Research Note

Constraining sub-grid physics with high-redshift spatially-resolved metallicity distributions

¹ Jeremiah Horrocks Insitute, University of Central Lancashire, Preston, PR1 2HE, UK
e-mail: bkgibson@uclan.ac.uk
² Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Physics & Astronomy, University of Alabama, Tuscaloosa, AL 35487-0324, USA

Received: 5 February 2013
Accepted: 5 April 2013

Abstract

Aims. We examine the role of energy feedback in shaping the distribution of metals within cosmological hydrodynamical simulations of L^∗ disc galaxies. While negative abundance gradients today provide a boundary condition for galaxy evolution models, in support of inside-out disc growth, empirical evidence as to whether abundance gradients steepen or flatten with time remains highly contradictory.

Methods. We made use of a suite of L^∗ discs, realised with and without “enhanced” feedback. All the simulations were produced using the smoothed particle hydrodynamics code Gasoline, and their in situ gas-phase metallicity gradients traced from redshift z ~ 2 to the present-day. Present-day age-metallicity relations and metallicity distribution functions were derived for each system.

Results. The “enhanced” feedback models, which have been shown to be in agreement with a broad range of empirical scaling relations, distribute energy and re-cycled ISM material over large scales and predict the existence of relatively “flat” and temporally invariant abundance gradients. Enhanced feedback schemes reduce significantly the scatter in the local stellar age-metallicity relation and, especially, the [O/Fe]−[Fe/H] relation. The local [O/Fe] distribution functions for our L^∗ discs show clear bimodality, with peaks at [O/Fe] =  −0.05 and + 0.05 (for stars with [Fe/H] > −1), consistent with our earlier work on dwarf discs.

Conclusions. Our results with “enhanced” feedback are inconsistent with our earlier generation of simulations realised with “conservative” feedback. We conclude that spatially-resolved metallicity distributions, particularly at high-redshift, offer a unique and under-utilised constraint on the uncertain nature of stellar feedback processes.