Colloquia Archives

CANCELLED Amanda Kepley (NRAO)
Thursday, April 30, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED Zhiyuan Ma (UMass)
Thursday, April 23, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED JJ Hermes (BU)
Thursday, April 16, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED Katharine Reeves (CfA)
Thursday, April 9, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED Anglés-Alcázar Daniel (Flatitron)
Thursday, April 2, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED Sandro Tacchella (CfA)
Thursday, March 26, 2020
3:45 p.m.
LGRT 1033
Title:
TBD
CANCELLED Jason Young (Mt. Holyoke College)
Thursday, March 12, 2020
3:45 p.m.
LGRT 1033
Title:
The Life Story of Low Surface Brightness Spirals
Abstract:
Low surface brightness spiral galaxies are paradoxical in that they are gas rich but have low star-formation rates. Combined ground-based/space-based data let us determine the spatially resolved star-formation histories of low surface brightness spirals. We aim to use these histories in tandem with velocity fields and metallicity profiles to determine the physical mechanism(s) that give these faint but numerous galaxies low star-formation rates despite ample gas supplies.
Brian Svoboda (NRAO)
Thursday, March 5, 2020
3:45 p.m.
LGRT 1033
Nir Mandelker (Yale)
Thursday, February 27, 2020
3:45 p.m.
LGRT 1033
Title:
The Multiphase Circum- and Intergalactic Media at the Nexus Between Galaxy Formation and Cosmology
Abstract:
Galaxies are not closed boxes. Rather, it has become clear in recent years that it is the flow of gas into and out of galaxies that shapes their evolution. Cycles of gas accretion, star-formation, galactic outflows and reaccretion, intimately link galaxies to the circumgalactic medium (CGM, gas outside galaxies but within dark matter halos) and the intergalactic medium (IGM, gas outside dark matter halos). While the diffuse gas in these regions has traditionally been very difficult to study, recent advances in both observations and numerical simulations are now providing a wealth of information on the gas around galaxies, revealing complex, multiphase and multiscale structure. I will describe my ongoing efforts to study the phase-structure of the C/IGM by combining novel cosmological magnetohydrodynamic moving-mesh simulations that I modified to overcome difficulties in resolving the diffuse gas in these regions, with analytic modeling and idealized numerical experiments that address detailed questions about physical processes affecting multiphase gas in the C/IGM. I will present two main results from these studies. I will first show how non-linear thermal instabilities cause hot gas to "shatter" into small-scale clouds of cool and dense gas. I will then present a model for the interaction of cold accretion streams with the ambient hot CGM by considering the Kelvin-Helmholtz Instability in a dense, supersonic, self-gravitating, and radiatively cooling cylinder. These have helped us to understand how the C/IGM are shaped by a complex interplay of hydrodynamical, thermal, and gravitational instabilities which we are beginning to put together in a coherent framework.
Paul Torry (Florida State)
Thursday, February 20, 2020
3:45 p.m.
LGRT 1033
Title:
Probing Galaxy Formation with Modern Cosmological Simulations
Abstract:
Cosmological simulations are among the most powerful tools available to probe the non-linear regime of cosmic structure formation. They also provide a clear test-bed for understanding the impact that hydrodynamics and feedback processes have on the evolution of galaxies. I will present an overview of modern galaxy formation simulations that couple a novel moving mesh computational method with explicit baryon feedback prescriptions. This approach results in detailed galaxy formation models that reproduce fundamental observations such as the galaxy stellar mass function, cosmic star formation rate density, and galaxy morphological diversity. I will briefly discuss the key physical model ingredients and explore in detail the cosmic coevolution of galaxies and their metals including specifically the mass-metallicity relation, fundamental metallicity relation, and metallicity gradient evolution. I will argue that metallicity observations may allow us to discriminate between bursty and non-bursty feedback models in the future with JWST.
Cassandra Hall (Smith College Faculty Candidate)
Thursday, February 13, 2020
3:45 p.m.
LGRT 1033
Title:
Gravitational Instability and Substructure in Protoplanetary Discs
Abstract:
In the ALMA era of observational astronomy, we are availed of a plethora of spatially resolved images of protoplanetary discs, the site of exoplanet formation. Significant substructure, such as spirals and ring-like gaps, has proved to be the norm, rather than the exception, in these systems. There is now a consensus that much of this substructure is caused by forming gas-giant exoplanets. However, this is problematic for our understanding of planet formation. These protoplanetary discs are typically a factor of 10 too young to have formed such massive planets in the standard core accretion paradigm, but it is also understood that planets do not form directly through gravitational collapse. When protoplanetary discs are very young, they are very massive relative to their host star, and therefore pass through a period of gravitational instability. This instability may accelerate the earliest stages of planet formation in the standard core accretion paradigm, offering a solution to the planet formation timescale problem. I discuss my research into gravitational instability and detection of substructure, and discuss future research plans which will explore the formation of exoplanets in dynamically evolving protoplanetary discs.
