 4: Introduction of new group members

Probing the terrestrial-planet forming zone using multiple tracers -- Sierra Grant

The study of protoplanetary disks benefits from a multi-wavelength and multi-method approach. This allows for the study of the gas and the dust over a range of spatial scales and temperatures. After my previous work using far-infrared and millimeter observations to trace the outer regions of disks, my recent focus has turned to near- and mid-infrared observations. I will briefly introduce three ongoing projects: 1) the characterization of the accretion rate—disk mass relationship for intermediate-mass stars, 2) using both high spectral and spatial resolution data to uncover the structure of the inner disk, and 3) the reduction and analysis of new CRIRES+ L- and M-band observations. Overall, these projects all probe the gas within a few AU of the central star and will give us a better understanding of the disk gas and dust structure. From this, we can investigate the evolution of these systems and the physical conditions in the terrestrial planet-forming zone.

The impact of external photoevaporation on the evolution of protoplanetary disks in the σ - Orioins Cluster -- Giulio Bettoni

Protoplanetary disks are the structures surrounding young protostars, in which planets are formed. Today there is strong evidence that viscosity is the main actor in the evolution of disks. However, other processes can occur, such as external photoevaporation, which is the external dispersion of a disk, due to the impact of Ultraviolet radiation fields emitted by the nearby class O-B stars. Models predict that this process would decrease the ratio between the disk mass M_disk and the mass accretion rate M_acc at which the disk gas accrete onto the central protostar.
In this tea talk I will present the results of my Master thesis that I did at the University of Milan. The aim was to quantify the impact of external photoevaporation on the evolution of protoplanetary disks. To reach this goal, we studied the spectra measured by the X-Shooter instrument of Very Large Telescope, of 31 targets in the σ - Orionis Cluster. By applying a fit procedure developed by Manara et al (2013), we derived M_acc for each target. We then studied the relation between the M_acc and the disk mass M_disk for the 31 targets, and for 8 additional targets taken from literature, looking for the expected signatures of external photoevaporation. We also searched for another signature of external photoevaporation, i.e. the profile and ratio of some forbidden lines from [NII] at 654.8 and 658.3 nm and [SII] at 671.6 and 673.1 nm. We took this information both from the study of our X-Shooter spectra and from previous studies.
We found that external photoevaporation is affecting the disks population within a projected distance from the σ -Ori stellar system of 1.2 pc, and possibly out to 2 pc.

Guillaume Bourdarot

In this introductory tea talk, I will present the work I developed during the three years of my PhD in Grenoble at IPAG. This work focuses on the study of young stars and their protoplanetary disks at the astronomical unit scale with infrared interferometry. It includes both observational and instrumental aspects. In the observational part, I focused on the study of the accretion outbursts occuring in the formation of young stars, through the observation of the star FU Orionis with near infrared interferometry. In the instrumental part of this work, I explored the extension of infrared interferometers to the recombination of a large number of telescopes and kilometric baselines, to overcome the current image reconstruction capabilities of infrared interferometry. In this perspective, we revisited the architecture of heterodyne interferometry, pioneered by Pr C.H.Townes and his team at UC Berkely, at the light of the recent progresses in the field of mid-infrared technologies. We provided a sensitivity analysis of a new architecture, knowing the strong sensitivity limitations of heterodyne interferomery in the infrared. In order to address the problem of correlation bandwidth of a large number of telescopes, we introduced so-called photonic correlation schemes, and implemented a preliminary laboratory demonstrator at 10µm to validate the complete detection and correlation chain. Finally, based on the intrinsic scalability of this technique, we described how these ideas could be apply to a technological pathfinder combining the 8 telescopes of the Very Large Telescopes Interferometer (VLTI) at 10 μm.

January 2022

January 28: No Tea Meeting

January 21: Introduction of new group members (Yixian Cao, Daryl Santos, and Felix Man)

January 14:  Dependence of the CO-to-H2 conversion factor (X_CO) on metallicity, intensity, and spatial scale in the interstellar medium -- Chia-Yu Hu

Star formation occurs in molecular hydrogen (H2) gas. As H2 does not emit radiation under typical conditions, we need a tracer for H2, and carbon monoxide (CO) is the most widely used tracer. Observationally, the H2 mass is inferred from the CO emission via the so-called CO-to-H2 conversion factor (X_CO). However, X_CO is not a universal constant, and its dependence on physical parameters such as metallicity is still not well understood. In this tea talk, I will present our recent hydrodynamical simulations of a feedback-regulated multiphase interstellar medium. By constructing synthetic CO emission maps with radiative transfer calculations, we study X_CO across a wide range of metallicity (0.1 <= Z/Z_sol <= 3). We find that the kpc-scale X_CO can be overestimated at low Z if assuming steady-state chemistry or assuming that the star-forming gas is H2-dominated. On parsec scales, X_CO varies by orders of magnitude from place to place, and it drops to the Milky Way value of 2e20 cm^-2 (K km s^-1)^-1 once dust shielding becomes effective, independent of Z. Our predicted X_CO is a multivariate function of metallicity, line intensity, and beam size, which can be used to more accurately infer the H2 mass.

