2021 NSF AAPF Symposium Schedule

We analyzed the HI mass content around 18 MHONGOOSE galaxies using the Green Bank Telescope. We find that nearly all of these galaxies contain detectable amounts of HI mass beyond their disks and even out to large radii in some cases. We were also able to show a strong correlation between the galaxy's baryonic mass and its diffuse HI gas fraction.

The smallest and faintest galaxies around the Milky Way are the most ancient, most metal-poor, and most dark-matter-dominated systems known. These extreme objects offer unique access to small scales where the stellar and dark matter content can be studied simultaneously and hold the promise of major breakthroughs in understanding the nature of dark matter, and a more complete picture of galaxy formation. Thus, their discovery and characterization are among the most important goals in the field. I will share our ongoing observational efforts to detect these faint systems around the Milky Way and beyond, and upcoming advances in the era of deep and wide imaging instrumentation.

The emergence of "red and dead" massive quiescent galaxies at high redshift, and their growth and persistence to the present day, point to some of the most fundamental outstanding questions in galaxy formation: what is the physical relationship between galaxies and the supermassive black holes (SMBHs) they host? Are those SMBHs responsible for quenching star formation, and if so, how? I will present some of my work seeking to understand the formation, evolution, and quenching of high-redshift galaxies with several simulation collaborations, describe the different approaches to studying SMBH growth and feedback in the context of galaxy formation simulations, and discuss the potential of synthesizing these techniques in future studies. In the latter portion of the talk, I will also discuss my educational work with the Northwestern Prison Education Program (NPEP), who run a college-level, degree-granting program for students incarcerated in Illinois state prisons.

I discuss recent results from the Romulus suite of cosmological simulations predicting the dynamical evolution of SMBH pairs within merging galaxies. With a unique model for dynamical friction, Romulus is the first ever large-scale cosmological simulation capable of accurately predicting where and when SMBH binaries are likely to form. In contrast with common assumptions, SMBH pairs often take Gyrs to form a close pair (D < 700 pc; the precursor to a bound binary system) following a galaxy merger. This has important implications for the formation of SMBH binaries and predictions of future gravitational wave detection with LISA. The simulations also predict that off-center, 'wandering' SMBHs are common in massive galaxies.

Our current understanding of black holes assumes that they are described by the Kerr solution to Einstein's equations. On April 10, 2019, the Event Horizon Telescope (EHT), released the first image of a black hole resolved to event horizon scales and the first measurement of the size of a black-hole shadow. In October of 2020 we published a new test of General Relativity at the 2PN order based on this measurement. I will discuss how we can use the Event Horizon Telescope to test the Kerr nature of black holes, both with this first image and in the future.

Line intensity mapping is an emerging observational technique to measure the large-scale structure of the Universe in three dimensions, traced by a redshifted atomic or molecular line, without resolving individual objects. Future experiments promise to extend the observable volume beyond the redshift reach of traditional galaxy surveys, improving precision on the LCDM cosmological model and extensions to it. I will discuss the science potential of such experiments, focusing on far-IR lines detectable at millimeter wavelengths. I will then present SuperSpec - a mm-wave spectrometer that performs the spectral separation entirely on a silicon wafer - and our imminent first demonstration at the Large Millimeter Telescope. Finally I will discuss how SuperSpec technology could power future intensity mapping instruments with orders of magnitude more sensitivity.

Fred Young Submillimeter Telescope (FYST) is a new 6 m crossed Dragone telescope designed to measure the Sunyaev-Zel’dovich effects of galaxy clusters, the CMB polarization and foregrounds, and the [CII] emission from the Epoch of Reionization. FYST will observe from a 5600 m altitude site on Cerro Chajnantor in the Atacama Desert. The novel optical design of the telescope combined with a high surface accuracy, and the exceptional atmospheric conditions of the site will enable sensitive broadband, polarimetric, and spectroscopic surveys at sub-mm to mm wavelengths. The first light instrument for FYST is currently being developed, and the telescope is under construction to achieve first light in late 2022.

