ASD Colloquium Series - Spring 2021

ASD Colloquium Series - Spring 2021

The Astrophysics Science Division colloquia occur virtuallly on Tuesdays at 3:45 pm. Schedules from past colloquium seasons are available.

Contact: Knicole Colón


Jan 05 No Colloquium - Week of Winter AAS Workshops
Jan 12 No Colloquium - Week of Winter AAS Meeting
Jan 19 No Colloquium - MLK Day Weekend, Inauguration Week
Jan 26 Virtual Colloquium
Richard Anantua (Center for Astrophysics | Harvard & Smithsonian, Flatiron Institute - Center for Computational Astrophysics, Event Horizon Telescope) - A Glimpse into EHT-Scale Physics Using Movies and Polarization Maps


Feb 02 No Colloquium
Feb 09 Virtual Colloquium
Naoko Kurahashi Neilson (Drexel University) - Experimental Neutrino Astrophysics and the Need for a Future Gamma-ray Observatory
Feb 16 No Colloquium - President's Day Weekend
Feb 23 Virtual Colloquium
Kate Grier (University of Arizona) - Quasars and Supermassive Black Holes: Uncovering Mysteries with Variability and Reverberation Mapping


Mar 02 No Colloquium
Mar 09 No Colloquium
Mar 16 Virtual Colloquium
Louise Edwards (California Polytechnic State University) - Galaxies Evolution in Cluster Cores and Outskirts
Mar 23 Virtual Colloquium
Jason Rowe (Bishop's University) - A Canadian Space Telescope for the Advancement of Exoplanet Astrophysics
Mar 30 Virtual Colloquium
Jessica Gaskin (NASA MSFC) - Lynx X-ray Observatory: X-Ray Vision for the Future


Apr 06 Virtual Colloquium - Easter Weekend
Carl E. Fields (RPF Fellow, Los Alamos National Laboratory) - Multidimensional Progenitor Models For Core-collapse Supernovae
Apr 13 Virtual Colloquium
Monica Colpi (University of Milano Bicocca) LISA and the Gravitational Wave Universe
Apr 20 Virtual Colloquium
Anne Jaskot (Williams College) - Illuminating Reionization with the Low-Redshift Lyman Continuum Survey
Apr 27 Virtual Colloquium
Jeff Filippini (University of Illinois at Urbana-Champaign) - Gazing Back to the Dawn of Time from Above the Clouds


May 04 Virtual Colloquium
Enrico Ramirez-Ruiz (UC Santa Cruz) - Cosmic Alchemy in the Era of Gravitational Wave Astronomy
May 11 Virtual Colloquium
Marcel Agüeros (Columbia University) - The Evolution of Cool Dwarf Spin Rates: Data, Models, and Surprises
May 18 Virtual Colloquium
Andra Stroe (Center for Astrophysics | Harvard & Smithsonian) - Shocking Tales of Structure Formation Evolving Galaxies and Black Holes in Evolving Environments
May 25 Virtual Colloquium
Antonija Oklopčić (University of Amsterdam) - Probing the Escaping Atmospheres of Exoplanets


Jun 01 Virtual Colloquium - Memorial Day Weekend
Esra Bulbul (Max Planck Institute for extraterrestrial Physics) - First Results from eROSITA Observations of Galaxy Clusters in the eFEDS Field and An Outlook for the All-Sky Survey
Jun 08 No Colloquium - Week of Summer AAS Meeting

A Glimpse into EHT-Scale Physics Using Movies and Polarization Maps

Richard Anantua

Center for Astrophysics | Harvard & Smithsonian, Flatiron Institute - Center for Computational Astrophysics, Event Horizon Telescope

Tuesday, Jan 26, 2021


Recent radio observations of emission from infalling and outflowing plasma in the vicinity of supermassive black holes are linked to simple phenomenological models via general relativistic magnetohydrodynamic simulations using a methodology called "Observing" Jet (or outflow)/Accretion flow/Black hole (JAB) Simulations. For Sagittarius A* in our Galactic Center, movies simulating hourly timescales show that these models can be classified into at least four types: 1.) thin, asymmetric photon ring with best fit spectrum; 2.) coronal boundary layer with thin photon ring and steep spectrum; 3.) thick photon ring with flat spectrum; and 4.) extended outflow with flat spectrum. For M87, a self-similar, stationary, axisymmetric model based on a force-free flow in a HARM jet simulation is used to generate Stokes maps at Global mm-VLBI Array (86 GHz) and Event Horizon Telescope (230 GHz) scales. This model varies plasma content from ionic (e-p) to pair (e-e+). Emission at the observed frequency is assumed to be synchrotron radiation from electrons and positrons, whose pressure is set to relate to the local magnetic pressure through parametric prescriptions. Polarization maps are found to be sensitive to the positron effects of decreasing intrinsic circular polarization and increased Faraday conversion.

