Missing Photons that Count: Galaxy Evolution via Absorbing Gas

Chris Churchill

Absorption lines in quasar spectra provide an astonishing array of detailed physical information at unrivaled sensitivities and over the full range of observable redshifts. Using the "missing light", the kinematic, ionization, and chemical conditions of galactic gas can be decoded from the time of the first quasars (employed as distant light beacons whose light paths provide "core samples" of the universe). More generally, evolution of absorption lines can be exploited for inferring evolution in galactic supernovae energetics and galactic superwinds. Moreover, absorption lines provide the only unbiased source of observational data required for us to glean insights into the cosmic evolutionary epochs when galaxies transition (i) from formation/build-up due to IGM and proto-galactic clump accretion (ii) to actively reprocessing gas into stars, (iii) to eventually decoupling from the IGM to enter a final "passive evolution" stage.