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Title:
Dynamical Masses of Early-Type Galaxies at z ~ 2: Are they Truly Superdense?
Authors:
Cappellari, Michele; di Serego Alighieri, S.; Cimatti, A.; Daddi, E.; Renzini, A.; Kurk, J. D.; Cassata, P.; Dickinson, M.; Franceschini, A.; Mignoli, M.; Pozzetti, L.; Rodighiero, G.; Rosati, P.; Zamorani, G.
Affiliation:
AA(Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK ), AB(INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy ), AC(Dipartimento di Astronomia, Università di Bologna, Via Ranzani 1, 40127 Bologna, Italy ), AD(CEA-Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France ), AE(INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy ), AF(Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany ), AG(Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003-9305, USA ), AH(NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719, USA ), AI(Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy ), AJ(INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy ), AK(INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy ), AL(Università di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova, Italy ), AM(European Southern Observatory, Karl Schwarzschild Street 2, 85748 Garching bei München, Germany), AN(INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna, Italy )
Publication:
The Astrophysical Journal Letters, Volume 704, Issue 1, pp. L34-L39 (2009). (ApJL Homepage)
Publication Date:
10/2009
Origin:
IOP
ApJ Keywords:
galaxies: elliptical and lenticular, cD, galaxies: evolution, galaxies: formation, galaxies: high-redshift
DOI:
10.1088/0004-637X/704/1/L34
Bibliographic Code:
2009ApJ...704L..34C

Abstract

We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M ≈ 1011 M sun) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 lsim z lsim 2.0. The σ are based on individual spectra for two galaxies at z ≈ 1.4 and on a stacked spectrum for seven galaxies with 1.6 < z < 2.0, with 202 hr 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), point-spread function, and slit effects into account. Our dynamical masses M Jeans agree within lsim30% with virial estimates M vir = 5 × Reσ2/G, although the latter tend to be smaller. Our M Jeans also agrees within a factor lsim2 with the M pop 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 appears to be required to ensure close agreement between M Jeans and M pop 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 R e.

Based on observations collected at the European Southern Observatory, Paranal, Chile, ESO Large Programs 173.A-0687.

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