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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

NASA MSFC

Tuesday, Mar 30, 2021

Abstract

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

Abstract

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

Abstract

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

Abstract

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.