DEEP NEAR-INFRARED SPECTROSCOPY OF PASSIVELY EVOLVING GALAXIES AT z {approx}> 1.4
- Institute for Astronomy, ETH Zuerich, Wolfgang-Pauli-strasse 27, 8093 Zuerich (Switzerland)
- INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122, Padova (Italy)
- Sub-Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom)
- CEA, Laboratoire AIM-CNRS-Universite Paris Diderot, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France)
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo (Japan)
- Institut d'Astrophysique de Paris, UMR7095, Universite Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris (France)
- Laboratoire d'Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12 (France)
- Spitzer Science Center, California Institute of Technology 220-06, Pasadena, CA 91125 (United States)
- Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, 40127 Bologna (Italy)
- Department of Astronomy, University of Massachusetts, Amherst, MA (United States)
- Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States)
- Center for Astrophysics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
- Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Tokyo (Japan)
- Department of Astronomy, Kyoto University, Kyoto 606-8502 (Japan)
We present the results of new near-IR spectroscopic observations of passive galaxies at z {approx}> 1.4 in a concentration of BzK-selected galaxies in the COSMOS field. The observations have been conducted with Subaru/MOIRCS, and have resulted in absorption lines and/or continuum detection for 18 out of 34 objects. This allows us to measure spectroscopic redshifts for a sample that is almost complete to K{sub AB} = 21. COSMOS photometric redshifts are found in fair agreement overall with the spectroscopic redshifts, with a standard deviation of {approx}0.05; however, {approx}30% of objects have photometric redshifts systematically underestimated by up to {approx}25%. We show that these systematic offsets in photometric redshifts can be removed by using these objects as a training set. All galaxies fall in four distinct redshift spikes at z = 1.43, 1.53, 1.67, and 1.82, with this latter one including seven galaxies. SED fits to broadband fluxes indicate stellar masses in the range of {approx}4-40 Multiplication-Sign 10{sup 10} M{sub Sun} and that star formation was quenched {approx}1 Gyr before the cosmic epoch at which they are observed. The spectra of several individual galaxies have allowed us to measure their H{delta}{sub F} indices and the strengths of the 4000 A break, which confirms their identification as passive galaxies, as does a composite spectrum resulting from the co-addition of 17 individual spectra. The effective radii of the galaxies have been measured on the COSMOS HST/ACS i{sub F814W}-band image, confirming the coexistence at these redshifts of passive galaxies, which are substantially more compact than their local counterparts with others that follow the local effective radius-stellar mass relation. For the galaxy with the best signal-to-noise spectrum we were able to measure a velocity dispersion of 270 {+-} 105 km s{sup -1} (error bar including systematic errors), indicating that this galaxy lies closely on the virial relation given its stellar mass and effective radius.
- OSTI ID:
- 22039178
- Journal Information:
- Astrophysical Journal, Vol. 755, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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