Astronomy Tea Talk
Speaker 1: Sunil Simha (Postdoc; Northwestern + UChicago)
Title: Do FRBs dream of metal-rich gas? A spatially resolved look at the FRB site metallicity with IFUs.
Abstract: In the last decade, the detection and precise localization of Fast Radio Bursts (FRBs) has become routine thanks to the efforts of radio facilities around the globe. Over a hundred of these bursts have associated host galaxies and thus redshift-based distance estimates in the literature. Yet, we are only beginning to scratch the surface when it comes to understanding the origin of these events. One approach is to search for correlations of host galaxy properties with burst properties. Thus far, host studies on sizeable samples of FRBs has been limited to global galaxy properties (M*, SFR, Z, etc.). I will, however, talk about our recent efforts to study galaxy properties on the local level, i.e. at the FRB-site within the host. Specifically, I will discuss our IFU-based gas-phase metallicity measurements with the Magellan/LLAMAS and Keck/KCWI IFUs of a small sample of hosts. Our findings suggest that FRBs occurring in star-forming regions show a wide range of metallicities. We also find that previous studies with long-slit spectroscopy of hosts are not representative of the burst site properties and thus require caution in inferring progenitor channel properties from global host galaxy measurements.
Speaker 2: Jared Siegel (Graduate student; Princeton)
Title: Evidence for a thermal pressure deficit in galaxy groups from the tSZ effect and weak lensing
Abstract: Measurements of the thermal Sunyaev-Zel'dovich (tSZ) effect have yet to form a consistent picture of the thermodynamic state of the gas in the intracluster medium: their interpretation is complicated by foreground contamination and uncertain halo masses. We present new measurements of the tSZ effect around the Dark Energy Spectroscopic Instrument (DESI) Luminous Red Galaxy (LRG) sample, together with galaxy-galaxy lensing (GGL) measurements that enable a like-with-like comparison to state-of-the-art hydrodynamical simulations. We robustly isolate the tSZ signal by directly modeling the dust and radio emission of the target galaxies using the Atacama Cosmology Telescope (ACT) single-channel temperature maps, substantially reducing uncertainties from astrophysical foregrounds. Across group mass halos at 0.5<z<1.0, we find that the hydrodynamical simulations significantly overpredict the observed tSZ signal within approximately twice the virial radius. Even the simulations with the strongest gas expulsion---which successfully reproduce the gas density inferred from kinetic SZ measurements of the same galaxy sample---overpredict the thermal pressure. Because the strongest feedback models already reproduce the observed gas density, the remaining discrepancy is difficult to explain with additional gas depletion alone. Instead, current hydrodynamical simulations appear to overpredict the thermal pressure of galaxy groups by a factor of two, pointing toward missing non-thermal pressure support or significant departures from hydrostatic equilibrium.