Thunch is a weekly grad-student run seminar series which gives local and visiting scholars, especially students, the opportunity to present their research to a broad audience at the Princeton Department of Astrophysical Sciences. Potential visiting speakers should contact the Thunch Czars, Yue Pan and Zack Andalman.
When: Thursdays at 12 pm (food), 12:15 pm (talk)
Where: Peyton Hall, "grand central" (big room in the center of the building)
What: food + 45 minute talk and discussion
Rules
- Priority goes to students and to those who have not given a talk recently.
- Visiting speakers must be explicitly invited by the department.
- There is no money in Thunch to pay for travel, so visitors need another source of funding.
- Speakers must send a title and abstract to the Thunch Czars at least one week in advance of their talk.
Now you know everything you need to know about Thunch. Join us for good food and good science. Reach out to the Thunch Czars with any questions.
Fall 2024 Upcoming Speakers:
| Date | Name and Institution | Title and Abstract |
|---|---|---|
| September 5th Grad student lightning talks | 1. Zack Andalman, Princeton University 2. Matt Sampson, Princeton University 3. Christian Kragh Jespersen, Princeton University | 1.Thunderstorm - Relativistic Electron Transport in KNe Ejecta 2. Latent ODEs for Astrophysical Systems 3. Inseparable Galaxies |
| September 12th | Bob Kirshner, Harvard University | Title: The Thirty Meter Telescope: Progress and Prospects Abstract: The Thirty Meter Telescope is a top-ranked priority of the Astro 2020 Decadal Survey because its combination of very large aperture and adaptive optics opens up vast areas for unique observational work across a broad swath of frontier science ranging from exoplanets to the fundamental physics that underlies cosmic acceleration. In this talk, I will describe the telescope and its first-light instrumentation; illustrate some of the science this enables; place the TMT in the context of the US Extremely Large Telescope program and the European-ELT, HST and JWST; and summarize the present status of the design, production. and funding of the TMT by philanthropy, the partners (Caltech and the University of California, Canada, India and Japan), and the US National Science Foundation. I will also describe our ongoing efforts in Hawaii to create a new model of community astronomy for this and other large scientific infrastructure projects. |
| September 19th | Jacqueline Antwi-Danso, University of Toronto | Title: Too Big to Be?: Searching for the Most Massive Galaxies in the Distant Universe Abstract: One of the unsolved problems in extragalactic astronomy is understanding the physics of how the most distant massive galaxies grow their stellar mass over cosmic time. Large-scale hydrodynamical simulations have been largely successful in matching the basic properties and number densities of these galaxies at z < 2.5 (covering the past 11 Gyr). This has given us confidence in our understanding of the physics that regulates star formation and quenching over most of cosmic history. However, at earlier times, simulations underestimate the number densities of massive quiescent galaxies by a shocking 1-2 orders of magnitude. Recent JWST discoveries of massive galaxies observed at even earlier times than we thought possible have brought this tension with theory back to the limelight. In this talk, I will give an overview of the systematics contributing to this discrepancy between theory and observations, as well as our best attempts at addressing it using (1) medium-band galaxy surveys; (2) novel color-color selection methods; (3) physically motivated star-formation histories; and (4) detailed spectroscopic characterization. |
| September 26th | Haowen Zhang, University of Arizona | Title: The empirical TRINITY model of galaxy--supermassive black hole connection: What can we learn from JWST and NANOGrav? Abstract: JWST has found many more supermassive black holes (SMBHs) at z>4 than we expected. In addition, some of these SMBHs show spectacular properties, such as their masses given their redshifts and host galaxy masses. Nonetheless, it is difficult to reconstruct their evolution histories and draw connections between these high-z SMBHs and lower redshift analogs. In this talk, I will present TRINITY, a new data-driven model to reconstruct SMBH growth histories in different galaxies from z=0-10. Based on my predicted galaxy—SMBH connection, I will show how different observed SMBH populations across cosmic time are connected with each other. In addition, I will show some preliminary results of incorporating gravitational wave background (GWB) detections to constrain TRINITY, and discuss the potential of multi-messenger constraints on empirical models of galaxy—SMBH connection. |
