Wine and Cheese Fall 2019

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2019.

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. Sessions in the Graduate Student Series will have three 15 minute talks, each with 5 minutes for questions.

9 September

Speaker (TDB)

Title
Abstract

16 September

Joshua Kable (JHU)

Using CMB Consistency Checks to Understand Tensions
In recent years tensions have arisen between cosmological measurements. The most serious involves the Hubble constant, but there are other tensions as well. In light of these tensions, consistency checks provide valuable checks of the presence of underestimated or unidentified systematic errors and may provide insights into potential extensions to LCDM to resolve tensions. Toward this end, we derived a new analytic method for calculating the correlations between correlated data sub-sets that can assess the consistency of parameter constraints from various CMB power spectra. We applied this method to the most recent SPTpol data set and conclude that these correlations need to be accounted for when performing internal TT vs TE vs EE consistency checks in future CMB experiments. In addition, I will discuss the degeneracy between H0 and the matter density across several current CMB experiments showing that the degeneracy directions are consistent with LCDM predictions (Kable et al. 2019).

Yajing Huang (JHU)

Accounting for Correlations When Fitting Extra Cosmological Parameters
Current cosmological tensions motivate investigating extensions to the standard $\Lambda$CDM model. Additional model parameters are typically varied one or two at a time, in a series of separate tests. The purpose of this paper is to highlight that information is lost by not also examining the correlations between these additional parameters, which arise when their effects on model predictions are similar, even if the parameters are not varied simultaneously. We show how these correlations can be quantified with simulations and Markov Chain Monte Carlo (MCMC) methods. As an example, we assume that $\Lambda$CDM is the true underlying model, and calculate the correlations expected between the phenomenological lensing amplitude parameter, $A_L$, the running of the spectral index, $n_{\rm run}$, and the primordial helium mass fraction, $Y_P$, when these parameters are varied one at a time along with the $\Lambda$CDM parameters in fits to the $\textit{Planck}$ 2015 temperature power spectrum. These correlations are not small, ranging from 0.31 ($A_L-n_{\rm run}$) to $-0.93$ ($n_{\rm run}-Y_P$). We find that the values of these three parameters from the $\textit{Planck}$ data are consistent with $\Lambda$CDM expectations within $0.9\sigma$ when the correlations are accounted for. This does not explain the 1.8-2.7$\sigma$ $\textit{Planck}$ preference for $A_L>1$, but provides an additional $\Lambda$CDM consistency test. For example, if $A_L>1$ was a symptom of an underlying systematic error or some real but unknown physical effect that also produced spurious correlations with $n_{\rm run}$ or $Y_P$ our test might have revealed this. We recommend that future cosmological analyses examine correlations between additional model parameters in addition to investigating them separately, one a time.

Sumit Dahal (JHU)

The Cosmology Larger Angular Scale Surveyor (CLASS) Detector Design and Performance
The Cosmology Large Angular Scale Surveyor (CLASS) aims to detect and characterize the primordial B-mode signal, and make a cosmic variance limited measurement of the optical depth to reionization. CLASS is a ground-based multi-frequency microwave polarimeter that surveys 70% of the microwave sky from the Atacama Desert. CLASS uses a unique combination of large sky coverage, control of systematic errors, and high sensitivity detectors to measure or place upper limits on the tensor-to-scalar ratio at a level of r = 0.01. In June 2019, CLASS fielded a 150/220 GHz dichroic detector array alongside the existing 40 and 90 GHz instruments. In this talk, I will focus on the design and performance of the CLASS detectors, and update on the current status of CLASS telescopes.

