Colloquia Archives

Prof. Marta Bryan (Assistant Professor at the University of Toronto)
Thursday, April 11, 2024
3:45 p.m.
LGRT 1033
Title:
Detection and characterization of gas giant exoplanets
Prof. Jeyhan Kartaltepe (Associate Professor at RIT)
Thursday, April 4, 2024
3:45 p.m.
LGRT 1033
Title:
Galaxy evolution and morphologies; PI of COSMOS
Professor Sarah Millholland, MIT
Monday, March 25, 2024
4:00 p.m.
LGRT 1033
Title:
Tidal Sculpting of Short-Period Exoplanets
Abstract:
A large fraction of exoplanetary systems contain planets that orbit very close to their host stars. With orbital periods in the range of days to weeks, tidal forces become important and lead to significant orbital and physical effects on the planets. In particular, time-varying tidal deformations lead to planetary orbital decay and tidal heating in the planetary interiors, which manifests physically as radius inflation. This talk will focus on various observational mysteries of short-period exoplanet demographics and show how tidal dynamics offer a compelling explanation for these puzzles. I will close by highlighting how our tidal theories can be tested with ongoing JWST observations.
Dr. Pratika Dayal (Kapteyn Astronomical Institute, The University of Groningen)
Monday, March 18, 2024
4:00 p.m.
LGRT 1033
Title:
The puzzling properties of early galaxies: implications for galaxy formation, reionization and gravitational wave astronomy
Abstract:
Galaxy formation in the first billion years mark a time of great upheaval in our cosmic history: the first sources of light in the Universe, these galaxies ended the 'cosmic dark ages' and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of 'cosmic reionization'. At the forefront of astronomical research, the past few years have seen cutting-edge instruments such as JWST and ALMA provide tantalising glimpses of such galaxies assembling in an infant Universe. Puzzlingly, these observations indicate an over-abundance of bright, dusty galaxies in addition to yielding unexpectedly numerous and massive black holes (up to a 100 million solar masses) within the first 600 million years, posing an enormous challenge for galaxy formation models. I will show how this data has provided an unprecedented opportunity to shed light on their dusty nature and study the key physics driving their formation and evolution. I will also show how these early systems provide a powerful testbed for Dark Matter models beyond "Cold Dark Matter". Finally, I will show the implications of these observations both for reionization and the gravitational wave event rates expected from early black holes in the Laser Interferometer Space Antenna Array (LISA) era
Dr. Yuan Li (University of North Texas)
Wednesday, March 13, 2024
4:00 p.m.
LGRT 1033
Title:
Supermassive Black Hole Feeding and Feedback in Massive Systems
Abstract:
Supermassive black holes (SMBHs) play a crucial role in shaping the evolution of galaxies, especially the massive ones. In this talk, I will briefly review our current knowledge of three key aspects of SMBHs -- their feeding, feedback, and connections to host galaxies. I will discuss some of the efforts my group has made to advance our understanding in these research areas. In particular, I will highlight our recent "mesoscale" simulations which follow multiphase SMBH accretion flows from galaxy scales all the way down to scales relevant for accretion disks. I will also discuss our recent observational analysis of the turbulent motion of the cool clouds in centers of galaxy clusters, which has significant implications on how SMBH feedback operates in these systems. The results also put unprecedented constraints on microscopic transport processes in the weakly collisional, magnetized intracluster plasma. I will also discuss some recent and ongoing work on SMBH-host galaxy scaling relations and how machine learning may transform this field. Lastly, I will briefly discuss some exciting future directions of my research program.
Dr. Chelsea Harris (Michigan State University)
Monday, March 11, 2024
4:00 p.m.
LGRT 1033
Title:
Constraining Supernova Progenitors via their Circumstellar Environments
Abstract:
Supernovae (SNe) are the explosive deaths of stars that serve as critical cosmic beacons and galactic energy sources. Yet, the identities of their stellar progenitors remain elusive. A key method for determining the stellar progenitors of SNe is to look for circumstellar material (CSM), which encodes information about stellar evolution prior to explosion. “Interacting SNe” are those in which the SN ejecta collide with CSM to form a bright shock wave, from which we can infer the CSM density profile. While the canonical picture of CSM is a smooth wind, discoveries in the last ~decade have revealed great diversity in how CSM is distributed around SNe. In particular, we see initially normal-looking SNe transform into interacting SNe months after explosion, because the CSM is distant from the progenitor. This distant CSM is likely formed by mass-loss processes in close binary star evolution, which makes it particularly interesting as we work to understand the progenitors of thermonuclear SNe and gravitational wave sources. With an eye on the upcoming Vera Rubin Observatory Legacy Survey of Space and Time (LSST), my research focuses on using theoretical models to analyze SNe with distant CSM. These events, which are currently rare, will become commonplace in the LSST era when hundreds of thousands of supernovae are discovered each year. In my talk, I will describe the three key theoretical ingredients for understanding these events: shock hydrodynamics, charged particle populations, and radiation transport. I will show examples of how theoretical advancements allow us to analyze old observations in a new light and pave the way for new discoveries. Primarily, I will focus on the work that needs to be done over the next ~decade on both the observational and theoretical sides to advance this science and pin down SN progenitors.
