The LEGA-C and SAMI Galaxy Surveys : Quiescent Stellar Populations and the Mass-Size Plane across 6 Gyr

Barone, Tania M. and D'Eugenio, Francesco and Scott, Nicholas and Colless, Matthew and Vaughan, Sam P. and Wel, Arjen van der and Fraser-McKelvie, Amelia and Graaff, Anna de and Sande, Jesse van de and Wu, Po-Feng and Bezanson, Rachel and Brough, Sarah and Bell, Eric and Croom, Scott M. and Cortese, Luca and Driver, Simon and Gallazzi, Anna R. and Muzzin, Adam and Sobral, David and Bland-Hawthorn, Joss and Bryant, Julia J. and Goodwin, Michael and Lawrence, Jon S. and Lorente, Nuria P. F. and Owers, Matt S. (2022) The LEGA-C and SAMI Galaxy Surveys : Quiescent Stellar Populations and the Mass-Size Plane across 6 Gyr. Monthly Notices of the Royal Astronomical Society, 512 (3). pp. 3828-3845. ISSN 0035-8711

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Abstract

We investigate the change in mean stellar population age and metallicity ([Z/H]) scaling relations for quiescent galaxies from intermediate redshift ($0.60\leq z\leq0.76$) using the LEGA-C Survey, to low redshift ($0.014\leq z\leq0.10$) using the SAMI Galaxy Survey. We find that, similarly to their low-redshift counterparts, the stellar metallicity of quiescent galaxies at $0.60\leq z\leq 0.76$ closely correlates with $M_*/R_\mathrm{e}$ (a proxy for the gravitational potential or escape velocity), in that galaxies with deeper potential wells are more metal-rich. This supports the hypothesis that the relation arises due to the gravitational potential regulating the retention of metals, by determining the escape velocity required by metal-rich stellar and supernova ejecta to escape the system and avoid being recycled into later stellar generations. On the other hand, we find no correlation between stellar age and $M_*/R_\mathrm{e}^2$ (stellar mass surface density $\Sigma$) in the LEGA-C sample, despite this being a strong relation at low redshift. We consider this change in the age--$\Sigma$ relation in the context of the redshift evolution of the star-forming and quiescent populations in the mass--size plane, and find our results can be explained as a consequence of galaxies forming more compactly at higher redshifts, and remaining compact throughout their evolution. Furthermore, galaxies appear to quench at a characteristic surface density that decreases with decreasing redshift. The $z\sim 0$ age--$\Sigma$ relation is therefore a result of building up the quiescent and star-forming populations with galaxies that formed at a range of redshifts and so a range of surface densities.