23 September

Henrique Reggiani (JHU)

Metal-poor Stars in the Inner Halo: Hints on Galaxy Formation and Chemical Evolution
We studied the Formation and early Chemical Evolution of the inner Galactic halo via precise chemical abundances of the metal-poor stellar component, via a sample of high-resolution, and high S/N spectra, analyzed with the line-by-line differential abundance technique. We see evidence that the inner halo was formed by one major merger event, and we use our abundance patterns to constrain a chemical evolution model. As byproduct of our analysis, we studied binary stellar evolution and nucleosynthesis in AGB stars using two Blue Stragglers. I will also show the results of a study focused on a pair of binary stars with further implications on the formation of the inner halo and the use of chemical tagging to constrain the birth environment of stars, and implications of possible planetary formation in metal-poor stars. At last, the outcome of atomic modeling for a non-LTE analysis of potassium line formation, and the study of the chemical evolution of potassium through cosmic history.

Andrei Vayner (JHU)

Quasar Host Galaxies and their Environments with Multi-Wavelength 3D Spectroscopy
I will present results from a multi-wavelength survey of distant (1.3 < z < 2.6) luminous quasars host galaxies. The data was obtained using the Keck integral field spectrograph (IFS) OSIRIS and laser guide star adaptive optics (LGS-AO) system, ALMA, HST, and VLA. Studying distant quasar host galaxies is essential for understanding the role of active galactic nuclei (AGN) feedback on the interstellar medium (ISM), and its capability of regulating the growth of massive galaxies and their supermassive black holes (SMBH). The combination of LGS-AO and OSIRIS affords the necessary spatial resolution and contrast to disentangle the bright quasar emission from that of its faint host galaxy. We resolve the nebular emission lines Hβ, [OIII], [NII], Hα and [SII] at a sub-kiloparsec resolution to study the distribution, kinematics, and dynamics of the warm-ionized ISM in each quasar host galaxy. The goal of the survey was to search for ionized outflows and relate their spatial extent and energetics to the star-forming properties of the host galaxy. Combining ALMA and OSIRIS, we directly test whether outflows detected with OSIRIS are affecting the molecular ISM. I will discuss the origins of outflows in these quasar host galaxies and their role in depleting the gas reservoir and the implication for massive galaxy formation and evolution. We are now obtaining detailed observations of the circumgalactic medium (CGM) of these systems with the newly commissioned Keck Cosmic Web Imager (KCWI). The gas in the CGM may play an essential role in the evolution of these galaxies. I will show preliminary results from deep observation on several sources taken over the last year.

30 September

Joshua Lothringer (JHU)

The Extreme Atmospheres of Ultra-hot Jupiters
Ultra-hot Jupiters are some of the highest signal-to-noise exoplanet targets. These hot Jupiters typically have equilibrium temperatures approaching and sometimes exceeding 3000 K, orbiting A, F, and early-G type stars on orbits less than 0.03 AU (10x closer than Mercury is to the Sun). The most extreme example, KELT-9b, is the hottest known hot Jupiter with a measured dayside temperature of 4600 K. I will describe our self-consistent PHOENIX atmosphere models of these extreme objects. Our modeling provides a look at the a priori expectations for these planets and helps us understand recent observations. We show that, in the hottest cases, all molecules are dissociated down to relatively high pressures. Additionally, these planets will likely have detectable temperature inversions created by a lack of cooling in the IR combined with heating from atoms and ions at UV and blue optical wavelengths.

Edmund Hodges-Kluck (GSFC)

The Hot Circumgalactic Medium
In the past ten years, Hubble’s Cosmic Origins Spectrograph has established that massive reservoirs of cool and warm circumgalactic gas are an essential part of the galactic ecosystem. However, the hot phase (T>1e6 K) may contain even more mass, metals, and energy. I will summarize recent results pointing to massive, extended, hot halos of gas accreted from the cosmic web around L* galaxies, discuss the major sources of uncertainty, and describe what we can expect to learn from upcoming and proposed X-ray observatories.

7 October

Pierre Boldrini (IAP)

Diversity of Transient Cores of Dwarf Galaxies in Lambda-CDM
The inconsistency of inner dark matter density profiles in dwarf galaxies (the cusp-core problem) and the large variety of shapes of dwarf rotation curves (the diversity problem) are two of the challenges, at small scales, for the cold dark matter paradigm. By using unprecedented high resolution fully GPU N-body simulations, I will show how DM substructures can induce a cusp-to-core transition by heating the central region of the DM host halo through passages. The central region of the host halo gains energy and the orbits of the DM particles are modified which in turn modifies the inner structure of the host halo. This results in a diversity of DM core sizes and can also lead to cusp regeneration for the host DM halo.

