Simulating the mass-metallicity relation from z 1^*

¹ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK e-mail: mm@astro.livjm.ac.uk
² Centre for Astrophysics, University of Central Lancashire, Preston, PR1 2HE, UK
³ School of Physics, University of Sydney, NSW, 2006, Australia
⁴ Centre for Astrophysics & Supercomputing, Swinburne University, Hawthorn, Victoria, 3122, Australia
⁵ The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA, 91101, USA

Received: 29 June 2007
Accepted: 29 February 2008

Abstract

Context. The chemical properties of galaxies and their evolution as a function of cosmic epoch are powerful constraints on their evolutionary histories.

Aims. This work provides a grid of numerical models for galaxy evolution over an extended cosmic epoch. The aims are to assess how well current models reproduce observed properties of galaxies, in particular the stellar mass versus gas phase metallicity relation, and to quantify the effect of the merging histories of galaxies on their final properties.

Methods. We use 112 N-body/hydrodynamical simulations in the standard cold dark matter universe, to follow the formation of galaxy-sized halos and investigate the chemical enrichment of both the stellar component and the interstellar medium of galaxies, with stellar masses higher than ~10⁹ .

Results. The resulting chemical properties of the simulated galaxies are broadly consistent with the observations. The predicted relationship between the mean metallicity and the galaxy stellar mass for both the stellar and the gaseous components at agree with the relationships observed locally. The predicted scatter about these relationships, which is traced to the differing merging histories amongst the simulated galaxies with similar final masses, is similar to what is observed. In the hierarchical formation scenario, we find that the more massive galaxies are typically more evolved than their low mass counterparts over the second half of the age of the Universe. The predicted correlations between the total mass and the stellar mass of galaxies in our simulated sample from the present epoch up to agree with observed ones. We find that the integrated stellar populations in the simulations are dominated by stars as old as  Gyr. In contrast with massive galaxies, for which the luminosity-weighted ages of the integrated stellar populations in the simulated sample agree with those derived from the modelling of observed spectral energy distributions, simulated galaxies with stellar masses ~10⁹ at tend to be older than the local galaxies with similar stellar masses.

Conclusions. The stellar mass versus metallicity relation and its associated scatter are reproduced by the simulations as a consequence of the increasing efficiency of the conversion of gas into stars with stellar mass and of the differing merging histories amongst the galaxies with similar masses. The old ages of simulated low mass galaxies at and the weak level of chemical evolution for massive galaxies suggest, however, that our modelling of the supernova feedback may be incomplete or that other feedback processes have been neglected.