The Leonard E Parker Center for Gravitation, Cosmology and Astrophysics holds frequent seminars on a broad range of ongoing cosmology and gravitation research topics. Unless otherwise noted, seminars are on Friday afternoons at 1:00 PM in KIRC 2175; there is a gathering for a brown bag lunch at 12:30.

Decoding multiphase Galactic HI with the 21-SPONGE survey
Claire Murray, University of Wisconsin, Madison, WI

The structure of interstellar hydrogen (HI) is crucial for star formation, feedback and accretion in galaxies. Absorption line spectroscopy is an important tool for understanding the multiphase nature of HI, especially in our own Galaxy where high sensitivity and resolution can be achieved. In this talk, I will present results from 21-SPONGE: the largest and most sensitive survey for Galactic HI absorption using the Karl G. Jansky Very Large Array. Our excellent sensitivity enables us to detect unexpectedly warm neutral gas at T=7000 K, which suggests a new found influence of the Lya radiation field density in the ISM. To isolate the dominant physics behind our observed spectral lines, we analyze 1000s of synthetic HI spectra from 3D numerical simulations from Kim et al. (2014) using machine learning and derivative spectroscopy. For the first time, we statistically quantify the ability of Gaussian spectral lines to recover simulated clouds and their important physical properties, such as temperature and density. Furthermore, with the biases of our analysis tools in hand, we measure the fractions of local HI in the cold, warm and thermally-unstable gas phases.