D. Vergani, M. Scodeggio, L. Pozzetti, A. Iovino, P. Franzetti, B. Garilli, G. Zamorani, D. Maccagni, F. Lamareille, O. Le FŤvre, S. Charlot, T. Contini, D. Bottini, V. Le Brun, J.-P. Picat, R. Scaramella, L. Tresse, G. Vettolani, A. Zanichelli, C. Adami, S. Arnouts, S. Bardelli, M. Bolzonella, A. Cappi, P. Ciliegi, S. Foucaud, I. Gavignaud, L. Guzzo, O. Ilbert, H. J. McCracken, B. Marano, C. Marinoni, A. Mazure, B. Meneux, R. Merighi, S. Paltani, R. PellÚ, A. Pollo, M. Radovich, E. Zucca, M. Bondi, A. Bongiorno, J. Brinchmann, O. Cucciati, S. de la Torre, L. Gregorini, Y. Mellier, P. Merluzzi, S. Temporin, C. J. Walcher
Aims. Investigating the history of mass assembly for galaxies of different stellar masses and types.
Methods. We select a mass limited sample of 4048 objects from the VIMOS VLT Deep Survey (VVDS) in the redshift interval 0.5 ≤ z ≤ 1.3. We then use an empirical criterion, based on the amplitude of 4000Å Balmer break (Dn4000) to separate the galaxy population in spectroscopically early- and late-type systems. The equivalent width of the [OII]3727 line is used as proxy for the star formation activity. We also derive typedependent stellar mass function in three redshift bins.
Results. We discuss to which extent stellar mass drives galaxy evolution, showing for the first time a direct comparison of stellar ages and stellar masses over the last 8 Gyr. Low-mass galaxies have small Dn4000 and at increasing stellar mass the galaxy distribution moves to higher Dn4000 values as observed in the local Universe (Kauffmann et al. 2004). We witness an increasing abundance of massive spectroscopically early-type systems at the expenses of the late-type systems with cosmic time. This spectral transformation of late-type systems into old massive galaxies at lower redshift, confirmed by the evolution of our type-dependent stellar mass function, is a process started at early epochs (z > 1.3) that continues efficiently down to the local Universe. The underlying stellar ages of late-type galaxies apparently do not show evolution, most likely as a result of a continuous and efficient formation of new stars. All star formation activity indicators consistently point towards a star formation history peaked in the past for massive galaxies, with little or no residual star formation taking place at all observed epochs. Vice-versa most of the low-mass systems show just the opposite characteristics with significant star formation still presents at all epochs. The activity and efficiency of forming stars are
mechanisms depending on galaxy stellar mass, resulting in a largely inefficient stellar mass assembly in massive systems up to z = 1.3. The concepts of downsizing in star formation and in mass (or archaeological downsizing) describe a single scenario which has a top-down evolutionary pattern in star formation as well as in mass assembly. The role of (dry) merging events seems to be only marginal at z < 1.3, as our estimated efficiency in stellar mass assembly can account for the progressive accumulation of observed passively evolving galaxies.
Astronomy and Astrophysics
Volume 487, Page 89