1,515 research outputs found
The entropy distribution in clusters: evidence of feedback?
The entropy of the intracluster medium at large radii has been shown recently
to deviate from the self-similar scaling with temperature. Using
N-body/hydrodynamic simulations of the LCDM cosmology, we demonstrate that this
deviation is evidence that feedback processes are important in generating
excess entropy in clusters. While radiative cooling increases the entropy of
intracluster gas, resulting in a good match to the data in the centres of
clusters, it produces an entropy-temperature relation closer to the
self-similar scaling at larger radii. A model that includes feedback from
galaxies, however, not only stabilises the cooling rate in the simulation, but
is capable of reproducing the observed scaling behaviour both in cluster cores
and at large radii. Feedback modifies the entropy distribution in clusters due
to its increasing ability at expelling gas from haloes with decreasing mass.
The strength of the feedback required, as suggested from our simulations, is
consistent with supernova energetics, providing a large fraction of the energy
reaches low-density regions and is originally contained within a small mass of
gas.Comment: 5 pages, 3 figures; accepted for publication in MNRA
Simulated X-ray Cluster Temperature Maps
Temperature maps are presented of the 9 largest clusters in the mock
catalogues of Muanwong et al. for both the Preheating and Radiative models. The
maps show that clusters are not smooth, featureless systems, but contain a
variety of substructure which should be observable. The surface brightness
contours are generally elliptical and features that are seen include cold
clumps, hot spiral features, and cold fronts. Profiles of emission-weighted
temperature, surface brightness and emission-weighted pressure across the
surface brightness discontinuities seen in one of the bimodal clusters are
consistent with the cold front in Abell 2142 observed by Markevitch et al.Comment: Submitted to Monthly Notices Royal Astronomical Societ
The baseline intracluster entropy profile from gravitational structure formation
The radial entropy profile of the hot gas in clusters of galaxies tends to
follow a power law in radius outside of the cluster core. Here we present a
simple formula giving both the normalization and slope for the power-law
entropy profiles of clusters that form in the absence of non-gravitational
processes such as radiative cooling and subsequent feedback. It is based on
seventy-one clusters drawn from four separate cosmological simulations, two
using smoothed-particle hydrodynamics (SPH) and two using adaptive-mesh
refinement (AMR), and can be used as a baseline for assessing the impact of
non-gravitational processes on the intracluster medium outside of cluster
cores. All the simulations produce clusters with self-similar structure in
which the normalization of the entropy profile scales linearly with cluster
temperature, and these profiles are in excellent agreement outside of 0.2
r_200. Because the observed entropy profiles of clusters do not scale linearly
with temperature, our models confirm that non-gravitational processes are
necessary to break the self-similarity seen in the simulations. However, the
core entropy levels found by the two codes used here significantly differ, with
the AMR code producing nearly twice as much entropy at the centre of a cluster.Comment: Accepted to MNRAS, 8 pages, 9 figure
The Sunyaev-Zel'dovich temperature of the intracluster medium
The relativistic Sunyaev-Zel'dovich (SZ) effect offers a method, independent
of X-ray, for measuring the temperature of the intracluster medium (ICM) in the
hottest systems. Here, using N-body/hydrodynamic simulations of three galaxy
clusters, we compare the two quantities for a non-radiative ICM, and for one
that is subject both to radiative cooling and strong energy feedback from
galaxies. Our study has yielded two interesting results. Firstly, in all cases,
the SZ temperature is hotter than the X-ray temperature and is within ten per
cent of the virial temperature of the cluster. Secondly, the mean SZ
temperature is less affected by cooling and feedback than the X-ray
temperature. Both these results can be explained by the SZ temperature being
less sensitive to the distribution of cool gas associated with cluster
substructure. A comparison of the SZ and X-ray temperatures (measured for a
sample of hot clusters) would therefore yield interesting constraints on the
thermodynamic structure of the intracluster gas.Comment: This version accepted for publication in MNRAS following minor
revisio
Galaxy cluster rotation revealed in the MACSIS simulations with the kinetic Sunyaev-Zeldovich effect
The kinetic Sunyaev-Zeldovich (kSZ) effect has now become a clear target for
ongoing and future studies of the cosmic microwave background (CMB) and
cosmology. Aside from the bulk cluster motion, internal motions also lead to a
