Tuesday, September 2
Speaker: Sirio Belli, Caltech
Location: Hearst Field Annex, B1 (also videoconferenced to 50-5026) – 1:10 pm
Title: “Deep Keck spectroscopy of 1 < z < 2.5 quiescent galaxies: constraining the size growth and the mass assembly of the red sequence”
Abstract: The most effective probe of the physical nature of quiescent galaxies is absorption line spectroscopy, which is particularly challenging at high redshift. Using the improved sensitivity of optical and infrared detectors at the Keck observatory, and the multiplex advantage of its new MOSFIRE spectrograph, we have undertaken a new spectroscopic survey of over 100 galaxies selected according to stellar mass and rest-frame optical color in the redshift range 1 < z < 2.5. Velocity dispersions and stellar ages derived from our spectra, together with HST-based sizes, provide valuable insight into the mass assembly of quiescent galaxies. We find that the stellar to dynamical mass ratio evolves with redshift, which might imply a change in the dark matter fraction or in the stellar initial mass function. We also find that recently quenched galaxies are systematically larger in size, which enables us to quantify how “progenitor bias” contributes to the observed size evolution. We conclude that at least half of the size evolution of the red sequence observed at z~1.5 is due to physical growth of individual galaxies.
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