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Mendel, J. Trevor; Beifiori, Alessandra; Saglia, Roberto P.; Bender, Ralf; Brammer, Gabriel B.; Chan, Jeffrey; Schreiber, Natascha M. Foerster; Fossati, Matteo; Galametz, Audrey; Momcheva, Ivelina G.; Nelson, Erica J.; Wilman, David J. and Wuyts, Stijn (2020): The Kinematics of Massive Quiescent Galaxies at 1.4 < z < 2.1: Dark Matter Fractions, IMF Variation, and the Relation to Local Early-type Galaxies*. In: Astrophysical Journal, Vol. 899, No. 1, 87

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Abstract

We study the dynamical properties of massive quiescent galaxies at 1.4 z K-band Multi Object Spectrograph (KMOS) on the ESO Very Large Telescope. We use these data to show that the typical dynamical-to-stellar mass ratio has increased by similar to 0.2 dex fromz = 2 to the present day, and we investigate this evolution in the context of possible changes in the stellar initial mass function (IMF) and/or fraction of dark matter contained within the galaxy effective radius,f(DM)[<r(e)]. Comparing our high-redshift sample to their likely descendants at low redshift, we find thatf(DM)[<r(e)] has increased by a factor of more than 4 sincez 1.8, fromf(DM)[<r(e)] = 6.6% 1.0% to similar to 24%. The observed increase appears robust to changes in the methods used to estimate dynamical masses or match progenitors and descendants. We quantify possible variation of the stellar IMF through the offset parameter alpha, defined as the ratio of dynamical mass in stars to the stellar mass estimated using a Chabrier IMF. We demonstrate that the correlation between stellar velocity dispersion and alpha reported among quiescent galaxies at low redshift is already in place atz = 2, and we argue that subsequent evolution through (mostly minor) merging should act to preserve this relation while contributing significantly to galaxies' overall growth in size and stellar mass.

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