Wine and Cheese Spring 2022

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Spring 2021.

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

7 February

Ari Cukierman (Stanford)

The Oscillating Sky: BICEP as an axion direct-detection experiment
I will describe how a CMB telescope can function as a direct-detection experiment for axion-like dark matter, and I will present first demonstrations with data from the BICEP series of experiments. A local axion field induces all-sky oscillations in CMB polarization. For axion masses between 1e-23 and 1e-18 eV, the oscillation periods are on the order of hours to years. As CMB scan strategies typically involve repeated observations over many years, we can set limits on the axion-photon coupling constant by searching for time variability in CMB polarization with data that have already been gathered. The expected sensitivity of current-generation CMB experiments is at the level of the leading axion limits in this mass range, and the search will continue with next-generation instruments.

14 February

Andrea Antonelli (JHU)

Approximating Gravitational Wave-Forms
The successes of gravitational-wave (GW) astrophysics rely on our ability to filter GW signals out of data. For this, accurate predictions from the relativistic two-body problem are needed. Two approaches are usually pursued: one can solve the Einstein equations numerically on supercomputers, or analytically within approximation schemes. The latter scheme gives less accurate, but faster-to-compute signal waveforms, and it forms the basis for the models used in LIGO-Virgo-KAGRA search and inference pipelines. I will discuss these approximation relativistic solutions, focussing mainly on their synergies.

Lara Cullinane (JHU)

The Magellanic Edges Survey (MagES)
I’m a new JHU astronomy postdoc, working with Karrie Gilbert on M33/M31. However, in this talk, I’ll discuss my previous thesis work on the Magellanic Edges Survey, or MagES, which kinematically maps the extremely low-surface-brightness periphery of the Magellanic Clouds. We use a combination of Gaia astrometry and spectroscopically-derived radial velocities, obtained with 2dF+AAOmega on the Anglo-Australian Telescope, to determine the first 3D kinematics for a wealth of stellar substructure extending to distances beyond 23 degrees from the Clouds’ centres. Our initial results focus on the LMC. We reveal a large northern substructure that, due to its discrepant kinematics relative to the LMC disk, was likely formed in ancient interactions with the SMC, and subsequently strongly influenced during a recent interaction with the Milky Way; and several structures in the southwestern LMC that new dynamical models reveal were likely formed in interactions with the SMC 400+Myr ago. These are the first kinematic constraints on the dynamical history of the Clouds prior to their most recent close passage, and represent an enormous step forward in understanding their complex interactions.

21 February

Kedron Silsbee (MPE)

Cosmic Rays in the Context of Star Formation: Effects and Propagation
Cosmic rays alter the chemistry and dynamics of the molecular gas that collapses to form young stellar systems. Despite this, their abundance, particularly in denser regions, remains uncertain. Although cosmic rays in distant locations are not directly observable, we can infer their presence in molecular clouds from chemical tracers of gas ionization, gamma ray and synchrotron emission and enhanced gas temperature.  These suggest that while cosmic rays above approximately 1 GeV propagate freely into clouds, lower energy cosmic rays are excluded from the denser gas. This is qualitatively in agreement with predictions from theoretical models of cosmic ray attenuation. However, depending on the physics that dominates the propagation, the degree of attenuation varies significantly, and current data is insufficient to distinguish between the models. In this talk I will give an overview of the different transport regimes thought to play a role (diffusion, free propagation, and self-modulation), and what predictions these make for the variation of the ionization rate with gas density.  The propagation of cosmic rays is influenced by the properties of small-scale turbulence in the interstellar medium.  I will then also discuss some recent related work I’ve done on the damping of MHD turbulence due to radiative cooling.

28 February

Gabriele Sato-Polito (JHU)

Combining Voxel Intensity Distributions and Intensity Mapping Power Spectra
Line-intensity mapping (LIM) is a promising technique to study the high-redshift Universe. Two of the main proposed summary statistics to study such maps are the LIM power spectrum and the voxel intensity distribution (VID), which is an estimator of the 1-point temperature probability distribution function. A joint analysis of the two observables has been shown to significantly reduce the uncertainties on theoretical parameters at cosmic noon (z=2~3) and has the potential to help break the degeneracy between astrophysics and cosmology. I will discuss the VID and the LIM power spectrum, the benefits of a joint analysis, and the first derivation of an analytical covariance between them. These results allow for general joint analyses of the VID and the line-intensity mapping power spectrum.

