Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 474, Issue 3, Pages 3140-3151Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx3057
Keywords
methods: numerical; galaxies: evolution; galaxies: formation; galaxies: high-redshift; galaxies: statistics
Categories
Funding
- Science and Technology Facilities Council [ST/N504105/1]
- Worcester College Oxford
- Oxford Martin School
- STFC
- Beecroft Fellowship
- Large Facilities Capital Fund of BIS
- French ANR [ANR-13-BS05-0005]
- Science and Technology Facilities Council [1645205] Funding Source: researchfish
- STFC [ST/R002363/1, ST/P002307/1] Funding Source: UKRI
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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 similar to 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 similar to 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 similar to 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-star < 10(10.5) M-circle dot) 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.
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