Identifying the progenitors of present-day early-type galaxies in observational surveys: correcting 'progenitor bias' using the Horizon-AGN simulation. Issue 3 (12th December 2017)

• Record Type: Journal Article
• Authors: Martin, G; Kaviraj, S; Devriendt, J E G; Dubois, Y; Pichon, C; Laigle, C
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 474:Issue 3(2018)
• Page Start: 3140
• Page End: 3151
• Publication Date: 2017-12-12
• Subjects: methods: numerical -- galaxies: evolution -- galaxies: formation -- galaxies: high-redshift -- galaxies: statistics; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stx3057
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: As endpoints of the hierarchical mass-assembly process, the stellar populations of local early-type galaxies encode the assembly history of galaxies over cosmic time. We use Horizon-AGN, a cosmological hydrodynamical simulation, to study the merger histories of local early-type galaxies and track how the morphological mix of their progenitors evolves over time. We provide a framework for alleviating 'progenitor bias' – the bias that occurs if one uses only early-type galaxies to study the progenitor population. Early types attain their final morphology at relatively early epochs – by z ∼ 1, around 60 per cent of today's early types have had their last significant merger. At all redshifts, the majority of mergers have one late-type progenitor, with late–late mergers dominating at z > 1.5 and early–early mergers becoming significant only at z < 0.5. Progenitor bias is severe at all but the lowest redshifts – e.g. at z ∼ 0.6, less than 50 per cent of the stellar mass in today's early types is actually in progenitors with early-type morphology, while, at z ∼ 2, studying only early types misses almost all (80 per cent) of the stellar mass that eventually ends up in local early-type systems. At high redshift, almost all massive late-type galaxies, regardless of their local environment or star formation rate, are progenitors of local early-type galaxies, as are lower mass ( M ⋆ < 10 10.5 M$_{_{\odot }}$ ) late-types as long as they reside in high-density environments. In this new era of large observational surveys (e.g. LSST, JWST ), this study provides a framework for studying how today's early-type galaxies have been built up over cosmic time.