| October 3rd | Bingjie Wang, Penn State University | Title: The James Webb Space Telescope (JWST) is transforming our understanding on galaxy formation and evolution, revealing distant galaxies deep into the epoch of reionization and revealing red sources that were simply unknown pre-JWST. In this talk, I will discuss two key areas, with a focus on the challenges in modeling the spectral energy distributions in the JWST era. First, a central science goal of JWST is finding the first galaxies, which often requires modeling of photometric data to select candidates for spectroscopic follow-up. I will show the modeling work that turns the nearby cluster A2744 to one of deepest views of our universe, as part of the UNCOVER survey. The resulting rich, public dataset, reveals stellar populations across 0.2 < z < 13, and helps to lead to the discovery of the surprisingly large galaxies at z > 12. I will also briefly discuss how this exquisite dataset is poised to redefine our census of galaxy populations. Second, the optical/IR sensitivity of JWST has led to the discovery of compact red sources, initially interpreted as apparently massive galaxies at z > 7. This interpretation yields a strongly accelerated time line compared to standard models of galaxy growth. Yet, major uncertainties remain about their nature due to the limited photometric data. I will present detailed studies of these so-far mysterious "little red dots", enabled by the spectroscopic data from the RUBIES program. Remarkably, we find clear signatures of evolved stellar populations, the formation histories of which extend hundreds of millions of years into the past in galaxies only 600–800 Myr after the big bang. Confusingly, some of them exhibit broad Balmer emission lines, suggesting that dust-reddened AGNs contribute to, or even dominate, the spectral energy distributions red-ward of ~rest 0.6μm. I will explore potential origins and evolutionary tracks, from the cores of massive galaxies to low-mass galaxies with over-massive black holes, and conclude with remaining puzzles and possible future directions to form a complete physical picture of these intriguing systems. |
| October 10th | Austen Gabrielpillai | Title: Semi-analytic satellites - Satellite evolution in Milky Way-like environments via a robust CGM co-evolution model Abstract: The evolution of satellite galaxies is an unsolved problem in galaxy formation. Recent observations such as the SAGA and ELVES surveys find tension in HI contents and star formation of satellites around their central host galaxies when compared to our own local environment, the Milky Way. These processes are potentially highly influenced by the host's circumgalactic medium (CGM), and to constrain these cases requires accurate and fast modeling of satellite-host interactions. In this work, we present our methodology for evolving z = 0 surviving satellites alongside their central galaxy in Sapphire, a semi analytic CGM co-evolution model of galaxy formation. We have added interstellar medium (ISM) structure, CGM and ISM ram pressure stripping, as well as satellite pre-enrichment via their host galaxy. Utilizing the Symphony zoom-in dark matter halo suite, we are able to reproduce observations such as the cumulative satellite stellar mass function and the stellar mass-metallicity relation of the local Milky Way satellites from the ultrafaints to the SMC and LMC. Our added framework is highly modular and sets the stage for multi-scale modeling and fast, robust Bayesian inference of satellite-related physical parameters. |
| October 17th | Jean Somalwar, Caltech | Title: Expanding the diversity of tidal disruption events Abstract: Tidal disruption events (TDEs) occur when a star is tidally shredded by a supermassive black hole (SMBH). They are a key probe of SMBH demographics and accretion physics. Optical surveys have been key for identifying TDEs, but searches have, until recently, relied on the properties of known TDEs to develop selection criteria, leading to TDE samples that likely suffer from significant selection effects. This talk will summarize efforts to expand the landscape of TDEs using both radio and optical surveys. I will first discuss highlights from radio TDE searches - in particular, a sample of radio+optical TDEs that suggest that expanding our TDE searches may illuminate fundamentally different (lower mass, gas-rich) systems. I’ll then discuss efforts to find unusual TDEs in optical surveys, including a unique repeating event. I’ll conclude with a brief summary of ongoing efforts to expand our optical TDE selection and initial results. |
