113 research outputs found
Thermal and non-thermal traces of AGN feedback: results from cosmological AMR simulations
We investigate the observable effects of feedback from Active Galactic Nuclei
(AGN) on non-thermal components of the intracluster medium (ICM). We have
modelled feedback from AGN in cosmological simulations with the adaptive mesh
refinement code ENZO, investigating three types of feedback that are sometimes
called quasar, jet and radio mode. Using a small set of galaxy clusters
simulated at high resolution, we model the injection and evolution of Cosmic
Rays, as well as their effects on the thermal plasma. By comparing, both, the
profiles of thermal gas to observed profiles from the ACCEPT sample, and the
secondary gamma-ray emission to the available upper limits from FERMI, we
discuss how the combined analysis of these two observables can constrain the
energetics and mechanisms of feedback models in clusters. Those modes of AGN
feedback that provide a good match to X-ray observations, yield a gamma-ray
luminosity resulting from secondary cosmic rays that is about below the
available upper limits from FERMI. Moreover, we investigate the injection of
turbulent motions into the ICM from AGN, and the detectability of these motions
via the analysis of line broadening of the Fe XXIII line. In the near future,
deeper observations/upper-limits of non-thermal emissions from galaxy clusters
will yield stringent constraints on the energetics and modes of AGN feedback,
even at early cosmic epochs.Comment: 24 pages, 20 figures. MNRAS accepted. A version of the paper with
higher quality figures can be found at this url:
http://www.ira.inaf.it/~vazza/papers/feedback_vazza.pd
The structure and fate of white dwarf merger remnants
We present a large parameter study where we investigate the structure of
white dwarf (WD) merger remnants after the dynamical phase. A wide range of WD
masses and compositions are explored and we also probe the effect of different
initial conditions. We investigated the degree of mixing between the WDs, the
conditions for detonations as well as the amount of gas ejected. We find that
systems with lower mass ratios have more total angular momentum and as a result
more mass is flung out in a tidal tail. Nuclear burning can affect the amount
of mass ejected. Many WD binaries that contain a helium-rich WD achieve the
conditions to trigger a detonation. In contrast, for carbon-oxygen transferring
systems only the most massive mergers with a total mass above ~2.1 solar masses
detonate. Even systems with lower mass may detonate long after the merger if
the remnant remains above the Chandrasekhar mass and carbon is ignited at the
centre. Finally, our findings are discussed in the context of several possible
observed astrophysical events and stellar systems, such as hot subdwarfs, R
Coronae Borealis stars, single massive white dwarfs, supernovae of type Ia and
other transient events. A large database containing 225 white dwarf merger
remnants is made available via a dedicated web page.Comment: 23 pages, 15 figures, submitted to MNRAS. A database containing 225
WD merger remnants is available for download at
http://www.hs.uni-hamburg.de/DE/Ins/Per/Dan/wdwd_remnants.htm
Shock heating by FR I radio sources in galaxy clusters
Feedback by active galactic nuclei (AGN) is frequently invoked to explain the
cut-off of the galaxy luminosity function at the bright end and the absence of
cooling flows in galaxy clusters. Meanwhile, there are recent observations of
shock fronts around radio-loud AGN. Using realistic 3D simulations of jets in a
galaxy cluster, we address the question what fraction of the energy of active
galactic nuclei is dissipated in shocks. We find that weak shocks that
encompass the AGN have Mach numbers of 1.1-1.2 and dissipate at least 2% of the
mechanical luminosity of the AGN. In a realistic cluster medium, even a
continuous jet can lead to multiple shock structures, which may lead to an
overestimate of the AGN duty cycles inferred from the spatial distribution of
waves.Comment: accepted by MNRAS Letter
Properties of gas clumps and gas clumping factor in the intra cluster medium
The spatial distribution of gas matter inside galaxy clusters is not
completely smooth, but may host gas clumps associated with substructures. These
overdense gas substructures are generally a source of unresolved bias of X-ray
observations towards high density gas, but their bright luminosity peaks may be
resolved sources within the ICM, that deep X-ray exposures may be (already)
capable to detect. In this paper we aim at investigating both features, using a
set of high-resolution cosmological simulations with ENZO. First, we monitor
how the bias by unresolved gas clumping may yield incorrect estimates of global
cluster parameters and affects the measurements of baryon fractions by X-ray
observations. We find that based on X-ray observations of narrow radial strips,
it is difficult to recover the real baryon fraction to better than 10 - 20
percent uncertainty. Second, we investigated the possibility of observing
bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock
X-ray observations for several instruments (XMM, Suzaku and ROSAT) and
extracted the statistics of potentially detectable bright clumps. Some of the
brightest clumps predicted by simulations may already have been already
detected in X- ray images with a large field of view. However, their small
projected size makes it difficult to prove their existence based on X-ray
morphology only. Preheating, AGN feedback and cosmic rays are found to have
little impact on the statistical properties of gas clumps.Comment: 17 pages, 11 figures. MNRAS accepte
In-depth Chandra study of the AGN feedback in Virgo elliptical galaxy M84
Using deep Chandra observations of M84 we study the energetics of the
interaction between the black hole and the interstellar medium of this
early-type galaxy. We perform a detailed two dimensional reconstruction of the
properties of the X-ray emitting gas using a constrained Voronoi tessellation
method, identifying the mean trends and carrying out the fluctuation analysis
of the thermodynamical properties of the hot ISM. In addition to the PV work
associated with the bubble expansion, we identify and measure the wave energy
associated with the mildly supersonic bubble expansion. We show that, depending
on the age of the cavity and the associated wave, the waves can have a
substantial contribution to the total energy release from the AGN. The energy
dissipated in the waves tends to be concentrated near the center of M84 and in
the direction perpendicular to the bubble outflow, possibly due to the
interference of the waves generated by the expansion of northern and southern
bubbles. We also find direct evidence for the escape of radio plasma from the
ISM of the host galaxy into the intergalactic medium.Comment: 6 pages, ApJ in press, Nov. 1 200
Star formation in shocked cluster spirals and their tails
Recent observations of ram pressure stripped spiral galaxies in clusters
revealed details of the stripping process, i.e., the truncation of all
interstellar medium (ISM) phases and of star formation (SF) in the disk, and
multiphase star-forming tails. Some stripped galaxies, in particular in merging
clusters, develop spectacular star-forming tails, giving them a jellyfish-like
appearance. In merging clusters, merger shocks in the intra-cluster medium
(ICM) are thought to have overrun these galaxies, enhancing the ambient ICM
pressure and thus triggering SF, gas stripping and tail formation. We present
idealised hydrodynamical simulations of this scenario, including standard
descriptions for SF and stellar feedback. To aid the interpretation of recent
and upcoming observations, we focus on particular structures and dynamics in SF
patterns in the remaining gas disk and in the near tails, which are easiest to
observe. The observed jellyfish morphology is qualitatively reproduced for,
both, face-on and edge-on stripping. In edge-on stripping, the interplay
between the ICM wind and the disk rotation leads to asymmetries along the ICM
wind direction and perpendicular to it. The apparent tail is still part of a
highly deformed gaseous and young stellar disk. In both geometries, SF takes
place in knots throughout the tail, such that the stars in the tails show no
ordered age gradients. Significant SF enhancement in the disk occurs only at
radii where the gas will be stripped in due course.Comment: 6 pages, submitted to MNRAS Letter
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