186 research outputs found
AGN feedback in numerical simulations
The passively evolving stellar population in elliptical galaxies (Es)
provides a continuous source of fuel for accretion on the central supermassive
black hole (SMBH), which is 1) extended over the entire galaxy life (but
declining with cosmic time), 2) linearly proportional to the stellar mass of
the host spheroid, 3) summing up to a total gas mass that is >100 times larger
than the currently observed SMBH masses, 4) available independently of merging
events. The main results of numerical simulations of Es with central SMBH, in
which a physically based implementation of radiative and mechanical feedback
effects is considered, are presented.Comment: 1 page, no figures. Invited talk to Joint Discussion 08 "Hot
Interstellar Matter in Elliptical Galaxies". To appear in Highlights of
Astronomy, Vol. 15, Proc. of the XXVIIth IAU General Assembly, Rio de
Janeiro, Brazil, August 2009, eds. D.-W. Kim and S. Pellegrini, Cambridge
University Pres
Galaxy formation from dry and hydro simulations
The effects of dry and wet merging on the Scaling Laws (SLs) of elliptical
galaxies (Es) are discussed. It is found that the galaxy SLs, possibly
established at high redshift by the fast collapse of gas-rich and clumpy
stellar distributions in preexisting dark matter halos following the
cosmological SLs, are compatible with a (small) number of galaxy mergers at
lower redshift.Comment: 1 page, no figures. Invited talk to Joint Discussion 01 "Dark Matter
in Early-Type Galaxies". To appear in Highlights of Astronomy, Vol. 15, Proc.
of the XXVIIth IAU General Assembly, Rio de Janeiro, Brazil, August 2009,
eds. L.V.E. Koopmans and T. Treu, Cambridge University Pres
Dynamical Friction from field particles with a mass spectrum
The analytical generalization of the classical dynamical friction formula
(derived under the assumption that all the field particles have the same mass)
to the case in which the masses of the field particles are distributed with a
mass spectrum is presented. Two extreme cases are considered: in the first,
energy equipartition is assumed, in the second all the field particles have the
same (Maxwellian) velocity distribution. Three different mass spectra are
studied in detail, namely the exponential, discrete (two components), and
power-law cases. It is found that the dynamical friction deceleration can be
significantly stronger than in the equivalent classical case, with the largest
differences (up to a factor of 10 or more in extreme cases) arising for test
particle velocities comparable to the mass-averaged velocity dispersion of the
field particles. The present results are relevant to our understanding of the
dynamical evolution of globular clusters, in particular in the modelization of
mass segregation and sedimentation of Blue Straggler stars and Neutron stars,
and for the study of binary black holes in galactic nuclei.Comment: 12 pages, 3 figures, proceedings of the international symposium
"Plasmas in the laboratory and in the universe: interactions, patterns, and
turbulence", Como 1-4 Dec. 2009, eds. G. Bertin et al., AIP Conf. Se
Stellar systems following the R^1/m luminosity law, IV : the total energy and the central concentration of galaxies
We expand our previous analytical and numerical studies of the family of Sérsic models, which are routinely used to describe early-type galaxies and the bulges of spiral galaxies. In particular, we focus on the total energy budget, an important dynamical property that has not been discussed in detail in previous works. We use two different methods to calculate the total energy for the Sérsic model family that result in two independent expressions that can be used along the entire sequence of Sérsic models. We use these expressions to investigate whether the Spitzer concentration index is a reliable measure for the intrinsic 3D concentration of galaxies, and we conclude that it is not a very useful measure for the central concentration. The popular Third Galaxy Concentration index, on the other hand, is shown to be a reliable measure for the intrinsic 3D concentration, even though it is based on the surface brightness distribution and not on the intrinsic 3D density
Stellar systems following the luminosity law. III. Photometric, intrinsic, and dynamical properties for all S\'ersic indices
The S\'ersic or model has become the de facto standard model to
describe the surface brightness profiles of early-type galaxies and the bulges
of spiral galaxies. The photometric, intrinsic, and dynamical properties of
this model have been investigated, but mainly for fairly large S\'ersic indices
. For small values of , appropriate for low-mass and dwarf ellipticals, a
detailed investigation of these properties is still lacking. In this study, we
used a combination of numerical and analytical techniques to investigate the
S\'ersic model over the entire range of S\'ersic parameters, focussing on the
small regime, where a number of interesting and surprising properties are
found. For all values , the model is characterised by a finite central
luminosity density, and for , even a central depression in the
luminosity density profile. This behaviour translates to the dynamical
properties: we show that all S\'ersic models with can be
supported by an isotropic velocity dispersion tensor, and that these isotropic
models are stable to both radial and non-radial perturbations. The models with
, on the other hand, cannot be supported by an isotropic velocity
dispersion tensor.Comment: 10 pages, 5 figures, accepted for publication in A&
X-ray haloes and star formation in early-type galaxies
High resolution 2D hydrodynamical simulations describing the evolution of the
hot ISM in axisymmetric two-component models of early-type galaxies well
reproduced the observed trends of the X-ray luminosity () and
temperature () with galaxy shape and rotation, however they also
revealed the formation of an exceedingly massive cooled gas disc in rotating
