113 research outputs found
Environmental Influences on the Morphology and Dynamics of Group Size Haloes
We use group size haloes identified with a ``friends of friends'' (FOF)
algorithm in a concordance GADGET2 (dark matter only)
simulation to investigate the dependence of halo properties on the environment
at . The study is carried out using samples of haloes at different
distances from their nearest massive {\em cluster} halo. We find that the
fraction of haloes with substructure typically increases in high density
regions. The halo mean axial ratio also increases in overdense regions,
a fact which is true for the whole range of halo mass studied. This can be
explained as a reflection of an earlier halo formation time in high-density
regions, which gives haloes more time to evolve and become more spherical.
Moreover, this interpretation is supported by the fact that, at a given
halo-cluster distance, haloes with substructure are more elongated than their
equal mass counterparts with no substructure, reflecting that the virialization
(and thus sphericalization) process is interrupted by merger events. The
velocity dispersion of low mass haloes with strong substructure shows a
significant increase near massive clusters with respect to equal mass haloes
with low-levels of substructure or with haloes found in low-density
environments. The alignment signal between the shape and the velocity ellipsoid
principal axes decreases going from lower to higher density regions, while such
an alignment is stronger for haloes without substructure. We also find, in
agreement with other studies, a tendency of halo major axes to be aligned and
of minor axes to lie roughly perpendicular with the orientation of the filament
within which the halo is embedded, an effect which is stronger in the proximity
of the massive clusters.Comment: 11 pages, 12 figures, accepted for publication in MNRA
Brightest cluster galaxies in cosmological simulations: achievements and limitations of AGN feedback models
We analyze the basic properties of Brightest Cluster Galaxies (BCGs) produced
by state of the art cosmological zoom-in hydrodynamical simulations. These
simulations have been run with different sub-grid physics included. Here we
focus on the results obtained with and without the inclusion of the
prescriptions for supermassive black hole (SMBH) growth and of the ensuing
Active Galactic Nuclei (AGN) feedback. The latter process goes in the right
direction of decreasing significantly the overall formation of stars. However,
BCGs end up still containing too much stellar mass, a problem that increases
with halo mass, and having an unsatisfactory structure. This is in the sense
that their effective radii are too large, and that their density profiles
feature a flattening on scales much larger than observed. We also find that our
model of thermal AGN feedback has very little effect on the stellar velocity
dispersions, which turn out to be very large. Taken together, these problems,
which to some extent can be recognized also in other numerical studies
typically dealing with smaller halo masses, indicate that on one hand present
day sub-resolution models of AGN feedback are not effective enough in
diminishing the global formation of stars in the most massive galaxies, but on
the other hand they are relatively too effective in their centers. It is likely
that a form of feedback generating large scale gas outflows from BCGs
precursors, and a more widespread effect over the galaxy volume, can alleviate
these difficulties.Comment: 17 pages, 14 figures, accepted for publication on MNRAS, comments
welcom
Dependencia ambiental de las propiedades de halos de materia oscura /
Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física, 2008
Kinetic AGN Feedback Effects on Cluster Cool Cores Simulated using SPH
We implement novel numerical models of AGN feedback in the SPH code GADGET-3,
where the energy from a supermassive black hole (BH) is coupled to the
surrounding gas in the kinetic form. Gas particles lying inside a bi-conical
volume around the BH are imparted a one-time velocity (10,000 km/s) increment.