| October 24th | David Robinson, University of Michigan | Title: Connecting galaxy cooling and heating functions to the incident radiation field with machine learning Abstract: In the era of JWST, observations are yielding more detailed information about the distribution and structure of star-formation regions in distant galaxies than ever before. To interpret these observations, galaxy simulations need to use increasingly sophisticated sub-grid models of star formation and feedback. One feedback mode is direct heating of gas by incident photons. Gas often needs to cool radiatively to reach the low temperatures and high densities required for star formation. Consequently, a key component of galaxy simulations is the gas cooling and heating functions, which control gas thermodynamics. These functions depend on both gas properties (temperature, density, metallicity) and the incident radiation field, which generally includes both a spatially constant extragalactic background and contributions from local light sources. Although cooling and heating functions can be computed exactly with photoionization codes, that is computationally expensive and impractical to do on-the-fly in hydrodynamic simulations. We train machine learning models to predict cooling and heating functions calculated with the photoionization code Cloudy at fixed metallicity. We find that models trained with as few as 3 averaged radiation field intensities can outperform a traditional interpolation approach at each fixed metallicity. |
| October 31st | Xiaowei Ou, MIT | Title: The “visible” and “invisible”: stars as tracers for the Milky Way formation Abstract: “How do galaxies form?” is one of the most important questions in modern astrophysics. Hierarchical galaxy formation, the most plausible theory behind galaxy formation, suggests that galaxies, including the Milky Way, grow through the accretion of smaller systems over a scaffolding of an invisible matter called Dark Matter. Such growth is evidenced by the different stellar structures found in the Galaxy over the last few decades, accelerated most recently by the Gaia space mission. Yet, we still lack a full picture of the formation of the Milky Way and its stellar structure, and we are even further in understanding its Dark Matter scaffolding. In this talk, I will present my research on stellar heavy element abundances and kinematic substructures from disrupted dwarf galaxy debris in the Milky Way, probing the galaxies that merged with the Milky Way in the past. Additionally, I will share our work on mapping the dark matter distributions in the Milky Way and one of its ultra-faint dwarf galaxies using stellar dynamics, combining simulations with observational data to study ongoing merger events and how hierarchical assembly shaped the Milky Way today. I will end with an outlook on how synthetic surveys from simulations are helping bridge gaps between theory and observation, offering a path toward a deeper understanding of how the Milky Way came to be. |
| November 7th | Nicholas Rui, Caltech | Title: Stellar mergers: an asteroseismic perspective Abstract: Stellar multiplicity is the norm and stellar interactions are common. However, stars which have experienced mass transfer or merger often appear superficially similar or even identical to isolated stars. Asteroseismology provides an avenue for recognizing stellar merger remnants by identifying unusual internal structures which single stellar evolution cannot make. I show that red giants which engulf close main-sequence companions on the red giant branch can have conspicuous mismatches between their asteroseismic masses and g-mode period spacings. Furthermore, I show that the mergers of cataclysmic variables may account for an observed population of asteroseismically identified undermassive red clump stars, and may also produce significantly over-inflated, carbon-rich core helium burning stars. |
