Wine and Cheese Fall 2016

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2016.

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.

September 19th

Massimo Robberto (STScI)

GMOX and SAMOS
NSF has recently funded a JHU-led collaboration to build SAMOS, a novel multi-slit spectograph for the 4.1m SOAR telescope in Chile. SAMOS exploits the ground-layer AO system to take hundreds of faint spectra in parallel at R~2000 over a 3’x’3’ field of view. At the same time, Gemini has contracted us with the study of an expanded version of SAMOS, GMOX, to be installed at the Multi-Conjugate extreme-AO system of Gemini South. GMOX covers the full U to K bandpass at R~5000 and can synthetize slits as small as a single HST/WFC3-vis pixel (40mas), reaching unpredentented levels of sensitivity in the near-IR from the ground. I will present the main characteristics of the instruments, their current status, and an outline of the type of science programs that can be carried out in the substantial amount of GTO time.

Bram Ochsendorf (JHU)

The Location, Clustering, and Propagation of Massive Star Formation in Giant Molecular Clouds
Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this talk, I will present results from a project utilizing data from several galaxy-wide surveys to build an unbiased dataset of ∼700 massive young stellar objects (MYSOs), ∼200 giant molecular clouds (GMCs), and ∼100 young (< 10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We have employed this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. The main results are as follows: (1) Massive stars do not typically form at the highest column densities nor centers of their parent GMCs. (2) Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. (3) The rate of massive star formation is significantly boosted in clouds near SCs. Yet, comparison of molecular clouds associated with SCs with those that are not reveals no significant difference in their global properties. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. I will compare our findings with Galactic studies and discuss this in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

September 26th

David Jones

Contaminated Cosmology: Measuring w with Photometrically Classified Supernovae from Pan-STARRS
The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for only 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 2,979 of these likely SNe and estimate that ∼1,100 are Type Ia SNe (SNeIa) with light-curve quality sufficient for a cosmological analysis. We use PS1 data and simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the dark energy equation of state, w. With the Bayesian Estimation Applied to Multiple Species (BEAMS) method, we simultaneously determine distances to SNe Ia and the contaminating CC SN distribution as a function of redshift. We use light-curve based SN classification priors for BEAMS as well as a new classification method based solely on host galaxy spectra. By applying several independent SN classification methods and CC SN parameterizations, we investigate the systematic error on w due to CC SN contamination. We find that w has an average systematic error of 0.012 due to CC SNe, ∼25% of the statistical error on w when using a cosmic microwave background prior. We find that Ia-like CCSNe in our sample are much brighter than expected from known CC SN luminosity functions.

Clément Bonnerot

Stream evolution in tidal disruption events
Tidal disruption events occur when a star gets scattered on a trajectory that takes it so close to a supermassive black hole that it is torn apart by strong tidal forces. Such events represent unique probes of otherwise quiescent black holes, which constitute the majority of black holes in the local universe. However, this great potential is hampered by the lack of a clear picture of how exactly these events take place. One particular uncertainty concerns the circularization process during which the stellar debris dissipate their large orbital energy to form an accretion disc around the black hole. Hydrodynamical simulations point towards shocks driven by debris self-intersections as an efficient dissipation mechanism. In my talk, I will present a recently developed semi-analytical model that treats the circularization process, accounting for the impact of both shocks and magnetic stresses. This model proves that the net effect of magnetic stresses is to strengthen shocks, thus accelerating circularization. It also allows to predict the form of the lightcurve associated to shock luminosity and demonstrates that the thermal energy excess imparted by shocks is most likely to cause the rapid formation of a thick structure. To conclude the talk, I will present latest advances on ongoing projects and mention future research directions.

October 3rd

David Hogg (NYU)

Chemical tagging of stars with a data-driven model
We have used tens of thousands of high-quality stellar spectra taken in the SDSS-III APOGEE survey to build a data-driven model of stars, and measure detailed chemical abundances at a scale and precision substantially better than any previous experiment. I discuss the model, its successes, and its potential as a tool for understanding stars and the Galaxy.

October 10th

Cole Miller (UMCP)

CDM versus Perceived Structure
Cold dark matter, along with dark energy, constitute 96% of the universe. Calculations using these components have successfully explained many aspects of structure formation, but as is appropriate for such a broad framework there have also been multiple challenges along the way. One recent challenge involves the existence of structure in the satellite galaxy distributions of the Galaxy and M31, such as thin planes with apparent kinematic coherence, which have been claimed to be inconsistent with the results from dark matter simulations. However, these are a posteriori claims: a pattern is seen in data, and then that particular pattern is analyzed for significance, which can easily lead to misleading assessments of improbability. I will discuss different statistical methods to determine more objectively whether observed patterns are consistent with data, and will also discuss planned future work to help compare different models of cold dark matter.

October 24th

Nathan Roth (UMCP)

What sets the line widths in tidal disruption events?
Flares from the tidal disruption of stars by supermassive black holes (TDEs) are providing a new perspective on accretion physics. While their emission can span a wide range of spectral energies, from hard x-rays through radio, a large collection of spectral data has now been collected in the optical and near UV. These spectra show a stunning amount of diversity. In addition to variations in the strengths of the lines, the widths can differ by over a factor of five between events, even when a similar mass is inferred for the black hole. In some events the lines mysteriously narrow over time. Many theoretical models predict that stellar material will be launched in an outflow, yet the spectra rarely display the P-Cygni line profiles associated with outflows in other astrophysical objects. In this talk I’ll present preliminary results from radiative transfer calculations designed to make sense of these observations.

