Wine and Cheese Fall 2024

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2024.

Wine and Cheese sessions with one speaker 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.

9 September

John Soltis (JHU)

Direct Estimation of Galaxy Cluster Mass Accretion Rate using Machine Learning
Galaxy cluster mass abundances provide an important cosmological constraint. Mass estimates, however, are biased by galaxy cluster dynamical state. The dynamical state, the intensity of physical disturbance in the galaxy cluster, is a direct result of its mass accretion rate. I will present a machine learning model for directly constraining the mass accretion rate of galaxy clusters from only X-ray and thermal Sunyaev-Zeldovich observations. Furthermore, I will discuss the different machine learning interpretability methods we employ to better understand the model, and the conclusions we draw from them.

Farhad Yusef-Zadeh (Northwestern)

Highlights of the MeerKAT Radio Survey of the Galactic Center
It has been 40 years since the magnetized radio filaments were first reported toward the Galactic center (GC), the first hint of an energetic activity in this region. Since then, a large number of synchrotron emitting filaments has been discovered in this high cosmic-ray pressure environment. In particular, the recent MeerKAT survey, which has been a gold mine in the study of the extreme environment of the GC, has increased the number of filaments by an order of magnitude. In this talk, I will discuss the statistical properties of the GC filaments, the comparison of the intracluster medium (ICM) and GC filaments, models of these enigmatic objects and the association of a milli-second pulsar powering a nonthermal radio filament near the magnetized Snake filament.

16 September

Priyanka Sarmah (Tsing Hua U)

Origin of a Strong Broadband 21 cm Cosmological Signal from Dark Matter Spin-Flip Interactions
We explore a novel mechanism, where dark matter spin-flip interactions with electrons through a light axial-vector mediator could directly induce a 21 cm absorption signal which is characteristically different from the expected absorption features in the standard cosmology and in models with excess gas cooling, which have been broached to explain the recently observed anomalous signal in the EDGES experiment. We find generically that our model predicts a strong,broadband absorption signal extending from frequencies as low as 1.4 MHz (z~1000), from early in the cosmic dark ages where no conventional signal is expected, all the way up to higher frequencies where star formation and X-ray heating effects are expected to terminate the absorption signal. We find a rich set of spectral features that could be probed in current and future experiments looking for the global 21 cm signal. Large swathes of our model parameter space of interest are safe from existing particle physics constraints, however future searches for short range spin-dependent forces between electrons on the millimeter to nanometer scale have the potential to discover the light mediator responsible for our predicted signal.

23 September

Chris Nagele (JHU)

Simulating Electromagnetic Signals from SBH Formation and Accretion onto Binary SMBH
The Laser Interferometer Space Antenna (LISA) will have the capacity to observe supermassive black hole binary mergers, even at high redshift. These observations will help determine much more precisely the mass function and binary fraction of supermassive black holes over cosmic time. Current observatories, however, can also be utilized to better understand the massive black hole population. In this talk, I will highlight two examples of this. The first centers around the origin of massive black holes at high redshift, namely modeling of transients associated with the birth of these massive black holes, these transients being observable to current and upcoming near infrared surveys. The second focuses on x-ray and optical variability of supermassive black hole binaries fed by a circumbinary accretion disk. In both cases, I will describe general relativistic hydrodynamical simulations of these systems and post processing for relevant observables.

Laura Flagg (JHU)

The Dispersal of Gas in Circumstellar Disks Based on Observations of H_2 in the FUV
Planets form in circumstellar disks. However, the main component of these disks, H_2, is extremely hard to detect. We have developed a new technique that increases our sensitivity to warm H_2 emission in medium resolution FUV spectra taken with HST using COS or STIS by better than a factor of 10. With this new technique, we detect H_2 in the spectra of TWA 7, a ~9 Myr M2 star with a cold debris disk but no clear signs of accretion and show that it likely comes from the debris disk itself, although closer in where the disk is relatively warm. We discuss detections of H_2 from stars without warm dust in Upper Sco. These detections of H_2 in older debris disk systems imply that H_2 may last longer than previous evidence had indicated. We also talk about the confusing presence of H_2 in the AU Mic system and what we learned about the star and its disk from analyzing it.

30 September

Vedant Chandra (Harvard)

To 100 kpc and Beyond: Tales from the Milky Way’s Distant Horizon
The outer halo of the Milky Way (MW) contains a fossil record of our galaxy’s assembly history, and traces the global gravitational field of the MW. We have been conducting an all-sky spectroscopic survey of the Galactic outskirts. I will summarize our recent results, from finding coherent structures imprinted by the MW’s last major merger, to discovering the long-sought stellar counterpart to the Magellanic Stream. I will then focus on the global dynamical response of the MW to the infalling Large Magellanic Cloud (LMC). Using distant halo stars as a reference, we measure that the inner MW is lurching sharply towards the LMC, suggesting a massive LMC dark matter halo that is > 15% the mass of the MW’s.

