ASD Colloquium Series - Fall 2017

ASD Colloquium Series - Fall 2017

The Astrophysics Science Division colloquia occur on Tuesdays at 3:45 pm, with an opportunity to meet the speaker at 3:30 pm, in building 34, room W150 (unless otherwise noted). Schedules from past colloquium seasons are available.

Contact: Eric Switzer


Sep 5 Andrei Mesinger - "Illuminating the Cosmic Dawn and Reionization"
Sep 12 Special Location: B34, W120 A/B
Randall Smith - "Arcus - Exploring the Formation and Evolution of Clusters, Galaxies, and Stars"
Sep 19 Special Location: B34, W120 A/B
Alexandra Pope - "Decoding the cosmic evolution of star formation and black hole growth imprinted on the interstellar medium in galaxies"
Sep 26 Special Location: B34, W120 A/B
Feryal Ozel - "A New Era of Compact Objects"


Oct 3 Cancelled
Elisabetta Cavazzuti - "Fermi Large Area Telescope and its recent results on Active Galactic Nuclei"
Oct 10 Amy Kimball - "The VLA Sky Survey (VLASS)"
Oct 17 Leo Singer - Black and Gold: Gravitational Waves and Electromagnetism from the Binary Neutron Star Merger GW170817/GRB170817A
Oct 24 Abigail Vieregg - "Discovering the Highest Energy Neutrinos Using a Radio Phased Array"
Oct 31 Chad Hanna (PSU) - "The next frontier of gravitational wave physics and astronomy with Advanced LIGO""


Nov 7 Daniel Stern - "The Euclid Mission"
Nov 14 Suzanne Staggs (Princeton University) - "Cosmology from the Cosmic Microwave Background: What We Know, How We Know It, and What's Left"
Nov 21 No Colloquium
Nov 28 Dan Kasen (UC Berkeley and Lawrence Berkeley Laboratory) - "Deciphering the origin of the heavy elements in the light and gravitational waves of a neutron star merger"


Dec 5 Eliza Kempton - "Revealing the Atmospheres of Extrasolar Super-Earths"
Dec 12 Jordan Camp - "Proposed Wide-Field GW Counterpart Missions for the 2020s"
Dec 19 No Colloquium
Dec 26 No Colloquium

Illuminating the Cosmic Dawn and Reionization

Andrei Mesinger

Tuesday, Sep 5, 2017


The birth of the first stars, black holes and galaxies heralded the end of the cosmic Dark Ages and the beginning of the Cosmic Dawn. The light from these objects heated and ionized almost every atom in existence, culminating in the Epoch of Reionization: the final major phase change of the Universe. This final frontier of astrophysical cosmology is undergoing a transition from an observationally-starved epoch to a "Big Data" field. This process will culminate with interferometric observations of the redshifted 21-cm line, eventually providing a 3D map of the first billion years of our Universe. I will discuss the recent clues to reionization, obtained from the CMB, high-redshift galaxies, and quasars. I will present the first detection (2 sigma) of ongoing reionization, found in the spectrum of a z=7.1 quasar. Finally, I will showcase the physical bounty of the upcoming 21-cm observations. I will discuss the innovative modeling techniques we are developing to tap into this bounty, allowing us to constrain astrophysical parameters in a fully Bayesian framework.

"Arcus - Exploring the Formation and Evolution of Clusters, Galaxies, and Stars"

Randall Smith


Tuesday, Sep 12, 2017


Arcus, a Medium Explorer (MIDEX) mission, was selected by NASA for a Phase A study in August 2017. The observatory provides high-resolution soft X-ray spectroscopy in the 12-50Å bandpass with unprecedented sensitivity: effective areas of >450 cm2 and spectral resolution >2500. The Arcus key science goals are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, groups, and clusters, (2) to trace the propagation of out owing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback and (3) to explore how stars, circumstellar disks and exoplanet atmospheres form and evolve. Arcus relies upon the same 12m focal length grazing-incidence silicon pore X-ray optics (SPO) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings, and the results are imaged with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest, and mission operations are straightforward, as most observations will be long (~100 ksec), uninterrupted, and pre-planned.

"Decoding the cosmic evolution of star formation and black hole growth imprinted on the interstellar medium in galaxies"

Alexandra Pope

University of Massachusetts

Tuesday, Sep 19, 2017


The prominent peak in the history of star formation and black hole accretion at cosmic noon suggests strong evolution in the mechanisms that grow stars and black holes in galaxies over time. Infrared observations canquantify the energy balance between star formation and active galactic nuclei (AGN) activity, and constrain the composition and conditions of the gas and dust available to form new stars. In order to understand the enhanced activity at cosmic noon, wemeasure the interstellar medium (ISM) conditions in high redshift galaxies by combining diagnostics from mid-IR spectroscopy, far-IR/(sub)mm continuum and CO molecular lines. While ground-based facilities such as ALMA and the Large Millimeter Telescope (LMT) probe the cold ISM, JWST will be crucial for measuring the warm ISM and small dust grains. Looking to the future, a cold infrared telescope like the Origins Space Telescope is needed to decode the ISM conditions in all galaxies over cosmic time.

