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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 (906)
BibTeX
@MISC{906preprinttypeset,
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 = {906}
}
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Abstract
We measured stellar velocity dispersions σ and dynamical masses of 9 massive (M ≈ 10 11 M⊙) earlytype 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. This suggests that sizes are not underestimated by more than a similar fraction. 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 appear to have on average comparable σ and mass surface density Σ50 inside Re as the most dense local ETGs of similar dynamical masses.
Keyphrases
dynamical mass early-type galaxy truly superdense preprint typeset atex style emulateapj detailed axisymmetric dynamical model virial estimate mvir close agreement similar fraction eso large telescope similar dynamical mass stellar velocity dispersion stacked spectrum gmass sample inferred mass-to-light ratio dense local etgs stellar population model age-sensitive rest frame u-band 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 earlytype galaxy individual spectrum