Nick White (GWU)

The Gamow Explorer: A High Redshift Universe Gamma-Ray Burst Mission
Gamma Ray Bursts (GRBs) can be used to address high priority scientific questions on the formation of the Universe including: When did star formation begin and how did it evolve? When and how did the intergalactic medium become re-ionized? What processes governed its early chemical enrichment? Long GRBs signal when a massive star explodes as a supernova and as such provide an independent tracer star formation. The GRB afterglow is a bright beacon lasting a few days that can be used out to the highest redshifts to both probe the intervening material from the host galaxy and intergalactic medium, and also trace star formation and its evolution. The Gamow Explorer will utilize a wide field of view X-ray telescope to detect and locate GRBs with arc minute precision and a sensitivity ten times Swift to identify z > 6 GRBs. A rapidly slewing spacecraft points an Infra-red telescope to obtain an arc second location and use the Lyman alpha dropout to determine which GRBs have a redshift greater than 6. An alert to the ground will enable follow up by large telescopes for z>6 GRBs. The Gamow Explorer will be proposed to the 2021 NASA MIDEX opportunity, for launch in 2028. It will be a key component in the multi-messenger era of JWST, 30-m class telescopes and next generation gravitational wave detectors.

14 October

Chris Belcynski (Copernicus Center, Warsaw)

Gravitational-wave Astrophysics: LIGO/Virgo BH-BH/BH-NS/NS-NS Mergers
I will discuss the astrophysical importance of the recent LIGO/Virgo direct detections of gravitational-waves. Despite the fact that massive BH-BH dominance in gravitational-wave signal was predicted prior the detections, it is not at all clear which one of the several formation scenarios produces these massive mergers. This inhibits astrophysical information inference from LIGO/Virgo observations, as conclusions are different within each formation scenario. There is quite an opposite problem with the first detection of NS-NS merger in an old elliptical host galaxy, as none of the formation channels can easily recover rather high NS-NS merger rate estimated by LIGO/Virgo. The recent detection of BH-NS merger seems to indicate the existence of compact objects in the first mass gap.

Additionally, all of the ten O1/O2 LIGO/Virgo BH-BH merger detections have low values for their effective spins. I will demonstrate how this can be naturally explained within framework of classical binary evolution scenario of the formation of BH-BH mergers. It appears that magnetic fields (Tayler-Spruit dynamo) play an important role in efficient transport of angular momentum and spin-down of massive stars that produce low-spinning black holes.

21 October

John Wu (JHU)

Insights on Galaxy Evolution from Multiwavelength Observations and Deep Learning
Modern galaxy formation and evolution models are able to match the statistical properties of galaxy populations across most of cosmic history. However, detailed observations and sophisticated analytical methods are still needed to test theoretical predictions in extreme scenarios, where the complex interplay of gas accretion, star formation, galaxy interactions, feedback, and other physical processes can have compounded impacts on interstellar medium properties. Far-infrared and submillimeter observations of massive, SZE-selected clusters reveal star-forming galaxies and rich cold gas reservoirs, despite a hostile intracluster medium. I also present new results from VLT/SINFONI observations targeting a sample of low-redshift compact starbursts that strongly resemble Lyman break galaxies (LBGs). Paschen alpha and H_2 ro-vibrational emission suggest that star formation feedback is the dominant excitation mechanism in LBG analogs. These systems are also characterized by high velocity dispersions, and I discuss how their small sizes may cause them to deviate from the usual kinematic scaling relations. Finally, I optimize a deep convolutional neural network (CNN) to predict the nebular metallicities of SDSS star-forming galaxies solely from three-band optical imaging. The trained CNN is not only able to accurately estimate metallicity, but also can reconstruct the empirical mass-metallicity relation with zero additional scatter. These results imply that morphological features are important for understanding the connection between galaxies' stellar mass assembly and chemical enrichment histories.

