NASA Astrophysics Theory Program (ATP) grant: dark-matter subhalos and stellar streams

NASA’s Astrophysics Theory Program (ATP) has awarded our team (PI Robyn Sanderson, co-PI Andrew Wetzel) a grant for Predicting observable signatures for dynamical interactions between dark-matter substructure and stellar streams in the Milky WayCongratulations to Robyn Sanderson, who led this grant!

The wealth of ongoing and upcoming observations of the Milky Way promise an era of ‘near-field cosmology’ to test the cold dark matter (CDM) paradigm. One of the most exciting and powerful probes of dark matter is using the Milky Way’s stellar streams as ‘gravitational antennae’, as close passages of small dark-matter subhalos dynamically perturb cold stellar streams, allowing us to test the diverging predictions of different dark-matter models for the low-mass end of the (sub)halo mass function. Our goal with this grant is to use our Latte suite of FIRE-2 simulations of Milky Way-like galaxies to model the dynamics of dark-matter subhalo interactions with stellar streams from disrupted globular clusters and satellite galaxies in realistic detail, including creating synthetic observations of these simulated perturbed streams. Our goal is to provide the first comprehensive end-to-end study that connects cosmological predictions from baryonic simulations to interpretations of, and predictions for, observable perturbations from dark-matter subhalos on stellar streams.

Sarah Loebman to start as assistant professor at UC Merced

Sarah Loebman

We are so excited that Sarah Loebman has accepted a faculty position at the University of California, Merced, where she will start as an assistant professor in their Department of Physics in fall 2020! We are doubly excited because, as one of their two inaugural astrophysics faculty, Sarah will start a new astrophysics program within their department. Fortunately for us, she will stay with our group at UC Davis for another year to finish her NASA Hubble Fellowship and Chancellor’s Postdoctoral Fellowship. Congratulations Sarah!!

Hubble Space Telescope (HST) Treasury Program: M31-6D survey

Space Telescope Science Institute has awarded our team

  • PI  Dan Weiz
  • co-PI  Nitya Kallivayalil
  • co-PI  Andrew Wetzel
  • co-investigators:  Jay Anderson, Gurtina Besla, Mike Boylan-Kolchin, Tom Brown, James Bullock, Andrew Cole, Michelle Collins, Mike Cooper, Alis Deason, Andrew Dolphin, Aaron Dotter, Mark Fardal, Annette Ferguson, Tobias Fritz, Marla Geha, Karoline Gilbert, Raja Guhathakurta, Rodrigo Ibata, Michael Irwin, Myoungwon Jeon, Evan Kirby, Geraint Lewis, Dougal Mackey, Steve Majewski, Nicholas Martin, Alan McConnachie, Ekta Patel, Mike Rich, Josh Simon, Evan Skillman, Tony Sohn, Erik Tollerud, Roeland van der Marel

a Hubble Space Telescope (HST) Treasury Program of 244 orbits for Tracing the 6-D Orbital and Formation History of the Complete M31 Satellite SystemThese Hubble Space Telescope (HST) observations will provide the initial baselines for long-term proper-motion measurements for all of the known satellite dwarf galaxies around Andromeda (M31). Our goal is to measure the orbital motions of these satellites as they move across the sky over the next ~10 years, to complete their full 6-dimensional orbital phase-space. Our key science goals are to:

  • Understand the effect of environment on low-mass galaxy evolution
  • Use dwarf galaxies as probes of the epoch of reionization
  • Dynamically measure the mass distribution of M31’s dark-matter halo
  • Test planar associations of satellite dwarf galaxies

Combined with our existing HST Treasury Program to measure proper motions for all of the satellite dwarf galaxies of the Milky Way, we will provide proper motions for all known satellite galaxies across the Local Group.

Hubble Space Telescope (HST) Legacy Theory grant: dwarf galaxies and reionization

Space Telescope Science Institute has awarded our team

a Hubble Space Telescope (HST) Legacy Theory grant for Probing the epoch of reionization with the fossil record of nearby dwarf galaxies. Our goal is to use our FIRE-2 simulations to rigorously test and characterize how well HST near-field observations of the star-formation histories of dwarf galaxies in the Local Group can measure the faint end of the galaxy ultra-violet luminosity function during the epoch of reionization at z ~ 7. Furthermore, we will create synthetic HST and JWST observations of these simulated dwarf galaxies, to quantify how accurately the SFHs from measured stellar populations in nearby dwarfs can infer their star formation rates and UV luminosities at z ~ 7, and we will release these synthetic observations and simulation data to the scientific community, to help leverage existing HST data and guide upcoming JWST observations.

Hellman Fellowship


The Hellman Fellows Program has selected me as a 2019 Hellman Fellow, for my proposed research program: Using stars as gravitational antennae to measure dark matter. The Hellman Fellows Program supports the research of assistant professors, and this fellowship grant will help support the work of our group to use our Latte FIRE simulations to develop new dynamical models to measure the nature of dark matter, by using streams of stars as ‘gravitational antennae’ for interactions with dark-matter subhalos, thus translating dark-matter theories directly into measurable predictions for stellar dynamics.


Scialog Fellowship and Heising-Simons grant

The Research Corporation, with support of the Heising-Simons Foundation and the Kavli Foundation, once again has selected me to be a Scialog Fellow. I was delighted again to join 50 fellows at the 2019 Scialog conference on Time Domain Astrophysics in Tuscon, Arizona, during which we discussed exciting applications of data from NASA’s TESS satellite, ESA’s Gaia satellite, and the Zwicky Transient Facility.

I am excited that the Heising-Simons Foundation selected the grant that Keith Hawkins, Jennifer van Saders, and I submitted during this meeting: Aging Gracefully: Stellar Ages Across the HR Diagram and Their Implications for Galactic Archaeology. With this seed funding, our goal is two-fold:

  1. Use the Latte FIRE-2 Milky Way-like simulations as a testbed to quantify the observational precision in stellar ages that we require for specific Milky Way studies.
  2. Compile a unified framework for combining/comparing different ways of measuring stellar ages in an easy-to-use Baysian framework.

    I am excited to work with Keith and Jen on this project over the next year!

Sierra Chapman graduates with Highest Honors

Sierra Chapman

Sierra Chapman, who has been pursuing research with our group as part of her Honor’s Thesis, graduates with her bachelor’s degree in physics. Moreover, for her excellent work on her Honors Thesis, in which she predicts the population of low-mass dark-matter subhalos that orbit close to the Milky Way, she earned Highest Honors. Sierra will continue to work with us over the summer to translate her thesis work into a paper to submit for publication. Congratulations Sierra!