Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys - IV.Influence of mergers in the evolution of faint field galaxies from z similar to 1
O. Le Fevre et al., Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys - IV.Influence of mergers in the evolution of faint field galaxies from z similar to 1, M NOT R AST, 311(3), 2000, pp. 565-575
Hubble Space Telescope images of a sample of 285 galaxies with measured red
shifts from the Canada-France Redshift Survey (CFRS) and Autofib-Low Disper
sion Spectrograph Survey (LDSS) redshift surveys are analysed to derive the
evolution of the merger fraction out to redshifts z similar to 1. We have
performed visual and machine-based merger identifications, as well as count
s of bright pairs of galaxies with magnitude differences delta m less than
or equal to 1.5 mag. We find that the pair fraction increases with redshift
, with up to similar to 20 per cent of the galaxies being in physical pairs
at z similar to 0.75-1. We derive a merger fraction varying with redshift
as proportional to(1+z)(3.2 +/- 0.6), after correction for line-of-sight co
ntamination, in excellent agreement with the merger fraction derived from t
he visual classification of mergers for which m=3.4 +/- 0.6. After correcti
ng for seeing effects on the ground-based selection of survey galaxies, we
conclude that the pair fraction evolves as proportional to(1+z)(2.7 +/- 0.6
). This implies that an average L* galaxy will have undergone 0.8-1.8 merge
r events from z=1 to z=0, with 0.5 to 1.2 merger events occuring in a 2-Gyr
time-span at around z similar to 0.9. This result is consistent with predi
ctions from semi-analytical models of galaxy formation. From the simple coa
ddition of the observed luminosities of the galaxies in pairs, physical mer
gers are computed to lead to a brightening of 0.5 mag for each pair on aver
age, and a boost in star formation rate of a factor of 2, as derived from t
he average [O II] equivalent widths. Mergers of galaxies are therefore cont
ributing significantly to the evolution of both the luminosity function and
luminosity density of the Universe out to z similar to 1.