Catálogo de publicaciones - libros

The high- progenitors of local massive early-type galaxies should be characterized by a strong level of clustering, larger than that measured for =3 Lyman Break Galaxies and comparable to that of ~ 1 EROs. First possible evidences for such strongly clustered objects at were found by the FIRES and K20 surveys, that have identified new classes of faint high- K-selected galaxies. Some details are given here for the new population of massive star-forming galaxies at ~ 2, found by the K20 survey in the GOODS-South area. Because of their much redder UV continuum, most of these galaxies would not be selected by the Lyman Break criterion. Such objects are good candidates for the precursors of local ellipticals caught in their formation phase. We have calibrated a two color criterion to allow the identification of these highest redshift galaxies in bright K-limited samples.

Determination of the star formation rate can be done using mid-IR photometry or Balmer line luminosity after a proper correction for extinction effects. Both methods show convergent results while those based on UV or on [OII]3727 luminosities underestimate the SFR by factors ranging from 5 to 40 for starbursts and for luminous IR galaxies, respectively. Most of the evolution of the cosmic star formation density is related to the evolution of luminous compact galaxies and to luminous IR galaxies. Because they were metal deficient and were forming stars at very high rates (40 to 100 M yr), it is probable that these (massive) galaxies were actively forming the bulk of their stellar/metal content at z ≤ 1.

The plethora of high redshift multifrequency surveys currently under way, that were extensively illustrated at this meeting will shortly provide us with a sequence of “fossil” galaxies, eventually disclosing the secret of their evolution, much as fossil organisms guided paleontologists tracing the evolution of species. Meanwhile we wish to remind to both theorists and to observers that the characterization of local galaxies, representing the boundary condition at =0 of any evolutionary model, is not yet fully achieved. With this purpose we conceived an extensive observational campaign aimed at providing the phenomenology of local galaxies in the broadest possible frequency range. We took observations and collected data from the literature for over 3600 local (<0.03) galaxies, mainly members to rich clusters, spending a large effort in making the literature data as homogeneous as possible with our own. The data cover the range from 2000 Å (UV) to the centimetric radio domain. The Web site “GOLDmine” (Galaxy On Line Database Milano Network) [10] is designed to provide world-wide access to this massive data-set on local galaxies.

We present new stellar population models that include the contribution of the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase also in the synthetic spectral energy distribution (SED). The TP-AGB phase is essential for a correct modeling of intermediate-age (0.2  /Gyr  1÷2) stellar populations, because it provides ~ 40% of the bolometric contribution, and up to ~ 80% of that in the -band. These models are obtained by coupling the energetic of the TP-AGB phase as calibrated with data of Magellanic Clouds star clusters [9], with empirical spectra of TP-AGB stars [3]. Now that the Spitzer Space Telescope (SST) allows the sigth of the rest-frame IR at high redshifts, these models provide the opportunity to use the TP-AGB phase as an age indicator also for high-redshift stellar populations. Here we focus on redshift ~ 3 and provide predictions of the colours of various galaxy models as will be measured by means of the IRAC imaging instrument on board the SST. We find a sizable magnitude difference between TP-AGB-dominated high-redshift stellar populations and those being older or younger. The first releases of GOODS data should allow a check of these predictions.

Using our models of absorption line indices that account for variable abundance ratios, we derive ages, total metallicities, and element abundance ratios of 126 early-type galaxies in various environments. The data are analyzed by comparison with mock galaxy samples created through Monte Carlo simulations taking the typical average observational errors into account, in order to eliminate artifacts caused by correlated errors. We find that all three parameters age, metallicity, and /Fe ratio are correlated with velocity dispersion. We further find evidence for an influence of the environment on the stellar population properties. Massive early-type galaxies in low-density environments appear on average several Gyrs younger and ~ 0.1 dex more metal-rich than their counterparts in clusters. No offsets in the /Fe ratios, instead, are detected. With the aid of a simple chemical evolution model, we translate the derived ages and /Fe ratios into star formation histories. We show that most star formation activity in early-type galaxies is expected to have happened between redshifts ~ 3 and 5 in high density and between redshifts 2 and 3 in low density environments.

Breaking age/metallicity degeneracy ([19], [1]) is crucial for understanding stellar populations in elliptical galaxies. Spectroscopic properties, such as line strength, can partially break age/metallicity degeneracy. Reference [19] found that H index, defined in [4] (Lick indices), is relatively sensitive to luminosity-weighted age of galaxies. But emission line makes H shallower, therefore correction of emission line effect is necessary. H and H indices, such as H, H, H and H, which are less affected by emission than H, are defined in [8] and [20]. However, those indices are still affected by age/metallicity degeneracy, since they are measured on low resolution spectra (9–11 Å). Reference [8] defined H to find it strongly sensitive to age. But H is much affected by velocity dispersion () of galaxies, since the bandpasses of feature and pseudocontinua are very narrow.

The properties of early-type galaxies drawn from the SDSS database depend weakly, but significantly, on environment. Objects in regions of lower density tend to have slightly lower luminosities, velocity dispersions, bluer colors, and to be less homogeneous than objects in denser cluster-like regions. The chemical abundances of early-type galaxies drawn from the SDSS database also depend weakly on environment. Since chemical abundances also evolve with redshift, the observed trends constrain how strongly the luminosity weighted age depends on environment, provided the low redshift population is simply a passively aged version of the more distant population. The constraint does not depend on the detailed properties of stellar population synthesis models.

We present observations of galaxy environmental dependencies using data from the 2dF Galaxy Redshift Survey. From a combined analysis of the luminosity function, Butcher-Oemler effect and trends in H line strengths we find support for a model where galaxy properties are mainly set by initial conditions at the time of their formation.

We discuss the detectability of the sources responsible for reionization with existing and planned telescopes. Our approach is based on the number of UV photons required for reionization and depends on relatively few undetermined parameters. We conclude that if the reionization sources are UV-efficient, minimum-luminosity sources, it may be difficult to detect them before the launch of the James Webb Space Telescope. Until then, the best approach may be either to exploit gravitational lensing by clusters of galaxies, or to search for strong Ly emission by narrow-band imaging or slitless grism spectroscopy.

The Cosmic Evolution Survey (COSMOS) will provide complete multi-wavelength imaging and spectroscopy of a 2 equatorial field aimed at sampling the full range of cosmological environments from voids to massive clusters to understand the coupled evolution of dark matter, luminous galaxies and clusters and AGN in the epoch of maximum formation activity from = 0.5 to 3. The COSMOS survey has several major primary components: 1) HST-ACS imaging covering the entire field in I-band (8100Å); 2) ground-based broadband imaging (Subaru, NOAO and CFHT) providing photometric redshifts (typical accuracy 10%); 3) low resolution optical spectra (R = 200 with VLT-VIMOS) for 90,000 galaxies with I < 25 mag. Over 60 astronomers from Europe, North America and Japan are actively involved in COSMOS multi- observations and science.