Colloquia Archives

Enrico Ramirez‑Ruiz (UC Santa Cruz)
Thursday, March 4, 2021
3:45 p.m.
Remote - Zoom
Title:
Cosmic Alchemy In the Era of Gravitational Wave Astronomy
Abstract:
The source of about half of the heaviest elements in the Universe has been a mystery for a long time. Although the general picture of element formation is well understood, many questions about the astrophysical details remain to be answered. Here I focus on recent advances in our understanding of the origin of the heaviest and rarest elements in the Universe. Enrico Ramirez-Ruiz is eager to understand our origins and, in some cases, is simply wild about things that go bang in the night sky. He works with computer models to understand the cataclysmic death of stars and recently led efforts to uncover the origin of the heaviest, most neutron-rich elements in the universe, like gold and uranium.
Chentao Yang (ESO Chile)
Thursday, February 25, 2021
3:45 p.m.
Remote - Zoom
Title:
Properties of the ISM in (strongly-lensed) high-redshift dusty galaxies
Abstract:
The discovery of a high-redshift submillimeter-bright (dusty) galaxies population has revolutionized our understanding of galaxy evolution and star formation in extreme conditions, yet their nature remains hotly debated. Recent wide-area extragalactic surveys at submm/mm bands have discovered hundreds of such galaxies that are strongly lensed at high redshifts. The boosted angular resolution and brightness open new exciting opportunities for studying the interstellar medium within. We have thus carefully selected a sample of the bright lensed dusty galaxies based on the Herschel-ATLAS sample. Through observations of the multiple transitions of the CO lines, we analyzed the physical conditions of the molecular gas. Additionally, we have also conducted the first multi-transition H2O line survey within these high-redshift galaxies. We have studied the properties of the far-infrared radiation fields with the H2O lines. The study provides us new constraints of the warm dense, extreme dust-obscured regions. ALMA 0".2-0".4 follow-up of one of the brightest sources (G09v1.97) in our sample shows very well agreement of the spatial distribution and kinematics between the CO, H2O, and H2O+ lines. Interestingly, this merger source shows a mismatch between the cold-dust continuum peak and the peak of the line emissions, suggesting a significant amount of cold gas is in the interacting region, similar to the local merger prototype, the Antennae galaxies. In parallel, we have conducted a line survey in Band 3 and 4 using ALMA, which resulted in detections of a rich series of molecules including HCN, HNC, HCO+, CCH, 13CO, C18O, CS, N2H+, and isotopologues of CO. The rich detections of molecules in multiple transitions enable us, for the first time, to have a detailed view of the astrochemical process and reveal rich information about the high-redshift physical properties of the molecular gas, the radiation field, and their interactions.
Brenda Frye (U. of Arizona) View(active tab)
Thursday, February 18, 2021
3:45 p.m.
Remote - Zoom
Title:
Planck-Herschel Detection (PHD) of Galaxy Overdensities from z = 3 to the Present
Abstract:
Galaxy clusters as gravitational lenses offer two advantages: to boost the brightnesses of objects in the background, and to study the dark matter in the lens. We introduce here a third use: to unveil properties near the caustic, whose lensing magnification factors can reach 10,000 or more. We begin by recounting a novel approach to detect galaxy overdense regions by their rest-frame far-infrared colors (and not by the Sunyaev-Z'eldovich effect). We will see why this selection picks up a combination of galaxy clusters at z > 1.5 and at z ~ 0.5. To investigate the lensing properties, we analyze Hubble Space Telescope WFC3-IR imaging in the fields of the lower-redshift classical giant arcs. We construct lensing models from the many examples of image multiplicities, and offer an explanation for some of their more nonstandard physical properties. We conclude with a discussion on the emerging field of caustic crossings and other local lensing events which yield insights into our understanding of dark matter substructure.
Lynne Hillenbrand (Caltech)
Thursday, February 11, 2021
3:45 p.m.
Remote - Zoom
Dr. Jorge Zavala
Thursday, February 4, 2021
3:45
Remote - Zoom
2nd Year Graduate Project Presentations Part 2: Ben Gregg
Thursday, November 19, 2020
4 p.m.
Remote - Zoom
Title:
Investigating Mid and Far-Infrared Color-Color Relations within Resolved Star Forming Regions in Local Galaxies
Abstract:
We present an extensive archival analysis of a diverse sample of local galaxies, combining multi-wavelength data from GALEX, SST and HSO in order to investigate "blue side" mid-IR and "red side" far-IR color-color correlations within the observed IR SEDs of resolved star forming regions. With archival data from the FUV through 500 micron, we measure photometry of individual star forming regions 36 arcseconds in size. We estimate SFRs and stellar masses and derive metallicity distributions throughout our galaxies. Focusing on the f(70)/f(500) "far-IR" and f(8)/f(24) "mid-IR" colors, we find that a sub-sample of galaxies demonstrate a strong far-IR versus mid-IR color-color correlation within their individual star forming regions, while others demonstrate uncorrelated colors. We identify that this division within our sample of galaxies appears to be driven by two main effects: 1) the local strength of SF and 2) the metal content of the ISM. We find that galaxies uniformly dominated by very high surface densities of SF (e.g. M83) demonstrate strong IR color-color correlations, while galaxies exhibiting relatively lower levels of SF (e.g. NGC5457) tend to demonstrate weaker correlations---likely explained by the increasing effect of varying ISM heating and metal content on the IR colors, specifically in the mid-IR. Our results are found to be consistent with published IR correlations for NGC4449, but present a more complicated picture. We find large dispersion in the SFR versus 8 micron luminosity relation that is traced by the metallicity distributions, consistent with many recent studies, highlighting its problematic use as a SFR indicator.
