Wine and Cheese Spring 2017

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2017.

Wine and Cheese sessions with one talk will have a 50 minute talk with 10 minutes for questions. Sessions with two speakers will have two 25 minute talks, each with 5 minutes for questions.

January 30th

Michael Fall (STScI)

Formation and Evolution of Star Clusters: A Simple, Unified Picture
This CAS seminar presents a simple, unified picture for the formation and evolution of star clusters. These objects are important in the structure and evolution of galaxies, primarily as the sites of star formation and stellar feedback. The seminar is organized around the mass function of star clusters (i.e., the spectrum of cluster masses) and how it evolves with time (age). Observations show some remarkable similarities in the mass functions of young star clusters in different galaxies, analogous to the similarities in stellar initial mass functions (IMFs). Explaining the near universality of the mass functions of star clusters is one of the goals and successes of the theory presented here. A byproduct of this theory is a unified concept of star clusters of all types (associations, open clusters, globular clusters, etc). In the new picture, clusters are characterized primarily by their masses and ages. The seminar is aimed at a broad audience of theorists and observers.

February 6th

Stephen Rinehart (GSFC)

The Transiting Exoplanet Survey Satellite (TESS): Opening the Door for Comparative Planetology
The idea that planets exist beyond our own solar system has been a feature of science fiction for many years, but it is only in the past few decades that the science fact of exoplanets has become known. With advances in ground based radial velocity measurements and the success of the Kepler mission, there are now over 1,000 confirmed exoplanets, and we continue to be amazed by the diversity and complexity of planetary systems. The Transiting Exoplanet Survey Satellite (TESS) will be the next step in this voyage of discovery. Kepler’s focus was on conducting a census of planets and on understanding the population statistics; TESS will find nearby planets amenable to detailed follow-up observations, so that we may begin to be able to truly understand these new worlds.

Andrew Ptak (GSFC)

The Survey and Time-domain Astrophysics Research eXplorer (STAR-X): Surveying the Ever-Changing Universe
STAR-X is a mission proposal that was submitted last December in response to the NASA MIDEX call. If selected it will launch in 2023 which is well positioned to complement LSST, WFIRST, JWST, Euclid, and SKA. The main science goals will be:
- Discover what powers the most violent explosions in the Universe
- Understand how black holes grow across cosmic time and mass scales
- Measure how structure formation heats the majority of baryons in the Universe
This talk will discuss these science goals and how they drove the design of STAR-X, which consists of an X-ray telescope with a 5” nearly-uniform PSF across a 1 deg. FoV and a rapid response capability.

February 13th

David Nataf (JHU)

The Extinction Curve toward the Bulge and Implications for the WFIRST Microlensing Campaign
The interstellar extinction toward the inner Milky Way is known to be significant (reaching Av ~ 80), variable, and non-standard in wavelength dependence. The issue of the net extinction, and first-order wavelength dependence, is largely solved by means of photometric data from OGLE (optical gravitational lensing experiment) and VVV (Vista Variables in the Via lactaea survey). Some uncertainties remain in mapping differential extinction, and extrapolating the extinction to other wavelengths. I place special emphasis on how it will affect the WFIRST microlensing campaign, a ~5-year, ~360 day programme that will be part of WFIRST's core programme.

Yi-kuan Chiang (JHU)

Galaxy Proto-clusters as an Interface between Structure, Cluster, and Galaxy Formation
Proto-clusters, the ancestor large-scale structures of present-day galaxy clusters, are unique laboratories to study dark matter assembly, cosmic baryon cycle, galaxy growth, and environmental impact on galaxy evolution. We extract LCDM predictions for the basic physical properties and observational signatures of galaxy proto-clusters as a function of cosmic time and cluster mass. Next I will talk about observation strategies and our ongoing efforts to search for and characterize z>~2 proto-clusters in photometric and spectroscopic galaxy surveys. I will then discuss cluster progenitors in the context of cluster formation, galaxy evolution and cosmic star formation, highlighting their unique roles linking scales from large to small, and epochs form active star-formation to quenching.

February 20th

Lucas Parker (JHU)

The Cosmology Large Angular Scale Surveyor
The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment to observe the polarization of the Cosmic Microwave Background (CMB) with the primary science goal of detecting the gravitational waves generated in the earliest moments of our universe. CLASS is unique among CMB polarimetry experiments in its frequency and angular scale coverage, designed to maximize sensitivity to the primordial gravitational wave signal at the largest angular scales and with frequency span to reject both dust and synchrotron foreground emission. The CLASS survey began observations in 2016 with a 38 GHz telescope, and will be deploying two 93 GHz band telescopes and a dichroic 150/220 GHz telescope over the next two years. This talk will describe the CLASS experiment design and give an update on the state of the survey.