Raymond Simons (JHU)

Assembly of Disk Galaxies from z~2 to Now
Early star-forming galaxies tend to be kinematically complex. When and how these galaxies develop a mature rotationally supported disk is an open question. I will discuss recent work aimed at characterizing the gas kinematics of star-forming galaxies with Keck/MOSFIRE at 1.3 < z < 2.5, the peak of cosmic star-formation. We combine these measurements with results from the DEEP2 survey at z < 1.2 and investigate trends in kinematics over a significant fraction of the age of the universe. I will show how star-forming galaxies have evolved from thick and turbulent systems at z~2 to well-ordered disks at z~0 by, on average, drastically declining in velocity dispersion and mildly increasing in rotation velocity. The fraction of galaxies that are rotationally supported steadily increases with time and is always larger at high mass, indicating that the development of disks is shaped through kinematic downsizing.

October 31st

Martin Sahlén (Uppsala)

Clusters, Voids, and Cosmological Constraints
Clusters and voids in the large-scale galaxy distribution are complementary probes of the growth of structure across cosmic time. In this talk, I will describe the first cosmological constraints based on void abundances, showing that the existence of the largest cluster and void provides strong evidence for dark energy. I will also discuss other recent results, and the prospects for future surveys with e. g. Euclid and WFIRST to constrain cosmological models using cluster and void samples.

Xilu Wang (Illinois)

How Not to Miss the Supernova of the Century: Gamma-Ray Alarms for a Galactic Type Ia Event
In our own Galaxy, any supernova explosion would be a spectacular “once in lifetime” event. Tragically, a Galactic Type Ia supernova could go entirely unnoticed due to the large optical and near-IR extinction in the Milky Way plane, low radio and X-ray luminosities, and a weak neutrino signal. Fortunately, I will show that Fermi/GBM and Swift/BAT can serve as Galactic SNIa early warning systems because they can monitor the nuclear γ- ray lines from the 56Ni -> 56Co -> 56Fe radioactive decay. I will present strategies for detection, localization and follow-up of the next Galactic SNIa.

November 7th

Anthony Pullen (NYU)

Revealing CII Emission with LSS Cross-correlations
The CII emission line tends to be the brightest line in star-forming galaxies, making it an ideal tracer of large-scale structure. Through the method of intensity mapping, astronomers hope to map CII emission at cosmological redshifts and large volumes, making CII and unprecedented probe of cosmology and reionization. However, the various models of the expected CII emission are highly uncertain by orders of magnitude, limiting our ability to predict how well potential CII surveys could probe large-scale structure. In this talk, I will present our measurement of excess emission from large scales at redshift z=2.5 potentially attributable to CII emission. This excess emission was measured by cross-correlating the 545 GHz broad-band microwave map from the Planck satellite and high-redshift quasars from the Sloan Digital Sky Survey. I will also discuss future opportunities with CII intensity mapping.

November 28th

Aki Roberge (GSFC)

Big Bang to Biosignatures: The LUVOIR Decadal Mission Concept
The Large UV/Optical/IR Surveyor (LUVOIR) is a concept for a highly capable, multi-wavelength observatory with ambitious science goals. This mission would enable a great leap forward in a broad range of astrophysics, from the epoch of reionization, through galaxy formation and evolution, to star and planet formation. LUVOIR also has the major goal of characterizing habitable exoplanets around Sun-like stars and searching them for signs of life.

LUVOIR is one of four Decadal Survey Mission Studies initiated in Jan 2016. The final report will be submitted to NASA and then the National Academies in 2019. Here I will summarize LUVOIR’s broad and revolutionary science goals. I’ll explain our current vision for the instrument suite and aperture sizes to be studied. Finally, I’ll discuss the study process and what will happen over the next years in preparation for the 2020 Decadal Survey.

December 5th

Panayiotis Tzanavaris (GSFC/UMBC/JHU)

Not the Blue Cloud and the Red Sequence, nor the X-ray Main Sequence: Just Star Formation in Compact Group Galaxies
With most galaxies residing in poor groups, and compact groups being the "poorest of the poor", these systems represent an extragalactic environment that continues to amaze us and is a key component in our understanding of galaxy evolution. In a series of publications, we have established unique observational bimodalities and I will present the latest updates on these results. I will also present new multi-wavelength results that explore the well-known X-ray luminosity vs. star formation rate relation in these systems, suggesting a tantalizing X-ray excess in star-forming, non-AGN, galaxies.

Mark Avara (UMCP)

Thin black hole accretion disks in the MAD state: heavy winds and 'quenched' jets
Shakura-Sunyaev thin disk theory is fundamental to black hole astrophysics. Though applications of the theory are wide-spread and powerful tools for explaining observations, such as Soltan's argument using quasar power, broadened iron line measurements of black hole spin, continuum fitting, and recently reverberation mapping, a significant large-scale magnetic field causes substantial devaitions from standard thin disk behavior. We have used fully 3D GRMHD simulations with initially ad hoc and more recently fully self-consistent radiative cooling, to explore the radiatively-efficient (i.e. thin) magnetically arrested disk (MAD) state. This work extends prior numerical studies of thicker disks, allowing us to measure how jet power scales with the disk state, providing a natural explanation of phenomena like jet quenching in the high-soft state of X-ray binaries. We additionally have simulated thin MAD disks with a misaligned black hole spin axis in order to understand further deviations from thin disk theory that may have implications for observations.