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.