Kimberly Ward-Duong (Smith College Faculty Candidate)
Thursday, February 6, 2020
3:45 p.m.
LGRT 1033
Title:
Low-mass Stars and Substellar Systems as Planet Hosts and Planet Analogs
Abstract:
The overwhelming majority of the galactic stellar population consists of low-mass M-dwarf stars. Their abundance makes them attractive targets for exoplanet searches and a critical regime of exploration at the low-mass end of the initial mass function. In this talk, I will describe my work using adaptive optics imaging, submillimeter observations, and high-resolution spectroscopy to understand the planet-forming potential of these stars and their binary and disk environments. Extending to even lower masses beyond the hydrogen burning limit, substellar objects and their atmospheres currently serve as our best and most characterizable analogs for exoplanet systems, illuminating our understanding of how brown dwarfs and giant planets form and evolve. Studies of these systems require innovative instrumentation at the modern limits of high contrast imaging and high spectral resolution, and I will discuss how these efforts will help inform next generation approaches to directly image (sub)-Jovian and terrestrial planets.
Jennifer Andrews (Smith College Faculty Candidate)
Thursday, January 30, 2020
3:45 p.m.
LGRT 1033
Title:
Supernovae as Forensic Labs for Massive Stars
Abstract:
Core collapse supernovae (CCSNe) represent the final evolutionary stage of stars more massive than 8 M☉. Just like their massive star progenitors, CCSN explosions are far from homogenous. The photometric and spectral evolution zoo of CCSNe can be better understood when the mass-loss histories of their progenitors are taken into context. We can now reconstruct the mass-loss history and physical parameters of the massive star progenitor with observations of SNe in the hours to years after explosion, without the need for rare pre-explosion Hubble Space Telescope imaging. Mass-loss rates and eruptive events in evolved massive stars impact the behavior of the terminal CCSN, including red supergiants, yellow hypergiants, and luminous blue variables. Red supergiants and yellow hypergiants have slower wind velocities and lower mass-loss rates than luminous blue variables, creating very different explosion environments, and by extension, very different observational characteristics of the supernova. I will present how I use these extremely bright and violent explosions to understand more about the final years of massive star evolution, and what tools are being used and developed to discover these SNe so rapidly in what is becoming the golden age of transient astronomy.
Miao Li (Flatiron)
Thursday, January 23, 2020
3:45 p.m.
LGRT 1033
Title:
The Nature and Impact of Supernovae Feedback in Galaxy Formation
Abstract:
Circumgalactic Medium (CGM), where cosmic inflows interact with galactic outflows, bears critical information for galaxy formation. Current cosmological simulations can model cosmic inflows but their galactic outflows usually rely on ad hoc sub-grid models. The path forward requires better understanding the feedback physics and using physically-based models in large-scale simulations. In this talk, I will first summarize the recent progress of small-box hydrodynamical simulations focusing on the nature of supernovae (SNe) feedback; particularly, the hot outflows are much more powerful than cool outflows while also appearing very simple. Then, I will introduce our galactic scale simulations, which adopt the outflow models from the small-box simulations. For a Milky Way-mass galaxy, when the star formation surface density is low, hot outflows form large-scale fountains in the halo; when it is high, the outflows are bipolar in shape and can escape from the dark matter halo. I will discuss the resultant multiphase CGM from 10^4-7 K and how they compare to multi-wavelength observations. I will also discuss the implications to the missing baryon and the missing metals problems.
Kiyoshi Masui (MIT)
Thursday, December 5, 2019
3:45 p.m.
LGRT 1033
Title:
Mapping the Universe with CHIME - a Digital Radio Telescope
Abstract:
A powerful tool for understanding the Universe is the distribution of matter on very large scales, and a number of upcoming surveys will map the large-scale structure at radio wavelengths using the 21 cm line from neutral hydrogen. I will describe the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which will make the largest-ever three-dimensional map of the Universe. This map will enable precise measurements of the expansion of the Universe to understand its anomalous acceleration and the dark energy hypothesized to be driving it. In addition, I will show how the digital design of the CHIME telescope allows it to simultaneously search for a new class of radio transient, fast radio bursts, which provide another probe of the Universe. CHIME belongs to a new class of radio telescope which are remarkably scalable, opening a new frontier in observational cosmology to understand both the evolution of the Universe and fundamental physics.