Danielle Sponseller (JHU)

Modeling CMB Foregrounds Using the Moment Method
As CMB polarization experiments become increasingly sensitive, foregrounds must be modeled and subtracted with greater accuracy to avoid biasing the recovered primordial B-mode signal. In particular, the thermal dust emission spectrum is expected to be far more complex than a single modified blackbody model due to variations in dust temperature both along the line of sight as well as across the sky. Here we investigate whether bias can be reduced to negligible levels without prior knowledge of the underlying distribution of dust temperatures. We use a moment expansion technique to model the emission spectrum of an unknown continuous dust temperature distribution. We then perform noiseless component separation simulations within a single pixel using three sample dust distributions and evaluating the spectra in the PICO frequency bands. We find that using the moment method can reduce bias to negligible levels while making minimal assumptions about the underlying dust physical parameters.

7 March

Avi Shporer (MIT)

Exoplanet Atmospheres with Orbital Phase Curves in the Space Age
We are living in the golden age of time series photometry, when large amounts of high-quality data are delivered by space-based surveys in visible light. This enables a detailed study of the minute variability following the orbital motion of star-planet systems. These orbital modulations are induced by atmospheric and gravitational processes, hence the phase curve shape contains information about the companion’s atmospheric characteristics and mass. I will present the science done with phase curves (reviewed in Shporer 2017). This includes the investigation of hot Jupiter exoplanet atmospheres where in one study we showed that the atmospheres of many exoplanets have their optical brightest region shifted Westward of the substellar point, indicating an inhomogeneous cloud coverage. We are now conducting a systematic full-sky study of phase curves of gas giant planets using data from the NASA TESS Mission. I will present the current results of our study, which is ongoing as TESS continues to survey the sky. I will also present a few examples of the science done with the phase curves gravitational component, shaped by the mass of the companion. As a whole, the above demonstrates the high scientific potential of the study of space-based phase curves.

14 March

Shmuel Bialy (UMd)

The Interaction of Cosmic Rays with Interstellar Gas, Across Scales and Cosmic Time
I will discuss the interaction of cosmic rays with interstellar gas clouds, through ionization and excitation. I will show that at high redshift, and in low metallicity galaxies, cosmic rays become the dominant heating gas mechanism. In these systems, cosmic rays may regulate the global star formation rate on galactic scales. I will then dive into a discussion of the interaction on smaller scales, of cold dense molecular clouds. I will show how the excitation of molecular hydrogen may be used as a new method to trace low-energy cosmic rays, making these clouds gigantic cosmic ray detectors (analogous to Super-Kamiokande) floating in space. Using this new method, future JWST observations will be able to constrain the spectrum of low-energy cosmic rays shedding light on the sources and propagation modes of cosmic rays.

21 March

Spring Break

28 March

Fatma Kuzey Edes Huyal (ITU & JHU)

Attempts at Dealing with Sparsity in the Classification of PLAsTiCC Light Curves
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe the southern sky in 6 photometric bands and gather approximately 20 TB data per night. The Wide Fast Deep (WFD) region observations will take up around 80-90% of the LSST mission’s observation time. Even though the WFD data will cover a large patch of the sky and contain a wide array of objects, including unknown astronomical events, the extreme sparseness of light curve data, especially for certain supernovae events, makes classification very difficult. We need efficient and robust algorithms to classify a vast amount of noisy, sparse and irregularly sampled data. I will talk about the classification of PLAsTiCC data (simulated light curve data trying to mimic the upcoming LSST observations) using machine learning methods and mention some of the difficulties in classifying sparse and noisy data.

Weichen Wang (JHU)

Studying the Galactic Winds at z~1 and Beyond with Keck and JWST
Galactic winds are considered as an important physical process in galaxy formation. This is especially the case for the cosmic epoch of z~1 or beyond when the winds are found to be ubiquitous. However, much has yet to be understood regarding where and how the winds at this cosmic epoch are launched inside galaxies. I will present an observational study of the galactic winds at z~1. The study is based on deep spectroscopic observations with the Keck/DEIMOS and is part of a large survey program named HALO7D (PI: Guhathakurta). I will first present a detailed view of the winds from an interesting massive star-forming galaxy at z=1.3, and then briefly review the properties of winds from the entire galaxy sample which spans two orders of magnitude in stellar mass. I will discuss the connection between winds and the star formation inside these galaxies. Finally, I will briefly discuss the prospect of performing similar types of studies beyond z~1 with JWST using the NIRSpec instrument onboard the telescope.

