162 research outputs found
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 in the equatorial
plane of a few hundreds and a typical covering factor of over . 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
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Dynamical and photometric imprints of feedback processes on the early evolution of E/S0 galaxies
We show that the observed Velocity Dispersion Function of E/S0 galaxies
matches strikingly well the distribution function of virial velocities of
massive halos virializing at z > 1.5, as predicted by the standard hierarchical
clustering scenario in a \LambdaCDM cosmology, for a constant ratio sigma/V_vir
= 0.55 \pm 0.05, close to the value expected at virialization if it typically
occurred at z > 3. This strongly suggests that dissipative processes and later
merging events had little impact on the matter density profile. Adopting the
above sigma/V_vir ratio, the observed relationships between photometric and
dynamical properties which define the fundamental plane of elliptical galaxies,
such as the luminosity-sigma (Faber-Jackson) and the luminosity-effective
radius relations, as well as the M_BH-sigma relation, are nicely reproduced.
Their shapes turn out to be determined by the mutual feedback of star-formation
(and supernova explosions)and nuclear activity, along the lines discussed by
Granato et al. (2004). To our knowledge, this is the first semi-analytic model
for which simultaneous fits of the fundamental plane relations and of the
epoch-dependent luminosity function of spheroidal galaxies have been presented.Comment: 14 pages, 6 figures, submitted to Ap
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