March 2020

February 2020

February 14: No Tea Meeting

February 7: No Tea Meeting

January 2020

January 31: Star-forming Galaxies at Cosmic Noon -- Natascha Foerster Schreiber

I will summarize selected aspects of our current knowledge from both censuses of population properties and detailed physical views of individual star-forming galaxies at z~1-3, and will highlight exciting prospects with upcoming instruments and facilities.

January 24: Metallicity measurements on galaxies -- Minju Lee

January 17: What sets the C/O ratio in giant exo-planetary atmospheres? -- Ewine van Dishoek

December 2019

December 6: The Molecular Gas Content of Local X-ray Selected AGN -- Taro Shimizu

For the past several years, BAT AGN Spectroscopic Survey (BASS) collaboration has been collecting CO spectra of local (z < 0.05) hard X-ray selected AGN, including my own IRAM 30m Large Program. I will present the initial results of the survey which represents the largest sample of molecular gas measurements of AGN host galaxies in the local universe. I compare the total molecular gas mass, gas fraction, and depletion time to a similar survey of inactive galaxies (xCOLDGASS) to assess the nature of galaxies hosting AGN as well as any potential impact the AGN could have on its host. Matching in both stellar mass and SFR, I find that AGN host galaxies have lower gas masses and gas fractions which then leads to shorter depletion times. 

November 2019

November 29: Hydrodynamical Simulations of the Interstellar Medium (ISM) -- Chia-Yu Hu

I'll give an (biased) overview of cosmological simulations of galaxy formation and discuss their current limitations, which motivate the need of small-scale ISM-resolving simulations. I'll then show some results of supernova-driven galactic outflows as well as dust and molecule (H2 & CO) formation that I plan to do at MPE.

November 22: No Talk -- IR Retreat

November 15:  Exoplanets -- Thomas Ott

I will give a brief introduction in the field of exoplanet research covering the current state of detecting and characterizing exoplanets, and an outlook for the immediate to the more long term activities. This is mostly based on the "Exoplanet Science Strategy" document of the National Academy of Science, written by Dave Charbonneau and Scott Gaudi (2018).

November 8: Polarization Measurements with GRAVITY -- Felix Widmann

I will give a summary about polarimetric observations with GRAVITY. While GRAVITY has all the capabilities of a polarimeter, some challenges arise due to the VLTI and make an additional calibration necessary. I will show what goes into this calibration, why it is necessary, and illustrate everything on an example dataset from the galactic center.

November 1: No talk -- All Saints Day

October 2019

October 26: Fast Infrared Observations of BHBs with CIRCE -- Yigit Dallilar

I will present selected observations of BHBs with CIRCE, mainly focusing on V404 Cygni. During our observations of the source, we discovered fast flaring activity in the infrared, in some cases reaching timescales less than a second. While the spectral index in the optical is consistent during quasi-continuous flaring activty as shown in the following night, our observations demonstrate irregular flaring activity with wildly changing spectral energy distribution at short timescales. This feature suggests rapidly changing physical conditions and inhomogeneities in the jet base. I will discuss the origin of the flaring activity and its possible relation to ejection events seen in BHBs. If time permits, I will talk about our experiences with fast infrared polarimetry using CIRCE.

October 18: Informal Discussion on Applying for Jobs -- Linda Tacconi

October 11: No talk

October 4: No talk -- Day after holiday

September 2019

September 27: No talk -- IR BBQ

September 20: The near infrared flux distribution of Sagittarius A* -- Sebastiano von Fellenberg

I will present the flux distribution created from the GRAVITY light curves obtained in the 2017 and 2018. During these periods we have been able to see Sgr A* in more then 97% of the 5 minute exposures. Because we see the flux distribution turn over, we measure the NIR median flux and the variability. This allows to place model-free constraints on the NIR SED. Furthermore, comparing the observed flux distribution (histogram) to model probability density functions shows that a single log-normal or power-law distribution function may not be enough to describe the observed fluxes.

September 13: GC Flare Modeling: an Update -- Michi Bauböck

I’ll discuss the current state of our understanding of the astrometry of flares at the Galactic Center. In particular, I’ll show the fits obtained by combining the data from multiple flares to constrain the radius, inclination, and position angle of the origin of the IR flares. 