Josh Kable (JHU)

An Exploration of an Early Gravity Transition in Light of Cosmological Tensions.
I will discuss the Transient Planck Mass (TPM) model, which is a modified gravity model that I have been working with to attempt to understand and potentially resolve current cosmological parameter tensions. In the TPM model, there is a step-like transition in the value of the Planck mass (or effective gravitational constant) prior to recombination. This transition leads to an expansion rate prior to recombination that is faster than in the LCDM case, which in turn leads to a smaller size of the sound horizon and a larger preferred value of the Hubble constant today. We fit the TPM model to CMB, BAO, and SNIa data and find that the data are able to precisely constrain the model despite allowing additional parameters that modify gravity. In particular, the data prefer a ~5% shift in the effective Planck mass and a transition that is free to occur over multiple decades of scale factor growth prior to recombination. Additionally, the model allows for both H_0 > 70 km s^{-1} Mpc^{-1} and S_8 < 0.80 simultaneously with lower values of S_8 arising because of a reduction the matter density to offset the increase in H_0. While the TPM model does not fully resolve either the H_0 or S_8 tensions, exploring other similar modified gravity models may be a productive avenue for resolving current cosmological parameter tensions.

4 April

Joan Najita (NOIRLab)

Two Quick Tales: How Protoplanetary Disks Accrete and Their Evolution into Debris Disks

This talk will revisit the classic problem of “how protoplanetary disks accrete” and explore the evolutionary connection between protoplanetary disks and debris disks.

Accretion: Processes that redistribute or remove angular momentum from disks can drive accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence for accretion, the process(es) responsible remain a mystery. MIR spectroscopy of nearly edge-on disks may shed new light on this long-standing problem, by probing accretion in action via supersonic “surface accretion flows.” The resulting inference, that disks are primarily quiescent at AU distances, is conducive to the formation and preservation of planets.

Debris Disks: The similar sizes of the rings observed in protoplanetary disks and debris disks suggest an evolutionary connection between these structures. Disk demographics, when combined with new calculations of the evolution of rings of pebbles and planetesimals, suggest a simple picture in which large protoplanetary disks with massive rings produce the known bright debris disks and debris-poor systems like the Solar System evolve from compact protoplanetary disks. The modest efficiency we infer for planetesimal formation constrains this fundamental---but otherwise observationally elusive---process in core accretion theory.

Arjun Dey (NOIRLab)

The DESI Survey and Galaxy Evolution: Lyman Alpha Emitters and the Andromeda Galaxy
At Kitt Peak National Observatory’s Mayall telescope, the Dark Energy Spectroscopic Instrument has begun its 5-year mission to explore the universe both near and far and map out its expansion history. In addition to its primary cosmological goals, DESI will provide new insights into the formation and evolution of galaxies, as well as map out the dynamics of our Milky Way. I will describe the overall project and its data, and highlight two explorations: one on high-redshift galaxies; and the other on the Andromeda Galaxy, one of our most accessible astrophysical laboratories for investigating galaxy formation.

April 11

Rachel Osten (STScI)

Perspectives on Pathways to Discovery in Astronomy and Astrophysics for the 2020s
Last November the National Academy of Sciences released released its Decadal Survey on the field of astronomy and astrophysics. This nearly 600 page report incorporated the input received from the community, and turned that into a set of recommendations for the next decade and beyond. As a member of the steering committee and the Executive Officer for the survey, I will give a brief summary of the key recommendations from the report, emphasizing where the report broke new ground or did things differently compared to previous decadal surveys.

