This is the unofficial website of the NSF AAPF program, run by the fellows themselves. For official information about the fellowship, please go to the NSF program announcement.
This year's AAPF symposium will be held from 1:00 PM on Saturday, January 8 - 5:00 PM on Monday, January 10 over Zoom due to the cancellation of AAS 239.
Even though we are no longer officially part of the AAS meeting, participants are still required to abide by the AAS Anti-Harassment Policy and the Guide to AAS Meeting Etiquette.
Keynote Speaker
Enrico Ramirez-Ruiz, Astro 2020 Decadal Survey Panel on State of the Profession and Societal Impacts Co-Chair; University of California, Santa Cruz
Report from the Astro2020 State of the Profession and Societal Impacts Committee
Keynote Speaker
Fiona Harrison, Astro 2020 Decadal Survey Committee Co-Chair; Caltech
Pathways to Discovery in Astronomy and Astrophysics for the 2020s
Panel - The Virtual Environment in a Post-Pandemic World
Chris Impey, University of Arizona
Wayne Schlingman, The Ohio State University
Jackie Faherty, The American Museum of Natural History
Erin MacDonald, Star Trek (ViacomCBS)
Panel - Applying for Permanent Positions Inside and Outside Academia
Jonathan Fortney, University of California, Santa Cruz
Kate Follette, Amherst College
Rachel Osten, Space Telescope Science Institute
Erin MacDonald, Star Trek (ViacomCBS)
Joe Antognini, Whisper
Panel - The Astro 2020 Decadal Survey and You
Fiona Harrison, Astro 2020 Decadal Survey Committee; Caltech
Enrico Ramirez-Ruiz, Astro 2020 Decadal Survey Panel on State of the Profession and Societal Impacts; University of California, Santa Cruz
Rachel Osten, Astro 2020 Decadal Survey Committee; Space Telescope Science Institute
Jonathan Fortney, Astro 2020 Decadal Survey Committee; University of California, Santa Cruz
Keith Hawkins, Astro 2020 Decadal Survey Panel on An Enabling Foundation for Research; University of Texas, Austin
This schedule is subject to change
All times refer to the Eastern time zone. Click on the talk title to scroll down to the abstract.
Neutrino Flavor Turbulence in Neutron Star Mergers
Sherwood Richers - UC Berkeley
Neutron star mergers are likely the source of many of the heavy elements in the universe and produce a brief transient that carries information about the fate of the merged object, the nature of dense matter, and the composition of ejected matter. Neutrinos play a key role in shaping all of these, but the result depends on how much of each flavor is present. I will show the first three-dimensional simulations of a flavor instability that is ubiquitous in neutron star mergers (but neglected in simulations), and show that it will be possible to create a sub-grid model for neutrino flavor changes. This will significantly improve the fidelity of neutron star merger simulations, allowing for more informative comparison with observed transients.
The Morpho-Kinematic Architecture of Super Star Clusters in the Center of NGC253
Rebecca Levy - University of Arizona
The bar-fed starburst in the center of the nearby galaxy NGC253 hosts a population of more than a dozen super star clusters (SSCs) revealed by submillimeter observations from ALMA and the VLA (Leroy et al. 2018; Levy et al. 2021; Mills et al. 2021). These SSCs are massive (M*≳10^5 M⊙), compact (R~1 pc), and gas-rich (Mgas/M*~1), and at least three of them show spectral evidence of molecular gas outflows. In projection, the SSCs appear as a thin, almost linear, structure about 170 pc in length, reminiscent of the Central Molecular Zone (CMZ) of the Milky Way. The individual SSCs are connected by more diffuse dust and molecular gas emission. However, precisely how gas is flowing from the larger scale bar (~2 kpc) down to the nuclear region (~200 pc) to power the nuclear starburst and result in the formation of these SSCs is not well measured. In this work, we use the SSCs themselves as the tracers of the gas flows. We use ALMA observations of the dust continuum and molecular gas emission with a spatial resolution of 47 milliarcseconds (0.8 pc) to morpho-kinematically determine the arrangement of the SSCs in the context of the larger scale bar flows and orbits. From the ALMA spectra, we have precise measurements of the systemic velocities of each of the SSCs. Many of the SSCs are kinematically distinct from the bulk gas motions traced by CO, with velocity offsets up to 100 km/s. By applying models developed for the CMZ to these observations, we find that the arrangement of the SSCs in NGC253 is consistent with an edge-on ring or crossing streams connected to the larger scale bar, both in terms of the morphology and the kinematics. From these constraints, we can make predictions for model-dependent cluster age gradients, which we will be able to test with our approved Cycle 1 JWST program.