Christina Lindberg (JHU)

The Multi-Scale Interstellar Medium of Local Group Galaxies
Observational constraints on the small-scale structure of the interstellar medium (ISM) are critical for understanding how star formation and feedback processes drive galaxy evolution across cosmic time. The last decade has seen an explosion of panchromatic HST imaging of nearby galaxies (e.g. PHAT/PHAST, HTTP, PHATTER, LUVIT, Scylla, etc.). With stellar SED fitting techniques like the Bayesian Extinction And Stellar Tool (BEAST), we can harness these rich data to simultaneously characterize individual resolved stars and extract information about the ISM. We review new findings on the formation conditions of massive stars in the Andromeda galaxy (M31; PHAT), present new parsec-scale dust extinction maps in the Magellanic Clouds (Scylla), and discuss future BEAST science to investigate how small-scale processes shape galaxy evolution.

07 October

Jack Neustadt (JHU)

Stochastic and Transient Variability around Supermassive Black Holes
Despite decades of intensive study of the UV/optical emission from active galactic nuclei (AGNs), we still do not understand what drives its variability. This emission must originate in the accretion disk surrounding the supermassive black hole (SMBH), and so understanding its variability is crucial to understanding the accretion process and the growth of SMBHs.

In the first half of my talk, I will introduce a new method of analyzing variability by inverting the multi-wavelength UV/optical lightcurves of AGNs into maps of the temperature fluctuations on the disk resolved in time and radius. These maps are dominated by fluctuations that must by driven by processes intrinsic to the disk, contrary to the current paradigm where disk variability is driven by reprocessing of X-rays emerging the innermost part of the AGN.

In the second half, I will address transient variability in AGNs and around quiescent SMBHs. These include: changing-look events, where an AGN changes from one "type"to another over timescales of months to years; tidal disruption events (TDEs), where a star is ripped apart by the tidal forces of a SMBH and some of the debris rapidly accreted, producing a luminous transient; and ambiguous nuclear transients (ANTs), which are transients that possess peculiar qualities that overlap with both AGN flares and TDEs. These various transients may help to reveal new aspects of AGN structure and how AGNs evolve with time.

Adam Langeveld (JHU)

The Nature of Low-Mass Stars and Giant Exoplanets: Brown-Dwarfs, Free-Floating Planetary-Mass Objects, and Ultra-Hot Jupiters
In the first half of this talk, I will overview recent advancements in the discovery and characterization of free-floating planetary-mass objects (FFPMOs), which is fundamental to our understanding of star and planet formation. I will showcase results from an extremely deep spectroscopic survey of the young star cluster NGC1333 using the NIRISS Wide Field Slitless Spectroscopy mode on JWST. We discover six new candidates with L-dwarf spectral types that are plausible planetary-mass members of NGC1333, with estimated masses between 5-15 MJup, including the lowest-mass object discovered to date with evidence of having a disk. The paucity of objects lower than 5 MJup, despite the survey's unprecedented sensitivity, suggests that our observations reach the lowest mass objects formed like stars in NGC1333. We also search for wide binaries in our images and report a young brown dwarf with a planetary-mass companion.

The second half of this talk will highlight my recent work on characterizing ultra-hot Jupiter (UHJ) atmospheres with high-resolution spectroscopy. I will showcase the first UHJ transmission spectrum observed with the new Gemini High-resolution Optical SpecTrograph (GHOST) at Gemini South, reporting findings from a survey of the planet’s atmospheric chemistry, and highlighting key results that reveal important insights into the chemical and dynamical processes in its upper atmosphere. These results and future observations will provide valuable context for comparative studies to investigate atmospheric trends in a broad population of UHJs with high-resolution spectroscopy, especially as we prepare to exploit the full power of the ELT in the coming 5-10 years.

21 October

Jonathan C. Tan (Chalmers/UVa)

The Seeding of Supermassive Black Holes from Pop III.1 Protostars
The origin of supermassive black holes (SMBHs) is a key open question for contemporary astrophysics and cosmology. Here we discuss the predictions of a model of SMBH formation from Pop III.1 protostars, i.e., metal-free stars forming in locally isolated dark matter minihalos, where dark matter annihilation has a chance to alter the structure of the star allowing growth to supermassive scales (Banik, Tan & Monaco 2019; Singh, Monaco & Tan 2023; Cammelli et al. 2024). The model predicts that all SMBHs have already formed by z ~ 20 with a spatial distribution that is initially relatively unclustered. We also present predictions for SMBH occupation fractions, host galaxy properties, frequency of binary AGN and the gravitational wave background from this SMBH population. These predictions are compared to latest results from HST, JWST and pulsar timing array observations.

28 October

Francesco Iacovelli (JHU)

Forecasting the Capabilities of Third–Generation Gravitational–Wave Detectors: from One to Many
The detection of gravitational waves in 2015, thanks to the LIGO and Virgo interferometers, opened a new window on our Universe. The discoveries during the first three observing runs already had an extraordinary impact on both astrophysics, cosmology and fundamental physics. The GW community is now looking at the next long–prepared step: ‘third–generation’ detectors. Thanks to an increase of more than one order of magnitude in sensitivity and a larger bandwidth, Einstein Telescope and Cosmic Explorer will have an outstanding potential, capable of triggering fundamental discoveries. Forecasting the capabilities of these extraordinary instruments, which are able to detect hundreds of thousands of sources per year, is a crucial aspect. I will give an overview of recent studies aimed at characterizing the parameter estimation for single sources at ET and CE on large populations, predictions for specific science cases of these third generation instruments, and recent forecasts of their capability of reconstructing the properties of the underlying population of sources.