Ultra-high energy (UHE, >10 PeV) neutrinos are unique messengers to the distant, high energy universe. As chargeless and weakly interacting particles, neutrinos arrive undeflected and unattenuated from cosmic distances, giving us key insights to the properties of astrophysical accelerators at the highest redshifts. In this talk, I will discuss the latest results in the search for UHE neutrinos using the Askaryan Radio Array, which produced the best limit on the flux of UHE neutrinos above 100 PeV of any in-ice radio neutrino detector. I will then discuss our work on the reconstruction of neutrino properties at UHE energies, such as their energy and direction. Finally, I will also briefly cover our efforts to optimize the design of the IceCube-Gen2 observatory, which will provide unprecedented sensitivity to the UHE neutrino flux.

Neutrinos drive core-collapse supernovae, though different flavors of neutrinos interact with and carry energy around the exploding star differently. In neutron star mergers, neutrinos of different flavors change protons into neutrons or the other way around, which determines whether such mergers are able to generate the heavy elements we see in the universe. However, in such extreme environments neutrinos undergo violent nonlinear flavor transformations, rapidly changing the identity of each neutrino in a way that is still poorly understood. I will present the first multidimensional simulations of this flavor instability as a first step toward understanding the content of each neutrino flavor in supernovae and mergers.

The James Webb Space Telescope (JWST), scheduled to launch in late 2021, will bring factors of 100x increases in sensitivity over current observatories in the near- and mid-infrared. My keynote seeks to answer the question, “How can early career scientists best take advantage of the science capabilities of JWST?” I will describe the mission timeline so that Fellows can place it in the context of their career arcs. I will summarize the scientific capabilities of JWST, and my tips on how to learn them and how they apply to Fellows’ research. I will summarize the timeline for the first year post-launch, including the major deployments, the commissioning of the telescope and the science instruments, and the beginning of science observations, with an emphasis on what data will be public early in the mission and ripe for harvest. I will give a heads-up about the Cycle 2 proposal cycle, and how Fellows can position themselves to write compelling Cycle 2 proposals. I will highlight paths for community members to provide input to the Project. I will close by highlighting the Early Release Science program TEMPLATES that I lead, and how we are planning to characterize JWST’s spectroscopic capabilities by targeting four lensed galaxies early in Cycle 1.

We present stellar age distributions of the Milky Way bulge region using ages for ~6000 high-luminosity (log(g)<2.0), metal-rich ([Fe/H] ≥ -0.5) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment. Ages are derived using The Cannon label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars (>8 Gyr). We find evidence that the planar region of the bulge (|Z_GC| < 0.25 kpc) is enriched in metallicity, Z, at a faster rate (dZ/dt ~ 0.0034 Gyr-1) than regions farther from the plane (dZ/dt ~ 0.0013 Gyr-1 at |Z_GC| > 1.00 kpc). We identify a nonnegligible fraction of younger stars (age ~2-5 Gyr) at metallicities of +0.2 < [Fe/H] < +0.4. These stars are preferentially found in the plane (|Z_GC| < 0.25 kpc) and at Rcy ~ 2-3 kpc, with kinematics that are more consistent with rotation than are the kinematics of older stars at the same metallicities. We do not measure a significant age difference between stars found inside and outside the bar. These findings show that the bulge experienced an initial starburst that was more intense close to the plane than far from the plane. Then, star formation continued at supersolar metallicities in a thin disk at 2 kpc < Rcy < 3 kpc until ~2 Gyr ago.

