On the Spatial and Kinematic Distributions of Mg ii Absorbing Gas in (Z) ∼0.7 Galaxies

Abstract

We present HIRES/Keck spectra having resolution ~6 km s^-1^ of MgII ?2796 absorption profiles that arise in the gas believed to beassociated with 15 identified galaxies over the redshift range (0.5 colors, and impact parametersD. We found no correlations at the 2.5 ? level between the measuredabsorption properties and galaxy properties. Of primary significanceis the fact that the QSO-galaxy impact parameter apparently doesnot provide the primary distinguishing factor by which absorptionproperties can be characterized. The absorption properties of MgII selected galaxies exhibit a large scatter, which, we argue, issuggestive of a picture in which the gas in galaxies arises froma variety of ongoing dynamical events. Inferences from our studyinclude the following: (1) The spatial distribution of absorbinggas in and around galaxies does not appear to follow a simple galactocentricfunctional dependence, since the gas distribution is probably highlystructured. (2) A single systematic kinematic model apparently cannotdescribe the observed velocity spreads in the absorbing gas. It ismore likely that galaxy/halo events giving rise to absorbing gaseach exhibit their own systematic kinematics, so that a heterogeneouspopulation of sub-galaxy scale structures are giving rise to theobserved cloud velocities. (3) The absorbing gas spatial distributionand overall kinematics may depend upon gas-producing events and mechanismsthat are recent to the epoch at which the absorption is observed.In any given galaxy, these distributions likely change over a fewGyr timescale (few dynamical times of the absorbing clouds), whichprovides one source for the observed scatter in the absorption properties.Based upon these inferences, we note that any evolution in the absorptiongas properties over the wider redshift range (0.4