Zooming in on LISA Sources: Cosmological Simulations of High-Redshift Dwarf Galaxy Mergers
Michael Tremmel - Yale University
I present preliminary results from high-resolution, zoom-in cosmological simulations of dwarf galaxy mergers occurring at z > 4. Because these types of mergers are very common and host SMBH pairs of mass 10^5-10^7 Msun, they are the most likely hosts for gravitational wave emission detectable during LISA’s initial 4-year mission. We selected dwarf mergers from the Romulus25 simulation and re-run them at 64 times better resolution (3e3 Msun and 87 pc mass and spatial resolution respectively). The galaxies are seeded with a 10^5 Msun SMBH at z ~ 12 and evolved until z = 2.5, 1 Gyr following the merger event. In this pilot study, we examine the effect of different SMBH model parameters related to accretion and feedback efficiency on the evolution of the SMBH pairs and their host dwarf galaxy. We discuss the evolution of the their host galaxies and accretion histories during and following the merger event relative to star formation, as well as the evolving kinematics of the gas feeding the SMBHs.
The Masses and Metallicities of Cool Giant Exoplanets
Paul Dalba - University of California Riverside
The union of the transit and radial velocity (RV) techniques, each of which measures a key exoplanet observable, has strongly guided the early development of exoplanet science. However, the short-period selection bias of the transit method has left a dearth of well characterized exoplanets at wider separations, limiting tests of planetary formation theories and contributing to the knowledge gap separating exoplanet and Solar System science. I will discuss results from th Giant Outer Transiting Exoplanet Mass (GOT 'EM) survey, which combines transits and RVs but confronts the transit method's selection bias by focusing on planets with orbital periods between 100 and 1,000 days. The Kepler and TESS missions have discovered a modest sample of these cool giant planets, most with temperatures well below 500 K, but their characterization is still an area of emerging research owing to their lengthy and logistically challenging follow-up process. I will describe our 3+ year effort to measure over a dozen planet masses and orbital eccentricities with Keck-HIRES as well as our methods to infer their bulk heavy element content. Individually, each giant exoplanet is a valuable stepping stone in the underexplored parameter space between hot Jupiters and the Solar System gas giants. Cumulatively, they offer tentative evidence that short and long-period planets accrete their heavy metals differently.
Local Group satellite dwarf galaxy quenching in the FIRE simulations
Jenna Samuel - UT Austin
The star formation and gas content of satellite dwarf galaxies in the Local Group (LG) seem to be highly sensitive to the environment around the Milky Way (MW) and Andromeda (M31). We use 240 satellite dwarf galaxies (Mstar>10^5 Msun) from the FIRE-2 simulations to investigate environmental quenching around 14 MW/M31-mass hosts. 90 per cent of all satellites are quenched at z=0, and 37 per cent of the quenched satellites stop forming stars within 1 Gyr of infall into the MW/M31-mass halo. As expected, more massive satellites take longer to quench after falling into the host halo. The low-mass (Mstar<10^7 Msun) satellite population is fully quenched, and the quiescent fraction of satellites decreases with increasing satellite stellar mass, consistent with the LG. The quiescent fraction is also broadly consistent with the SAGA survey, except for the lowest mass bin of SAGA, which is highly star-forming compared to the simulations. We find higher satellite quiescent fractions around more massive host halos. However, we find no significant dependence on isolated versus paired/LG-like environments. We also find evidence for group preprocessing, such that satellites of Mstar>10^7 Msun with a prior host are 1.8 times more likely to be quenched than those that did not have a prior host. 45 per cent of quenched satellites quench within 1 Gyr of infall into any host, and nothing above Mstar~3x10^6 Msun quenches significantly before infall into any host, suggestive of an upper mass limit for dwarfs able to quench in isolation.