Erica Nelson (Harvard)
Thursday, November 21, 2019
3:45 p.m.
LGRT 1033
Title:
The emergence of galactic structure
Abstract:
Abstract: Using a combination of the Hubble Space Telescope, the Keck telescopes, and the ALMA millimeter interferometer, we have begun to piece together a picture of the emergence of galactic structure: how the Universe evolved from its uniform state shortly after the Big Bang to the rich diversity of galaxies today. In this talk, I will discuss recent observations and the impact they have had on our understanding of the formation and evolution of galaxies. This includes a method to directly image the emergence of galactic structure in the distant past using Hubble, a spatially resolved census of star formation at early times, and new findings about the enigmatic galaxies that ruled the early universe. Finally, the impending launch of the James Webb Space Telescope will revolutionize our understanding of early galaxy formation. I will conclude with a discussion of where the field is moving and the rich discovery space in this new era of extragalactic astrophysics.
Meng Gu (Princeton)
Thursday, November 14, 2019
3:45 p.m.
LGRT 1033
Title:
Stellar Populations and Assembly Histories of Galaxies in Nearby Massive Clusters
Abstract:
Understanding how massive galaxies form and grow is important to galaxy evolution and cosmology. In this talk, I will present the stellar population study of massive galaxies and their surrounding environments in nearby galaxy clusters, with particular focus on the scaling relations between stellar mass and galaxy central stellar population properties, as well as the radial profiles where their stellar population bear the imprint of the assembly history. I will begin by introducing the `coordinated assembly` picture for massive galaxies with a case study of an ongoing brightest cluster galaxy assembly at z=0.1. I will then present our `Deep Coma` project in the SDSS IV/MaNGA collaboration. The deep integral field spectroscopy and full spectral modeling method enabled detailed analysis at the low surface brightness regime. We are therefore able to demonstrate the stellar populations of various types of targets in the Coma Cluster. Last, I will briefly discuss the `coordinated assembly` picture in the IllustrisTNG simulations.
Lars Hernquist (Harvard)
Thursday, November 7, 2019
3:45 p.m.
LGRT 1033
Title:
The IllustrisTNG Project
Abstract:
A predictive theory of galaxy formation remains elusive, even after more than 50 years of dedicated effort by many renowned astrophysicists. The problem of galaxy formation is made difficult by the large range in scales involved and the many non-linear physical processes at play. This talk describes a new generation of numerical models that are designed to overcome these difficulties based on nove schemes for solving the fluid equations on a moving mesh. In particular, I will describe an ongoing project that extends results from the Illustris simulation by employing refined models for feedback from stars and supermassive black holes. Several applications will be described, including the color evolution of galaxies, low surface brightness galaxies, and the statistics of large-scale structure, pertaining to high precision cosmological surveys.
Song Huang (Princeton)
Thursday, October 31, 2019
3:45 p.m.
LGRT 1033
Title:
The Bright and Dark Sides of Massive Galaxies from the Hyper Suprime-Cam Survey
Abstract:
Abstract: Massive galaxies are valuable targets for studying cosmology and galaxy-halo connection as they help us locate massive dark matter halos across the history of the universe. Although the general behavior of stellar-halo mass relation (SHMR) is reasonably constrained at low-redshift, there is still much to learn about the connection between the assembly of massive galaxies to the growth of their host dark matter halos. Using deep images from the Hyper Suprime-Cam (HSC) survey and taking advantage of its unprecedented weak lensing capabilities, we reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass. Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes. We explain this connection with a phenomenological model, showing that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on stellar mass within 10 kpc. This two-parameter model provides a more accurate picture of the galaxy–halo connection at the high-mass end than the simple SHMR and opens a new window to connect the assembly history of halos with those of central galaxies. I will also discuss potential applications of our model on topics from the assembly of massive galaxies to cosmology using massive clusters.
Karin Sandstrom (UCSD)
Thursday, October 24, 2019
3:45 p.m.
LGRT 1033
Title:
Interstellar Dust at Low Metallicity
Abstract:
Dust plays critical roles in many of the processes occurring in the interstellar medium and dust’s infrared emission serves as a tracer for the ISM and star formation from the nearby universe out to high redshift. While most of our knowledge of dust is built from observations of the local area of the Milky Way, it is clear that dust properties change dramatically in low metallicity conditions which may be prevalent at high redshift and in nearby dwarf galaxies. I will discuss what we know about how dust properties change with metallicity and how this can impact physical processes occurring in the ISM. I will also present new results studying low-metallicity dust in the Small Magellanic Clouds and other nearby galaxies.
