Are strong MgII Absorbers Signatures of Outflows?

¹ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, Garching 85748, Germany ;
e-mail: nbouche@mpe.mpg.de
² Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
³ Observatoire Astronomique de Marseille-Provence, 13388 Marseille Cedex 13, France

Abstract

Low-ionization transitions such as the Mg iiλ2796/2803 doublet trace cold gas in the vicinity of galaxies. The exact physical origin of this cold gas traced by QSO absorption lines is debated. Does it trace gas in disks, halos, merger tails, and even in outflows? Recent studies of strong starbursts and post-starbursts at intermediate redshifts have shown that Mg ii are seen in outflows, with blue-shifted velocities ∼500 − 1500km s⁻¹. Strong intervening Mg ii absorbers (with equivalent width W_r^λ2796 > 1Å) may be tracing the denser and colder gas of starburst-driven outflows. Indeed, based on Mg ii statistics, our clustering analysis has shown that the host-galaxy mass is anti-correlated with the line-of-sight velocity Δv (as measured from W_r^λ2796). If Mg ii absorbers were virialized in galaxy halos, a positive M_h–W_r correlation would have been observed. Our result thus shows that the Mg ii clouds are not virialized in the gaseous halos of the host-galaxies.