Dr. Maria Charisi (Washington State University)
Monday, February 26, 2024
4:00 p.m.
LGRT 1033
Title:
Frontiers of multi-messenger astrophysics with pulsar timing arrays
Abstract:
A Pulsar Timing Array (PTA) is a galactic-scale detector that relies on precision timing of milli-second pulsars. As of last summer, all major PTA collaborations have found evidence of a low-frequency gravitational wave background. The most likely origin of this background is a population of supermassive black hole binaries (SMBHBs) formed in galaxy mergers. I will present the exciting recent results from the North American Nanohertz Observatory for Gravitational waves (NANOGrav) collaboration, and their meaning for extragalactic astronomy. I will also describe the next major milestone, which is likely the detection of an individual resolved binary. These systems, which should stand above the background, are also expected to be bright sources of electromagnetic emission, and can be detected as quasars with periodic variability. I will summarize the status of current electromagnetic searches and their challenges. Finally, I will discuss my plans to combine electromagnetic and gravitational-wave data and bring the first multi-messenger detection of a SMBHB within closer reach.
Dr. Dongzi Li
Thursday, February 22, 2024
4:00 p.m.
LGRT 1033
Title:
Mysteries of fast radio bursts
Abstract:
Making use of exponential increases in computing power and memory per dollar, radio astronomers have been able to search larger areas of sky with ever higher bandwidth at high time and frequency resolution. In 2007, a mysterious millisecond-duration burst was found around the cellphone band. This kind of signal is now known as fast radio burst (FRB), energetic bursts visible at a cosmological distance. FRBs are a new probe of cosmological matter, since each burst carries information on the number of electrons it encounters before reaching the earth. In this talk, I will review the current understanding of the origin of FRBs, as well as the many remaining mysteries, including the location of the FRBs, the magneto-environment and the long-term periodicity. I will also discuss the observed properties of special pulsar systems that help us understand FRBs. In the next few years, current and upcoming instruments will detect more FRBs with orders of magnitude better spatial resolution. The result will be an explosion of opportunity for related fields, such as cosmology, dynamics of compact objects, magnetars and their surrounding medium.
Dr. Christopher Hayward (CCA/Flatiron)
Tuesday, February 13, 2024
4:00 p.m.
LGRT 1033
Title:
Bursty star formation: physical drivers and implications for JWST observations of high-redshift galaxies
Abstract:
A complete theory of galaxy formation requires understanding the details of how gas is converted into stars over cosmic time, which is affected by gas supply, star formation, and feedback-driven outflows. I will present a physical picture for galaxy formation that exhibits two distinct phases: at high redshift, stellar feedback causes all star-forming galaxies to undergo rapid fluctuations in their star formation rates on ~10-Myr timescales. Bursts of star formation are followed by strong outflows, which cause the star formation rate to drop precipitously. Fresh gas supply from galactic fountains rejuvenates star formation and restarts the cycle. At z ~ 1, simulations of massive galaxies exhibit a qualitative transition: outflows are no longer driven effectively, and the galaxies transition to steadily star-forming, well-order disk galaxies. I will discuss the physical causes of bursty star formation and the aforementioned transition to time-steady star formation, in addition to some implications for JWST observations of high-redshift galaxies. I will also describe how we can test this theoretical picture via more sophisticated comparisons between theoretical models and observations than are currently performed.
Dr. Rachel Cochrane (Columbia University)
Thursday, February 8, 2024
4:00 p.m.
LGRT 1033
Title:
Resolving galaxies with observations and simulations
Abstract:
Large surveys have put critical constraints on the spatially-integrated properties of galaxies across cosmic time. This has enabled extragalactic astronomers to constrain key galaxy scaling relations and to chart the assembly of stellar mass in the Universe. However, a more complete understanding of the physical processes driving galaxy evolution requires a high angular resolution, multi-wavelength approach, alongside theoretical modelling. In the first part of the talk, I will discuss spatially-resolved observations of galaxies around the peak of cosmic star formation (z~2) and outline some challenges involved in interpreting them. In the second part of the talk, I will show how galaxy formation simulations, in particular synthetic observations generated from these simulations, can guide observations and interpretations of data. Using radiative transfer, we have generated synthetic maps of multi-wavelength emission for highly-resolved zoom-in simulations[1]. I will illustrate the many exciting uses of this dataset, highlighting a study of the physical nature of 'HST-dark' sources[2].