We perform hydrodynamical simulations of isolated cluster (total mass 10^14 /h
M_sun), which is initially evolved to form a dense cool core, having central
T<10^6 K. A BH resides at the cluster center, and ejects energy. The
feedback-driven fast wind undergoes shock with the slower-moving gas, which
causes the imparted kinetic energy to be thermalized. Bipolar bubble-like
outflows form propagating radially outward to a distance of a few 100 kpc. The
radial profiles of median gas properties are influenced by BH feedback in the
inner regions (r<20-50 kpc). BH kinetic feedback, with a large value of the
feedback efficiency, depletes the inner cool gas and reduces the hot gas
content, such that the initial cool core of the cluster is heated up within a
time 1.9 Gyr, whereby the core median temperature rises to above 10^7 K, and
the central entropy flattens. Our implementation of BH thermal feedback (using
the same efficiency as kinetic), within the star-formation model, cannot do
this heating, where the cool core remains. The inclusion of cold gas accretion
in the simulations produces naturally a duty cycle of the AGN with a
periodicity of 100 Myr.Comment: 22 pages, 11 figures, version accepted for publication in MNRAS,
references and minor revisions adde
The early phases of galaxy clusters formation in IR: coupling hydrodynamical simulations with GRASIL3D
We compute and study the infrared and sub-mm properties of high redshift () simulated clusters and proto-clusters. The results of a large set
of hydro-dynamical zoom-in simulations including active galactic nuclei (AGN)
feedback, have been treated with the recently developed radiative transfer code
GRASIL-3D, which accounts for the effect of dust reprocessing in an arbitrary
geometry. Here, we have slightly generalized the code to adapt it to the
present purpose. Then we have post-processed boxes of physical size 2 Mpc
encompassing each of the 24 most massive clusters identified at z=0, at several
redshifts between 0.5 and 3, producing IR and sub-mm mock images of these
regions and SEDs of the radiation coming out from them.
While this field is in its infancy from the observational point of view,
rapid development is expected in the near future thanks to observations
performed in the far IR and sub-mm bands. Notably, we find that in this
spectral regime our prediction are little affected by the assumption required
by this post-processing, and the emission is mostly powered by star formation
rather than accretion onto super massive black hole (SMBH).
The comparison with the little observational information currently available,
highlights that the simulated cluster regions never attain the impressive star
formation rates suggested by these observations. This problem becomes more
intriguing taking into account that the brightest cluster galaxies (BCGs) in
the same simulations turn out to be too massive. It seems that the interplay
between the feedback schemes and the star formation model should be revised,
possibly incorporating a positive feedback mode.Comment: 14 pages, 11 figures, MNRAS in press. Minor editorial improvement
On the role of AGN feedback on the thermal and chemodynamical properties of the hot intra-cluster medium
We present an analysis of the properties of the ICM in an extended set of
cosmological hydrodynamical simulations of galaxy clusters and groups performed
with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations,
we carried out two sets of simulations including radiative cooling, star
formation, metal enrichment and feedback from supernovae, one of which also
accounts for the effect of feedback from AGN resulting from gas accretion onto
super-massive black holes. These simulations are analysed with the aim of
studying the relative role played by SN and AGN feedback on the general
properties of the diffuse hot baryons in galaxy clusters and groups: scaling
relations, temperature, entropy and pressure radial profiles, and ICM chemical
enrichment. We find that simulations including AGN feedback produce scaling
relations that are in good agreement with X-ray observations at all mass
scales. However, our simulations are not able to account for the observed
diversity between CC and NCC clusters: unlike for observations, we find that
temperature and entropy profiles of relaxed and unrelaxed clusters are quite
similar and resemble more the observed behaviour of NCC clusters. As for the
pattern of metal enrichment, we find that an enhanced level of iron abundance
is produced by AGN feedback with respect to the case of purely SN feedback. As
a result, while simulations including AGN produce values of iron abundance in
groups in agreement with observations, they over-enrich the ICM in massive
clusters. The efficiency of AGN feedback in displacing enriched gas from halos
into the inter-galactic medium at high redshift also creates a widespread
enrichment in the outskirts of clusters and produces profiles of iron abundance
