108 research outputs found
Hydrodynamical simulations of cluster formation with central AGN heating
We analyse a hydrodynamical simulation model for the recurrent heating of the
central intracluster medium (ICM) by active galactic nuclei (AGN). Besides the
self-gravity of the dark matter and gas components, our approach includes the
radiative cooling and photoheating of the gas, as well as a subresolution
multiphase model for star formation and supernova feedback. Additionally, we
incorporate a periodic heating mechanism in the form of hot, buoyant bubbles,
injected into the intragalactic medium (IGM) during the active phases of the
accreting central AGN. We use simulations of isolated cluster halos of
different masses to study the bubble dynamics and the heat transport into the
IGM. We also apply our model to self-consistent cosmological simulations of the
formation of galaxy clusters with a range of masses. Our numerical schemes
explore a variety of different assumptions for the spatial configuration of
AGN-driven bubbles, for their duty cycles and for the energy injection
mechanism, in order to obtain better constraints on the underlying physical
picture. We argue that AGN heating can substantially affect the properties of
both the stellar and gaseous components of clusters of galaxies. Most
importantly, it alters the properties of the central dominant (cD) galaxy by
reducing the mass deposition rate of freshly cooled gas out of the ICM, thereby
offering an energetically plausible solution to the cooling flow problem. At
the same time, this leads to reduced or eliminated star formation in the
central cD galaxy, giving it red stellar colours as observed.Comment: 22 pages, 15 figures, minor revisions, MNRAS accepte
Intracluster stars in simulations with AGN feedback
We use a set of high-resolution hydrodynamical simulations of clusters of
galaxies to study the build-up of the intracluster light (ICL), an interesting
and likely significant component of their total stellar mass. Our sample of
groups and clusters includes AGN feedback and is of high enough resolution to
accurately resolve galaxy populations down to the smallest galaxies that are
expected to significantly contribute to the stellar mass budget. We describe
and test four different methods to identify the ICL in simulations, thereby
allowing us to assess the reliability of the measurements. For all of the
methods, we consistently find a very significant ICL stellar fraction (~45%)
which exceeds the values typically inferred from observations. However, we show
that this result is robust with respect to numerical resolution and integration
accuracy, remarkably insensitive to changes in the star formation model, and
almost independent of halo mass. It is also almost invariant when black hole
growth is included, even though AGN feedback successfully prevents excessive
overcooling in clusters and leads to a drastically improved agreement of the
simulated cluster galaxy population with observations. In particular, the
luminosities of central galaxies and the ages of their stellar populations are
much more realistic when including AGN. In the light of these findings, it
appears challenging to construct a simulation model that simultaneously matches
the cluster galaxy population and at the same time produces a low ICL
component. We find that intracluster stars are preferentially stripped in a
cluster's densest region from massive galaxies that fall into the cluster at
z>1. Surprisingly, some of the intracluster stars also form in the intracluster
medium inside cold gas clouds that are stripped out of infalling galaxies.Comment: 17 pages, 16 figures, submitted to MNRA
The role of AGN feedback and gas viscosity in hydrodynamical simulations of galaxy clusters
We study the imprints of AGN feedback and physical viscosity on the
properties of galaxy clusters using hydrodynamical simulation models carried
out with the TreeSPH code GADGET-2. Besides self-gravity of dark matter and
baryons, our approach includes radiative cooling and heating processes of the
gas component and a multiphase model for star formation and SNe feedback.
