Preprint typeset using L ATEX style emulateapj v. 08/22/09 DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z ∼ 2: ARE THEY TRULY SUPERDENSE? 1 (2009)
BibTeX
@MISC{09preprinttypeset,
author = {},
title = {Preprint typeset using L ATEX style emulateapj v. 08/22/09 DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z ∼ 2: ARE THEY TRULY SUPERDENSE? 1},
year = {2009}
}
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Abstract
We measured stellar velocity dispersions σ and derived dynamical masses of 9 massive (M ≈ 10 11 M⊙) early-type galaxies (ETG) from the GMASS sample at redshift 1.4 � z � 2.0. The σ are based on individual spectra for two galaxies at z ≈ 1.4 and on a stacked spectrum for 7 galaxies with 1.6 < z < 2.0, with 202-h of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), PSF and slit effects into account. Our dynamical masses MJeans agree within � 30 % with virial estimates Mvir = 5 ×Reσ 2 /G, although the latter tend to be smaller. Our MJeans also agrees within a factor � 2 with the Mpop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L)U in the very age-sensitive rest frame U-band are consistent with passive evolution in the past ∼ 1 Gyr (formation redshift zf ∼ 3). A ‘bottom-light ’ stellar Initial Mass Function (IMF) appears to be required to ensure close agreement between MJeans and Mpop at z ∼ 2, as it does at z ∼ 0. The GMASS ETGs are on average more dense than their local counterpart. However a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ50 inside Re.
Keyphrases
dynamical mass early-type galaxy truly superdense preprint typeset atex style emulateapj virial estimate mvir close agreement eso large telescope similar dynamical mass age-sensitive rest frame u-band stacked spectrum gmass sample inferred mass-to-light ratio stellar velocity dispersion stellar population model passive evolution deep hst ac observation jean equation dynamical mass gmass etgs formation redshift bottom-light stellar initial mass function observed surface brightness slit effect latter tend band photometry dynamical mass mjeans mass surface density detailed axisymmetric dynamical model inside re local counterpart local etgs early-type galaxy individual spectrum
