Wine and Cheese Spring 2020

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2020.

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.

3 February

Brice Menard (JHU)

Deprojecting Astronomical Sky Maps
We see the sky in 2D but, in order to conduct astrophysical studies, we need 3D information. I will show how to take any large-scale map of the sky, at any wavelength, and extract 3D extragalactic information from it using clustering measurements. I will then apply this technique to observations of galaxies and diffuse components across the electromagnetic spectrum.

10 February

Alberto Bolatto (UMd)

Synergies Between IFU and Molecular Gas Surveys
The internal structure of galaxies harbors important clues of the processes that shape their evolution. The last several years have seen the completion of a number of galaxy surveys using Integral Field Units that produce complete spectroscopic mapping at optical wavelengths (MaNGA, CALIFA, SAMI). Those data have produced invaluable information about the stellar and ionized gas components of galaxies. Information about the neutral and molecular phases of the gas, the largest gas reservoirs, has however historically lagged behind. I will present some results from EDGE-CALIFA, a follow up of 126 CALIFA galaxies in CO emission that is currently starting to be expanded with ALMA, and I will discuss future prospects with existing and planned instruments, in particular the ngVLA (a proposal to the Astro2020 Decadal).

17 February

Duncan Watts (JHU)

Beyond Optical Depth: Future Determination of Ionization History from the CMB
Cosmic microwave background (CMB) photons are partially polarized, both by free electrons around recombination, and by free electrons from reionization. The free electron fraction as a function of redshift directly affects the observed large-scale polarized CMB, by changing both the amplitude and the shape of the E-mode power spectrum. Planck and WMAP have constrained the reionization optical depth, but this integrated quantity can only constrain the redshift of reionization assuming the intergalactic medium (IGM) instantaneously transitions from neutral to ionized. In this talk, I will demonstrate that future CMB measurements with a near cosmic variance-limited E-mode measurement will be able to distinguish between different models of reionization that have not yet been ruled out by direct measurements of the ionization state of the IGM. Specifically, I will consider a simple model with a period of an early ionization fraction of 5% at z~28 in addition to the standard reionization scenario. I will also demonstrate that a cosmic variance measurement requires a moderate sensitivity of 10 μK arcmin, and will be achieved by the CLASS experiment.

Mihoko Yukita (GSFC)

The Hard X-ray View of Nearby Galaxies with NuSTAR
NuSTAR is the world's first focusing hard X-ray telescope, allowing unprecedented access to the sky above 10 keV. Thanks to its sensitivity and spatial resolution, we are now able to resolve individual X-ray binaries in nearby galaxies and study their populations. X-ray binaries had traditionally been classified via their companion stars, e.g. high-mass or low-mass counterparts. With NuSTAR, we can identify them by their compact objects as black holes or neutron stars and study their accretion states in detail. We have now amassed enough information on X-ray binaries in nearby galaxies with NuSTAR to compare the compact object population to properties of their host galaxies including their mass, star-formation activity, and morphology.

24 February

Bingjie Wang (JHU)

A Systematic Study of Galactic Outflows via Fine-Structure Emission: Implications for their Size and Structure
Galactic outflows play a major role in the evolution of galaxies, but the underlying physical processes are poorly understood. This is mainly because we have little information about the outflow structure, especially on large scales. In this project, we probe the structure of galactic outflows in low-z starbursts by using a combination of HST UV spectroscopy and imaging of the fine-structure emission lines associated with the strongly blue-shifted resonance absorption lines. We find that in the majority of cases the observed emission lines are much weaker and narrower than the absorption lines, originating in the star-forming interstellar medium and/or the slowest-moving part of the inner outflow. However, we find that in a minority of cases, the outflowing absorbing material does make a significant contribution to the fine-structure emission. These latter systems are characterized by both strong Lyα emission lines and weak low-ionization absorption lines (both known to be empirical signs of Lyman continuum leakage). We argue that the observed weakness of emission from the outflow seen in the majority of cases is due to the missing emission arising on scales larger than those encompassed by the HST/COS aperture. This implies shallow radial density profiles in these outflows, and suggests that most of the observed absorbing material must be either created or injected at radii much larger than that of the starburst. This has important implications for our understanding of both the physics of galactic outflows and for our estimation of their principal properties.

