ENVIRONMENTAL EFFECTS IN THE INTERACTION AND MERGING OF GALAXIES IN zCOSMOS
- Institute of Astronomy, ETH Zuerich, CH-8093 Zuerich (Switzerland)
- Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS-Universite de Provence, BP8, F-13376 Marseille Cedex 12 (France)
- INAF Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
- INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
- Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, Irfu/Service d'Astrophysique, CEA-Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France)
- Berkeley Laboratory and Berkeley Center for Cosmological Physics, University of California, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS 50-5005, Berkeley, CA (United States)
- Max-Planck-Institut fuer Extraterrestrische Physik, D-84571 Garching (Germany)
- SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3 HJ (United Kingdom)
We analyze the environments and galactic properties (morphologies and star formation histories) of a sample of 153 close kinematic pairs in the redshift range 0.2 < z < 1 identified in the zCOSMOS-bright 10 k spectroscopic sample of galaxies. Correcting for projection effects, the fraction of close kinematic pairs is three times higher in the top density quartile than in the lowest one. This translates to a three times higher merger rate because the merger timescales are shown, from mock catalogs based on the Millennium simulation, to be largely independent of environment once the same corrections for projection are applied. We then examine the morphologies and stellar populations of galaxies in the pairs, comparing them to control samples that are carefully matched in environment so as to remove as much of the well-known effects of environment on the properties of the parent population of galaxies as possible. Once the environment is properly taken into account in this way, we find that the early-late morphology mix is the same as for the parent population, but that the fraction of irregular galaxies is boosted by 50%-75%, with a disproportionate increase in the number of irregular-irregular pairs (factor of 4-8 times), due to the disturbance of disk galaxies. Future dry mergers, involving elliptical galaxies comprise less than 5% of all close kinematic pairs. In the closest pairs, there is a boost in the specific star formation rates of star-forming galaxies of a factor of 2-4, and there is also evidence for an increased incidence of post-starburst galaxies. Although significant for the galaxies involved, the 'excess' star formation associated with pairs represents only about 5% of the integrated star formation activity in the parent sample. Although most pair galaxies are in dense environments, the effects of interaction appear to be largest in the lower density environments. By preferentially bringing more pairs into the sample in lower density environments, this could dilute the dependence of pair fraction on environment and may introduce other biases into the observational study of mergers, especially those based on morphological criteria.
- OSTI ID:
- 22167312
- Journal Information:
- Astrophysical Journal, Vol. 762, 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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