The dark matter haloes and host galaxies of Mg II absorbers at z ∼ 1

Strong foreground absorption features from singly ionized magnesium (Mg II) are commonly observed in the spectra of quasars and are presumed to probe a wide range of galactic environments. To date, measurements of the average dark matter (DM) halo masses of intervening Mg II absorbers by way of large-scale cross-correlations with luminous galaxies have been limited to z < 0.7. In this work, we cross-correlate 21 strong (Wλ2796 r 0.6 Å) Mg II absorption systems detected in quasar spectra from the Sloan Digital Sky Survey Seventh Data Release with ∼32 000 spectroscopically confirmed galaxies at 0.7 ≤ z ≤ 1.45 from the DEEP2 galaxy redshift survey. We measure DM halo biases of bG = 1.44 ± 0.02 and bA = 1.49 ± 0.45 for the DEEP2 galaxies and Mg II absorbers respectively, indicating that their clustering amplitudes are roughly consistent. Haloes with the bias we measure for the Mg II absorbers have a corresponding mass of 1.8 ± 4.2 1.6 × 1012 h−1 M , although the actual mean absorber halo mass will depend on the precise distribution of absorbers within DM haloes. This mass estimate is consistent with observations at z = 0.6, suggesting that the halo masses of typical Mg II absorbers do not significantly evolve from z ∼1. We additionally measure the average Wλ2796 r ≥ 0.6 Å gas covering fraction to be f c = 0.5 within 60 h−1 kpc around the DEEP2 galaxies, and we find an absence of coincident strong Mg II absorption beyond a projected separation of ∼40 h−1 kpc. Although the star-forming z > 1 DEEP2 galaxies are known to exhibit ubiquitous blueshifted Mg II absorption, we find no direct evidence in our small sample linking Wλ2796 r ≥ 0.6 Å absorbers to galaxies with ongoing star formation.