whose slope is in better agreement with observations.Comment: 23 pages, 14 figures, 1 table, accepted for publication in MNRA
Cool Core Clusters from Cosmological Simulations
We present results obtained from a set of cosmological hydrodynamic
simulations of galaxy clusters, aimed at comparing predictions with
observational data on the diversity between cool-core (CC) and non-cool-core
(NCC) clusters. Our simulations include the effects of stellar and AGN feedback
and are based on an improved version of the smoothed particle hydrodynamics
code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical
instabilities by including a suitable artificial thermal diffusion. In this
Letter, we focus our analysis on the entropy profiles, the primary diagnostic
we used to classify the degree of cool-coreness of clusters, and on the iron
profiles. In keeping with observations, our simulated clusters display a
variety of behaviors in entropy profiles: they range from steadily decreasing
profiles at small radii, characteristic of cool-core systems, to nearly flat
core isentropic profiles, characteristic of non-cool-core systems. Using
observational criteria to distinguish between the two classes of objects, we
find that they occur in similar proportions in both simulations and in
observations. Furthermore, we also find that simulated cool-core clusters have
profiles of iron abundance that are steeper than those of NCC clusters, which
is also in agreement with observational results. We show that the capability of
our simulations to generate a realistic cool-core structure in the cluster
population is due to AGN feedback and artificial thermal diffusion: their
combined action allows us to naturally distribute the energy extracted from
super-massive black holes and to compensate for the radiative losses of
low-entropy gas with short cooling time residing in the cluster core.Comment: 6 pages, 4 figures, accepted in ApJL, v2 contains some modifications
on the text (results unchanged
Temperature Structure of the Intra-Cluster Medium from SPH and AMR simulations
Analyses of cosmological hydrodynamic simulations of galaxy clusters suggest
that X-ray masses can be underestimated by 10% to 30%. The largest bias
originates by both violation of hydrostatic equilibrium and an additional
temperature bias caused by inhomogeneities in the X-ray emitting intra-cluster
medium (ICM). To elucidate on this large dispersion among theoretical
predictions, we evaluate the degree of temperature structures in cluster sets
simulated either with smoothed-particle-hydrodynamics (SPH) and
adaptive-mesh-refinement (AMR) codes. We find that the SPH simulations produce
larger temperature variations connected to the persistence of both
substructures and their stripped cold gas. This difference is more evident in
no-radiative simulations, while it is reduced in the presence of radiative
cooling. We also find that the temperature variation in radiative cluster
simulations is generally in agreement with the observed one in the central
regions of clusters. Around R_500 the temperature inhomogeneities of the SPH
simulations can generate twice the typical hydrostatic-equilibrium mass bias of
the AMR sample. We emphasize that a detailed understanding of the physical
processes responsible for the complex thermal structure in ICM requires
improved resolution and high sensitivity observations in order to extend the
analysis to higher temperature systems and larger cluster-centric radii.Comment: 13 pages, 12 figures, 4 table
Evidence of major dry mergers at M* > 2 x 10^11 Msun from curvature in early-type galaxy scaling relations?
For early-type galaxies, the correlations between stellar mass and size,
velocity dispersion, surface brightness, color, axis ratio and color-gradient
all indicate that two mass scales, M* = 3 x 10^10 Msun and M* = 2 x 10^11 Msun,
are special. The smaller scale could mark the transition between wet and dry
mergers, or it could be related to the interplay between SN and AGN feedback,
although quantitative measures of this transition may be affected by
morphological contamination. At the more massive scale, mean axis ratios and
color gradients are maximal, and above it, the colors are redder, the sizes
larger and the velocity dispersions smaller than expected based on the scaling
at lower M*. In contrast, the color-sigma relation, and indeed, most scaling
relations with sigma, are not curved: they are well-described by a single power
law, or in some cases, are almost completely flat. When major dry mergers
change masses, sizes, axis ratios and color gradients, they are expected to
change the colors or velocity dispersions much less. Therefore, the fact that
scaling relations at sigma > 150 km/s show no features, whereas the size-M*,
b/a-M*, color-M* and color gradient-M* relations do, suggests that M* = 2 x
10^11 Msun is the scale above which major dry mergers dominate the assembly
histories of early-type galaxies.Comment: 5 pages, 3 figures. Accepted for publication in MNRA
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