McCullen Sandora (UPenn)

Biosignature Surveys and Exoplanet Yields
Upcoming biosignature searches focus on indirect indicators to infer the presence of life on other worlds. Aside from just signaling the presence of life, however, proposed biosignatures also contain information about the state that a planet's biosphere has achieved. This additional information can be used to measure what fractions of planets achieve certain key stages, corresponding to the advent of life, photosynthesis, multicellularity, and technological civilization. We forecast the uncertainties of each measurement for upcoming surveys, and outline the key factors that determine these uncertainties. The dependence on survey size, likeliness of the transition, and several measures of degrees of confidence are discussed, as well as how combining data from different missions can affect the inference. Our analysis can be used to determine policy recommendations for mission design to minimize these measurement uncertainties.

28 October

Sylvain Veilleux (UMCP)

Astrophotonics: The Next Wave in Astronomical Instrumentation
Recent breakthroughs in astrophotonics -- photonics applied to astronomical instrumentation -- have opened the door to replace the large lenses, mirrors, and gratings of conventional astronomical spectrographs with optoelectronic components to reduce the mass and volume of these instruments by two to three orders of magnitude, shorten delivery times, lower the risk, and cut the cost proportionally. Photonic instruments are also more amenable to complex light manipulation and massive multiplexing, cheaper to mass produce, easier to control, much less susceptible to vibrations and flexures, and best of all, have higher throughput. In this talk, I will discuss the latest results from our effort to develop in-house photonic near-infrared (1.0 - 1.7 micron) spectrometers where the dispersing optics are replaced by miniature (~1 cubic-centimeter) arrayed waveguide gratings imprinted using buried silicon nitride (``nano-core) technology, the leading solution for low-loss waveguides (throughput > 50%). We have also developed highly sophisticated photonic filters using complex waveguide Bragg gratings, produced on the same platform technology as the photonic spectrometers and equally small. These novel spectrometers and filters offer a wide range of possible astronomical applications, from spectroscopic studies of the distant universe to searches for biosignatures in the atmospheres of exoplanets.

Max Gronke (UCSB)

Cold gas around galaxies: how it can survive, grow -- and we can observe it
Galactic winds are large-scale, multiphase outflows from galaxies, crucial for the galactic ecosystem, and a potent probe for the underlying feedback mechanisms. A common picture is that the cold gas has been accelerated by ram pressure forces due to the hot gas. However, reproducing this ubiquitous observation in hydrodynamical simulations has proven to be challenging - simply because the cold gas is destroyed prior to obtaining the observed velocities. During my talk, I will show some analytical estimates and results from recent (magneto-)hydrodynamics simulations which suggest a solution to this classical "entrainment problem". I will furthermore discuss the long-term evolution of this cold gas and potential implications for the `circumgalactic medium'. Time -- and interest -- provided, I want to present some observables of this cold gas. In particular I will show that the Lyman-alpha line is a powerful probe of the (small-scale) structure of neutral hydrogen.

4 November

Erini Lambrides (JHU)

A Large Population of Obscured AGN in Disguise as Low Luminosity AGN in Chandra Deep Field South
Population synthesis models of actively accreting super-massive black holes (or active galactic nuclei -- AGN) predict a large fraction that must grow behind dense, obscuring screens of gas and dust. Deep X-ray surveys are thought to have provided the most complete and unbiased samples of AGN, but there is strong observational evidence that a portion of the population of obscured AGN is being missed. In this paper we use a sample of AGN derived from the deepest X-ray survey to date, the Chandra 7Ms GOODS-South Survey, to investigate the nature of low flux X-ray sources. We maximize the diverse wavelength coverage of the GOODS-South field, and cross-match our objects with wavelengths from the Radio to the IR. We find the low X-ray flux AGN in our sample have X-ray luminosities that indicate low-luminosity AGN classification, while their radio, infrared and optical counterparts indicate moderate to powerful AGN classification. We find the predicted column densities is on average an order of magnitude higher than the calculated column densities via X-ray detections for X-ray faint sources. We interpret our results as evidence of obscured AGN disguising as low-luminosity AGN via their X-ray luminosities. When we compare the estimation of the obscured AGN space density with and without these objects, we find a difference of 40\% in the lowest X-ray luminosity regime probed by our sample.

