Dust and Nebular Emission in Star Forming Galaxies

Star forming galaxies exhibit a variety of physical conditions, from quiescent normal spirals to the most powerful dusty starbursts. In order to study these complex systems, we need a suitable tool to analyze the information coming from observations at all wavelengths. We present a new spectro-photometric model which considers in a consistent way starlight as reprocessed by gas and dust. We discuss preliminary results to interpret some observed properties of VLIRGs.Comment: 8 pages, to be published in "The link between stars and cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico, by Kluwer, eds. M. Chavez, A. Bressan, A. Buzzoni, and D. Mayy

Dust Enshrouded AGN Models for Hyperluminous High Redshift IR Galaxies

We investigate models for the power supply and broad-band spectral energy distribution (SED) of hyperluminous IR galaxies, recently discovered at high redshifts, in terms of the emission from an active nucleus embedded in a torus-like dusty structure. We find consistent solutions in terms of a simple torus model extended several hundreds of parsecs, with $A_V$ in the equatorial plane of a few hundreds and a typical covering factor of over $50\%$. Objects as different as the prototype high-z galaxy \fd, the z=0.93 IR object \fq, \fz\ found in a high-z cooling flow, and the optically selected BAL "Cloverleaf" quasar, are all fitted by the same solution, for decreasing values of the polar angle to the line-of-sight and proper scaling of the luminosities. We suggest that such luminous high-z IR objects are heavily buried quasars surrounded by large amounts of dust with high covering factors and large optical depths. Comparison with UVX QSOs suggests that they are observed during a transient phase. Forthcoming observations in the far-IR will soon allow probing this phase and its relationship with the -- possibly concomitant -- formation of the nuclear black hole and of the host galaxy.Comment: 12 pages including 3 figures. To appear on APJ

Brightest cluster galaxies in cosmological simulations: achievements and limitations of AGN feedback models

We analyze the basic properties of Brightest Cluster Galaxies (BCGs) produced by state of the art cosmological zoom-in hydrodynamical simulations. These simulations have been run with different sub-grid physics included. Here we focus on the results obtained with and without the inclusion of the prescriptions for supermassive black hole (SMBH) growth and of the ensuing Active Galactic Nuclei (AGN) feedback. The latter process goes in the right direction of decreasing significantly the overall formation of stars. However, BCGs end up still containing too much stellar mass, a problem that increases with halo mass, and having an unsatisfactory structure. This is in the sense that their effective radii are too large, and that their density profiles feature a flattening on scales much larger than observed. We also find that our model of thermal AGN feedback has very little effect on the stellar velocity dispersions, which turn out to be very large. Taken together, these problems, which to some extent can be recognized also in other numerical studies typically dealing with smaller halo masses, indicate that on one hand present day sub-resolution models of AGN feedback are not effective enough in diminishing the global formation of stars in the most massive galaxies, but on the other hand they are relatively too effective in their centers. It is likely that a form of feedback generating large scale gas outflows from BCGs precursors, and a more widespread effect over the galaxy volume, can alleviate these difficulties.Comment: 17 pages, 14 figures, accepted for publication on MNRAS, comments welcom