Velocity dispersions and stellar populations of the most compact and massive early-type galaxies at redshift 1

Abstract

We present Gran-Telescopio-Canarias/OSIRIS optical spectra of four of the most compact and massive early-type galaxies (ETGs) in the Groth Strip Survey at redshift z ∼ 1, with effective radii R e = 0.5-2.4kpc and photometric stellar masses M * = (1.2-4) × 10 11 M ·. We find that these galaxies have velocity dispersions σ = 156-236 km s-1. The spectra are well fitted by single stellar population models with approximately 1Gyr of age and solar metallicity. We find that (1) the dynamical masses of these galaxies are systematically smaller by a factor of ∼6 than the published stellar masses using BRIJK photometry, and (2) when estimating stellar masses as 0.7× M dyn, a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of ETGs. © 2011. The American Astronomical Society. All rights reserved.