People involved at OAB: Lanzoni, Mignoli, Pozzetti, Zamorani.
The Bologna Observatory participates, with the observatories of Arcetri, ESO and Rome, in an ESO VLT Large Program (PI Cimatti, Arcetri Obs.), which started in 1999. This program (called K20 ) aims at deriving the redshift distribution of a galaxy sample complete at in order to obtain stringent clues on the formation and evolution of present-day massive galaxies (Cimatti et al. 2002). The sample consists of about 500 galaxies selected from a sub-area of the Chandra Deep Field (CDF) and from a field around the quasar 00552659 (). Seventeen VLT nights have been allocated to this project over a period of two years. The survey makes use of both optical (FORS1/FORS2) and near-IR (ISAAC) spectroscopy. The observations were completed in 2000. In addition, ultradeep spectroscopy was obtained in November 2002 with FORS2 to derive information on previously unidentified EROs and galaxies. We have provided spectra of 92% of the galaxies down to a completeness level of about . Moreover, the K20 survey is triggering several follow up studies in which we are involved. High resolution spectroscopy (PI Cimatti) was recently obtained with FORS2 to study the kinematics of galaxies in order to estimate their dynamical masses. The CDFS sub-area of the K20 survey is also a target of the HST+ACS GOODS Treasury Programme (PI Giavalisco) and of the SIRTF GOODS (PI Dickinson) Legacy Programme.
The scientific analysis is still in progress and the main results obtained up to now can be summarized as follows (details can be found also in the previous reports):
This year we have completed, in collaboration with the Rome Observatory, the study of the Galaxy Stellar Mass Function and its evolution to (Fontana, Pozzetti et al. 2004, in press). We found that the typical mass-to-light ratio of massive early type galaxies is larger than that of less massive ones, suggesting that their stellar population formed at higher . The final K20 galaxy sample spans a range of stellar masses from to : massive galaxies ( ) are common at , and are detected also up to . The Galaxy Stellar Mass Function shows only a mild evolution (i.e. by 20-30%) up to . At , the evolution in the GSMF appears to be much faster: at , about 35% of the present day stellar mass in objects with appears to have assembled. Moreover we found that at , all galaxies with are early type, while at higher a population of massive star-forming galaxies progressively appears. The predictions from hierarchical models range from severe underestimates to slight overestimates of the observed mass density at (see Fig. 9).
From ultradeep spectroscopy we have furthermore investigated the population of galaxies (Daddi et al. 2004). We found a new population of massive galaxies, with HST irregular morphology, and with multi-band photometry and average spectrum consistent with high star formation rate absorbed by a large amount of dust, young stellar populations and high metallicity (De Mello et al. 2004, in press). This population is consistent with being the progenitor of massive local ellipticals.
At present, in Bologna, we are completing the analysis of the spectroscopic K20 sample, both studying the properties of the single object spectra, and constructing average templates for different spectral classes and/or different redshift bins, with the aim of characterizing a possible spectral evolution. In addition, we are collaborating with Arcetri in the study of the star formation history using different SFR indicator ([OII], H, UV flux) up to .
Finally, in collaboration with the Arcetri Observatory (Alighieri, Cimatti, Vernet) we are involved in the analysis of the high resolution spectra of a subsample of early and late type galaxies at , recently obtained. In particular we are carrying out the spectral analysis of early type galaxies using high resolution model templates (Bruzual & Charlot 2003) to derive new constraints on their stellar population and on the epoch of formation of massive elliptical galaxies. Moreover, we are comparing the dynamical properties, derived from high-resolution spectra of both elliptical and spiral galaxies, with those obtained by the hierarchical model GalICs (Hatton et al. 2003). From observations we found well defined scaling relations, as the Tully-Fisher and the Fundamental Plane. Preliminary results show that model galaxies define scaling relations similar to those observed, even if the zero point and scatter appear not to be exactly the same. A more detailed comparison and the interpretation of results in terms of the capability of the hierarchical scenario in describing galaxy formation is still in progress.