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 their first 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 Hubble Fellowship. Congratulations Sarah!!!

Hubble Space Telescope – 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 – 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 Fund 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 our grant proposal, Aging Gracefully: Stellar Ages Across the HR Diagram and Their Implications for Galactic Archaeology, that Keith Hawkins, Jennifer van Saders, and I submitted during the on-the-spot grant writing and proposal part of this meeting. With this seed funding, our goal is twofold:
(1) use the Latte FIRE 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 u
nified 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!

radial distribution of satellite galaxies: first student-led paper from our group!

Radial distribution of satellite dwarf galaxies around MW-mass hosts in the FIRE simulations, as compared with the MW and M31

Excited to announce the first student-led paper from our group, led by Ph.D. student Jenna Samuel: A profile in FIRE: resolving the radial distributions of satellite dwarf galaxies in the Local Group with simulations. Jenna examined the radial distribution of satellite dwarf galaxies around MW/M31-mass hosts in our FIRE simulations, which she showed are consistent with the Local Group. The satellites of MW-like galaxies from the SAGA survey have 2D radial profiles that are similar to our simulations too. Interestingly, more massive host galaxies have fewer satellites at small distances, which is caused by tidal destruction from the central galaxy. Jenna also quantified the destruction of subhalos by comparing our baryonic simulations to their dark matter-only versions, finding 10x destruction within the inner 20 kpc. Finally, Jenna applied approximations of observational completeness in the LG to our simulations, predicting that there may be 2-10 satellites with stellar mass > 10^5 Msun to be discovered around the MW, and 6-9 around M31. Congratulations to Jenna for such a good first paper!

Frontera supercomputer: 106 million core-hours

The National Science Foundation (NSF) has awarded our FIRE collaboration an allocation of 106 million core-hours on the Texas Advanced Computing Center‘s new Frontera Supercomputer, which debuted as 5th most powerful supercomputer in the world. With this allocation, we plan to push forward on a range of large simulation projects, including our FIREbox large-volume simulation and a suite of simulations including alternative dark matter models. Congratulations to the whole FIRE collaboration!

Samantha Benincasa joins us as a postdoc

Samantha Benincasa

Samantha Benincasa joins our group as a postdoctoral research scholar. Sam recently earned her Ph.D. in physics at McMaster University, working with James Wadsley on simulations of galaxy formation. Sam works on the inter-stellar medium (ISM) gas in galaxies, with particular emphasis on giant molecular clouds (GMCs) and how they are affected by stellar feedback. We welcome Sam to our group!