Mg II Absorption Characteristics of a Volume-Limited Sample of Galaxies at z ~ 0.1

TL;DR

This study investigates Mg II absorption in the halos of low-redshift galaxies using SDSS data and Keck observations, revealing a partial covering fraction and potential links to galaxy environment and star formation.

Contribution

First systematic survey of Mg II absorption around low-redshift SDSS galaxies, providing insights into halo gas covering fraction and its dependence on galaxy properties.

Findings

Approximately 40% covering fraction for Mg II absorbers at impact parameters <= 35 kpc/h.

Strong Mg II absorption detected in 6 out of 20 systems.

Absorber presence correlates with galaxy star formation and environment.

Abstract

We present an initial survey of Mg II absorption characteristics in the halos of a carefully constructed, volume-limited subsample of galaxies embedded in the spectroscopic part of the Sloan Digital Sky Survey. We observed quasars near sightlines to 20 low-redshift (z ~ 0.1), luminous M_r <= -20.5 galaxies in SDSS DR4 and DR6 with the LRIS-B spectrograph on the Keck I telescope. The primary systematic criteria for the targeted galaxies are a redshift z >~ 0.1 and the presence of an appropriate bright background quasar within a projected 75 kpc/h of its center, although we preferentially sample galaxies with lower impact parameters and slightly more star formation within this range. Of the observed systems, six exhibit strong [EW(2796) >= 0.3 Ang.] Mg II absorption at the galaxy's redshift, six systems have upper limits which preclude strong Mg II absorption, while the remaining observations rule out very strong [EW(2796) >= 1-2 Ang] absorption. The absorbers fall at higher impact parameters than many non-absorber sightlines, indicating a covering fraction f_c <~ 0.4 for >= 0.3-Angstrom absorbers at z ~ 0.1, even at impact parameters <= 35 kpc/h (f_c ~ 0.25). The data are consistent with a possible dependence of covering fraction and/or absorption halo size on the environment or star-forming properties of the central galaxy.