Keisuke Osumi(JHU)

Mapping the CMB with the Cosmology Large Angular Scale Surveyor (CLASS)
The Cosmology Large Angular Scale Surveyor (CLASS) is an array of telescopes in the Atacama Desert, Chile that observes 75% of the sky at 4 bands: 40, 90, 150, and 220 GHz. The primary objective is to measure the cosmic microwave background (CMB) polarization at the largest angular scales to constrain the tensor-to-scalar ratio at the r = 0.01 level and make a sample variance limited measurement of the optical depth to reionization, τ. This will be achieved through the use of rapid front-end polarization modulation along with multi-frequency observations to distinguish the CMB from galactic foregrounds. CLASS will be releasing its first set of results from the initial 40 GHz survey in the near future. In this talk, I will present part of my contributions to the data analysis pipeline. Namely, the destriping mapmaker which plays a critical role in the data reduction and analysis of our dataset.

Michael Busch (JHU)

The Structure and Environment of "CO-Dark" Molecular Gas in the Perseus Arm We report the results from a new, highly sensitive (∆Tmb ∼ 3mK) survey for thermal OH emission at 1665 and 1667 MHz over a dense, 9 x 9-pixel grid covering a 1 square degree patch of sky in the direction of L = 105.00, B = +2.50 towards the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope (GBT) 1667 MHz OH results with archival CO(1-0) observations from the Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey within the velocity range of the Perseus arm at these galactic coordinates. Of the 81 statistically-independent pointings in our survey area, 86% show detectable OH emission at 1667 MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits, CO emission does not appear until the volume density exceeds 100-200 cm−3 . These results demonstrate that a combination of low column density and low volume density can explain the lack of CO emission at sightlines exhibiting OH emission.

11 November

David Rupke (Rhodes College)

How Big are Galactic Winds?
Intense star formation and rapid black hole accretion in the centers of galaxies produce energy that propels gas outward. These galactic winds affect the evolution of their host galaxies, and may self-regulate the future growth of stars and black holes. Galaxies are also known to be surrounded by enormous reservoirs of gas. Galactic winds are a likely mechanism by which these reservoirs are created. However, we don't know how far most galactic winds extend into their surroundings. I will discuss observations of galactic winds driven by star formation and black holes that probe their extent and illuminate the connection between galaxies and their surroundings.

18 November

Kimmy Wu (Chicago)

Lensing and Delensing: Results and Updates from BICEP/Keck and the South Pole Telescope
Gravitational lensing of the cosmic microwave background (CMB) encodes information from the low-redshift universe. Therefore, its measurement is useful for constraining cosmological parameters that describe structure formation, e.g. Omega_m, sigma_8, and the sum of neutrino masses. In this talk, I will present a measurement of and the cosmological constraints from the CMB lensing potential and its power spectrum using data from the SPTpol 500 deg^2 survey. From the minimum-variance combination of the lensing estimators from all combinations of SPTpol temperature and polarization data, we measure the lensing amplitude A_MV = 0.944 \pm 0.058 (Stat.) \pm 0.025 (Sys.), which constitutes the tightest lensing amplitude measurement using ground-based CMB data alone. Using this lensing spectrum measurement, we constrain sigma_8*Omega_m^0.25 to 4%, compared to Planck lensing’s 3% measurement. In combination with galaxy BAO and a BBN prior, SPTpol lensing measures H0 to be ~2 sigma higher than the Planck measurement. Looking to the future, high signal-to-noise measurements of lensing enabled by deep polarization maps is crucial for constraining the sum of neutrino masses and the amplitude of inflationary gravitational waves through delensing. If time permits, I will give an update on the current effort of delensing the BICEP/Keck telescope data.

