Spectro-photometric close pairs in GOODS-S: major and minor companions of intermediate-mass galaxies
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2010
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Abstract
Aims. Recent work has shown that major mergers of disc galaxies can only account for ~20% of the growth of the galaxy red sequence between z = 1 and z = 0. Our goal here is to provide merger frequencies that encompass both major and minor mergers, derived from close pair statistics. We aim to show that reliable close pair statistics can be derived from galaxy catalogues with mixed spectroscopic and photometric redshifts.
Methods. We use B-band luminosity- and mass-limited samples from a Spitzer/IRAC-selected catalogue of GOODS-S. We present a new methodology for computing the number of close companions, , when spectroscopic redshift information is partial. The methodology extends the one used in spectroscopic surveys to make use of photometric redshift information. We select as close companions those galaxies separated by 6 h-1 kpc < rp < 21 h-1 kpc in the sky plane and with a difference Δ v ≤ 500 km s-1 in redshift space.
Results. We provide for four different B-band-selected samples. It increases with luminosity, in good agreement with previous estimations from spectroscopic surveys. The evolution of with redshift is faster in more luminous samples. We provide of ≥ 1010 galaxies, finding that the number including minor companions (, mass ratio μ ≥ 1/10) is roughly two times the number of major companions alone (, mass ratio μ ≥ 1/3) in the range 0.2 ≤ z < 1.1. We compare the major merger rate derived by close pairs with the one computed by morphological criteria, finding that both approaches provide similar merger rates for field galaxies when the progenitor bias is taken into account. Finally, we estimate that the total (major+minor) merger rate is ~1.7 times the major merger rate.
Conclusions. Only 30% to 50% of the ≥ 1010 early-type (E/S0/Sa) galaxies that appear between z = 1 and z = 0 may have undergone a major or a minor merger. Half of the red sequence growth since z = 1 is therefore unrelated to mergers.
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© ESO 2010.
We dedicate this paper to the memory of our six IAC colleagues
and friends who met with a fatal accident in Piedra de los Cochinos,
Tenerife, in February 2007. With a special thanks to Maurizio Panniello, whose
teachings of python were so important for this paper.
We thank the anonymous referee for his/her pertinent comments that have improved
the original manuscript. We also thank Ignacio Trujillo, Carmen ElicheMoral,
and Rubén Sanchez-Janssen for useful discussions and suggestions.
This work was supported by the Spanish Programa Nacional de Astronomía y Astrofísica through project number AYA2006-12955, AYA2006-02358, and AYA 2006-15698-C02-02. This work was partially funded by the Spanish MEC under the Consolider-Ingenio 2010 Programme grant CSD2006-00070: First Science with the GTC (http://www.iac.es/consolider-ingenio-gtc/). This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, Caltech under NASA contract 1407.This work uses the Millennium Galaxy Catalogue, which consists of imaging data from the Isaac Newton Telescope and spectroscopic data from the Anglo Australian Telescope, the ANU 2.3 m, the ESO New Technology Telescope, the Telescopio Nazionale Galileo, and the Gemini North Telescope. The survey was supported through grants from the Particle Physics and Astronomy Research Council (UK) and the Australian Research Council (AUS). The data and data products are publicly available from http://www.eso.org/similar to jliske/mgc/or on request from J. Liske or S. P. Driver.P.G.P.G. acknowledges support from the Ramón y Cajal Programme financed by the Spanish Government and the European Union.