Graeme Addison (JHU)

Cosmic Inconsistency?
The precision of a range of cosmological measurements has improved rapidly in recent years. While no individual data set provides compelling evidence for physics beyond the standard LambdaCDM model, the values of parameters, particularly the Hubble constant, inferred from different data sets now exhibit significant tension. I will discuss how measurements from the early universe and more local, low-redshift observations interact to provide cosmological constraints and why it is challenging to accommodate current data in either the standard model or some commonly-considered extensions.

March 6th

Kate Rowlands (JHU)

Caught in the act: charting galaxy transformation over cosmic time
One of the key problems in astrophysics is understanding how and why galaxies switch off their star formation, building the “red-sequence” that we observe in the local Universe. Post-starburst (“E+A”) galaxies, where a galaxy has recently undergone a massive starburst, are sufficiently common at z~1-2 that they may contribute significantly to the growth of the red-sequence at this important epoch. It is not well known how much post-starburst galaxies contribute to the build-up of the red sequence at z<1, due to small number statistics in previous redshift surveys, and aperture bias at very low redshifts (e.g. in SDSS). Using wide-area photometric and spectroscopic surveys I will explore the gas, dust and stellar population properties of post-starburst galaxies to determine whether these galaxies are quenching, and determine how important they could be for accounting for the growth of the red galaxy population.

Jeremy Schnittman (GSFC)

Radiation Transport in Dynamic Spacetimes
We present early results from a new radiation transport calculation of gas accretion onto merging binary black holes. We use the Monte Carlo radiation transport code Pandurata, now generalized for application to dynamic spacetimes. The time variability of the metric requires careful numerical techniques for solving the geodesic equation, particularly with tabulated spacetime data from numerical relativity codes. Using a new series of general relativistic magneto-hydrodynamical simulations of magnetized flow onto binary black holes, we investigate the possibility for detecting and identifying unique electromagnetic counterparts to gravitational wave events.

March 27th

Suvi Gezari (UMCP)

Exploring Supermassive Black Hole Demographics with Time Domain Observations
We are entering an era of increasingly powerful wide-field optical synoptic surveys that are transforming the study of the variable night sky. I will highlight the capability of time domain observations to study supermassive black holes (SMBHs), and in particular, to study their demographics (mass, spin, binarity). I will present our past results from the Pan-STARRS1 Medium Deep Survey and new results from the Intermediate Palomar Transient Factory that probe SMBHs in the nuclei of galaxies, including dormant SMBHs via the tidal disruption and accretion of a star, binary SMBHs via periodic quasar variability, and active SMBHs caught in the act of turning on. I will conclude with the exciting potential of the upcoming Zwicky Transient Facility and the Large Synoptic Survey Telescope to map the demographics of SMBHs over cosmic time.

April 3rd

Massimo Ricotti (UMd)

X-ray Twinkles and Pop III Stars
I will present new calculations on the optimal level of X-ray emission in the early universe that can promote the formation of the first stars (Pop~III). This is important in determining the number of dwarf galaxies formed before reionization and their fossils in present day universe.

X-ray emissivity above the optimal level reduces the number of Pop~III stars because it increases the Jeans mass of the intergalactic medium (IGM), while a lower emissivity suppresses the formation rate of molecular hydrogen, preventing or delaying star formation in minihalos above the Jeans mass. The build up of the H_2 dissociating background is slower than the X-ray background due to the shielding effect of resonant Lyman lines. Hence, the nearly unavoidable X-ray emission from SN remnants of the first stars is sufficient to boost their number to few tens per comoving Mpc^3 at redshift z~5. High-mass X-ray binaries instead have a negligible effect with respect to SNe.

Moreover, if a non-negligible fraction of Pop~III stars end their lives as hypernovae, their soft X-ray emission is sufficient promote the formation of Pop~III stars to about 400 per comoving Mpc^3, that is near the theoretically-allowed maximum number of Pop~III stars with typical masses 10-40~M_sun. A higher X-ray flux, for instance produced by accretion onto intermediate mass black holes and miniquasars, would suppress the number of first stars because of the excessive heating of the IGM. In these models the increased ionization fraction of the IGM from X-rays contributes negligibly to the optical depth to Thompson scattering, but the bursty ionization from UV emission by Pop~III stars can have a significant effect on tau_e .

April 10th

Jay Felix Lockman (NRAO)

Neutral Gas Outside the Disks of Local Group Galaxies
Most of the neutral Hydrogen in the Local Group resides in the disks of the large spirals, but there are important exceptions, some of which are tied to basic processes in galaxy evolution. After giving a brief survey of recent science with the Green Bank Telescope, I'll discuss the different populations of neutral hydrogen that are found outside the disks of galaxies in the Local Group. The most puzzling are the clouds found between M31 and M33, which have the mass of dwarf galaxies but do not appear to contain any stars.