Asteroseismology is the best tool for providing precise ages for stars beyond the solar vicinity, where Galactic evolution models are only recently being tested in detail. Comprising more than 20,000 red giant stars with asteroseismic masses, the third and final data release of the K2 Galactic Archaeology Program (K2 GAP DR3) is the largest asteroseismic data set to date. We establish that K2 GAP DR3 radii and masses are in very good agreement with both Gaia radii and open cluster masses & radii, after corrections to the large frequency separation indicated from the literature. We identify small, percent-level systematics among first-ascent red giant branch stars in both the frequency at maximum power and the large frequency separation, even after such corrections. We also find evidence for percent-level asteroseismic corrections required of the red clump scaling relations, which have not been appreciated to this point, and which are suggestive of shortcomings in red clump stellar structure models. Using thousands of calibrated K2 GAP DR3 asteroseismic ages in combination with GALAH abundances, we constrain state-of-the-art Galactic chemical evolution models of r-process and s-process elements. The K2 GAP DR3 giants show age-abundance patterns that suggest nucleosynthetic yields from neutron star—neutron star mergers are insufficient to produce the observed Eu enrichment history, which prefers significant contributions from prompt sites of production. We discuss the observed Ba enrichment history in the context of prior claims of mass-dependent Ba production. Age-abundance patterns for other neutron-capture elements, alpha elements, and iron-peak elements are also presented.

Each year, hundreds of thousands of college students enroll in introductory Astronomy, Geoscience, and Biology courses to fulfill their institutions’ science requirement. For many of these students, these introductory courses will be their last formal exposure to science. Oftentimes, however, introductory courses focus on covering a wide range of topics quickly, and do not provide students with insight into how science actually works. To address this limitation, we have developed a new set of science investigations that are developmentally appropriate for general education college students, and that have an instructional pathway that gives these students a robust experience analyzing contemporary data. This work aims to build upon the success of a previous NSF-IUSE funded effort to incorporate Zooniverse-based research experiences into introductory astronomy courses, specifically. The Zooniverse is the largest online citizen science platform in the world. Since the launch of its first project (Galaxy Zoo) in 2007, the Zooniverse has supported over 200 projects, connecting researchers with over 1.8 million volunteers around the world. This has resulted in over 150 peer-reviewed publications across a multitude of disciplines. As part of our efforts, we have developed a new curricular model that uses a three-pronged approach to bring citizen science to the classroom in an accessible and interactive way. We will present how this curricular model was adopted to create two citizen science-based labs that are fully adaptable to the online classroom. The pilot testing efforts for our labs began during the Fall 2020 semester with over 1,000 student participants. Preliminary findings from student surveys indicated that our labs lead to increased data literacy, increased self efficacy with regard to contributing to science, and a nearly unanimous interest in continued engagement in science through citizen science platforms like the Zooniverse.

Over the past few years, the groundbreaking detections of gravitational wave signals from merging binary black holes and neutron stars by LIGO/Virgo have opened a new window to the cosmos. One key question regarding these gravitational wave sources concerns the nature of their origin. Dynamical formation in dense stellar environments like globular clusters has emerged as an important formation channel, corroborated by recent numerical simulations and observational indications suggesting that globular clusters contain dynamically significant populations of stellar-mass black holes throughout their lifetimes. I use N-body simulations to study ways black hole populations influence the dynamical evolution and observable properties of globular clusters and discuss the dynamical formation of merging black hole binaries that may be detectable by LIGO/Virgo and LISA and various other stellar exotica including tidal disruption events and X-ray binaries. I will also discuss briefly my Cosmos in Concert outreach program that presents live concerts combining music and astronomy.

One of the best laboratories to study strong-field gravity is the inner 100s of kilometers around black holes and neutron stars in binary systems with low-mass stars like our Sun. The X-ray light curves of these systems show variability on timescales from milliseconds to months — the rapid variability can appear as quasi-periodic oscillations (QPOs), which may be produced by general relativistic effects. My research looks at QPOs from black holes and neutron stars by applying state-of-the-art “spectral-timing” techniques to constrain the physical origin of these signals. Here I will present the three facets of compact objects in my fellowship: scientific results, the Stingray open-source spectral-timing software package, and doing outreach with school classes in these COVID times.