2nd Year Graduate Project by Luan Luan
Thursday, November 12, 2020
4 p.m.
Zoom
Title:
THE INFLUENCE OF MASS ACCRETION ON THE BAR FORMATION AND EVOLUTION OF GALAXIES
Abstract:
We present several N-body simulations of disk galaxy with mass evolution model to study the influence of mass accretion on the bar formation and evolution. Using techniques of orbit family recognition and harmonic decomposition, we find that the formation of the bar is always accompanied by the formation of a stellar cusp, which may correspond to the bulge in the disk. As the mass growth of the cusp, it destroys the bar, which indicates that bar is not always long-lived and stable structure. We also find that the strength of bar and the time to form the bar depend on the mass accretion rate and the accretion radius.
Irene Shivaei (U Arizona) View(active tab)
Thursday, November 5, 2020
4 p.m.
Remote - Zoom
Title:
Dusty Distant Universe
Abstract:
Dust is one of the most mysterious components of galaxies. It not only plays an important role in the physics and chemistry of the interstellar medium, but also shapes our views of galaxies by absorbing and scattering UV and optical light and re-emitting it in longer infrared wavelengths. Despite its importance, we know very little about dust at high redshifts. In this talk, I will highlight our recent results on dust and obscured star formation in typical galaxies at redshift of z~2, the peak of cosmic star formation, using our current multi-wavelength facilities, such as Hubble, Keck, and Spitzer, and the prospects with ALMA and JWST. The synergies among these powerful facilities will give us a complete picture of the dust content of galaxies during the peak epoch of star formation activity in the universe. Moreover, as a member of the JWST/MIRI US GTO science team, I will introduce our extragalactic survey to probe star formation and AGN activity at high redshifts. JWST/MIRI will be revolutionary in advancing our knowledge about the dust-obscured star formation in typical high-redshift galaxies, owing to its significantly higher sensitivity and resolution compared to those of its predecessors.
Feng Long, SMA Fellow, Center for Astrophysics View(active tab)
Thursday, October 29, 2020
3:45 p.m.
Zoom
Title:
The ALMA view of protoplanetary disks: mass, size, and morphology
Abstract:
Planets are assembled from the gas and dust in the disks orbiting around young stars. How these disks evolve from primordial gas and dust into planetary systems like our own solar system is still not well understood. With the powerful Atacama Large Millimeter/submillimeter Array (ALMA), we are now able to study the planet-forming-disks in greater detail and towards larger samples. These observations are transforming our view of disks and offering new insights in planet formation. In this talk, I will share results from ALMA disk surveys, which reveal the general disk properties including masses and sizes, and the detailed dust grain distributions. The implications of the assembly and early evolution of planetary systems will be discussed based on these results.
Daniel Anglés-Alcázar (CCA Flatiron/UConn)
Thursday, October 22, 2020
3:45 p.m.
Zoom
Title:
Multi-scale cosmological simulations of massive black hole growth and feedback
Abstract:
Supermassive black holes play a key role in galaxy evolution and large-scale structure but the physical processes driving black hole growth and feedback into the surrounding medium remain a major uncertainty in current models. In this talk, I will present recent progress in understanding the nature of black hole-galaxy co-evolution by means of (1) the SIMBA large volume cosmological hydrodynamic simulations, (2) FIRE cosmological zoom-in simulations of individual galaxies with resolved multi-phase interstellar medium, and (3) new hyper-refinement simulations that for the first time resolve explicitly the transport of gas down to sub-pc scales in the nuclear regions of massive galaxies in a full cosmological setting. I will highlight some of the lessons learned from these multi-scale simulation techniques, with important implications including black hole-galaxy scaling relations, AGN demographics and the nature of luminous quasars, the star formation-AGN connection, and galaxy quenching. Looking forward, I will outline two opposite but complementary approaches under current development: the Interscale Galactic NucleI Simulations (IGNIS) to explicitly resolve black hole growth and feedback and significantly increase the predictive power of current models, and the Cosmology and Astrophysics with MachinE Learning Simulations (CAMELS) project containing thousands of cosmological volumes with feedback parameter variations to marginalize over uncertainties in baryonic effects and maximize the science return of next generation cosmological experiments.
Sandro Tacchella (CfA)
Thursday, October 15, 2020
3:45 p.m.