April 17th

Margaret Meixner (StScI)

The Life Cycle of Dust in the Magellanic Clouds: Insights from Spitzer and Herschel
The life cycle of dust in a galaxy involves the exchange of material between the interstellar medium (ISM) and stars. Dust is formed in the winds of dying stars, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, and the explosion of supernovae. In the ISM, the dust may be shattered and vaporized by supernova blast waves or accreted onto seed grains in the denser ISM. Dust is consumed in the star formation process and appears in the circumstellar environments of newly forming stars. By tracing the lifecycle of dust, we gain insights into the dust evolution processes and the origin of galactic dust. The Spitzer Space Telescope and Herschel Space Observatory provide a sensitive probe of circumstellar and interstellar dust. The Spitzer Surveying the Agents of Galaxy Evolution (SAGE; the ISM and stars) and the Herschel Inventory of the Agents of Galaxy Evolution (HERITAGE) surveys of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) focus on the lifecycle of dust. The LMC and SMC are ideal astrophysical laboratories for this study because their proximity to us permits detailed studies of the stars and their relation to the ISM from local to galaxy wide scales. For example, the masses of the circumstellar dust shells of stars and ISM dust clouds can be determined producing a more precise dust budget than possible for our own Milky Way galaxy. I will present key results from the SAGE and HERITAGE projects that quantify the stellar origin of dust, its evolution in the ISM and its consumption by star formation. Our measurements of dust mass-loss rates from entire populations of AGB and RSG stars and the discovery of ~0.5 solar masses of dust in the ejecta of supernova, SN1987A, provide the dust production rates by the stars. The maps of dust masses and gas-to-dust ratios of the ISM reveal how dust is destroyed and possibly created in the ISM. Our discovery of thousands of young stellar object candidates shows us locations of active star formation and enables us to quantify the star formation rate. I will end with a brief summary of the potential of a large cryogenically cooled telescope, such as the Origins Space Telescope to extend this research.

April 24th

Special Graduate Seminar: Philip Engelke

The Structure of "Dark" Gas in Star-Forming Regions: OH as an Alternate Molecular Tracer
Despite its near-universal acceptance, use of the CO(1-0) transition as a molecular gas tracer has been drawn into controversy for molecular gas for low densities, and evidence from gamma-ray and IR surveys suggest the presence of undetected gas in the Galaxy, which is likely molecular and which likely contains a mass similar to the mass of known molecular gas (Grenier et al. 2005, Tibaldo et al. 2015). I have worked with Drs. Ron Allen (STScI / JHU) and David Hogg (NRAO) to study the OH 18 cm transitions as an alternate tracer for molecular gas, using the Green Bank telescope for blind surveys towards the Outer Galaxy. These observations indicate that OH can be a viable alternative tracer for molecular gas and appears to trace a larger component of the molecular ISM than does CO, being widely detected in places many of which have no CO(1-0) detections in the literature. My thesis project applies the use of OH as an alternate molecular gas tracer to the W5 star-forming region. In order to do this, I have performed an OH survey with the Green Bank telescope over W5, which contains a free-free continuum background and a mixture of emission and absorption features. I will report findings regarding the OH line excitation temperatures in the region which are needed before column densities can be calculated, as well as describe a second method for determining excitation temperatures using the VLA. I will also show preliminary results on molecular gas column densities in W5 as derived from OH, and compare them to the column densities derived from the corresponding CO data from the literature.

May Day

Philip Hopkins (Caltech)

Stars Re-Shaping Galaxies
The most fundamental unsolved problems in galaxy formation revolve around "feedback" from massive stars and black holes. I'll present new results from the FIRE simulations which combine new numerical methods and physics in an attempt to realistically model the diverse physics of the interstellar medium, star formation, and feedback from stellar radiation pressure, supernovae, stellar winds, and photo-ionization. These mechanisms lead to 'self-regulated' galaxy and star formation, in which global correlations such as the Schmidt-Kennicutt law and the global inefficiency of star formation -- the stellar mass function -- emerge naturally. Within galaxies, feedback regulates the structure of the interstellar medium, but more radically drives outflows which can actually change the dynamics, morphologies, and sizes of galaxies, in addition to transforming cusps into cores and suppressing star formation. We are actually reaching the point where different stellar feedback and stellar types can produce observable differences on extra-galactic scales. Finally, I'll discuss where stellar feedback fails, and additional feedback, perhaps from AGN, is really needed to explain observations.

May 8th

Patrick Breysse

High-Redshift Astrophysics Using Every Photon
Large galaxy surveys have dramatically improved our understanding of the complex processes which govern gas dynamics and star formation in the nearby universe. However, we know far less about the most distant galaxies, as existing high-redshift observations can only detect the very brightest sources. Intensity mapping surveys provide a promising tool to access this poorly-studied population. By observing emission lines with low angular resolution, these surveys can make use of every photon in a target line to study faint emitters which are inaccessible using traditional techniques. With upcoming carbon monoxide experiments in mind, I will demonstrate how an intensity map can be used to measure the luminosity function of a galaxy population, and in turn how these measurements will allow us to place robust constraints on the cosmic star formation history. I will then show how cross-correlating CO isotopologue lines will make it possible to study gas dynamics within the earliest galaxies in unprecedented detail.