The vast majority of stars host exoplanets, and the vast majority of stars conclude their evolution as white dwarfs. Therefore, we expect the majority of white dwarfs to host exoplanets, but these planets are extremely difficult to detect. Because white dwarfs are so small (roughly Earth-sized), transits require precise edge-on orbital alignments, and transits are very short (minutes). However, these transits are also very deep and do not require space-photometry precision to detect. The Zwicky Transient Facility is obtaining hundreds of millions of snapshots of white dwarfs---enough to overcome the minuscule likelihood of a transit occurring at any given time. I describe my ongoing effort to discover the first exoplanets transiting white dwarf stars in the Zwicky Transient Facility survey photometry, and the challenges that I have encountered along the way.

The orbital architectures of known giant planets indicate that a rich variety of formation and evolutionary processes are in play. In the Solar System, Jupiter and Saturn are cold, distant worlds that have been meticulously studied through decades of spacecraft exploration. In exoplanet systems, readily detectable hot-Jupiters orbit their stars every few days and endure blisteringly high temperatures. Both flavors of giant planet provide important, complementary clues about how planets form and migrate over time. However, what about the intermediate cases? A modest sample of giant transiting exoplanets, which are amenable to mass and radius measurements, with orbital periods of 100's to 1000 days is known to exist. Yet, the formidable challenges of measuring their masses have so far precluded investigations to explain how these stepping stones between hot-Jupiters and the Solar System giant planets form and evolve. Here, I will describe progress toward measuring the masses and properties of long-period giant exoplanets discovered by the Kepler mission and the ongoing, transit-hunting TESS mission. Challenges such as waiting out these planets' several-hundred-day orbits and acquiring observations at key epochs (that may occur even less frequently than a blue moon) have proven difficult, but first results are in. I will describe the characterization of several truly unique exoplanets from this sample and set the stage for the scientific finale of these efforts that is expected next year.

In order to obtain spectral analysis of exoplanetary atmospheres, high contrast imaging (HCI) systems are being developed to spatially resolve planetary sources from their host star. The most advanced HCI instruments can reliably detect planets at a contrast ratio of ~10^-6, but improvements are needed to meet the expected contrast ratio of earth-sized planets in reflected light of 10^-8. Focal plane wavefront sensing is one of many proposed upgrades for existing extreme adaptive optic systems to achieve this contrast ratio. One such sensing technique is coherent differential imaging (CDI) where the deformable mirror of the system is used to diffract starlight from speckles in a series of probes to amplitude-modulate the background speckle signal. Several groups have demonstrated CDI techniques on-sky, but the MKID Exoplanet Camera (MEC) has the advantage of having read-out rates in the 10s of kHz, at least an order of magnitude faster than similar counterparts. This read-out rate allows us to probe and remove the speckles that evolve on atmospheric timescales, on order of ~1 us. Here I present results from simulations on performance of the coherent differential imaging (CDI) technique using an in-house simulation routine called the MKID Exoplanet Direct Imaging Simulator (MEDIS). We show an expected contrast ratio for exoplanetary detection of 10^-7 for a variety of atmospheric conditions.

In the years since the iconic, ringed image of HL Tau was taken by ALMA, it has become increasingly clear that planet formation is already well underway in the 1-5 Myr-old “protoplanetary disks” that have traditionally been studied in pursuit of understanding the planet formation process. As a result, attention has turned to the <1 Myr-old “protostellar disks” to illuminate the beginnings of planet formation. Tantalizingly, disk substructures (rings, asymmetries, spirals, etc.) that are common in protoplanetary disks and frequently associated with young planets or planetary embryos have also started turning up in these young, protostellar disks as well. Here I will present new observations from the VANDAM: Orion ALMA survey that doubles the number of protostellar disks known to have such substructures, and discuss how these observations inform planet formation or whether they are signposts of binary formation at early times.