July 26 - September 6

Summer Break

July 2019

July 19: Re-aligning the stars: distortion correction in the frame(s) of Gemini GeMS-GSAOI -- Vincent Garrel

 Similar to the future MPE-led ELT instrument MICADO with the AO module MAORY, the Gemini GSAOI is an imager covering 85x85 square arsecond with a mosaic of NIR-sensitive 20mas pixel scale detectors. GSAOI is fed by GeMS, a MCAO system providing routinely quasi-diffraction limited images (FWHM<90mas PSF in K-band, 10-15%-level uniformity over the full field) since 2013. Due to its conception, configuration and current operational model, the image distortion over the mosaic display a complex and varying pattern. I review the current popular science cases covered by the instrument and the need for more accurate calibrations. I introduce recent progresses on the comprehension of the phenomena inducing distortion. Then, with the help of an astrometric calibration mask I installed in 2017 and the GAIA DR2 high-precision data, I look how to model a varying World Coordinate Systems solution to deliver easy-to-use data for astronomers.

July 12: Subjective Report on Lindau Nobel Laureate Meeting -- Hannah Übler

I will give a subjective report on last week's Nobel Laureate meeting in Lindau - photos, personal highlights, thoughts - which could potentially lead to some discussion.

July 5: LBT & ARGOS -- Sebastian Rabien

With being handed over to the observatory, ARGOS is now available for the LBT community for regular observing.
In this tea talk I will give a brief overview on the LBT and it's instrumentation suite and report on ARGOS, the LBT's LGS ground layer adaptive optics facility. Under regular observing conditions, ground layer adaptive optics can decrease the PSF size by a factor 2-3, tailored to the two custom slit MOS spectrographs LUCI1 and LUCI2, enhancing their spectral and spatial resolution. I will report on the ground layer adaptive optics performance, and highlight some results from the ARGOS commissioning.

June 2019

June 28: The future of exoplanet characterisation is optical interferometry -- Sylvestre Lacour

For those of you who did not listen to my talk last week, I will redo it in a slightly different fashion. The context is still GRAVITY+, and the amazing results that we obtained during the last year. I will update you on paper 2 (on the exoplanet Beta Pictoris b), and on the latest observations. But of this session will be to talk about the next scientific objectives that we could reach with an upgraded GRAVITY. It does include GRAVITY+ along the way. But hopefully, there will be a GRAVITY++.

June 21: No talk -- Day after Corpus Christi

June 14: No talk -- Fachbeirat Rehearsals

June 7: Zooming in on AGN-Driven Outflows at z~2 with SINFONI-AO -- Rebecca Davies

AGN-driven outflows are detected in the majority of high mass galaxies at z~2, and are likely to play an important role in quenching star formation. However, the mechanisms by which AGN accretion energy couples to the surrounding gas and the efficiency of this coupling are the subject of ongoing debate. In this talk I will discuss the insights gained from a detailed analysis of three AGN-driven outflows at z~2, based on SINFONI-AO data. These three systems form a unique sample, because they allow us to study the impact of AGN-driven outflows from circumnuclear to intergalactic scales, and at different phases in the evolution of both the galaxy and the outflow.

May 2019

May 31: No talk -- Day after Ascension

May 24: S2 - an update -- Stefan Gillesen

May 17: Polarisation signatures of hotspots around Sgr A* -- Alejandra Jiménez Rosales

Polarisation offers a new window to study light at event horizon scales and therefore have an insight into strong gravity, magnetic field configurations and plasma physics. I’ll present a study of the polarised properties of a simulated hotspot orbiting a black hole and show how these allow for mapping of the magnetic field configuration near event horizon scales for the first time and an estimation of the magnetic field strength, which has implications on basic accretion physics, including black hole growth and jet launching. I’ll also show a comparison to the recent GRAVITY collaboration near-infrared flare results (2018).

