Identifying the progenitors of local early-type galaxies with hydrodynamical simulations
Date Submitted
2017-03-27 09:13:14
ModMorph
Garreth Martin
Hertfordshire
Poster
S. Kaviraj (Hertfordshire), J.E.G.Devriendt (Oxford), Y. Dubois (IAP), C. Pichon (IAP), C. Laigle (Oxford)
As endpoints of the hierarchical mass assembly process, the stellar populations of local early-type galaxies encode the evolutionary patterns of galaxies over cosmic time. We use Horizon AGN, a cosmological hydrodynamical simulation, to study the merger histories of local early-types and track how the morphological mix of galaxies that are the progenitors of early-types changes over time. By calculating probabilities for late-type galaxies to be progenitors we provide a framework for alleviating progenitor bias, the bias that occurs if one uses only early-type galaxies (or proxies like the red sequence) to study the progenitor population at earlier epochs. Early-types attain their final morphology at relatively early epochs – by redshift 1, 60 percent of today's early-types have had their last significant merger. Progenitor bias is severe at all but the lowest redshifts: e.g. at redshift 0.6, less than half the stellar mass in today's early-types is actually in progenitors that have early-type morphology. At high redshift, almost all massive late-type galaxies, regardless of their local environment or star formation rate, are progenitors, as are lower-mass galaxies occupying regions of high density. However, at fixed stellar mass, progenitor fractions increase as the star formation rate decreases i.e. late-type galaxies with lower specific star formation rates are more likely to be progenitors (at a given stellar mass). In the impending era of large observational surveys (e.g. LSST, EUCLID, JWST), this study provides a framework for accurate studies of the evolution of local early-type galaxies.