"A New Era of Compact Objects"

Feryal Ozel

Tuesday, Sep 26, 2017


The discovery of many diverse populations of neutron stars and black holes is happening at an accelerating rate. The computational advances in calculating the properties of these compact objects, their multiwavelength observations, and the new avenues of studying them with gravitational waves have led to a new understanding of their formation, evolution, and of the fundamental physics that shapes their characteristics. In this talk, I will describe these parallel advances and show how this multi-faceted approach helps pin down our understanding of the evolution of massive stars, supernova explosions, and coalescing compact objects.

"Fermi Large Area Telescope and its recent results on Active Galactic Nuclei (tentative)"

Elisabetta Cavazzuti

Tuesday, Oct 3, 2017


The Fermi Gamma-ray Space Telescope has operated for more than 9 years and provided unprecedented information about many source classes, including Active Galactic Nuclei. I will review the most recent results and milestones concerning this apparently well-known source class. Although these broad-band, bright objects are extensively studied across the entire electromagnetic spectrum, we still do not understand their intrinsic nature, and new paradigms are being explored.

"The VLA Sky Survey (VLASS)"

Amy Kimball

Tuesday, Oct 10, 2017


The VLA Sky Survey (VLASS) is a new modern radio sky survey that will be produced by the National Radio Astronomy Observatory (NRAO), motivated by the enhanced observing and software capabilities of the upgraded Karl G. Jansky Very Large Array (VLA). This community-driven survey will cover the entire sky visible to the VLA (> -40deg decl.) in three observing epochs (reaching rms ~120 microJy per epoch) with a frequency coverage of 2-4 GHz and angular resolution of ~2.5 arcsec. NRAO will provide continuum images as well as spectral and full polarisation image cubes. Scientific applications include the study of radio transients, Faraday tomography of radio galaxies, and demographics of the radio loud/intermediate AGN population. I will give an overview of the current status and developments for VLASS, including the status of the VLASS Pilot study and challenges faced by the VLASS team.

I will also describe two commensal surveys that are ongoing at the VLA. The VLA Low-band Ionosphere and Transient Experiment (VLITE) runs in parallel to VLA observing, providing ~6200 hours/year of science-ready data products across 64 MHz of bandwidth centered on 352 MHz, processed by a custom correlator in real-time. "realfast" is a system for real-time fast transient searches on the VLA using a dedicated pipeline that processes a high-speed duplicate of the primary VLA observing stream, and will automatically identify exotic transient systems such as fast radio bursts and milli-second pulsars.

"Discovering the Highest Energy Neutrinos Using a Radio Phased Array"

Abigail Vieregg

Tuesday, Oct 24, 2017


Ultra-high energy neutrino astronomy sits at the boundary between particle physics and astrophysics. The detection of high energy neutrinos is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. IceCube has detected astrophysical neutrinos at lower energies, but the best limit to date on the flux of ultra-high energy neutrinos comes from the ANITA experiment, a NASA balloon-borne radio telescope designed to detect coherent radio Cherenkov emission from cosmogenic ultra-high energy neutrinos. The future of high energy neutrino detection lies with ground-based radio arrays, which would represent a large leap in sensitivity. I will discuss a new radio phased array design that will improve sensitivity enormously and could push the energy threshold for radio detection down to overlap with the energy range probed by IceCube.

The next frontier of gravitational wave physics and astronomy with Advanced LIGO

Chad Hanna


Tuesday, Oct 31, 2017


Advanced LIGO has been a tremendously successful observatory starting with the first direct detection of gravitational waves in September, 2015. Since then, LIGO has confirmed the detection of four additional gravitational wave sources. The most recently published gravitational wave event came from a new source - merging neutron stars. This discovery ushered in a new era of multi-messenger astronomy with the observation of gravitational waves simultaneously with electromagnetic emission spanning gamma-rays to radio. In this colloquium, I will provide some background for how LIGO achieved this monumental task and discuss the implications for physics and astrophysics of such joint observations.

"The Euclid Mission"

Daniel Stern

Tuesday, Nov 7, 2017


Euclid is an ESA M-class mission with significant NASA participation designed to study the geometry and nature of the dark universe. Currently scheduled for launch in late 2020, the mission has been optimized for measurement of two primary probes of Dark Energy: (1) weak gravitational lensing, and (2) galaxy clustering, including both baryonic acoustic oscillations and redshift space distortions. By making sensitive imaging and spectroscopic measurements over 15,000 deg2 of extragalactic sky, significant ancillary science is also eagerly anticipated. Euclid will consist of a 1.2-meter space telescope with two instruments: a wide-field optical camera for imaging, and a wide-field near-infrared camera for both imaging and spectroscopy. The optical camera takes advantage of the high resolution afforded by space to make very accurate measurements of galaxy shapes, while the near-infrared camera takes advantage of the very low background in orbit to make precise measurements of galaxy fluxes and accurately measure the distances to millions of galaxies. I will discuss the current status of the Euclid mission, with an emphasis on the primary efforts of the NASA-funded US members of the Euclid Consortium. I will also discuss Euclid in the context of WFIRST, both in terms of mission design, and for lesson's learned.

