Journal article

The zCOSMOS redshift survey: evolution of the light in bulges and discs since z similar to 0.8

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 similar to 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 4)% and (74 4)%, respectively. When compared with rest-frame B-band measurements of galaxies in the local Universe in the same mass range (10(9)M circle dot M10(11.5).M circle dot),we find that the B-band light in discs decreases by -30% from z similar to 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 to earlier types and ultimately into spheroids.


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