Preparing for the Enhanced CLASS Cosmology Telescope
Sarah Marie Bruno - Johns Hopkins University
The Cosmology Large Angular Scale Surveyor (CLASS) is a highly sensitive ground-based observational cosmology telescope array located in the Atacama Desert, Chile. The CLASS instrument is designed to measure the polarization of the Cosmic Microwave Background (CMB) at unprecedentedly large angular scales to detect evidence of primordial gravitational waves. With three currently operational telescopes on-site in Chile, CLASS surveys 75% of the sky at millimeter wavelengths in frequency bands near 40 GHz, 90 GHz, 150 GHz and 220 GHz. The CLASS telescope focal planes contain closely packed feedhorn-coupled arrays of superconducting Transition Edge Sensor (TES) bolometers designed to detect and measure CMB photons with extremely high sensitivity. CLASS also employs a unique variable-delay polarization modulator (VPM) to enable unparalleled polarization measurement precision. Two major upgrades planned for the next several years include (1) deployment of the fourth CLASS array telescope containing a second 90 GHz TES array, and (2) deployment of a next-generation enhanced 40GHz array. I will introduce the CLASS instrument, focusing on the detector and readout development for the upcoming upgrades. I will discuss the ongoing assembly, integration and testing of the new 90 GHz TES modules.
A Preview of Dwarf Galaxy Discoveries in the Next Decade
Burcin Mutlu-Pakdil - University of Chicago
I will present a preview of the faint dwarf galaxy discoveries that will be possible with the Vera C. Rubin Observatory and Subaru Hyper Suprime-Cam in the next decade. We recently combined deep ground-based images from the Panoramic Imaging Survey of Centaurus and Sculptor and extensive image simulations to investigate the recovery of faint, resolved dwarf galaxies in the Local Volume with a matched-filter technique. We adopted three fiducial distances (1.5, 3.5, and 5 Mpc) and quantitatively evaluate the effects on dwarf detection of varied stellar backgrounds, ellipticity, and Milky Way foreground contamination and extinction. We show that near-future surveys will be able to probe at least ∼4.5 mag below the tip of the red giant branch (TRGB) for a distance of up to 1.5 Mpc and ∼2 mag below the TRGB at 5 Mpc. This will push the discovery frontier for resolved dwarf galaxies to fainter magnitudes, lower surface brightnesses, and larger distances. Our simulations show the secure census of dwarf galaxies down to Mv ≈ −5, −7, and −8 will soon be within reach, out to 1.5, 3.5, and 5 Mpc, respectively, allowing us to quantify the statistical fluctuations in satellite abundances around hosts and parse environmental effects as a function of host properties.
Novel algorithm for image reconstruction of EHT data
Lia Medeiros - Institute for Advanced Study
The sparse interferometric coverage of the Event Horizon Telescope (EHT) poses a significant challenge for reconstruction of black-hole images. I will then discuss a new principal components analysis based algorithm for image reconstruction that uses the results of high-fidelity general relativistic, magnetohydrodynamic (GRMHD) plus radiative transfer simulations of low-luminosity accretion flows as a training set. This allows us to reconstruct images that are both consistent with the interferometric data and that live in the space of images that is spanned by the simulations.
The Dynamics of Black Holes in Dense Star Clusters
Kyle Kremer - Caltech/Carnegie Observatories
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.