Colloquium Jamboree 3: New Postdocs
Thursday, October 17, 2019
3:45 p.m.
LGRT 1033
Title:
New Postdoc Research
Abstract:
Becky Arnold Stars, Stats, Software I will present a brief outline of my research to date. I will describe my work using N-body simulations to study the evolution of star clusters with a focus on binary clusters. I will then discuss statistical methods for quantifying and comparing spatial-velocity substructures. Finally I will go into my interest in good software development practice for rigorous and reproducible research. Chris Faesi PHANGs: Connecting cloud-scale star formation to galaxy evolution Star formation drives the secular evolution of galaxies across cosmic time. However it is not yet understood how this key process, which occurs on a localized basis within molecular clouds (10s of pc scales), couples to the kpc scale processes and environments of galaxies. The Physics at High Angular Resolution in Nearby Galaxies (PHANGs) collaboration is undertaking a comprehensive series of observational and modeling efforts to systematically explore the cloud-scale star-forming interstellar medium (ISM) in the nearby universe. With ongoing sub-arcsecond resolution ALMA, VLT/MUSE, and Hubble large programs mapping full disks of dozens of nearby galaxies, we are poised to revolutionize our understanding of molecular clouds, HII regions, star clusters, star formation efficiency, and feedback, as well as to explore their environmental dependences. I will highlight some first PHANGs science results and outline the exciting path forward in the coming years, which includes many opportunities for students to get involved. As one example, I am leveraging the MUSE data to map the Balmer decrement-derived dust extinction at 50 pc scales and comparing to ALMA CO emission to understand the cloud-scale distribution of dust and gas across galaxy disks. Matteo Messa Title: Young Star Cluster and Clumps in the local (and far) Universe Abstract: I will briefly go through what I have done, I am doing, and I would like to do, concerning the optical-NIR study of clumpy star formation. This includes: the effects of galaxy environment on the formation and evolution of star clusters; new machine-learning methods to fully exploit the large set of clusters’ observations; the clumpiness of nearby starburst galaxies and their relation with high-redshift galaxies; the use of lensed galaxies to test resolution-effects on the properties of massive clumps at high-redshift. Basically, I will try to convince you (in ~10 min.) that star clusters and star-forming clumps are powerful tools to study star-formation across space and time. Mimi Song Title: Tracing galaxy growth over cosmic time with galaxy stellar mass functions Abstract: Over the last decade the advent of the Hubble Space Telescope (HST) Wide Field Camera 3 has enabled us to build statistically significant samples of galaxies out to z=8. We have subsequently witnessed remarkable progress in our understanding of galaxy evolution in the early universe. However, our understanding of the galaxy stellar mass growth in this era has been limited due to the lack of rest-frame optical data at a comparable depth as the HST data. In this talk, I will first talk about observationally constraining the galaxy stellar mass function at z = 4–8 using deep Hubble and Spitzer data in the CANDELS GOODS fields. Then, I will present an empirical model for galaxy evolution out to z = 8 by combining the dark matter halo growth history extracted from cosmological simulations with the the observed galaxy stellar mass functions over cosmic time.
Elena Sabbi (STScI)
Thursday, October 10, 2019
3:45 p.m.
LGRT 1033
Title:
Title: Young Massive Cluster in the Local Group: unraveling the process of star formation under extreme conditions
Abstract:
Abstract: Young massive clusters trace episodes of intense star formation. Through their intense radiation and feedback they shape the evolution of galaxies, yet the processes that regulate their formation and evolution are still elusive and poorly constrain by observations. The few examples of young massive clusters in the Local Groups are gold mines to test the theories of cluster, star and planet formation and probe their evolution under extreme condition, analog to those found in high redshift star forming regions. I will discuss how, through stellar population characterization, dynamics studies and time series, HST and JWST can be used to dissect how star formation develops in space and time in the young massive clusters that can be resolved into single stars.
Daisuke Nagai (Yale)
Thursday, October 3, 2019
3:45 p.m.
LGRT 1033
Title:
A New Frontier for Cosmology & Galaxy Formation
Abstract:
A synergetic combination of multi-wavelength astronomical surveys promises to provide an ever more comprehensive view of cosmic structures, by mapping out the distributions of dark matter, gas, stars and black holes in the universe. Such datasets will reveal rich physics of galaxies, clusters and cosmic web and ultimately shed light on the nature of dark matter and dark energy that govern their formation and evolution. However, new astronomical datasets will be large and complex. New way of thinking and problem solving are required. In this talk, I will discuss new opportunities and future challenges at the crossroads of large cosmological surveys, computational astrophysics and data science.