19 November

Chi-Ho Edwin Chan (Tel Aviv)

Tidal Disruption Events in Active Galactic Nuclei
A fraction of tidal disruption events (TDEs) occur in active galactic nuclei (AGNs) whose black holes possess accretion disks; these TDEs can be confused with common AGN flares. The disruption itself is unaffected by the disk, but the evolution of the bound debris stream is modified by its collision with the disk when it returns to pericenter. The outcome of the collision is largely determined by the ratio of the stream mass current to the azimuthal mass current of the disk rotating underneath the stream footprint, which in turns depends on the mass and luminosity of the AGN. To characterize TDEs in AGNs, we simulated a suite of stream--disk collisions with various mass current ratios. The collision excites shocks in the disk, leading to inflow and energy dissipation orders of magnitude above Eddington. However, much of the radiation is trapped in the inflow and advected into the black hole, so the actual luminosity may be closer to Eddington. The rapid inflow causes the disk interior to the impact point to be depleted within a fraction of the mass return time. If the stream is heavy enough to penetrate the disk, part of the outgoing material eventually hits the disk at larger radii, dissipating its kinetic energy there; another part becomes unbound, emitting synchrotron radiation as it shocks with surrounding gas.

2 December 2019

Joseph Cleary (JHU)

Building the CLASS Telescope Array
The Cosmology Large Angular Scale Surveyor (CLASS) aims to measure the polarization of the CMB at the largest angular scales. To achieve this, CLASS uses an array of four telescopes observing at frequencies of 40, 90, 150, and 220 GHz. The 40 and 90 GHz telescopes were installed in Spring 2016 and Spring 2018, and a dichroic 150/220 GHz telescope was deployed during Summer 2019. Each of these telescope deployments is the culmination of years of work by the CLASS collaboration. In this talk, I will discuss the work that goes into getting a CLASS telescope operational in the field.

Alex de la Vega (JHU)

Dust Attenuation Assumptions and Spatially Resolved Quenching in CANDELS
Determining how galaxies stop forming stars remains an open issue in our understanding of galaxy evolution. The mechanisms behind the cessation of star formation can be identified by studying the radial profiles of the specific star formation rate (sSFR, SFR / stellar mass) for galaxies of different integrated masses, star formation properties, and at different redshifts. Estimating radial sSFR profiles, however, depends sensitively on assumptions of the nature of dust attenuation within galaxies. We examine the effects of assuming different attenuation curves in integrated and spatially resolved spectral energy distribution fitting of massive galaxies at redshift about 1 in the CANDELS survey. Surprisingly, the integrated SFRs for massive galaxies vary dramatically depending on the assumed attenuation curve, yet the nature of quenching within these galaxies is qualitatively the same, independent of dust attenuation assumptions. In this talk, I present preliminary results and hints of a varying slope of the attenuation curve within galaxies, provided other parameters degenerate with dust are accounted for adequately.

Hsiang-Chih Hwang (JHU)

Lifetime of Main-Sequence Contact Binaries
Binaries play a crucial role in stellar evolution, providing sources for gravitational-wave astronomy, type-Ia supernovae, and other stellar mergers. Binaries must evolve to close configuration while on the main sequence in order to result in these interesting phenomena. One key open question is how main-sequence binaries lose their angular momentum to shrink the orbits. Several mechanisms have been proposed, including pre-main-sequence interaction, three-body interactions (the Kozai-Lidov mechanism), and magnetic braking. These mechanisms are operating on different timescales. However, the age of binaries is notoriously difficult to measure and it is still unclear which is the dominant mechanism. Fortunately, because stars' motion becomes more randomized when they age, stellar kinematics provides a unique way to determine the binary age. In this talk, we will use the kinematics of main-sequence contact binaries to understand when and how they are formed, and when they merge.