Bars and their Influence on Galaxy Evolution
Dhanesh Krishnarao (DK) - Johns Hopkins University / Colorado College
Bars are prominent features of disk galaxies that transfer angular momentum across large scales, funnel gas across large radial extents, and drive resonances out to large scales. The combination of our Galaxy, SDSS MaNGA and the citizen science project Galaxy Zoo:3D provide a unique sample to examine these complex phenomena through statistical studies. This talk will discuss some background of the large scale effects of bars based on N-body and hydrodynamic simulations of Milky Way like galaxies and apply their insight towards extragalactic samples of MaNGA galaxies. Two key results are: 1) gas surrounding bars tend to have unusual ionized gas properties compared to the rest of the disk and the inter bar regions. 2) The g-band light distribution of face on-barred galaxies may be used to identify bar resonances without requiring any kinematic information.
Probing maximum rotation velocities of dwarf galaxies
Amy Sardone - Ohio State University
The number of observed low mass galaxies is in conflict with the number predicted by standard cosmological models. Rotation velocities of galaxies provide the observational link to compare the number density of galaxies with a dark matter halo (velocity function). We have used highly sensitive observations of extremely low mass galaxies to populate the unconstrained low mass end of the velocity function of galaxies and compare these observations with simulations of dark matter halos.
Planet Candidates Transiting White Dwarf Stars from the Zwicky Transient Facility
Keaton Bell - University of Washington
Earth-sized white dwarfs are the final remnants of intermediate- and low-mass stars. The planets that orbit white dwarfs reveal the ultimate fates of most planets that orbit main sequence stars. Such planets are difficult to discover since white dwarfs are geometrically small targets to be transited. Any transits will be short (minutes) but deep (even total). The Zwicky Transient Facility (ZTF) is obtaining thousands of snapshots of hundreds of thousands of white dwarfs in the Northern sky---finally a sufficient data volume to overcome the minuscule likelihood of observing a white dwarf during a transit. I share an update of my efforts to identify potential transits in the ZTF data, the confirmation of deep eclipses with high-speed Agile photometry from Apache Point Observatory, and my next steps for discerning current candidates from eclipsing binaries with radial velocity measurements.
Asteroseismic Galactic Archaeology
Joel Zinn - American Musuem of Natural History
A wide range of stellar and galactic physics contributes to the age—velocity dispersion relation (AVR), which links the velocity dispersion of a stellar population to the age of that population. Close to home in the solar vicinity, it is unclear to what extent the observed AVR reflects the turbulent velocity of gas at the time of stars' birth versus subsequent kinematic heating of stars. Further afield, recent analyses indicate unexpected behavior of the AVR in the Milky Way's outer disc, which may signal the influence of dwarf galaxy mergers setting the kinematics at the edges of the Galaxy. Understanding the kinematics of the outer disc requires stellar ages that are not possible without red giant asteroseismology, which is the only age-dating technique that can deliver accurate ages for old stars at large distances. I will discuss the current state of the art in red giant asteroseismology as applied to the outer disc AVR, and will go on to describe efforts at constraining the physics that sets the local AVR using analytic galaxy formation simulations in combination with asteroseismic data.
High Mass X-ray Binaries as Probes of Massive Binary Stellar Evolution
Margaret Lazzarini - California Institute of Technology
High mass X-ray binaries (HMXBs) are systems that contain a compact object (neutron star or black hole) that accretes from a massive stellar companion. HMXBs are highly observable due to their bright X-ray luminosities, making them an important observational window into the complex process of massive binary stellar evolution. In this talk I will present previous and ongoing work to characterize the HMXB populations of M31 and M33 using observations from the Hubble Space Telescope, the Chandra X-ray Observatory, and NuSTAR. With these overlapping, multi-wavelength observations we can determine HMXB "population demographics" in these galaxies, characterizing both the accreting compact object and its companion star in the context of their parent stellar populations. The ultimate goal of this work is to use the population demographics of HMXBs in nearby galaxies to constrain models of massive binary stellar evolution.