| November 14th | Christina Willecke Lindberg, Johns Hopkins University | Title: Reading between the Stars: Resolving the Multi-Scale Interstellar Medium of Local Group Galaxies Abstract: Observational constraints on the small-scale structure of the interstellar medium (ISM) are critical for understanding how star formation and feedback processes drive galaxy evolution across cosmic time. The last decade has seen an explosion of panchromatic HST imaging of nearby galaxies (e.g. PHAT/PHAST, HTTP, PHATTER, LUVIT, Scylla, etc.). With stellar SED fitting techniques like the Bayesian Extinction And Stellar Tool (BEAST), we can harness these rich data to simultaneously characterize individual resolved stars and extract information about the ISM. We review new findings on the formation conditions of massive stars in the Andromeda galaxy (M31; PHAT), present new parsec-scale dust extinction maps in the Magellanic Clouds (Scylla), and discuss future BEAST science to investigate how small-scale processes shape galaxy evolution. |
| November 21st | Claire Ye, University of Toronto | Title: Connecting Compact Object Dynamics with Multi-Messenger Observations in Dense Star Clusters Abstract: Frequent dynamical encounters in globular clusters significantly enhance the production of multi-messenger phenomena. It is now well established that globular clusters host robust populations of compact objects, including low-mass X-ray binaries, millisecond pulsars, and gravitational wave sources. The evolution of these compact objects is intricately linked within dense star clusters. Black holes impact the dynamics of neutron stars and white dwarfs. In turn, the collapse of white dwarfs and neutron stars through accretion or mergers plays a crucial role in explaining various observations of more massive compact objects. In this talk, I will use binary black hole mergers and millisecond pulsar observations as examples to illustrate the dynamical evolution of black holes, neutron stars, and white dwarfs in dense star clusters. I will demonstrate how we can connect these dynamics with rich observational data to understand compact object formation and evolution. |
| December 5th | Viraj Pandya, Columbia University | Title: New Puzzles in Galaxy Formation: From the Cosmic Web to the Origin of the Hubble Sequence Abstract: I will present surprising observational results on the 3D shapes and large-scale alignments of high-redshift galaxies from JWST. I will show that there are many more linear, elongated dwarf galaxies than there are round, circular dwarf galaxies seen in projection at high redshift (z>1). This puzzle was first hinted at with HST ~30 years ago but has defied a clear explanation since. After ruling out a detection bias against faint, face-on disks with JWST, I will explore a variety of solutions. One reasonable interpretation is that, unlike in the local Universe, the majority of high-redshift dwarf galaxies (including Milky Way progenitors at z>2) may be significantly flattened along two axes like prolate (cigar-shaped) or triaxial (surfboard-shaped) ellipsoids. This preferential elongation is naturally expected from the tidal field of the filamentary cosmic web, in which case we should also see strong intrinsic alignments. I will present evidence for such alignments when averaging over the orientations of background galaxies in a "blank" JWST deep field. We cannot yet rule out a lensing origin for the alignments and I will discuss implications for upcoming weak lensing searches with Roman and Euclid. If confirmed, this new dominant class of early elongated protogalaxies may hold unique clues about the origin of the Hubble Sequence and the emergence of early cosmic web filaments. Finally, I will also summarize how this seemingly niche puzzle bridges together many different areas of astrophysics and cosmology (including Galactic archaeology, dynamics and dark matter phenomenology), unlocks fresh science cases for the upcoming era of Extremely Large Telescopes, and requires a mixture of theory, observations, statistics and AI/ML to fully understand. |