Experimental Neutrino Astrophysics and the Need for a Future Gamma-ray Observatory

Naoko Kurahashi Neilson

Drexel University

Tuesday, Feb 09, 2021


IceCube is a high-energy neutrino observatory that aims to resolve sources of astrophysical neutrinos. Most of the source search analyses in IceCube rely extensively on gamma-ray observations, and particularly on Fermi observations because of the full-sky nature of the instrument. Despite our numerous searches correlating the GeV gamma ray band and the TeV neutirno band, no discoveries have been made to date, except for one strong evidence of a possible correlation. This talk will cover what the experimental neutrino astrophysics community wishes for in a gamma-ray instrument, and why it is crucial to have MeV observations, like AMEGO-X, for the future of neutrino astrophysics.

Quasars and Supermassive Black Holes: Uncovering Mysteries with Variability and Reverberation Mapping

Kate Grier

University of Arizonay

Tuesday, Feb 23, 2021


Supermassive black holes, with masses that range from tens of thousands to billions of times the mass of our Sun, are thought to be present in nearly every galaxy in the Universe and may affect the growth and evolution of these galaxies. To understand how supermassive black holes interact with their host galaxies, we require accurate measurements of supermassive black hole masses in galaxies across the entire universe, as well as an understanding of their physical environments. We obtain this information by observing objects called active galactic nuclei, or quasars, which have supermassive black holes with large amounts of matter falling into them. These sources are highly variable, and we can use their variability to both measure their masses and learn about the physical environment very close to the black holes. We do this by examining the time delays between continuum flux variations and the response of distant gas as it reprocesses the ionizing radiation into emission lines which thus seem to “reverberate,” echoing the continuum variations; this technique is called reverberation mapping. In my talk, I will discuss supermassive black holes, active galactic nuclei/quasars, and the use of time variability -- primarily the technique of reverberation mapping -- to learn about these phenomena. I will focus specifically on my recent and planned work on large-scale reverberation-mapping projects using data from large surveys such as the Sloan Digital Sky Survey, which have allowed us to investigate large numbers of quasars at much greater distances than ever before.

Galaxies Evolution in Cluster Cores and Outskirts

Louise Edwards

California Polytechnic State University

Tuesday, Mar 16, 2021


When and how does environment impact the evolution of galaxies? We will approach this question by considering two extreme environments. First, the cores of massive clusters. Here, the largest, reddest galaxies of the local universe are found, Brightest Cluster Galaxies (BCGs). These galaxies are found mixed with diffuse intracluster light (ICL) and often on top of the cooling intracluster medium (ICM). We'll explore recent results from an integral field unit survey of local cluster cores which provides photometric and spectroscopic evidence of a break in age, between the old red and dead BCG cores, and the ICL that surrounds them. Second, cluster scale filaments. Here, galaxies find themselves in moderate density environments, potentially able to interact with each other, and the intracluster medium, initiating starbursts and undergoing quenching. Recent SITELLE observations from CFHT provide pinpoint a clear excess of star forming galaxies in the filaments along two superclusters.

A Canadian Space Telescope for the Advancement of Exoplanet Astrophysics

Jason Rowe

Bishop's University

Tuesday, Mar 23, 2021


A near-ultra-violet and infrared imaging space telescope on-board a micro-satellite platform has the ability to characterize the atmospheres of known transiting extrasolar planets, and to detect new, potentially habitable, rocky planets around low-mass stars and brown dwarfs. A Canadian led micro-satellite with an efficient photometer fed by a 20-cm telescope would be capable of making significant contributions to exoplanet astrophysics. The envisioned Mission would obtain high duty-cycle, ultra precise photometry of exoplanet host stars and could discover potentially habitable worlds transiting stars cooler than the Sun and would characterize the atmospheres of known exoplanets through detection of scattered light.

The expected science return is the discovery of new habitable-zone planets and the characterization of the atmosphere of at least 30 known transiting exoplanets. These science goals require an instrument in space. The timescale for an exoplanet transit range from a few hours to more than a day and occur once per orbital cycle, which severely inhibits the ability to perform our experiment from the ground. A micro-satellite with a prime mission to study extrasolar planets aligns well with the priorities identified by the Canadian Astronomy community through its LRP2020 process. As we enter the Era of Extrasolar Astrobiology, a Canadian mission to discover habitable zone planets and characterize the atmosphere is well timed. We may be the first generation of humans able to gather observational evidence of life beyond the Earth.