Allison Michelle Kirkpatrick, The University of Kansas
Thursday, December 7, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Taylor Hutchison, NASA
Thursday, November 30, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Eliot Vrijimoet, UMass Astronomy Department
Thursday, November 16, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Kyoungsoo Lee, Purdue University
Thursday, November 9, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Sarah Jeffreson, Harvard University
Thursday, November 2, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Anna Wright, John Hopkins University
Thursday, October 26, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
John Weaver, UMass Astronomy Department
Thursday, October 19, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Alex Gagliano, Massachuetts Institute of Technology
Thursday, October 12, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Shreyas Vissapragada, Harvard University
Thursday, October 5, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Paul Goldsmith, NASA Jet Propulsion Laboratory/Robotic Space
Thursday, September 28, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Jamboree
Thursday, September 21, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
Jamboree
Thursday, September 14, 2023
3:45 p.m.
LGRT 1033
Title:
TBD
TBA
Thursday, August 10, 2023
12:00 noon
ILCN 101
Title:
FCAD Undergraduate Research Symposium
Abstract:
The 2023 FCAD Undergraduate Research Symposium will be on Thursday, August 10th from 12:00 PM - 2:30 PM at the Integrated Learning Center N101. Please join us to hear about the great research that the students have done over the summer. Please arrive a few minutes early to get a seat as talks will start promptly at noon. This year there will be 11 presentations, each presentation will consist of 6 min talk + 3 min Q&A. Antonio's Pizza and soda will be provided for lunch and will be served from 1:00 PM - 1:40 PM
Ranita Jana - Tel Aviv University
Monday, July 31, 2023
12:00 noon
LGRT 533
Title:
X-ray signatures of galactic outflows in the circumgalactic medium
Abstract:
Extraplanar X-ray emission around galaxies reveals the nature of the circumgalactic medium (CGM) and how it interacts with feedback from the galaxy. Using idealized hydrodynamical simulations, we study how galactic outflows modify the X-ray signature of the hot CGM. We consider different initial CGM profiles and different energy injection mechanisms to account for model uncertainties. We find that outflows from the center shock-heat the inner CGM and remove gas from the center. The shock heating increases the brightness and also creates flatter X-ray (0.5 − 2 keV) surface brightness profiles within the inner 10’s of kpc, consistent with recent eROSITA observations. We also find that the effects of such outflows, including X-ray surface brightness can be modeled using a spherical shock propagation model in the CGM. Our models also produce X-ray luminosities that are consistent with Chandra observations of star-forming galaxies. Our models, therefore, provide a way to understand observed surface brightness profiles in terms of the energy from galactic outflows.
Joe Burchett, NMSU
Thursday, May 11, 2023
3:45 p.m.
LGRT 1033
Title:
A UV Spectroscopist's Apology: Slime Mold, Cosmic Ecosystems, and Why We Need an X-ray Imaging Microcalorimeter Probe
Abstract:
As galaxies bathe in their gaseous environments, whether it be their local circumgalactic medium (CGM) or the larger-scale intergalactic medium (IGM), it is clear that the symbiosis between them must drive galaxy evolution. I will present evidence from both observational and theoretical perspectives on the connection between galaxy evolution and the CGM/IGM. With a little help from slime mold, my team has developed a new framework to reconstruct the latent cosmic web structure within spectroscopic galaxy surveys. Given that our methodology enables us to infer cosmological overdensity far from galaxy positions, we can use traditional absorption line techniques as well as fast radio bursts to probe the gas physical conditions within the IGM permeating the large-scale structure. Using the TNG100 cosmological simulation, we have examined the relationship between galaxy star formation (SF) and large-scale environment over cosmic time. We have found a pronounced onset of the SF-environmental relationship, providing a critical test for galaxy formation theory in the era of surveys such as DESI, Roman, PFS, and LSST. Lastly, I will contend that the path forward to truly elucidating the connections among galaxies, feedback processes, and their gas reservoirs on both local and large scales must happen in the X-ray regime, particularly through imaging microcalorimetry in the next NASA probe mission. Hopefully, together, we can help this UV spectroscopist come to grips with that.
Chris Hayward, Research Scientist, Flatiron Institute
Thursday, May 4, 2023
3:45 p.m.
LGRT 1033
Title:
What can high-redshift, infrared-luminous galaxies tell us about galaxy formation physics and cosmology?
