Identifying the progenitors of present-day early-type galaxies in observational surveys: Correcting 'progenitor bias' using the Horizon-AGN simulation

Journal article

As endpoints of the hierarchical mass-assembly process, the stellar populations of local earlytype galaxies encode the assembly history of galaxies over cosmic time. We useHorizon-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 lowermass (M* < 10 10.5 M ⊙ ) 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.

Authors: Martin, G; Kaviraj, S; Devriendt, J; Dubois, Y; Pichon, C

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 474
• Issue: 3
• Pages: 3140-3151
• Publication date: 2017-12-12
• Acceptance date: 2017-11-23
• DOI: 10.1093/mnras/stx3057
• EISSN: 1365-2966
• ISSN: 0035-8711
• Keywords: galaxies: formation; galaxies: high-redshift; galaxies: evolution; methods: numerical; galaxies: statistics