Lynx X-ray Observatory: X-Ray Vision for the Future

Jessica Gaskin


Tuesday, Mar 30, 2021


The Lynx X-ray Observatory, one of four Large-mission concepts submitted for prioritization in the 2020 Astrophysics Decadal Survey, has the power to transform our understanding of the cosmos through unprecedented X-ray vision into the otherwise invisible Universe. Lynx will provide leaps in capability over previous and planned X-ray missions through orders of magnitude improvement in sensitivity and spectroscopic capability. As Lynx is a Flagship mission, it will operate as an observatory with a large variety of science observations to be carried out via a competed and peer-reviewed General Observer program. Lynx science is grouped into three broad science pillars that include: 1) seeing the dawn of black holes, 2) revealing the drivers of galaxy formation and evolution, and 3) unveiling the energetic side of stellar evolution and stellar ecosystems. The Lynx architecture and mission have been designed to accommodate the most stressing observations, while strong heritage and substantial maturity in key new technologies result in a credible and feasible cost for this Great Observatory-class mission.

Multidimensional Progenitor Models For Core-collapse Supernovae

Carl E. Fields

RPF Fellow, Los Alamos National Laboratory

Tuesday, Apr 06, 2021


Core-collapse supernova explosions (CCSN) are one possible fate of a massive star. Simulations of CCSNe rely on the properties of the massive star at core-collapse. As such, a critical component is the realization of realistic initial conditions. Multidimensional progenitor models can enable us to capture the chaotic nuclear shell burning occurring deep within the stellar interior. I will discuss ongoing efforts to progress our understanding of the nature of massive stars through next-generation hydrodynamic stellar models. In particular, I will present recent results of three-dimensional hydrodynamic massive star models evolved for the final 10 minutes before collapse. These recent results suggest that realistic 3D progenitor models can be favorable for obtaining robust models of CCSN explosions and are an important aspect of massive star explosions that must be taken into consideration. I will conclude with a brief discussion of the implications our models have for predictions of multi-messenger signals from CCSNe.

LISA and the Gravitational Wave Universe

Monica Colpi

University of Milano Bicocca

Tuesday, Apr 13, 2021


The Laser Interferometer Space Antenna (LISA) - a gigameter scale space-based gravitational wave observatory - will explore the gravitational wave universe in the band from below 0.1 mHz to above 0.1 Hz. LISA will grant us access to a huge cosmological volume with unprecedented reach deep into space, detecting signals up to redshifts 20-30 and even beyond if sources exist. LISA will detect massive black hole coalescences to unveil the yet unknown origins of the first quasars and to shed light into the teeming population of middleweight black holes forming in galactic dark matter halos. LISA will discover the link between the most energetic phenomena in the universe - accreting and merging black holes - and the grand design of galaxy assembly. I will then address how the X-ray mission Athena joining LISA in concurrent multi-messenger observations of massive black hole coalescences will enhance immensely our knowledge of gas accreting in the violently changing spacetime of a merger.

Illuminating Reionization with the Low-Redshift Lyman Continuum Survey

Anne Jaskot

Williams College

Tuesday, Apr 20, 2021


The reionization of the intergalactic medium (IGM) at z > 6 is one of the major transformations in the universe’s history, but we do not yet fully understand how it occurred. The most likely explanation is that Lyman continuum (LyC) radiation escaped into the IGM from early star-forming galaxies. Because IGM absorption prevents us from directly measuring LyC during the epoch of reionization itself, we must investigate LyC escape at lower redshift. To address this issue, we have undertaken the Low-Redshift Lyman Continuum Survey, the largest survey of LyC emission at low redshift to date. With HST UV observations of 66 galaxies, we have nearly tripled the number of low-redshift LyC detections, enabling us to systematically test proposed indirect diagnostics of LyC and establish the physical properties of LyC-emitting galaxies. I will share the initial results from the survey and their implications for our understanding of cosmic reionization.

Gazing Back to the Dawn of Time from Above the Clouds

Jeff Filippini

University of Illinois at Urbana-Champaign

Tuesday, Apr 27, 2021


Inflation is thought to have seeded the cosmos with a hum of primordial gravitational waves - unique messengers from the universe's earliest moments. If present, these should have left a unique but vanishingly faint signature in the polarization of the cosmic microwave background. SPIDER is a powerful balloon-borne instrument designed to tease out this faint polarization pattern amidst obscuring Galactic foregrounds, from a vantage point 35 km above the Antarctic ice. I will discuss SPIDER's successful long-duration balloon flight, its recently-released constraints on cosmology and Galactic foregrounds, and the program's upcoming second flight, which will make deep maps of Galactic dust with new 280 GHz receivers. I will also preview upcoming missions to explore different epochs of cosmic history from stratospheric balloons, including TIM, which will observe the history of star formation through far-infrared line-intensity mapping.

Cosmic Alchemy in the Era of Gravitational Wave Astronomy

Enrico Ramirez-Ruiz

University of California, Santa Cruz

Tuesday, May 4, 2021


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.