Abstract:
Interstellar dust is pervasive throughout the Universe, and most light from young, massive stars is absorbed by dust and reradiated as thermal emission in the infrared. Submillimeter galaxies (SMGs), a class of very infrared-luminous distant galaxies, are some of the most extreme star-forming galaxies known, forming stars at rates hundreds or even thousands of times greater than our own Milky Way. I will review our understanding of this enigmatic population, which has challenged galaxy formation theories since their discovery in the late 1990s. I will highlight how the population provides novel constraints on galaxy formation physics, cosmology, and possibly even the nature of dark matter. I will also show how they serve as beacons of galaxy clusters in the process of formation.
Erin Kara, MIT
Thursday, April 27, 2023
3:45 p.m.
LGRT 1033
Title:
Probing the causal connection between inflow and outflow in accreting black holes
Abstract:
Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying the inner accretion flow, at the intersection of inflow and outflow, is essential for understanding how black holes grow and affect galaxy evolution. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and the black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and will show how extending these spectral-timing techniques to transient accretion events like Tidal Disruption Events and black hole X-ray binaries is helping us probe the formation of X-ray coronae, jets and other relativistic outflows.
Laurent Pueyo, STSci Astronomer
Thursday, April 20, 2023
3:45 p.m.
LGRT 1033
Title:
Resolved images of giant exoplanet in the era of JWST
Abstract:
In this presentation I will discuss how the one-year-old James Webb Space Telescope will revolutionize our understanding of giant planet formation and evolution. I will start by describing our current observational knowledge about giant planets, tying together solar system bodies, known exoplanets and their massive Brown Dwarf cousins. I will then briefly review highlights of JWST commissioning and its unique capabilities when it comes to giant exoplanets. Most of the talk will focus on three key observational diagnostics: giant planets as the low mass extension of the Brown Dwarf Initial Mass Function, atmospheric composition of giant planets at long and short orbital periods, and imaging giant planets at solar system scales. For each diagnostic I will review results obtained by our team using a combination of Hubble and ground-based telescopes and present very recent JWST observations that demonstrate the promises of this new observatory. I will conclude by discussing future NASA missions aimed at imaging habitable exoplanets, in particular drawing from the lessons we have learned through this first year of giant planet science with JWST.
Grant Wilson / University of Massachusetts Amherst
Thursday, April 13, 2023
3:45 p.m.
LGRT 1033
Title:
Swinging for the Fences - An Update on the TolTEC Project
Abstract:
The TolTEC Imaging Polarimeter is a new, 7000 pixel, millimeter wavelength camera. The camera is now installed and making commissioning observations at the Large Millimeter Telescope, after which it will both start a series of Legacy Surveys and be available for PI-led LMT projects. In this talk I will endeavor to bring everyone up to date on the instrument's status and prospects for new data. I will describe key aspects of the technologies that underlie the camera, review the key science questions that motivated its construction, describe its capabilities on the LMT, and focus in on our plans for the initial set of our TolTEC Legacy Surveys. I'll conclude the talk by returning to my laptop to continue working on the commissioning data.
Rachel Bezanson, University of Pittsburgh
Thursday, April 6, 2023
3:45 p.m.
LGRT 1033
Title:
How it started . . . How it’s going: tracing the formation and evolution of massive galaxies through cosmic time
Abstract:
Galaxies are extraordinarily complex collections of stars, gas, and dark matter. The largest galaxies, though relatively rare in number, host most of the stars in the Universe and deep in their cores harbor the most extreme supermassive black holes. Today massive galaxies are red and dead ellipticals with little ongoing star formation or organized rotation; naturally they were expected to be relics of a much earlier formation epoch. In this talk I will briefly review the paradigm that has emerged over the last decade, discussing the structural and kinematic evolution of massive galaxies during and after they stopped forming stars (“quenched”) and eventually transformed from rotationally supported disks into kinematically hot ellipticals. I will describe my team’s observational efforts to characterize the histories of galaxies like our Milky Way and larger at several critical moments in the 14 billion year history of the Universe, each corresponding to a large spectroscopic program. Spectroscopic studies of distant galaxies reveal the chemical compositions, detailed star formation histories, and internal motions of stars and gas and are necessary to answer open questions about the details of that cosmic formation and shutdown. This work includes studying galaxy metamorphosis at ~half the age of the Universe, highlighting results from the ultra-deep LEGA-C spectroscopic survey of ~3500 massive galaxies and the focused multi-wavelength SQUIGGLE survey of post-starburst galaxies caught immediately following their cosmic shutdown. I will discuss our JWST UNCOVER treasury program that will extend deep spectroscopic studies of galaxies to the earliest moments in cosmic history. Finally, my team will connect-the-dots through the peak of cosmic star formation (~10 billion years ago) using the next-generation massively multiplexed Prime Focus Spectrograph on the Subaru Telescope.

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