DYNAMICAL MASSES OF EARLY-TYPE GALAXIES AT z approx 2: ARE THEY TRULY SUPERDENSE?

Journal Article · Sat Oct 10 04:00:00 EDT 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/704/1/L34· OSTI ID:21367426

Cappellari, Michele ^[1]; Di Serego Alighieri, S ^[2]; Cimatti, A ^[3]; Daddi, E ^[4]; Renzini, A ^[5]; Kurk, J D ^[6]; Cassata, P ^[7]; Dickinson, M ^[8]; Franceschini, A; Rodighiero, G ^[9]; Mignoli, M; Pozzetti, L; Zamorani, G ^[10]; Rosati, P ^[11]

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1. Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford, OX1 3RH (United Kingdom)
2. INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze (Italy)
3. Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, 40127 Bologna (Italy)
4. CEA-Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex (France)
5. INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova (Italy)
6. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany)
7. Department of Astronomy, University of Massachusetts, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA 01003-9305 (United States)
8. NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
9. Universita di Padova, Dipartimento di Astronomia, Vicolo dell'Osservatorio 2, 35122 Padova (Italy)
10. INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127 Bologna (Italy)
11. European Southern Observatory, Karl Schwarzschild Street 2, 85748 Garching bei Muenchen (Germany)

We measured stellar velocity dispersions sigma and derived dynamical masses of nine massive (M approx 10{sup 11} M{sub sun}) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 approx< z approx< 2.0. The sigma are based on individual spectra for two galaxies at z approx 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{sub Jeans} agree within approx<30% with virial estimates M{sub vir} = 5 x R{sub e}sigma{sup 2}/G, although the latter tend to be smaller. Our M{sub Jeans} also agrees within a factor approx<2 with the M{sub 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) {sub U} in the very age-sensitive rest-frame U band are consistent with passive evolution in the past approx1 Gyr (formation redshift z{sub f} approx 3). A 'bottom-light' stellar initial mass function appears to be required to ensure close agreement between M{sub Jeans} and M {sub pop} at z approx 2, as it does at z approx 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 sigma and mass surface density SIGMA{sub 50} inside R{sub e}.

• OSTI ID: 21367426
• Journal Information: Astrophysical Journal (Online), Journal Name: Astrophysical Journal (Online) Journal Issue: 1 Vol. 704; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
AXIAL SYMMETRY
BRIGHTNESS
EQUATIONS
EVOLUTION
GALACTIC EVOLUTION
GALAXIES
MASS
OPTICAL PROPERTIES
PHOTOMETRY
PHYSICAL PROPERTIES
RED SHIFT
SPECTRA
SYMMETRY
TELESCOPES