3,517 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
One-zone models for spheroidal galaxies with a central supermassive black-hole. Self-regulated Bondi accretion
By means of a one-zone evolutionary model, we study the co-evolution of
supermassive black holes and their host galaxies, as a function of the
accretion radiative efficiency, dark matter content, and cosmological infall of
gas. In particular, the radiation feedback is computed by using the
self-regulated Bondi accretion. The models are characterized by strong
oscillations when the galaxy is in the AGN state with a high accretion
luminosity. We found that these one-zone models are able to reproduce two
important phases of galaxy evolution, namely an obscured-cold phase when the
bulk of star formation and black hole accretion occur, and the following
quiescent hot phase in which accretion remains highly sub-Eddington. A
Compton-thick phase is also found in almost all models, associated with the
cold phase. An exploration of the parameter space reveals that the closest
agreement with the present-day Magorrian relation is obtained, independently of
the dark matter halo mass, for galaxies with a low-mass seed black hole, and
the accretion radiative efficiency ~0.1.Comment: Accepted for publication in A&A, 12 pages, 5 figure
Radial-orbit instability in modified Newtonian dynamics
The stability of radially anisotropic spherical stellar systems in modified
Newtonian dynamics (MOND) is explored by means of numerical simulations
performed with the N-body code N-MODY. We find that Osipkov-Merritt MOND models
require for stability larger minimum anisotropy radius than equivalent
Newtonian systems (ENSs) with dark matter, and also than purely baryonic
Newtonian models with the same density profile. The maximum value for stability
of the Fridman-Polyachenko-Shukhman parameter in MOND models is lower than in
ENSs, but higher than in Newtonian models with no dark matter. We conclude that
MOND systems are substantially more prone to radial-orbit instability than ENSs
with dark matter, while they are able to support a larger amount of kinetic
energy stored in radial orbits than purely baryonic Newtonian systems. An
explanation of these results is attempted, and their relevance to the MOND
interpretation of the observed kinematics of globular clusters, dwarf
spheroidal and elliptical galaxies is briefly discussed.Comment: 9 pages, 4 figures, accepted for publication in MNRA
Feedback from Central Black Holes in Elliptical Galaxies: Two-dimensional Models Compared to One-dimensional Models
We extend the black hole (BH) feedback models of Ciotti, Ostriker, and Proga
to two dimensions. In this paper, we focus on identifying the differences
between the one-dimensional and two-dimensional hydrodynamical simulations. We
examine a normal, isolated galaxy subject to the cooling flow instability
of gas in the inner regions. Allowance is made for subsequent star formation,
Type Ia and Type II supernovae, radiation pressure, and inflow to the central
BH from mildly rotating galactic gas which is being replenished as a normal
consequence of stellar evolution. The central BH accretes some of the infalling
gas and expels a conical wind with mass, momentum, and energy flux derived from
both observational and theoretical studies. The galaxy is assumed to have low
specific angular momentum in analogy with the existing one-dimensional case in
order to isolate the effect of dimensionality. The code then tracks the
interaction of the outflowing radiation and winds with the galactic gas and
their effects on regulating the accretion. After matching physical modeling to
the extent possible between the one-dimensional and two-dimensional treatments,
we find essentially similar results in terms of BH growth and duty cycle
(fraction of the time above a given fraction of the Eddington luminosity). In
the two-dimensional calculations, the cool shells forming at 0.1--1 kpc from
the center are Rayleigh--Taylor unstable to fragmentation, leading to a
somewhat higher accretion rate, less effective feedback, and a more irregular
pattern of bursting compared to the one-dimensional case.Comment: 15 pages, 10 figures, ApJ 237:26. Updated to match published versio
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
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