Pete Schloerb
Thursday, September 26, 2019
3:45 p.m.
LGRT 1033
Title:
The Large Millimeter Telescope
Abstract:
The LMT is a 50m-diameter millimeter-wave antenna located atop Sierra Negra in the state of Puebla, Mexico. The telescope was built in a collaboration between UMass Amherst and the country of Mexico, represented by the Instituto Nacional de Astrofisica, Optica, y Electronica. The telescope is instrumented with an array of instruments for spectroscopy and continuum mapping. Recording instruments for Very Long Baseline Interferometry have also been installed, enabling LMT's participation in the recent successful imaging of the black hoe in M87 by the Event Horizon Telescope. In this talk Professor Schloerb will review the recent developments in the project and discuss prospects and plans for the future.
Special Event: Jamboree 2
Thursday, September 19, 2019
3:45 p.m.
LGRT 1033
Title:
Introduction to Department Research
Abstract:
Faculty Research Presentations by: Kate Whitaker, Min Yun, Daniel Wang, Kate Follette, Rob Gutermuth, Houjun Mo, Mauro Giavalisco, Gopal Narayanan
Special Event: Jamboree 1
Thursday, September 12, 2019
3:45 p.m.
LGRT 1033
Title:
Introduction to Department Research
No Colloquium
Thursday, September 5, 2019
3:45 p.m.
LGRT 1033
Title:
First day of classes
Claudia Scarlata, University of Minnesota
Thursday, May 2, 2019
3:45 p.m.
LGRT 1033
Title:
Pushing the limits with extreme emission line galaxies
Abstract:
Low-z "Green Peas” show star formation rate (SFR) per unit stellar mass an order of magnitude above the star-forming main sequence, while their very low nebular oxygen abundance places them equally far below the luminosity—metallicity relation at z~0. Combined with ubiquitous bright Lya emission they are considered the best local analogues of many of the galaxies identified in high-z surveys. While these objects offer many insights into how star formation proceeds in the most extreme environments, they are manifestly not dwarf galaxies, and neither are they close analogues of the faintest high-z galaxy building blocks. Thus they do not offer a sample in which to significantly extend scaling relations, nor push to the lowest masses/SFRs in absolute terms. I will present the results of a spectroscopic campaign targeting a new sample of extreme emission line galaxies, selected to be similar to the Green Peas, but at least one order of magnitude less massive.
Erin Kara, University of Maryland
Thursday, April 25, 2019
4:00 p.m.
LGRT 1033
Title:
A NICER view of black hole accretion
Abstract:
The Neutron Star Interior Composition Explorer (NICER) is NASA’s newest X-ray telescope. A small Mission of Opportunity (about the size of a washing machine), it is perched on the International Space Station, with the main science objective of measuring the equation of state of ultra dense matter in neutron stars. Beyond this prime science goal, NICER is also making groundbreaking measurements of black holes. In this talk, I will highlight two recent and ongoing studies from NICER, one on measuring X-ray reverberation light echoes in the bright X-ray transient MAXI J1820+070, which have allowed us to map out scales closer to the event horizon of a stellar mass black hole than ever before. And second, I will present ongoing work on a multi-wavelength monitoring campaign of a transitioning AGN, 1ES 1927+654, which we observed transitioning from a Type 2 to a Type 1 AGN on timescales of a few months. Both of these observations are shedding light on the evolution of the X-ray emitting corona and its connection to the accretion disc and relativistic jets.
Jessica Werk, University of Wisconsin
Thursday, April 18, 2019
3:45 p.m.
LGRT 1033
Title:
Colossal Galaxy Adventure
Abstract:
The circumgalactic medium (CGM; non-ISM gas within a galaxy virial radius) regulates the gas flows that shape the assembly and evolution of galaxies. Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of HST/COS, observations and simulations of the CGM have emerged as the new frontier of galaxy evolution studies. In the last decade, we have learned that the CGM of Milky Way mass galaxies likely contains enough material to harbor most of the metals lost in galaxy winds and to sustain star-formation for billions of years. Remarkably, this implies that most of the heavy elements on earth cycled back and forth multiple times through the Milky Way's own CGM before the formation of the solar system. In the spirit of MS-DOS adventure games, I have designed a fully interactive colloquium that operates on a complex network of powerpoint hyperlinks. In this adventure, you will choose any of 36 possible tracks on which to explore observational and simulated signatures of cosmic gas flows.

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