Zhihui Li (JHU)

Inferring Lyman Continuum Leakage through Radiative Transfer Modeling of the Mg II Doublet
In recent years, Mg II doublet emission has gained significant attention as an indirect tracer of Lyman continuum (LyC) photons, serving as a key probe for studying cosmic reionization. In this talk, I will present our recent work on detailed radiative transfer (RT) modeling of Mg II emission line profiles in 33 low-redshift LyC leakers, using a multiphase, clumpy circumgalactic medium (CGM) model. Our RT models successfully reproduce the observed Mg II profiles, revealing that strong LyC leakage is linked to both high maximum clump outflow velocities and low total Mg II column densities. These results support a "picket fence" CGM geometry, where high Mg II outflow velocities and low Mg II column densities may correlate with low-density H I channels that facilitate LyC escape.

04 November

Sarah Burke Spolaor (WVa)

Beware: Multi-messenger Monsters
Binary supermassive black holes (biggest in the universe!) might be fairly prolific, inhabiting recent galaxy mergers in the universe. None have yet been conclusively detected… but may be soon! This talk will describe the status of the road to multi-messenger detection of these systems. In particular, I will highlight recent results from Pulsar Timing Arrays, including what our characterization of the gravitational-wave background means for galaxy evolution and our ongoing battle with "astrophysical noise." I will also discuss the current roadmap of direct multi-messenger detection, highlighting recent work that characterizes these supermassive binaries using both pulsar timing arrays and electromagnetic light.

11 November

Jason Wright (PSU)

The Search for Extraterrestrial Intelligence in the 2020's
Searches for signs of alien life via its technology ("technosignatures") go back to the pioneering efforts of Frank Drake in 1960, who searched for narrowband radio beacons, and the search for extraterrestrial intelligence (SETI) via radio signals has remained the most visible and well funded aspect of the field since then. I will briefly discuss the history of the field through the heyday of the 1980's at NASA, the government funding drought of the 1990's, and the resurgence more recently via philanthropic funds. In particular, I'll discuss how other technosignatures have remained a viable, if often overlooked, path for the discovery of life, relying on different assumptions about the nature of alien life and technology. I'll discuss some of my own work, including the Ĝ survey, the development of a SETI curriculum, and the recently founded Penn State Extraterrestrial Intelligence Center.

18 Novembre

Michael Niemack (Cornell)

New Windows in the Submillimeter Sky with the CCAT Observatory
The CCAT Observatory is building the Fred Young Submillimeter Telescope, a novel, high-throughput, 6-meter aperture telescope, to enable a wide range of new measurements. The science goals include line-intensity mapping of cosmic reionization, studying galaxy clusters, galactic magnetic fields, astronomical transients, and others. The Observatory is under construction at 5600 meters on Cerro Chajnantor, Chile. The complementarity of CCAT and related experiments will be highlighted, including recent results from the Atacama Cosmology Telescope and plans for Simons Observatory and CMB-S4. CCAT will make the most sensitive submillimeter measurements over a broad range of scales with its first high-throughput science receiver: Prime-Cam. This camera is designed to support over 10^5 kinetic inductance detectors and enable over 10x faster mapping speed than previous submillimeter observatories in atmospheric windows from 0.3 – 1.1 mm (280 – 850 GHz). We describe the project status, plans for early science observations starting in 2026, and possible future line-intensity mapping upgrades to probe cosmology.

02 December

Suvi Gezari (STScI)

Searching for the Tidal Disruption of Stars from Massive Black Holes Over Cosmic Time
The tidal disruption of a star that wanders too close to a central black hole is a unique probe of quiescent supermassive black holes lurking in the nuclei of galaxies. Over the last 5 years, we have demonstrated the ability to discover and spectroscopically classify large samples of tidal disruption events (TDEs) in the optical from the Zwicky Transient Facility (ZTF) Northern Sky Survey, with systematic high-energy follow-up with Swift and XMM-Newton. One of the most exciting applications of TDEs is the ability to probe intermediate mass black holes (IMBHs) that are expected to reside in dwarf galaxies, with demographics that encode the seeding mechanism of massive black holes in the Early Universe. One novel way to probe IMBHs is to catch them in the act of tidally disrupting and accreting a white dwarf. White dwarfs are so dense, that they can only be ripped apart outside the event horizon around an IMBH sized black hole. Furthermore, there is a theoretical prediction for a radioactively powered thermonuclear explosion at the time of maximum compression of the star as it passes through pericenter, that could be strong enough to ignite thermonuclear runaway, and a peculiar Type Ia like explosion. I will present our strategy in the next decade for searching for TDEs across the black hole mass function, and over cosmic time, by extending our sensitivity to TDEs to lower central black hole masses and higher redshifts, by exploiting the discovery power of the next generation of wide-field time domain surveys, including Rubin, Roman, ULTRASAT, and UVEX.