4,436 research outputs found
The Impact of Galaxy Formation on the Diffuse Background Radiation
The far infrared background is a sink for the hidden aspects of galaxy
formation. At optical wavelengths, ellipticals and spheroids are old, even at
Neither the luminous formation phase nor their early evolution is
seen in the visible. We infer that ellipticals and, more generally, most
spheroids must have formed in dust-shrouded starbursts. In this article, we
show how separate tracking of disk and spheroid star formation enables us to
infer that disks dominate near the peak in the cosmic star formation rate at z
\lapproxeq 2 and in the diffuse ultraviolet/optical/infrared background,
whereas spheroid formation dominates the submillimetre background.Comment: 12 pages, 5 figures, to appear in proceedings of IAU symp.204, "The
Extragalactic Infrared Background and its Cosmological Implications", Martin
Harwit and Michael G. Hauser, ed
Ultraviolet absorption lines in cosmic ray heated H I regions
Ultraviolet absorption lines in cosmic ray heated H I region
Star Formation-Regulated Growth of Black Holes in Protogalactic Spheroids
The observed relation between central black hole mass and spheroid velocity
dispersion is interpreted in terms of a self-regulation model that incorporates
a viscous Keplerian accretion disk to feed the black hole, embedded in a
massive, self-gravitating star forming disk that eventually populates the
spheroid. The model leads to a constant ratio between black hole mass and
spheroid mass which is equal to the inverse of the critical Reynolds number for
the onset of turbulence in the accretion disk surrounding the central black
hole. Applying the fundamental plane correlation for spheroids, we find that
the black hole mass has a power-law dependence on the spheroid velocity
dispersion with a slope in the range of 4-5. We explain the larger scatter in
the Magorrian relation with respect to the black hole mass-spheroid velocity
dispersion relationship as a result of secular evolution of the spheroid that
primarily affects its luminosity and to a much lesser extent its velocity
dispersion.Comment: 12 pages, no figures, submitted to ApJ Letter
On breaking the age-metallicity degeneracy in early-type galaxies: Outflows versus Star Formation Efficiency
A simple model of chemical enrichment in cluster early-type galaxies is
presented where the main parameters driving the formation of the stellar
component are reduced to four: infall timescale (tf), formation epoch (zF),
star formation efficiency (Ceff) and fraction of gas ejected in outflows
(Bout). We find that only variations in Bout or Ceff can account for the
colour-magnitude relation, so that the most luminous galaxies had low values of
ejected gas and high efficiencies. The combination of chemical enrichment
tracks with population synthesis models is used to explore the correlation
between mass-to-light ratios and masses. A significant slope mismatch is found
between stellar and total M/L ratios, which cannot be explained by an age
spread and implies a non-linear correlation between total and stellar mass. The
sequences driven by star formation efficiency and outflows are shown to predict
different trends at high redshift. Measurement of the dependence of the tilt of
the fundamental plane on redshift will break the degeneracy between outflows
and star formation efficiency, which will enable us to determine whether the
colour-magnitude relation is controlled by age or metallicity.Comment: 8 pages, 5 figures. To be published in MNRA
On the Fueling of Massive Black Holes and the Properties of their Host Spheroids
We study the relation between nuclear massive black holes and their host
spheroid gravitational potential. Using simple models, we analyze how gas is
expected to be transported in the nuclear regions of galaxies. When we couple
it with the expected gas lifetime given by the Kennicutt-Schmidt Law, this
naturally leads to the `M_BH - M_virial' and `M_BH - sigma' relations. We also
numerically test, using AMR simulations, our simple models for the mass
transport with satisfactory results.Comment: Reduced version that fit the 4-page limit. In press ApJ Letter
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