kSZ signal. In this work, we study the rotational kSZ effect caused by coherent
large-scale motions of the cluster medium using cluster hydrodynamic
cosmological simulations. To utilise the rotational kSZ as a cosmological
probe, simulations offer some of the most comprehensive data sets that can
inform the modeling of this signal. In this work, we use the MACSIS data set to
specifically investigate the rotational kSZ effect in massive clusters. Based
on these models, we test stacking approaches and estimate the amplitude of the
combined signal with varying mass, dynamical state, redshift and map-alignment
geometry. We find that the dark matter, galaxy and gas spins are generally
misaligned, an effect that can cause a sub-optimal estimation of the rotational
kSZ effect when based on galaxy catalogues. Furthermore, we provide
halo-spin-mass scaling relations that can be used to build a statistical model
of the rotational kSZ. The rotational kSZ contribution, which is largest in
massive unrelaxed clusters (100 K), could be relevant to studies
of higher-order CMB temperature signals, such as the moving lens effect. The
limited mass range of the MACSIS sample strongly motivates an extended
investigation of the rotational kSZ effect in large-volume simulations to
refine the modelling, particularly towards lower mass and higher redshift, and
provide forecasts for upcoming cosmological CMB experiments (e.g. Simons
Observatory, SKA-2) and X-ray observations (e.g. \textit{Athena}/X-IFU).Comment: Submitted to Monthly Notices of the Royal Astronomical Society.
Comments and discussions are welcome. Data and codes can be found at
https://github.com/edoaltamura/macsis-cosmosi
On the cross-section of Dark Matter using substructure infall into galaxy clusters
We develop a statistical method to measure the interaction cross-section of
Dark Matter, exploiting the continuous minor merger events in which small
substructures fall into galaxy clusters. We find that by taking the ratio of
the distances between the galaxies and Dark Matter, and galaxies and gas in
accreting sub-halos, we form a quantity that can be statistically averaged over
a large sample of systems whilst removing any inherent line-of-sight
projections. In order to interpret this ratio as a cross-section of Dark Matter
we derive an analytical description of sub-halo infall which encompasses; the
force of the main cluster potential, the drag on a gas sub-halo, a model for
Dark Matter self-interactions and the resulting sub-halo drag, the force on the
gas and galaxies due to the Dark Matter sub-halo potential, and finally the
buoyancy on the gas and Dark Matter. We create mock observations from
cosmological simulations of structure formation and find that collisionless
Dark Matter becomes physically separated from X-ray gas by up to 20h^-1 kpc.
Adding realistic levels of noise, we are able to predict achievable constraints
from observational data. Current archival data should be able to detect a
difference in the dynamical behaviour of Dark Matter and standard model
particles at 6 sigma, and measure the total interaction cross-section sigma/m
with 68% confidence limits of +/- 1cm2g^-1. We note that this method is not
restricted by the limited number of major merging events and is easily extended
to large samples of clusters from future surveys which could potentially push
statistical errors to 0.1cm^2g^-1.Comment: 14 pages, 11 figure
Relativistic SZ temperature scaling relations of groups and clusters derived from the BAHAMAS and MACSIS simulations
The Sunyaev-Zeldovich (SZ) effect has long been recognized as a powerful
cosmological probe. Using the BAHAMAS and MACSIS simulations to obtain
simulated galaxy groups and clusters, we compute three temperature
measures and quantify the differences between them. The first measure is
related to the X-ray emission of the cluster, while the second describes the
non-relativistic thermal SZ (tSZ) effect. The third measure determines the
lowest order relativistic correction to the tSZ signal, which is seeing
increased observational relevance. Our procedure allows us to accurately model
the relativistic SZ (rSZ) contribution and we show that a
underestimation of this rSZ cluster temperature is expected when applying
standard X-ray relations. The correction also exhibits significant mass and
redshift evolution, as we demonstrate here. We present the mass dependence of
each temperature measure alongside their profiles and a short analysis of the
temperature dispersion as derived from the aforementioned simulations. We also
discuss a new relation connecting the temperature and Compton- parameter,
which can be directly used for rSZ modelling. Simple fits to the obtained
scaling relations and profiles are provided. These should be useful for future
studies of the rSZ effect and its relevance to cluster cosmology.Comment: Accepted by MNRA
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