| December 12th | Andrew Casey-Clyde, Yale University | Title: Multi-messenger Constraints on Supermassive Black Hole Binaries Abstract: Pulsar timing array experiments around the world have reported evidence of a stochastic gravitational wave background (GWB) at nanohertz frequencies. This background is thought to be sourced by a cosmic population of supermassive black hole binaries (SMBHBs) — systems of two gravitationally bound supermassive black holes emitting gravitational waves as they co-orbit each other at sub-parsec separations. Quasars have long been associated with galaxy mergers, suggesting a link with SMBHBs. In this talk, I will show how we can constrain the mass, volume, and local number density of the SMBHB population using a multi-messenger, quasar-based SMBHB population model. I will then talk about how the discrete nature of SMBHBs can manifest as excursions from, and breaks in, the expected fGW-2/3 power-law behavior of the GWB strain spectrum. I will also discuss how we can use SMBHB population models to interpret the observed spectrum of the GWB. Finally, I will show how candidate binary quasars — identified via periodicities in their light curves — can be used to constrain the fraction of quasars hosting a SMBHB. I will also show how this compares to the predicted fraction of galaxies hosting a SMBHB. |
Spring 2024
February 8th: Benjamin Remy (Princeton University)
February 15th: Lauren Weiss (University of Notre Dame)
February 22rd: Martin Elvis (Harvard)
February 29th: Dom Rowan (Ohio State University)
March 7th: Yubo Su (Princeton University)
March 21st: Pascal Marichalar (French National Center for Scientific Research)
March 28th: Yuanhong Qu (University of Nevada, Las Vegas)
April 4th: Nick Kokron (Princeton University)
April 11th: Kovi Rose (University of Sydney)
April 18th (double talk)
Jamila Pegues (Space Telescope Science Institute)
Kris Pardo (University of Southern California)
April 25th: Jackie Faherty (American Museum of Natural History)
May 2nd: Trung Ha (University of North Texas)
May 16th: Stephane Werner (Durham University)
Fall 2023:
September 7th: Andrew Saydjari (Harvard)
September 14th: Samantha Wu (CalTech)
September 21st: Viraj Karambelkar (CalTech)
September 28th: Fan Zou (Penn State)
October 5th: Zhuhai Li (CalTech)
October 12th: Prof. Yue Shen (University of Illinois Urbana-Champaign)
October 19th: Mor Rozner (Israel Institute of Technology)
October 26th: Shangjia Zhang (University of Nevada)
November 2nd: Teodor Grosu
November 9th: Hsiang-Chih Hwang (IAS)
November 16th: Kishore Patra (Berkeley)
November 30th: Princeton Graduate Students
Spring 2023:
February 16th: Chia-Yu Hu (University of Florida)
February 23rd: Dan Foreman-Mackey (CCA)
March 2nd: Lyla Jung (ANU)
March 16th: Vicente Valenzuela-Villaseca (Princeton University)
March 30th: Roohi Dalal (Princeton)
April 6th: David Velasco (Princeton)
April 13th: Zili Shen (Yale)
April 20th: Sabrina Appel (Rutgers)
May 4th: Ewine van Dishoeck Leiden (Leiden Observatory, the Netherlands)
May 11th: Charlotte Ward (Princeton University)
Fall 2022:
September 15th: Aritra Ghosh (Graduate Student, Yale University)
September 22nd: Thales Gutcke (NASA Hubble Fellow and Lyman Spitzer, Jr. Postdoctoral Fellow, Princeton)
September 29th: Fengwu Sun (Graduate Student, University of Arizona)
October 6th: Yubo Su (Lyman Spitzer Jr. Postdoctoral Fellow, Princeton)
October 13th: Yinhao Wu (Graduate Student, Leicester University)
October 20th: Fall break
October 27th: Lizhong Zhang (Graduate Student, University of California, Santa Barbara)
November 3rd: Oliver Zier (Graduate Student, Max Planck Institute for Astrophysics, Garching, Germany)
November 10th: Chang-Goo Kim (Post-Doctoral Associate Research Scholar, Princeton)
November 17th: Tsun Hin Navin Tsung (Graduate Student, University of California, Santa Barbara)
December 1st: Ore Gottlieb (Rothschild Fellow, CIERA Postdoctoral Fellow, Northwest University)
December 8th: Sihao Cheng (Postdoc Member at the Institute for Advanced Study)
Spring 2022:
February 3rd: Benjamin Crinquand (Post-Doctoral Associate Research Scholar, Princeton)
February 10th: Matthew Coleman (Post-Doctoral Associate Research Scholar, Princeton)
February 17th: Riddhi Bandyopadhyay (Post-Doctoral Associate Research Scholar, Princeton)
February 24th: Alex Gagliano (Pre-Doctoral Fellow, CCA Flatiron)
March 10th: Igor Andreoni (Postdoctoral Fellow, Joint Space-Science Institute)
March 17th: Sihao Cheng (Postdoctoral Fellow, Johns Hopkins University)
March 24th: Keith Hawkins (Assistant Professor, University of Texas at Austin)
March 31th: Frank van den Bosch (Professor of Theoretical Astrophysics, Yale)
April 7th: Mor Rozner (Graduate Student, Technion - Israel Institute of Technology)
April 14th: Sam Yee (Graduate Student, Princeton)
Click here for the latest schedule information