The Evolution of Cool Dwarf Spin Rates: Data, Models, and Surprises

Marcel Agüeros

Columbia University

Tuesday, May 11, 2021


Stellar ages are notoriously difficult to measure accurately for main-sequence low-mass stars, which limits our ability to address questions ranging from the evolutionary state of exoplanets to the chemical history of the Galaxy. Gyrochronology, which uses stellar rotation as a proxy for age, is a promising solution to this quandary. Unfortunately, however, empirical and theoretical models of the age-rotation relation have been hampered by a lack of rotational measurements for large numbers of low-mass stars with a wide range of well-known ages. We are still far from being able to describe fully the evolution of rotation for low-mass stars, or from being able to use rotation measurements to estimate accurately the ages of isolated field stars. I will summarize recent ground-based and space-based work to characterize the rotational behavior of G, K, and M dwarfs in open clusters ranging in age from 125 Myr (the Pleiades) to 3 Gyr (Ruprecht 147), and then compare these data to each other and to models for stellar spin-down to appraise our current understanding of the age-rotation relation.

Shocking Tales of Structure Formation Evolving Galaxies and Black Holes in Evolving Environments

Andra Stroe

Center for Astrophysics | Harvard & Smithsonian

Tuesday, May 18, 2021


Understanding the interplay between galaxy evolution, star formation, and black hole activity from the perspective of structure formation remains one of the most fascinating challenges in modern astrophysics. On the largest scales, pairs of galaxy clusters colliding drive the growth of structure. Cluster mergers are the most energetic events since the Big Bang, which release 10^64 ergs over 1-2 billion years and produce dramatic, long-lasting effects. By bringing together panchromatic observations, I will discuss how the merger of galaxy clusters can trigger star formation and black hole activity in cluster galaxies, shape the evolution of cluster galaxies, and reverse typical environmental trends observed in relaxed clusters at low redshift. With approximately half the galaxy clusters in the local Universe undergoing mergers, this recent work has revealed gaps in our understanding of the growth of structure in the Universe and showed the potential for discovery in this understudied field. I will draw parallels between the fundamental drivers of galaxy and black hole evolution in low-redshift clusters and the processes relevant in the context of proto-clusters and high-redshift clusters, where mergers and associated non-thermal phenomena were far more common than in the nearby Universe. A treasure trove of cluster samples at increasingly large redshifts will be delivered by new generation of instruments, including eROSITA, GMT, ELT, ATHENA, Lynx, and SKA. The detail with which we can study clusters in the nearby Universe provides us the calibration for the physics of high redshift events and helps guide discoveries in the field of galaxy and black hole evolution at the epoch when structures first formed.

Probing the Escaping Atmospheres of Exoplanets

Antonija Oklopčić

University of Amsterdam

Tuesday, May 25, 2021


Atmospheric escape is an important process in the evolution of exoplanet atmospheres, especially highly irradiated planets orbiting very close to their host stars. However, many aspects of atmospheric escape remain poorly understood, in part due to a limited number of direct observations that have been available until recently. In the last couple of years, transmission spectroscopy in the helium line at 1083 nm has been established as a powerful new probe of the extended and escaping exoplanet atmospheres. These observations allow us to constrain the atmospheric mass loss rates and give us valuable insights into the dynamics of upper atmospheres. In this talk, I will discuss how we can use these observations, together with theoretical models and 3D hydrodynamic simulations of planetary winds, to improve our understanding of the physical processes that drive atmospheric escape. I will also present some of the main challenges involved in our data interpretation, including the uncertainties in the extreme ultraviolet spectra of exoplanet host stars. Finally, I will describe how radiation polarization in the helium 1083 nm line, if observed with the current or next-generation high-resolution spectropolarimeters, could be used to directly probe the magnetic fields of exoplanet atmospheres.

First Results from eROSITA Observations of Galaxy Clusters in the eFEDS Field and An Outlook for the All-Sky Survey

Esra Bulbul

Max Planck Institute for extraterrestrial Physics

Tuesday, Jun 1, 2021


Galaxy clusters trace the highest peaks in the cosmic density field and offer an independent and powerful probe of the growth of structure and their abundance is strongly dependent on the underlying cosmology. The availability of the new catalogues with 100000 clusters, eROSITA All-Sky Survey in the X-ray band will put us on the verge of a breakthrough in precision cosmological measurements. I will summarise the results on galaxy groups and clusters of galaxies from the eROSITA Final Equatorial Survey (eFEDS) performed during the Performance Verification phase. I will also present the new results from the first All-Sky Survey and provide an outlook for rich science that eROSITA will offer when combined with the other multi-wavelength surveys.

Past Colloqia Schedules

2020: Fall, Spring
2019: Fall, Spring
2018: Fall, Spring
2017: Fall, Spring
2016: Fall, Spring
2015: Fall, Spring
2014: Fall, Spring
2013: Fall, Spring, Summer
2012: Fall, Spring
2011: Fall, Spring
2010: Fall, Spring

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