Jacob Hamer (JHU)

Hot Jupiters and Ultra-Short-Period Planets: Testing Tidal Dissipation
On their extreme orbits, hot Jupiters and Ultra-short-period planets represent the perfect testing ground for our understanding of tidal dissipation. While cooler giant planets are often observed with non-zero eccentricities, the small, circular orbits of hot Jupiters suggest that tidal dissipation plays a significant role in their formation. Once on these circular orbits, tidal dissipation should allow the rapidly orbiting planet to transfer angular momentum to the slowly spinning host star, which may result in the inspiral of the planet. However, we do not yet know if hot Jupiters survive the main sequence of their host stars, as the efficiency of this process is uncertain by orders of magnitude, and because tidal decay has never been unambiguously observed. If tidal decay causes hot Jupiters to be destroyed while their host stars are on the main sequence, then hot Jupiter hosts should be relatively young compared to a sample of similar field stars not hosting hot Jupiters. We use data from Gaia DR2 to show that hot Jupiter hosts have a smaller Galactic velocity dispersion than similar stars without hot Jupiters. As Galactic velocity dispersion is correlated with the age of a population, this implies that hot Jupiter hosts are a relatively younger population due to the inspiral of their planets. This observation requires that the tidal quality factor be less than 10^7. If hot Jupiters inspiral, then it can be shown that so too should Ultra-short-period planets. Any differences between the two populations would reveal that the efficiency of tidal dissipation in the host star depends on the period and/or mass of the planet. We show that Ultra-short-period planet hosts have kinematics consistent with a sample of similar stars not hosting these planets. Therefore, we argue that Ultra-short-period planets are stable against tidal inspiral, supporting period- or mass-dependent models of tidal dissipation.

Brian Welch (JHU)

RELICS: New High-Resolution Hubble Imaging of the Longest Lensed z ~ 6 Arc
Gravitational lensing magnifies the distant universe, allowing us to study the high redshift universe at otherwise impossible spatial resolution. I will present preliminary results from new Hubble Space Telescope imaging of the longest known gravitationally lensed arc at redshift z ~ 6. Recently discovered in the RELICS HST Treasury Program, this 15" long arc promises the most detailed view to date of star formation in the first billion years. In this talk, I will present a preliminary analysis of our recently obtained images, including our lens modeling, source-plane reconstruction of the z ~ 6 galaxy, and measurements of the brightest multiply-imaged clumps. This lensed galaxy provides an excellent opportunity to study the details of star and galaxy formation within the first billion years, and it will be an excellent target for high-resolution imaging and spectroscopy with JWST.

2 March

Anatoly Spitkovsky (Princeton)

Pulsar Magnetosphere: the Incredible Machine
Pulsars are rotating magnetized neutron stars that emit repeating pulses of radiation spanning all of the electromagnetic spectrum. 50 years after their discovery, more than 2000 pulsars are known, and they have been used as sensitive astronomical probes of diverse phenomena ranging from the properties of interstellar medium to the predictions of general theory of relativity. Despite great observational successes, our theoretical understanding of how pulsar magnetospheres work is woefully incomplete. Pulsars bring together aspects of classical and quantum electrodynamics, coupled with strongly magnetized plasma physics in curved rotating spacetime of a massive compact object. The nonlinear interplay of these effects makes it a difficult but rewarding problem to study. I will review the status and progress of pulsar magnetospheric modeling in various approximations, including force-free and relativistic magnetohydrodynamics, culminating with recent developments in fully kinetic simulations of pulsar magnetospheres. These simulations allow us to find the shape of the magnetosphere and the location of particle acceleration regions, constraining the origin of high energy and radio emission. The pulsar magnetosphere is a prototype for other strongly magnetized astrophysical objects, and I will discuss how the lessons from pulsar modeling can be useful in understanding the physics of black hole magnetospheres and in predicting electromagnetic counterparts to gravitational wave sources.

9 March

Ruth Daly (PSU&CCA)

Black Hole Spin and Accretion Disk Magnetic Field Strengths for over 700 Sources
Black hole systems, composed of a black hole, accretion disk, and collimated outflow, will be discussed. Three active galactic nucleus (AGN) samples including 753 AGNs and 102 measurements of four stellar-mass galactic black holes (GBHs) will be considered. General expressions for black hole spin functions and accretion disk magnetic field strengths will be derived and applied to obtain the black hole spin function, spin, and accretion disk magnetic field strength in dimensionless and physical units for each source. Relatively high spin values of about (0.6─1) are obtained for the sources. The distributions of accretion disk magnetic field strengths for the three AGN samples are quite broad and have mean values of about 104 G, while those for stellar-mass GBHs have mean values of about 108 G. Good agreement is found between spin values obtained here and published values obtained with well-established methods; comparisons for one GBH and six AGNs indicate that similar spin values are obtained with independent methods. Black hole spin and disk magnetic field strength demographics indicate that black hole spin functions and spins are similar for all of the source types studied, including GBHs and different categories of AGNs. The method applied here does not depend on any specific accretion disk emission model and does not depend on a specific model that relates jet beam power to compact radio luminosity; hence, the results obtained here can be used to constrain and study these models.