Two Talks: Speakers: Anna Kwa (UC, Irvine); Allison Strom (CalTech)

Monday November 21, 2016 12:00 pm
Marlar Lounge 37-252

Speaker 1: Anna Kwa, University of California, Irvine
Hidden Sector Atomic Dark Matter: Implications for Small-scale Structure

I will discuss the atomic physics and the astrophysical implications of a model in which the dark matter is the analog of hydrogen in a secluded sector. The self interactions between dark matter particles include both elastic scatterings as well as inelastic processes due to a hyperfine transition. The self-interaction cross sections are computed by numerically solving the coupled Schrodinger equations for this system. The velocity-dependence of the self-interaction cross sections produces the low dark matter density cores seen in spiral galaxies while maintaining consistency with constraints from observations of galaxy clusters. Significant cooling losses may occur due to inelastic excitations to the hyperfine state and subsequent decays (up to about 10% of the collisional heating rate) in this region of parameter space, with implications for the evolution of low mass halos and early growth of black holes. Finally, the minimum halo mass is in the range of 10^3 to 10^7 solar masses for viable regions of parameter space, which is significantly larger than the typical predictions for weakly-interacting dark matter models.

Speaker 2: Allison Strom, Caltech
The rest-UV and rest-optical spectra of high-redshift galaxies: clues regarding star-formation history and chemical enrichment in the early Universe

Galaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. Further, z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations, especially their ionizing radiation fields. Thus, jointly observing galaxies’ HII regions (in the rest-UV and rest-optical) and massive stars (in the rest-UV) is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and for self-consistently explaining the trends observed in the high-redshift population. I will present results from the Keck Baryonic Structure Survey (KBSS), which uniquely combines observations of the rest-optical spectra of ~400 individual galaxies (obtained with Keck/MOSFIRE) with deep rest-UV spectroscopy of many of the same galaxies (obtained with Keck/LRIS). These measurements represent one of the most comprehensive spectroscopic studies of z~2-3 galaxies to date and, when compared with predictions from photoionization models, offer compelling evidence that high-redshift galaxies exhibit chemical abundance patterns distinct from local galaxies, likely as the result of systematic differences in their star-formation histories.