Towards Understanding the Mass-Metallicity relation of Quasar Absorbers: Evidence for bimodality and consequences

Abstract

One way to characterize and understand HI-selected galaxies is to study their metallicity properties. In particular, we show that the metallicity of absorbers is a bivariate function of the HI column density (NHI) and the MgII equivalent width (Wr(2796)). Thus, a selection upon Wr(2796) is not equivalent to a HI selection for intervening absorbers. A direct consequence for damped absorbers with NHI>20.3 from the bivariate metallicity distribution is that any correlation between the metallicity [X/H] and velocity width (or Wr(2796)) arises from the HI cut and therefore can not be interpreted as a signature of the mass-metallicity relation akin to normal field galaxies. Thus DLA samples are intrinsically heterogeneous. On the other hand, a sample of MgII-selected absorbers, which are statistically dominated by lowest NHI systems (sub-DLAs), are found to have a more uniform metallicity distribution. We postulate that the bivariate metallicity distribution can be explained by two different physical origins of absorbers, namely sight-lines through the ISM of small galaxies and sight-lines through out-flowing material. Several published results follow from this bivariate [X/H] distribution such as (a) the two classes of DLAs, reported by Wolfe et al., and (b) the constant dust-to-gas ratio for MgII-absorbers.

6 pages, 4 figures, accepted for publication in MNRAS

References in corpus (19)

• The Mass-Metallicity Relation at z~2
• Mass, Metal, and Energy Feedback in Cosmological Simulations
• Velocity-Metallicity Correlation for high-z DLA Galaxies: Evidence for a Mass-Metallicity Relation?
• New perspectives on strong z=0.5 MgII absorbers: are halo-mass and equivalent width anti-correlated?
• On the Nature of Velocity Fields in High z Galaxies
• Lensing, reddening and extinction effects of MgII absorbers from z=0.4 to z=2
• Searching for Low Surface-brightness Galaxies in the Hubble Ultra Deep Field: Implications for the Star Formation Efficiency in Neutral Gas at z ~ 3
• The missing metals problem. III How many metals are expelled from galaxies?
• The SINFONI MgII Program for Line Emitters (SIMPLE): Discovering starbursts near QSO sight-lines
• The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
• On the Halo Occupation of Dark Baryons
• A Homogeneous Sample of Sub-DLAs IV: Global Metallicity Evolution
• An efficient technique for pre-selecting low redshift damped Lyman alpha systems
• The nature of damped Lyman alpha and sub-damped Lyman alpha absorbers
• New abundance determinations in z < 1.5 QSO absorbers: seven sub-DLAs and one DLA
• The connection between metallicity and metal-line kinematics in (sub-)damped Lyman-alpha systems
• The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems at z < 1.5
• Relationships between the HI 21-cm line strength, MgII equivalent width and metallicity in damped Lyman-alpha absorption systems
• A catalogue of absorption-line systems in QSO spectra

Cited by in corpus (3)

• Damped Lyman Alpha Systems in Galaxy Formation Simulations
• Revisiting the origin of the high metallicities of sub-damped Lyman-alpha systems
• The kinematic signature of damped Lyman alpha systems: Using the D-index to screen for high column density HI absorbers