We studied the chronology of galactic bulge and disc formation by analysing the relative contributions of these components to the B-band rest-frame luminosity density at different epochs. We present the first estimate of the evolution of the fraction
of rest-frame B-band light in galactic bulges and discs since redshift z~0.8. We performed a bulge-to-disc decomposition of HST/ACS images of 3266 galaxies in the zCOSMOS-bright survey with spectroscopic redshifts in the range 0.7 < z < 0.9. We find that the fraction of B-band light in bulges and discs is $(26 pm 4)%$ and $(74 pm 4)%$, respectively. When compared with rest-frame B-band measurements of galaxies in the local Universe in the same mass range ($10^{9} M_{odot}lessapprox M lessapprox 10^{11.5} M_{odot}$), we find that the B-band light in discs decreases by ~30% from z~0.7-0.9 to z~0, while the light from the bulge increases by ~30% over the same period of time. We interpret this evolution as the consequence of star formation and mass assembly processes, as well as morphological transformation, which gradually shift stars formed at half the age of the Universe from star-forming late-type/irregular galaxies toearlier types and ultimately into spheroids.
[Abridged] We investigate the global galaxy evolution over 12 Gyr (0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a single homogeneous spectroscopi
c redshift sample, totalizing about 11000 galaxies. We estimate the rest-frame FUV luminosity function (LF) and luminosity density (LD), extract the dust attenuation of the FUV radiation using SED fitting, and derive the dust-corrected SFRD. We find a constant and flat faint-end slope alpha in the FUV LF at z<1.7. At z>1.7, we set alpha steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire range 0<z<4.5, and at z>2 it is on average brighter than in the literature, while phi* is smaller. Our total LD shows a peak at z=2, present also when considering all sources of uncertainty. The SFRD history peaks as well at z=2. It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag. As times goes by, the total SFRD is dominated by fainter and fainter galaxies. The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is compelling for models of galaxy formation. The mean dust attenuation A_FUV of the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2, reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after the SFRD peak, implying a contribution from the intermediate-mass stars to the dust production at z<2.
From the VIMOS VLT Deep Survey we use a sample of 6447 galaxies with I_{AB} < 24 to identify 251 pairs of galaxies, each member with a secure spectroscopic redshift, which are close in both projected separation and in velocity. We find that at z ~ 0.
9, 10.9 +/- 3.2 % of galaxies with M_B(z) < -18-Qz are in pairs with separations dr < 20 kpc/h, dv < 500 km/s, and with dM_B < 1.5, significantly larger than 3.76 +/- 1.71 % at z ~ 0.5; we find that the pair fraction evolves as (1+z)^m with m = 2.49 +/- 0.56. For brighter galaxies with M_B(z=0) < -18.77, the pair fraction is higher and its evolution with redshift is somewhat flatter with m=1.88 pm 0.40, a property also observed for galaxies with increasing stellar masses. Early type, dry mergers, pairs increase their relative fraction from 3 % at z ~ 0.9 to 12 % at z ~ 0.5. We find that the merger rate evolves as N_{mg}=(9.05 +/- 3.76) * 10^{-4}) * (1+z)^{2.43 +/- 0.76}. We find that the merger rate of galaxies with M_B(z) < -18-Qz has significantly evolved since z ~ 1. The merger rate is increasing more rapidly with redshift for galaxies with decreasing luminosities, indicating that the flat evolution found for bright samples is not universal. The merger rate is also strongly dependent on the spectral type of galaxies involved, late type mergers being more frequent in the past, while early type mergers are more frequent today, contributing to the rise in the local density of early type galaxies. About 20 % of the stellar mass in present day galaxies with log(M/M_{sun}) > 9.5 has been accreted through major merging events since z ~ 1, indicating that major mergers have contributed significantly to the growth in stellar mass density of bright galaxies over the last half of the life of the Universe.