April 18

Kedron Silsbee (MPE)

Cosmic rays in the Context of Star Formation: Effects and Propagation
Cosmic rays alter the chemistry and dynamics of the molecular gas that collapses to form young stellar systems. Despite this, their abundance, particularly in denser regions, remains uncertain. Although cosmic rays in distant locations are not directly observable, we can infer their presence in molecular clouds from chemical tracers of gas ionization, gamma ray and synchrotron emission and enhanced gas temperature. These suggest that while cosmic rays above approximately 1 GeV propagate freely into clouds, lower energy cosmic rays are excluded from the denser gas. This is qualitatively in agreement with predictions from theoretical models of cosmic ray attenuation. However, depending on the physics that dominates the propagation, the degree of attenuation varies significantly, and current data is insufficient to distinguish between the models. In this talk I will give an overview of the different transport regimes thought to play a role (diffusion, free propagation, and self-modulation), and what predictions these make for the variation of the ionization rate with gas density. The propagation of cosmic rays is influenced by the properties of small-scale turbulence in the interstellar medium. I will then also discuss some recent related work I’ve done on the damping of MHD turbulence due to radiative cooling.

April 25

Joseph Cleary (JHU)

Long-Timescale Stability in CMB Observations at Multiple Frequencies using Front-End Polarization Modulation
The Cosmology Large Angular Scale Surveyor (CLASS) is a telescope array observing the Cosmic Microwave Background (CMB) at frequencies of 40, 90, 150, and 220 GHz. CLASS measures the CMB polarization on the largest angular scales to constrain the inflationary tensor-to-scalar ratio and the optical depth to reionization. To achieve the long time-scale stability necessary for this measurement from the ground, CLASS utilizes a front-end, variable-delay polarization modulator on each telescope. Here we report on the improvements in stability afforded by front-end modulation using five years of data across all four CLASS frequencies.

Jacob Hamer (JHU)

Relative Stellar Ages Reveal the Origins of Hot Jupiters and Departures from Commensurability in Kepler Multiple-planet Systems​
Tidal interactions between short-period planets and their host stars circularize eccentric orbits, realign angular momenta, alter rotation periods, and remove orbital energy. Theoretical predictions about the efficiency of these tidal processes are highly uncertain, and stellar age uncertainties further complicate exoplanet system formation and evolution inferences. To overcome these problems, we used the Galactic velocity dispersion of a thin disk stellar population as a proxy for the relative ages of exoplanet host stars to study hot Jupiter systems with obliquity measurements and Kepler multiple-planet systems close to mean-motion resonances. We found that misaligned hot Jupiter systems are older than aligned hot Jupiter systems and argue that the best explanation for this observation is that misaligned hot Jupiters arrive at their orbits at late times. We observed that Kepler multiple-planet systems with near-resonant planet pairs are younger than systems far from resonance, even for systems where tidal dissipation cannot be responsible for moving planet pairs away from commensurability. This latter observation implies that non-tidal secular processes drive systems away from resonances. These results challenge two long-standing and widely-held ideas: (1) that a single process forms hot Jupiters with a wide range of obliquities and (2) that tidal dissipation is responsible for the pile-up of planets with period ratios just wide of resonance.

Alexander de la Vega (JHU)

The Effects of Different SED-fitting Assumptions on Our Understanding of Star-Formation in Galaxies at Intermediate Redshift
Determining how star-formation radially proceeds in galaxies remains an open issue in our understanding of galaxy evolution. This can be examined by studying the radial profiles of the star-formation rate (SFR), measured from fitting spectral energy distributions (SEDs), for galaxies of different masses and redshifts. In this talk I present how varying SED-fitting assumptions (e.g., parameters related to the dust attenuation and star-formation histories) affects fits to radial SEDs of galaxies. We measure radial profiles of stellar mass, SFR, dust, and age in ~1200 massive galaxies at redshifts 0.4<z<1.5 from the CANDELS survey. The radial profiles of these parameters are estimated by fitting the SED at each radius using multi-band Hubble images and the Bayesian SED-fitting code, BEAGLE. We fit the SED at each radius under different sets of assumptions, spanning the default assumptions in the literature to more complex assumptions as revealed by recent studies. I will show how radial profiles of the SFR, dust attenuation, and age vary between the different sets of fits, as well as differences in the measured half-mass radius as a function of redshift when using the various sets of SED-fitting assumptions. I will present how different assumptions can lead to different conclusions when assessing the spatial distribution of star-formation in galaxies.