PROTO-GROUPS AT 1.8 < z < 3 IN THE zCOSMOS-DEEP SAMPLE

Journal Article · Sun Mar 10 04:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/765/2/109· OSTI ID:22126993

Diener, C.; Lilly, S. J.; Knobel, C.; Kampczyk, P.; Carollo, C. M.; Caputi, K. ^[1]; Zamorani, G.; Bardelli, S.; Bolzonella, M. ^[2]; Lemson, G. ^[3]; Scoville, N. ^[4]; Contini, T. ^[5]; Kneib, J. -P.; Le Fevre, O. ^[6]; Mainieri, V. ^[7]; Renzini, A. ^[8]; Scodeggio, M. ^[9]; Bongiorno, A. ^[10]; Cucciati, O. ^[11]; De la Torre, S. ^[12] ; others, and

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1. Department of Physics, Institute for Astronomy, ETH Zurich, 8093-CH Zurich (Switzerland)
2. INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
3. Max Planck Institut fuer Astrophysik, D-85748 Garching (Germany)
4. Department of Astronomy, California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
5. Institut de Recherche en Astrophysique et Planetologie, CNRS, 14, avenue Edouard Belin, F-31400 Toulouse (France)
6. Laboratoire d'Astrophysique de Marseille, CNRS/Aix-Marseille Universite, 38 rue Frederic Joliot-Curie, F-13388 Marseille cedex 13 (France)
7. European Southern Observatory, D-85748 Garching (Germany)
8. INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
9. INAF-IASF Milano, I-20133 Milano (Italy)
10. Max Planck Institut fuer Extraterrestrische Physik, D-85741 Garching (Germany)
11. INAF Osservatorio Astronomico di Brera, I-20121 Milan (Italy)
12. Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH93HJ (United Kingdom)

We identify 42 ''candidate groups'' lying between 1.8 < z < 3.0 from a sample of 3502 galaxies with spectroscopic redshifts in the zCOSMOS-deep redshift survey within this same redshift interval. These systems contain three to five spectroscopic galaxies that lie within 500 kpc in projected distance (in physical space) and within 700 km s{sup -1} in velocity. Based on extensive analysis of mock catalogs that have been generated from the Millennium simulation, we examine the likely nature of these systems at the time of observation, and what they will evolve into down to the present epoch. Although few of the ''member'' galaxies are likely to reside in the same halo at the epoch we observe them, 50% of the systems will have, by the present epoch, all of the member galaxies in the same halo, and almost all (93%) will have at least some of the potential members in the same halo. Most of the candidate groups can therefore be described as ''proto-groups''. A crude estimate of the overdensities of these structures is also consistent with the idea that these systems are being seen as they assemble. We also examine present-day halos and ask whether their progenitors would have been seen among our candidate groups. For present-day halos between 10{sup 14} and 10{sup 15} M{sub Sun} h {sup -1}, 35% should have appeared among our candidate groups, and this would have risen to 70% if our survey had been fully sampled, so we can conclude that our sample can be taken as representative of a large fraction of such systems. There is a clear excess of massive galaxies above 10{sup 10} M{sub Sun} around the locations of the candidate groups in a large independent COSMOS photo-z sample, but we see no evidence in this latter data for any color differentiation with respect to the field. This is, however, consistent with the idea that such differentiation arises in satellite galaxies, as indicated at z < 1, if the candidate groups are indeed only starting to be assembled.

• OSTI ID: 22126993
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 765; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION SPECTROSCOPY
ASTRONOMY
ASTROPHYSICS
CATALOGS
COLOR
COMPUTERIZED SIMULATION
EMISSION SPECTROSCOPY
GALAXIES
RED SHIFT