systems. In a follow-up of this study, here we investigate the effects of star
formation in the disc, including the consequent injection of mass, momentum and
energy in the pre-existing interstellar medium. It is found that subsequent
generations of stars originate one after the other in the equatorial region;
the mean age of the new stars is Gyr, and the adopted recipe for star
formation can reproduce the empirical Kennicutt-Schmidt relation. The results
of the previous investigation without star formation, concerning
and of the hot gas, and their trends with galactic shape and
rotation, are confirmed. At the same time, the consumption of most of the cold
gas disc into new stars leads to more realistic final systems, whose cold gas
mass and star formation rate agree well with those observed in the local
universe. In particular, our models could explain the observation of
kinematically aligned gas in massive, fast-rotating early-type galaxies.Comment: 20 pages, 10 figures, 5 tables. Accepted for publication in MNRA
The effects of stellar dynamics on the X-ray emission of flat early-type galaxies
Observational and numerical studies gave hints that the hot gaseous haloes of
ETGs may be sensitive to the galaxy internal kinematics. By using high
resolution 2D hydro simulations, and realistic two-component (stars plus dark
matter) axisymmetric galaxy models, we study the evolution of the hot haloes in
a suite of flat ETGs of fixed mass distribution, but with variable amounts of
azimuthal velocity dispersion and rotational support, including the possibility
of a counter-rotating inner stellar disc. The hot halo is fed by stellar mass
losses and heated by SNIa explosions and thermalization of stellar motions. We
measure the value of the thermalization parameter gamma (the ratio between the
heating due to the relative velocity between the stellar streaming and the ISM
bulk flow, and the heating attainable by complete thermalization of the stellar
streaming motions). We find that 1) the X-ray emission and the average
temperature are larger in fully velocity dispersion supported systems; 2)
0.1<gamma<0.2 for isotropic rotators (with a trend for being larger for lower
dark mass models); 3) systems that are isotropic rotators at large radii with
an inner counter-rotating disc, or fully velocity dispersion supported systems
with an inner rotating disc, have gamma=1, again with a trend to increase for
lower dark mass contents. We also find that the lower X-ray luminosities of
isotropic rotators cannot be explained just by their low gamma, but are due to
the complicated flow structure, consequence of the angular momentum stored at
large radii. X-ray emission weighted temperatures and luminosities nicely match
observed values; the X-ray isophotes are boxy in case of significant galaxy
rotation. Overall, it is found that rotation has an important role to explain
the observational result that more rotationally supported ETGs on average show
a lower X-ray emission [abridged].Comment: 22 pages, 13 figures, accepted for publication in MNRAS. Comments
welcom
The Effects of Galaxy Shape and Rotation on the X-ray Haloes of Early-Type Galaxies
We present a detailed diagnostic study of the observed temperatures of the
hot X-ray coronae of early-type galaxies. By extending the investigation
carried out in Pellegrini (2011) with spherical models, we focus on the
dependence of the energy budget and temperature of the hot gas on the galaxy
structure and internal stellar kinematics. By solving the Jeans equations we
construct realistic axisymmetric three-component galaxy models (stars, dark
matter halo, central black hole) with different degrees of flattening and
rotational support. The kinematical fields are projected along different lines
of sight, and the aperture velocity dispersion is computed within a fraction of
the circularized effective radius. The model parameters are chosen so that the
models resemble real ETGs and lie on the Faber-Jackson and Size-Luminosity
relations. For these models we compute T_* (the stellar heating contribution to
the gas injection temperature) and T_gm (the temperature equivalent of the
energy required for the gas escape). In particular, different degrees of
thermalisation of the ordered rotational field of the galaxy are considered. We
find that T_* and T_gm can vary only mildly due to a pure change of shape.
Galaxy rotation instead, when not thermalised, can lead to a large decrease of
T_*; this effect can be larger in flatter galaxies that can be more
rotationally supported. Recent temperature measurements T_x, obtained with
Chandra, are larger than, but close to, the T_* values of the models, and show
a possible trend for a lower T_x in flatter and more rotationally supported
galaxies; this trend can be explained by the lack of thermalisation of the
whole stellar kinetic energy. Flat and rotating galaxies also show lower L_x
values, and then a lower gas content, but this is unlikely to be due to the
small variation of T_gm found here for them.Comment: 16 pages, 7 figures, accepted for publication in MNRA
Disk dynamics and the X-ray emission of S0 and flat early-type galaxies
With 2D hydrodynamical simulations, we study the evolution of the hot gas
flows in early-type galaxies, focussing on the effects of galaxy rotation on
the thermal and dynamical status of the ISM. The galaxy is modelled as a
two-component axisymmetric system (stars and dark matter), with a variable
amount of azimuthal velocity dispersion and rotational support; the presence of
a counter rotating stellar disk is also considered. It is found that the ISM of
the rotationally supported (isotropic) model is more prone to thermal
instabilities than the fully velocity dispersion counterpart, while its ISM
temperature and X-ray luminosity are lower. The model with counter rotation
shows an intermediate behaviour.Comment: 2 pages, 2 figures. Proceedings of the International Conference
"X-ray Astronomy: towards the next 50 years!", Milan, 1-5 Oct 201
- …