Searching for the Highest Energy Neutrinos
Brian Clark - Michigan State University
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 ongoing work to discover UHE neutrinos with the radio detection technique, highlighting the latest results from a diffuse search with the Askaryan Radio Array. I will then discuss our work on the reconstruction of neutrino properties, particularly the polarization of received signals and the reconstructed shower energy. I will also briefly cover our efforts to design and optimize the IceCube-Gen2 detector.
How Much Mass do Streamers Pour into the Youngest Planet-Forming Disks?
Dominique Segura-Cox - University of Texas at Austin
Streamers are a component of low-mass star formation that have been relatively recently found in the past three years, although modern simulations have shown signs of streamers for at least a decade. The youngest planet-forming disks in the Class 0 and I star-forming phases are still embedded in (and feeding from) their larger natal envelopes. Streamers---long and asymmetric infall pathways---may extend far beyond the traditional envelopes and could provide an additional fast track for mass to pour into the young protostellar disks. The mystery of exactly how much material is being funneled into young disks through streamers, and hence how much streamers could impact the protostellar mass accretion process, is starting to be unraveled observationally. Comparing streamer observations with simulations can test the reliability of observational methods, determine how the chemical compositions of streamers and disks evolve with time, and shed light on how common or important streamers are in the early phases of star formation.
The Spatial Distribution of Extreme Metallicity Dwarf Galaxies in the Local Universe
Jacqueline Monkiewicz - Arizona State University
Extremely metal-deficient (XMD) galaxies, with nebular oxygen abundances of less than one-tenth the Solar abundance, are a rare class of nearby dwarf galaxies commonly treated as Local analogs for early protogalaxies. Their status as true primordial galaxies is contradicted by the presence of underlying evolved stellar populations and [alpha/Fe] ratios consistent with multiple prior generations of star formation. The low metallicities of XMDs are therefore commonly understood to be the result of low galactic halo masses, which permit efficient ejection the products of stellar nucleosynthesis into the intergalactic medium. I discuss the completeness of current XMD samples, and the spatial distribution of XMDs within D < 100 Mpc. I find that XMDs are preferentially located along the edges of large-scale filaments and superclusters. In the local universe (D < 50 Mpc), the bulk of XMDs are clustered at right ascensions between 9h - 10h, to the west of the Virgo cluster, with a roughly co-linear north-south alignment. In three dimensions, this resolves to a large (~20 Mpc in extent) filamentary structure, approximately parallel to previously-known filaments on the western side of the Virgo cluster. The existence of this filament suggests that the ongoing star formation in XMDs is fueled by a common reservoir of nearly pristine intergalactic gas, located to the west of the Virgo supercluster.
Development of the First Light Instrument for CCAT-prime
Steve Choi - Cornell University
The Prime-Cam receiver on the Fred Young Submillimeter Telescope (FYST) for the CCAT-prime project aims to address important astrophysical and cosmological questions with sensitive broadband, polarimetric, and spectroscopic measurements. The primary frequency bands in development include 280, 350, and 850 GHz for the polarization-sensitive broadband channels and 210--420 GHz for the spectrometers. Microwave kinetic inductance detectors (MKIDs) are a natural choice of detector technology for the simplicity in multiplexed readout needed for large format arrays at these high frequencies. I will present the initial lab characterization of the feedhorn-coupled 280 GHz polarimetric MKID array, and outline the plans for the subsequent MKID arrays and the development of the testbed to characterize them.
I Can't Believe Its Not Radiative Transfer: Surrogate Modeling for Protoplanetary Disk Models
Patrick Sheehan - Northwestern University
Radiative transfer modeling has proven to be a powerful technique for understanding the properties of protoplanetary disks. At the same time, its utility has been limited by the extreme cost, the most of which comes from the cost of radiative transfer calculations, of coupling such models with powerful modern fitting techniques such as Markov Chain Monte Carlo. In this talk I will discuss early returns on my efforts to make radiative transfer modeling a more tractable problem through the use of surrogate modeling. This machine-learning-adjacent technique replaces the computationally expensive radiative transfer calculations with cheap but accurate approximations, and therefore has the potential to dramatically speed up rigorous modeling to help bring it in to the 21st century.