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STScI Webcast

2018 Spring Science Colloquia

Late Bloomers: What ELSE Influences Star Formation Histories of Galaxies?

Presented by: Alan Dressler (Carnegie Institution for Science)
Category: Science Colloquia   Duration: 1 hour   Broadcast date: May 16, 2018
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Measuring the star formation histories (SFHs) and stellar mass growth of individual galaxies is challenging because stellar populations older than 2 Gyr have largely degenerate spectrophotometric properties. For this reason, the SFHs of present-epoch galaxies are largely obscured: the ubiquitous "tau-model" of explonential decline of the the star formation rate is a result of that insensitivity. In contast, the study of galaxies between 5 and 7 Gyr in lookback time allows a reliable measure of individual SFHs from z~1 to z ~ 0.5 and secure comparison to star formation before z~1. From this better vantage point, we have found a great diversity of SFHs in our photometric/spectroscopic study of ~8000 galaxies of 10^10-11 to 10^11 Msun. In particular, our group has identified a ~20% population of "late bloomers"--Milky Way mass galaxies that formed most of their stellar mass between z~1 and z~0.5. This discovery could have important implications for popular models where quasi-universal SFHs derived by abundance matching or integrating SFR scaling laws are "quenched" later in life, if not for the utility of linking stellar mass to dark matter halo growth, in general.