Additionally, we introduce a prescription for physical viscosity in GADGET-2,
based on a SPH discretization of the Navier-Stokes and general heat transfer
equations. Adopting the Braginskii parameterization for the shear viscosity
coefficient, we explore how gas viscosity influences the properties of
AGN-driven bubbles. We also introduce a novel, self-consistent AGN feedback
model where we simultaneously follow the growth and energy release of massive
black holes embedded in a cluster environment. We assume that black holes
accreting at low rates with respect to the Eddington limit are in a radiatively
inefficient regime, and that most of the feedback energy will appear in a
mechanical form. Thus, we introduce AGN-driven bubbles into the ICM with
properties, such as radius and energy content, that are directly linked to the
black hole physics. This model leads to a self-regulated mechanism for the
black hole growth and overcomes the cooling flow problem in host halos, ranging
from the scale of groups to that of massive clusters. (Abridged)Comment: 6 pages, 4 figures. To appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Non gravitational heating mechanisms in galaxy clusters
The study of the formation and growth of cosmic structures is one of the most fascinating and challenging fields of astrophysics. In the currently favoured cosmological model, the so-called LCDM cosmogony, dark matter structures grow hierarchically, with small clumps forming first at very early epochs. The merging of these dark matter halos in the following evolution leads to the formation of more massive objects with time, ultimately resulting in a complex cosmic web composed of filaments of dark matter and galaxies, rich galaxy clusters, and voids in between. While we have some knowledge how these dark matter structures evolve with cosmic time, the relationship between the "dark" and the "luminous" content of the Universe is still far from being fully understood and it poses many puzzling questions, both for observational and theoretical investigations. Galaxy clusters, the largest virialized objects in the Universe, are especially interesting for cosmological studies because they are ideal laboratories to study the physical processes relevant in structure formation, like those that shape the properties of galaxies, the intergalactic and intracluster media, and the active galactic nuclei (AGN) that originate from super-massive black holes (BHs) in cluster centres. The study of clusters is remarkably promising right now, both because of the wealth of new data from X-ray telescopes such as XMM-Newton and Chandra or from optical surveys such as SDSS, and also due to the increasing power of cosmological simulations as a theoretical tool. The latter can track the growth of cosmological structures far into the highly non-linear regime, and have recently become faithful enough to include for the first time physical processes such as AGN activity and its effect on galaxy evolution. Therefore the aim of this Thesis was to incorporate AGN heating process in fully self-consistent cosmological simulations of structure formation, and to constrain the relevance of this feedback mechanism for galaxy and galaxy cluster formation and evolution
A physical model for cosmological simulations of galaxy formation: multi-epoch validation
We present a multi-epoch analysis of the galaxy populations formed within the
cosmological hydrodynamical simulations presented in Vogelsberger et al.
(2013). These simulations explore the performance of a recently implemented
feedback model which includes primordial and metal line radiative cooling with
self-shielding corrections; stellar evolution with associated mass loss and
chemical enrichment; feedback by stellar winds; black hole seeding, growth and
merging; and AGN quasar- and radio-mode heating with a phenomenological
prescription for AGN electro-magnetic feedback. We illustrate the impact of the
model parameter choices on the resulting simulated galaxy population properties
at high and intermediate redshifts. We demonstrate that our scheme is capable
of producing galaxy populations that broadly reproduce the observed galaxy
stellar mass function extending from redshift z=0 to z=3. We also characterise
the evolving galactic B-band luminosity function, stellar mass to halo mass
ratio, star formation main sequence, Tully-Fisher relation, and gas-phase
mass-metallicity relation and confront them against recent observational
estimates. This detailed comparison allows us to validate elements of our
feedback model, while also identifying areas of tension that will be addressed
in future work.Comment: 22 pages, 10 figures, submitted to MNRAS. Volume-rendering movies and
high-resolution images can be found at
http://www.cfa.harvard.edu/itc/research/arepogal
Following the flow: tracer particles in astrophysical fluid simulations
We present two numerical schemes for passive tracer particles in the
hydrodynamical moving-mesh code AREPO, and compare their performance for
various problems, from simple setups to cosmological simulations. The purpose
of tracer particles is to allow the flow to be followed in a Lagrangian way,
tracing the evolution of the fluid with time, and allowing the thermodynamical
history of individual fluid parcels to be recorded. We find that the
commonly-used `velocity field tracers', which are advected using the fluid
velocity field, do not in general follow the mass flow correctly, and explain
why this is the case. This method can result in orders-of-magnitude biases in
simulations of driven turbulence and in cosmological simulations, rendering the
velocity field tracers inappropriate for following these flows. We then discuss
a novel implementation of `Monte Carlo tracers', which are moved along with
fluid cells, and are exchanged probabilistically between them following the
mass flux. This method reproduces the mass distribution of the fluid correctly.
The main limitation of this approach is that it is more diffusive than the
fluid itself. Nonetheless, we show that this novel approach is more reliable
than what has been employed previously and demonstrate that it is appropriate
for following hydrodynamical flows in mesh-based codes. The Monte Carlo tracers
can also naturally be transferred between fluid cells and other types of
particles, such as stellar particles, so that the mass flow in cosmological
simulations can be followed in its entirety.Comment: Accepted for publication in MNRAS, minor updates to match accepted
version. 19 pages, 14 figure
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