Zoom
Title:
The Diversity of Building up the Quiescent Sequence at z~
Abstract:
Abstract: I present evidence for a diversity of pathways for building up the quiescent galaxy population at early cosmic times. Specifically, I will present observational constraints on star-formation histories and quenching timescales by combining Keck DEIMOS spectroscopic data with >10-band photometry. I will discuss how one can self-consistently fit both photometric and spectroscopic data together with the tool Prospector, which allows fitting for non-parametric star-formation histories and complex stellar, nebular, and dust physics. Although the apparent diversity, we find that the most massive, compact galaxies have formed their stars the earliest and most rapidly. Finally, I will relate these findings to numerical simulations (in particular IllustrisTNG), putting forward that most galaxies not change their morphology significantly during quenching.
Zheng Zheng (University of Utah) View(active tab)
Thursday, October 8, 2020
3:45 p.m.
Zoom
Title:
The Curious Case of Lyman-alpha Emitting Galaxies Abstract:
Abstract:
Lyman-alpha Emitting galaxies or Lyman-alpha emitters (LAEs), star-forming galaxies selected through their strong Lyman-alpha emission, are becoming an important probe of galaxy formation, cosmic reionization, and cosmology. I will present our recent and ongoing work towards understanding properties of those galaxies based on Lyman-alpha radiative transfer modeling, discussing the role of the anisotropic gas distribution around galaxies and the origin of the extended Lyman-alpha emission around LAEs. I will then talk about the anisotropic clustering of LAEs induced by the radiative transfer effect and the current observational status. During the talk, I will also discuss a few puzzles in the study of LAEs.
Zhiyuan Ma (UMass Amherst)
Thursday, October 1, 2020
3:45 p.m.
Zoom
Abstract:
TolTEC is a new camera that will be mounted on the Large Millimeter Telescope (LMT). Once there, it will provide simultaneous, polarization-sensitive imaging at 2.0, 1.4, and 1.1mm wavelengths through its ~7000 Lumped Element Kinetic Inductance Detectors (LeKIDs). The TolTEC data analysis software stack (TolTECA) is developed to facilitate all the data related tasks including instrument diagnosing, data reduction, data product management, and visualization. TolTECA is used both at the observing time to provide the quasi real-time feedback ("quick look") for the observer, and at later times at the data analysis facilities (high performance clusters) to produce science-ready data products. Moreover, it provides a web-based solution to host interactive science-oriented services like S/N calculators, observation simulators, and SZ effect simulators - all designed to facilitate the exploration of the science cases enabled by TolTEC. The two key components of TolTECA are the Python package tolteca, and the highly optimized data reduction engine citlali written in C++. Tolteca implements the general data management and handling submodules that serve at the highest levels, while citlali is the high performance data reduction engine that carries out the the time-ordered data (TOD) reduction and mapmaking. In this talk, I will first cover the overall architecture of TolTECA, and then describe some of its more novel components in detail, which includes the LeKIDs data modeling, the highly configurable parallelization framework that we used in citlali, as well as the tolteca data analysis workflow and data product management. The second part of the talk will focus on some of our on-going efforts in using simulations to explore the science cases that are enabled by TolTEC.
Dara Norman (NSF NOIRLab)
Thursday, September 24, 2020
3:45 p.m.
Zoom
Title:
Advancing The Inclusion Revolution
Abstract:
The field of Astronomy and Astrophysics has seen major changes in the last couple of decades. There have been discoveries that have evolved our understanding of the Universe. The development of new methods and gathering of datasets have expanded topical areas of the field in profound ways. We have even seen the community begin to recognize and understand that the health and well-being of the workforce cannot be ignored if we intend to continue with scientific breakthroughs. However, advancing this understanding requires the evolution our scientific culture. In this talk, I will highlight some growing trends toward more diversity and inclusion in the field, the importance of access to decision making and research opportunities to promote these trends, as well as, the structural changes needed to usher in an Astronomical inclusion revolution.
Brian Svoboda (NRAO)
Thursday, September 17, 2020
3:45 p.m.
Zoom
Title:
Towards a Multi-Scale View of Dense Gas in the Milky Way
Abstract:
High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. Current theories of star formation disagree on the timing, initial masses of dense cloud-cores, and the role of gravity versus turbulence during the nascent phases of star cluster evolution. These long-standing uncertainties are now being addressed with the statistical power of multi-wavelength Galactic Plane surveys and the unprecedented sensitivity of ALMA. In this talk I shall review current surveys of the dense, star-forming gas of the Milky Way and discuss studies we have carried out to understand the physical conditions during the earliest phases of high-mass star formation. I shall further describe a novel Bayesian analysis framework to process large gas-kinematic surveys and discuss the results of an application to nearby clouds. In closing, I shall discuss how the wide-field capabilities of both current and next-generation cm/mm-wavelength facilities, such as the LMT, GBT, ALMA, and J/ngVLA, will expand our understanding of star formation in the Milky Way.
Astro Jamboree Week 2
Thursday, September 3, 2020
3:45 p.m.
Zoom
Title:
Meet & Greet Part 2
Astro Jamboree Week 1
Thursday, August 27, 2020
3:45 p.m.
Zoom
Title:
Meet & Greet Part 1
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.

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