Bibcode
López-Sanjuan, C.; Balcells, M.; Pérez-González, P. G.; Barro, G.; Gallego, J.; Zamorano, J.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 518, id.A20
Fecha de publicación:
7
2010
Revista
Número de citas
31
Número de citas referidas
28
Descripción
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, N_c, 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 N_c
for four different B-band-selected samples. It increases with
luminosity, in good agreement with previous estimations from
spectroscopic surveys. The evolution of N_c with redshift is faster in
more luminous samples. We provide N_c of Mstar ≥
1010 M&sun; galaxies, finding that the number
including minor companions (N_c^m, mass ratio μ ≥ 1/10) is roughly
two times the number of major companions alone (N_c^M, 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
Mstar ≥ 1010 M&sun; 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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