Large-scale environment and the CGM: the hidden variables of galaxy transformation?

While the environments in which galaxies live have long been known to correlate with their star formation activity and morphology, the mechanisms inducing these effects, particularly at low environmental densities, are not well understood. I will present results leveraging the HST/COS archive, SDSS, and my own observational campaign showing that properties of the circumgalactic medium (CGM) strongly correlate with galaxy environment across a wide range of densities, from voids to clusters. Because these effects are evident on scales of even moderately populated groups, the implications are quite profound: Environmental processes are first detectable in the galaxies' halo gas, well before effects arise in their stellar or neutral gas components. In turn, UV absorption line spectroscopy provides detailed thermal, chemical, and kinematic information about this intervening medium and offers key insight to previously 'hidden variables' in phenomena such as galactic conformity and strangulation.

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