May 10: No talk

May 3: Corona Australis: a young region with old disks -- Paolo Cazzoletti

In recent years, the disk populations in a number of young star-forming regions have been surveyed with the Atacama Large Millimeter/submillimeter Array (ALMA). Understanding the disk properties and their correlation with the properties of the central star is critical to understanding planet formation. In particular, a decrease of the average measured disk dust mass with the age of the region has been observed, consistent with grain growth and disk dissipation. We conducted high-sensitivity continuum ALMA observations of  43 Class II young stellar objects in CrA. The continuum fluxes are used to estimate the dust masses of the disks, and a survival analysis is performed to estimate the average dust mass. We also obtained new VLT/X-Shooter spectra for 12 of the objects in our sample for which spectral type (SpT) information was missing. Twenty-four disks were detected, and stringent limits have been put on the average dust mass of the  nondetections. Taking into account the upper limits, the average disk mass in CrA is 6+-3M_Earth. This value is significantly lower than that of disks in othe young (1-3 Myr) star forming regions (Lupus, Taurus, Chamaeleon I, and Ophiuchus) and appears to be consistent with the average disk mass of the 5-10 Myr-old Upper Sco. The position of the stars in our sample on the Herzsprung-Russel diagram however seems to confirm that CrA has an age similar to Lupus. Neither external photoevaporation nor a lower-than-usual stellar mass distribution can explain the low disk masses. On the other hand, a low-mass disk population could be explained if the disks were small, which could happen if the parent cloud had a low temperature or intrinsic angular momentum, or if the angular momentum of the cloud were removed by some physical mechanism such as magnetic braking. Our results suggest that in order to fully explain and understand the dust mass distribution of protoplanetary disks and their evolution, it may also be necessary to take into consideration the initial conditions of star- and disk-formation process. These conditions at the very beginning may potentially vary from region to region, and could play a crucial role in planet formation and evolution.

April 2019

April 26: The Star Formation Histories of Quiescent Galaxies -- Sirio Belli

The stellar light emitted by high-redshift galaxies contains absorption lines that can be used to derive the past histories of these systems, and estimate their ages. I will discuss the spectral fitting technique that makes this possible, and present recent results from the analysis of deep Keck spectra of quiescent galaxies at 1<z<2.5.

April 19: No talk - Good Friday

April 12: No talk

April 5:  Continuum and Line FItting for circumstellar disks -- Yao Liu

We present CLIcK, a flexible tool to simultaneously fit the continuum and line emission for circumstellar disks. The DDN01 continuum model (Dullemond et al. 2001) and a plane-parallel slab of gas in local thermodynamic equilibrium are adopted to simulate the continuum and line emission respectively, both of them are fast enough for homogeneous studies of large disk samples. We applied CLIcK to fit the observed water spectrum of the AA Tau disk and obtained water vapor properties that are consistent with literature results. We also demonstrate that CLIcK properly retrieves the input parameters used to simulate the water spectrum of a circumstellar disk. CLIck will be a versatile tool for the interpretation of future James Webb Space Telescope spectra.

March 2019

March 22:  A conference summary: is our changing look now only partially obscured? -- Ric Davies

These are the same slides I used at the AGN meeting held at the end of 2018. I will reflect on the talks and posters presented during that meeting, to assess the current status of our understanding of the 'torus'. I will address how our picture has developed in recent years. And I will emphasize how we need to think of the torus in the context of the structures around it on both larger and smaller scales; put some focus on temporal aspects; and consider some pitfalls.

March 15: Electron densities of two dusty starbursts at z=4.7 using [NII] lines at far-infrared -- Minju Lee

The most massive galaxies in the local universe are often located in clusters and the fossil record of their stellar population indicates the formation epoch of z~5 with bursts of star formation. However, the detailed physics of the formation mechanism and the impact from/to the environment during the formation are largely unconstrained. Dusty starbursts and quasars at high redshifts have been considered as promising progenitors of these massive populations, which could help to pin down the unknowns above. With this motivation, we have been studying a pair of dusty starbursts (SMG-QSO) at z=4.7 in detail. In this tea talk, I will present recent progress based on the detection of [NII] lines at 122 um and 205 um using ALMA. The detection allows us to constrain the electron densities of the two dusty starbursts for the first time at this redshift, giving statistically different values between the SMG and the QSO. I will discuss the results and a potential extension of this project using larger samples.

March 8: A galactic centre gravitational-wave beacon -- Odele Straub

In my first Tea Talk I will stay close to the tea theme and tell you how teapots and saucers are connected to the galactic centre. In other words, I will show with a back-of-the-envelope calculation, that the energy supply of a single star is sufficient to sustain a planetary mass in orbit around the central massive black hole and produce a long-lasting and strong gravitational-wave signal that can permeate the whole Galaxy. 

March 1: The Life Cycle of Star-forming Gas in Galaxies -- Andreas Schruba

Star formation in individual molecular clouds and whole galaxies is inefficient and we lack a good understanding why this is so. Observational and theoretical studies identify gas and galaxy dynamics, gas turbulence, and stellar and AGN feedback as key physical processes but we lack quantitative knowledge of timescales and efficiencies of the gas-star cycle. I have contributed to the formulation of a new statistical method that extracts these timescales and efficiencies from observations sampling molecular clouds and young stars across galaxies. In our first study, we apply this method to sensitive ALMA observations of the nearby, flocculent galaxy NGC 300 and find star formation to be fast and inefficient due to short-lived molecular clouds and rapid feedback (Nature, accepted). Next, we will study the gas-star cycle across 80 nearby galaxies across the star-forming main sequence observed by the PHANGS ALMA, MUSE, HST Large Programmes.

