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.

DOI: https://doi.org/10.1111/j.1365-2966.2011.19208.x

Abstract

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 (W^λ2796r≳ 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 b_G= 1.44 ± 0.02 and b_A= 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 W^λ2796r≥ 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 W^λ2796r≥ 0.6 Å absorbers to galaxies with ongoing star formation.

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