30 research outputs found
The Relation between Nuclear Activity and Stellar Mass in Galaxies
The existence of correlations between nuclear properties of galaxies, such as
the mass of their central black holes, and larger scale features, like the
bulge mass and luminosity, represent a fundamental constraint on galaxy
evolution. Although the actual reasons for these relations have not yet been
identified, it is widely believed that they could stem from a connection
between the processes that lead to black hole growth and stellar mass assembly.
The problem of understanding how the processes of nuclear activity and star
formation can affect each other became known to the literature as the
Starburst-AGN connection. Despite years of investigation, the physical
mechanisms which lie at the basis of this relation are known only in part. In
this work, we analyze the problem of star formation and nuclear activity in a
large sample of galaxies. We study the relations between the properties of the
nuclear environments and of their host galaxies. We find that the mass of the
stellar component within the galaxies of our sample is a critical parameter,
that we have to consider in an evolutionary sequence, which provides further
insight in the connection between AGN and star formation processes.Comment: 13 pages, 10 figures, accepted for publication on MNRAS. Reference to
the mass derivation procedure correcte
The role of dark matter in the galaxy mass-size relationship
The observed relationship between stellar mass and effective radius for early
type galaxies, pointed out by many authors, is interpreted in the context of
Clausius' virial maximum theory. In this view, it is strongly underlined that
the key of the above mentioned correlation is owing to the presence of a deep
link between cosmology and the existence of the galaxy Fundamental Plane. Then
the ultimate meaning is: understanding visible mass - size correlation and/or
Fundamental Plane means understanding how galaxies form. The mass - size
relationship involves baryon (mainly stellar) mass and its typical dimension
related to the light, but it gets memory of the cosmological mass variance at
the equivalence epoch. The reason is that the baryonic component virializes by
sharing virial energy in about equal amount between baryons and dark matter,
this sharing depending, in turn, on the steepness of the dark matter
distribution. The general strategy consists in using the two-component tensor
virial theorem for determining the virialized baryonic configurations. A King
and a Zhao density profile are assumed for the inner baryonic and the outer
dark matter component, respectively, at the end of the relaxation phase. All
the considerations are restricted to spherical symmetry for simplicity. The
effect of changing the dark-to-baryon mass ratio, m, is investigated inside a
LambdaCDM scenario. A theoretical mass - size relation is expressed for the
baryonic component, which fits fairly well to the data from a recently studied
galaxy sample. Finally, the play of intrinsic dispersion on the mass ratio, m,
is discussed in the light of the cusp/core problem and some consequences are
speculated about the existence of a limit, m_l, expected by the theory.Comment: 36 pages, 8 figures (Accepted for publication in New Astronomy
On the tilt of Fundamental Plane by Clausius' virial maximum theory
The theory of the Clausius' virial maximum to explain the Fundamental Plane
(FP) proposed by Secco (2000, 2001,2005) is based on the existence of a maximum
in the Clausius' Virial (CV) potential energy of a early type galaxy (ETG)
stellar component when it is completely embedded inside a dark matter (DM)
halo. At the first order approximation the theory was developed by modeling the
two-components with two cored power-law density profiles. An higher level of
approximation is now taken into account by developing the same theory when the
stellar component is modeled by a King-model with a cut-off. Even if the DM
halo density remains a cored power law the inner component is now more
realistic for the ETGs. The new formulation allows us to understand more deeply
what is the dynamical reason of the FP tilt and in general how the CV theory
may really be the engine to produce the FP main features. The degeneracy of FP
in respect to the initial density perturbation spectrum may be now full
understood in a CDM cosmological scenario. A possible way to compare the FPs
predicted by the theory with those obtained by observations is also
exemplified.Comment: 35 pages, 8 figure
The hybrid solution for the Fundamental Plane
By exploiting the database of early-type galaxies (ETGs) members of the WINGS
survey of nearby clusters, we address here the long debated question of the
origin and shape of the Fundamental Plane (FP). Our data suggest that different
physical mechanisms concur in shaping and tilting the FP with respect to the
virial plane (VP) expectation. In particular, an hybrid solution in which the
structure of galaxies and their stellar population are the main contributors to
the FP tilt seems to be favoured. We find that the bulk of the tilt should be
attributed to structural non-homology, while stellar population effects play an
important but less crucial role. Our data indicate that the differential FP
tilt between the V and K-band is due to a sort of entanglement between
structural and stellar population effects, for which the inward steepening of
color profiles (V-K) tends to increase at increasing the stellar mass of ETGs.
The same analysis applied to the ATLAS3D and SDSS data in common with WINGS
(WSDSS throughout the paper) confirms our results, the only remarkable
difference being the less important role of the stellar mass-to-light-ratio in
determining the FP tilt. The ATLAS3D data also suggest that the tilt depends as
well on the dark matter (DM) fraction and on the rotational contribution to the
kinetic energy (Vrot/sigma). We show that the global properties of the FP can
be understood in terms of the underlying correlation among mass, structure and
stellar population of ETGs, for which, at increasing the stellar mass, ETGs
become (on average) older and more centrally concentrated. Finally, we show
that a Malmquist-like selection effect may mimic a differential evolution of
the mass-to-light ratio for galaxies of different masses. This should be taken
into account in the studies investigating the amount of the so called
downsizing phenomenon.Comment: 22 pages, 17 figure
Nuclear activity and stellar mass in galaxies
It is widely believed that the correlations between Supermassive Black Holes and host galaxies descend from a connection between black hole growth and stellar mass assembly. Here we present the results of our investigation on star formation a nd nuclear activity, studying the relations between the circum-nuclear environments of both active and quiescent galaxies. We find that the mass of the stellar component is a critical paramete r that we have to consider to gain further insight into the connection between AGN and star formation processes
Toward Understanding the origin of the Fundamental Plane for Early-Type Galaxies
We present a panoramic review of several observational and theoretical
aspects of the modern astrophysical research about the origin of the
Fundamental Plane (FP) relation for Early-Type Galaxies (ETGs). The discussion
is focused on the problem of the tilt and the tightness of the FP, and on the
attempts to derive the luminosity evolution of ETGs with redshift. Finally, a
number of observed features in the FP are interpreted from the standpoint of a
new theoretical approach based on the two-component tensor virial theorem.Comment: 30 pages, 3 figure