The morphological, kinematic, and halo gas properties of magnesium II absorption selected galaxies at intermediate redshift

This research focuses on understanding the formation and evolution of galaxies via their extended gaseous halos using the methods of quasar absorption line systems. Galaxy-absorber pairs provide direct observational constraints on competing scenarios aimed at establishing the role of gas in galaxy formation and evolution. Our sample consists of 40 intermediate redshift galaxy-absorber pairs, imaged with HST . The absorption line data are from VLT/UVES and Keck/ HIRES high resolution quasar spectra. Ten galaxy rotation curves are measured from Keck/ESI spectra. We also analyze simulated quasar absorption line observations of galaxies and their gaseous halos in LCDM cosmological simulations in order to constrain the dynamic interaction of the galaxy/halo/ cosmic web environment and the distribution of gas within halos. We present new results on the morphological and kinematic connections between Mg II absorption selected galaxies and their halo gas.

We find intriguing correlations between galaxy color, orientation, and Mg II absorption properties, suggesting that late-type galaxies produce stronger absorption than early-type galaxies, and that disk-like halo geometries may be preferred. We find previous results suggesting spherical halos having a uniform distribution of gas are not consistent with our data nor with simulations. Statistically, gaseous halos have sizes of 60-125 kpc with a gas covering fraction of ~ 50%. Previous observational results from six galaxies suggest that halo gas velocities are consistent with extended disk-like rotation at galactocentric distances of 25-72 kpc. Our new results indicate that the bulk of Mg II absorption velocities do indeed lie in the range of the observed galaxy rotation velocities. We demonstrate that the gas velocities are mostly inconsistent with being kinematically coupled by rotation to the galaxy over similar galactocentric distances.

In the simulations, Mg II absorption selects metal enriched "halo" gas, out to ~ 100 kpc, from, tidal streams, filaments, small satellite galaxies and the galaxy. The majority of the simulated Mg II absorption arises in the filaments/ tidal streams and is infalling towards the galaxy with velocities between ~ ±200 km s -1 . The line-of-sight velocity distribution of the Mg II absor ption spans ~ ±200 km s -1 of the galaxy systemic velocity. This demonstrates why observed absorption velocities fall within the range of the galaxy rotation curve velocities, even though the gas arises in a variety of kinematic structures.