"Cosmology from the Cosmic Microwave Background: What We Know, How We Know It, and What's Left"

Suzanne Staggs

Princeton University

Tuesday, Nov 14, 2017


In the 50+ years since its discovery, the cosmic microwave background (CMB) has yielded surprisingly detailed and precise information about the form, content and dynamics of the early universe. Recent satellite CMB data cap off a remarkably successful series of ground-based and balloon-borne experiments. In fact, those data confirm a surprisingly simple parameterization of the so-called background cosmology. High angular resolution maps, and polarization data at all angular scales, are the focus of current and next-generation instruments. I will describe what we already know about the universe from the CMB, and lay the ground for future revelations from the CMB, with special emphasis on the Atacama Cosmology Telescope, and its instrumentation and recent data.

"Deciphering the origin of the heavy elements in the light and gravitational waves of a neutron star merger"

Dan Kasen

UC Berkeley and Lawrence Berkeley Laboratory

Tuesday, Nov 28, 2017


The discovery of the gravitational wave source GW170817 and its associated electromagnetic (EM) counterpart provides a remarkable opportunity to dissect the physics of merging neutron stars and address long standing questions as to the origin of the heaviest elements. Theoretical modeling has suggested that matter ejected in the violent merger of neutron stars may assemble into heavy isotopes in a process of rapid neutron capture ("r-process") nucleosynthesis. The radioactive decay of these isotopes has been theorized to power a distinctive thermal EM glow (a "kilonova"). In addition, relativistic outflows may produce non-thermal emission from gamma-ray to radio wavelengths. I will review our theoretical understanding of mergers and compare the expected signals to the extraordinary data now obtained for GW170817 and its EM counterpart. Observations at optical through infrared wavelengths closely resemble theoretical predictions of a kilonova, and allow us to infer the production of two spatially distinct components of ejecta, one composed of light (atomic mass number A < 140) and one of heavy (A > 140) r-process material. Estimating a merger rate, the inferred mass ejected implies that mergers are a dominant mode of r-process production in the universe. This marks the emergence of a new field of astrophysics, whereby we can constrain the dynamics of neutron star mergers and analyze the signatures of heavy elements at their production site.

"Revealing the Atmospheres of Extrasolar Super-Earths"

Eliza Kempton

Tuesday, Dec 5, 2017


Discoveries of extrasolar planets over the last two decades have reshaped our understanding of how planetary systems form. Super-Earths – planets intermediate in size/mass between Earth and Neptune – do not exist in our Solar System, and the discovery of such planets poses a challenge to theories of planetary formation and composition based on the Solar System paradigm. Through observations of the atmospheres of these planets, we can learn about their formation history, their climate, and in some cases their propensity to support life. This talk will focus on the modeling of super-Earth atmospheres as it relates to current and future observations. I will detail the current state of characterization efforts for super-Earth atmospheres, focusing on the challenges and successes in modeling and interpreting the early observations of these objects. I will conclude with a forward-looking view of super-Earth atmospheric studies over the next 5-10 years, in the era of JWST and 30-meter class ground-based telescopes.

"Proposed Wide-Field GW Counterpart Missions for the 2020s"

Jordan Camp


Tuesday, Dec 12, 2017


Recent gravitational wave (GW) events detected by LIGO-Virgo have stimulated great interest in the search for related electromagnetic counterparts. In this talk we present two wide-field GW counterpart missions now under study: ISS-TAO (Transient Astrophysics Observer on the ISS), and TAP (Transient Astrophysics Probe). ISS-TAO, a $70M Mission of Opportunity recently awarded a Phase A study, is a wide-field X-ray transient detector proposed to be deployed on the International Space Station in 2022. Through its unique Lobster imaging X-ray optics that allow high FoV, and good position resolution and sensitivity, ISS-TAO will observe X-ray counterparts of LIGO gravitational wave detections involving neutron stars and black holes. TAP, selected for a funded Probe Concept Study, is a $1B wide-field high-energy transient satellite proposed for flight starting in the late 2020s. TAP includes a soft X-ray telescope and IR telescope as well as Lobster X-ray optics. TAP will observe X-ray and IR counterparts of GWs involving neutron stars and stellar mass black holes detected by LIGO, and possibly X-ray counterparts of GWs from supermassive black holes, detected by LISA and Pulsar Timing Arrays. Both missions will also observe many events per year of X-ray transients related to compact objects, including tidal disruptions of stars, supernova shock breakouts, neutron star bursts and superbursts, and high redshift Gamma-Ray Bursts.

Past Colloqia Schedules

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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