1,728 research outputs found
The Infrared-X-ray continuum correlation in Active Galactic Nuclei
The correlation between the soft X-ray and near infrared emission from AGN is
analysed using composite models by the code SUMA. We find new evidences for
differences in ranges of parameters which characterize the NLR of Seyfert
galaxies and LINERs. Results obtained by modelling the Einstein and the ROSAT
samples of galaxies are in full agreement. In order to fit the infrared and
X-ray continua, an eta factor is defined, which accounts for the emitting area
of the cloud. If the infrared emission is due to bremsstrahlung and comes from
the same cloud producing the soft X-rays, the eta values obtained from both
emissions must be the same. Therefore, if eta_IR < eta_soft-X there must be a
strong contribution of soft X-rays from the active centre. From the eta values
we expect to identify the objects that could present strong variability. \Comment: 11 pages,13 figures, in press in MNRAS. in press in MNRA
On the formation and physical properties of the Intra-Cluster Light in hierarchical galaxy formation models
We study the formation of the Intra-Cluster Light (ICL) using a semi-analytic
model of galaxy formation, coupled to merger trees extracted from N-body
simulations of groups and clusters. We assume that the ICL forms by (1) stellar
stripping of satellite galaxies and (2) relaxation processes that take place
during galaxy mergers. The fraction of ICL in groups and clusters predicted by
our models ranges between 10 and 40 per cent, with a large halo-to-halo scatter
and no halo mass dependence. We note, however, that our predicted ICL fractions
depend on the resolution: for a set of simulations with particle mass one order
of magnitude larger than that adopted in the high resolution runs used in our
study, we find that the predicted ICL fractions are ~30-40 per cent larger than
those found in the high resolution runs. On cluster scale, large part of the
scatter is due to a range of dynamical histories, while on smaller scale it is
driven by individual accretion events and stripping of very massive satellites,
, that we find to be the major contributors
to the ICL. The ICL in our models forms very late (below ), and a
fraction varying between 5 and 25 per cent of it has been accreted during the
hierarchical growth of haloes. In agreement with recent observational
measurements, we find the ICL to be made of stars covering a relatively large
range of metallicity, with the bulk of them being sub-solar.Comment: Accepted for Publication in MNRAS, 19 pages, 13 figures, 1 tabl
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