February 2019

February 22: Sub-pc dust structure and gas kinematics of a nearby AGN -- Jason Dexter

I’ll show preliminary GRAVITY AGN team results for the nearby Seyfert 1 NGC 3783. We see elongated and asymmetric dust structure at sub-mas scale with an orientation roughly matching that of the broad emission line velocity gradient. This suggests a common physical origin of the hot dust and ionized gas. It could either be a (counter-)rotating, flattened, equatorial structure or an extended radial outflow. 

February 15: No talk

February 8: No talk

February 1: What stellar orbit is needed to measure the spin of the Galactic Center black hole from astrometric data?  -- Idel Waisberg

One of the main goals of GRAVITY is to constrain the spin of SgrA*. Although that might be possible through flare astrometry, a cleaner measurement could rely on astrometric monitoring of a yet to be discovered inner star through Lense-Thirring precession. I will talk about the prospects of a spin detection with GRAVITY by combining simulations of relativistic stellar orbits with the known properties of the Galactic Center stellar cluster. How many stars are expected within the GRAVITY field of view? What is the chance that they could lead to a spin detection for a reasonable observing campaign? What is the role played by radial velocities in spin detection? 

January 2019

January 25: Hunting for fainter stars around SgrA*  -- Feng Gao

One of the main science goal for GRAVITY in the Galactic Center region is to find stars within the S2 orbit. In this tea talk, I will introduce the nature of this "source-detection" problem, summarize what we have done with the past two years of GRAVITY data, and speculate for the upcoming observations this year. 

January 18: The GRAVITY AGN Large Program -- Eckhard Sturm

December 2018

December 14: ERIS, the new instrument for the VLT on 2020 -- Ángela Cortes

I will describe the two instruments that are part of ERIS, and the different observing modes that they will offer, plus some details about the AO module and performance, to end up with the details on what we will change, at MPE on SPIFFI to get SPIFFIER.

December 6: The ISM properties of local analogs of high redshift Main Sequence Galaxies -- Alessandra Contursi

I will present the results of the analysis of PACS spectroscopy and photometry data of a sample of Lyman Break Analogs (LBAs). These are local galaxies that share many properties with the high redshift galaxies selected with the Lyman break technique. I will try to answer the question of whether these systems have ISM typical of galaxies above the local main sequence or rather of z~1-2 MS star forming galaxies.

November 2018:

November 30: No talk

November 23: Molecular outflows in nearby galaxies -- Dieter Lutz

November 2: No talk, day after holiday (All Saints' Day)

October 2018:

October 26: Gas Content and Star formation of Quasar Host Galaxies -- Jinyi Shangguan

The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. The infrared spectral energy distribution (SED) provides abundant information of the dust and gas in different phases across the galaxy. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated SED, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass.  Using this method, we find the low redshift quasars are not capable to blow the cold gas out of the host galaxy via the so-called "quasar mode" feedback, and study the star formation of starburst galaxies along the merger sequence.  I will briefly introduce some ongoing works using ALMA Compact Array to measure the CO emission in some quasar host galaxies, which may shed light on some future observations.

October 17: Getting out the most of SINFONI data and the Equivalence principle -- Felix Widmann

I will show the changes we did to the SINFONI data reduction and calibration and how they lead to better radial velocities. This helped us to, for example, test the Einstein Equivalence Principle around Sgr A*. I will show the results from this and shortly comment on other applications, as for example the search for binaries among the S-Stars.     

October 12: Molecular Outflows Near and Far  -- Rodrigo Herrera-Camus

October 5: Some submillimeter results on the Galactic center  -- Liu Hauyu (ESO)

I will (informally) present some of my previous and ongoing observational studies about the gaseous accretion flows towards the Galactic center, from 20 pc scales to few tens of AU scales. I will provide some of my opinions about how  potentially infrared and (sub)millimeter and radio observations are complementary with each other,  which I would be happy to discuss with the audience. 

September 2018:

September 28: PHIBSS1, 2 and Beyond... -- Linda Tacconi

I will summarize what we've learned from the IRAM PHIBSS surveys, and discuss the IR-group's plans for NOEMA^3D, our planned legacy program for the newly upgraded NOEMA. 

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

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.