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

Lundgren, Britt F.; Wake, David A.; Padmanabhan, Nikhil; Coil, Alison and York, Donald G. (2011). The dark matter haloes and host galaxies of Mg II absorbers at z~ 1. Monthly Notices of the Royal Astronomical Society, 417(1) pp. 304–313.



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 (Wλ2796r≳ 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 ±4.21.6× 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 Wλ2796r≥ 0.6 Å gas covering fraction to be fc= 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 Wλ2796r≥ 0.6 Å absorbers to galaxies with ongoing star formation.

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