70 research outputs found
Constraining galaxy cluster temperatures and redshifts with eROSITA survey data
The nature of dark energy is imprinted in the large-scale structure of the
Universe and thus in the mass and redshift distribution of galaxy clusters. The
upcoming eROSITA mission will exploit this method of probing dark energy by
detecting roughly 100,000 clusters of galaxies in X-rays. For a precise
cosmological analysis the various galaxy cluster properties need to be measured
with high precision and accuracy. To predict these characteristics of eROSITA
galaxy clusters and to optimise optical follow-up observations, we estimate the
precision and the accuracy with which eROSITA will be able to determine galaxy
cluster temperatures and redshifts from X-ray spectra. Additionally, we present
the total number of clusters for which these two properties will be available
from the eROSITA survey directly. During its four years of all-sky surveys,
eROSITA will determine cluster temperatures with relative uncertainties of
Delta(T)/T<10% at the 68%-confidence level for clusters up to redshifts of
z~0.16 which corresponds to ~1,670 new clusters with precise properties.
Redshift information itself will become available with a precision of
Delta(z)/(1+z)<10% for clusters up to z~0.45. Additionally, we estimate how the
number of clusters with precise properties increases with a deepening of the
exposure. Furthermore, the biases in the best-fit temperatures as well as in
the estimated uncertainties are quantified and shown to be negligible in the
relevant parameter range in general. For the remaining parameter sets, we
provide correction functions and factors. The eROSITA survey will increase the
number of galaxy clusters with precise temperature measurements by a factor of
5-10. Thus the instrument presents itself as a powerful tool for the
determination of tight constraints on the cosmological parameters.Comment: accepted for publication in A&A; 17 pages, 20 figure
Scaling Properties of Galaxy Groups
Galaxy groups and poor clusters are more common than rich clusters, and host
the largest fraction of matter content in the Universe. Hence, their studies
are key to understand the gravitational and thermal evolution of the bulk of
the cosmic matter. Moreover, because of their shallower gravitational
potential, galaxy groups are systems where non-gravitational processes (e.g.,
cooling, AGN feedback, star formation) are expected to have a higher impact on
the distribution of baryons, and on the general physical properties, than in
more massive objects, inducing systematic departures from the expected scaling
relations. Despite their paramount importance from the astrophysical and
cosmological point of view, the challenges in their detection have limited the
studies of galaxy groups. Upcoming large surveys will change this picture,
reassigning to galaxy groups their central role in studying the structure
formation and evolution in the Universe, and in measuring the cosmic baryonic
content. Here, we review the recent literature on various scaling relations
between X-ray and optical properties of these systems, focusing on the
observational measurements, and the progress in our understanding of the
deviations from the self-similar expectations on groups' scales. We discuss
some of the sources of these deviations, and how feedback from supernovae
and/or AGNs impacts the general properties and the reconstructed scaling laws.
Finally, we discuss future prospects in the study of galaxy groups.Comment: 36 pages, 8 figures, and 2 tables. This review article is part of the
special issue "The Physical Properties of the Groups of Galaxies", edited by
L. Lovisari and S. Ettori. Published in MDPI - Universe:
https://www.mdpi.com/journal/universe/special_issues/PPGG
Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy Cluster
Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters
are typically quenched giant ellipticals. A recent study hinted that
star-forming galaxies with large disks, so-called superluminous spirals and
lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing
optical data it was not possible to constrain whether the superluminous disk
galaxies reside at the center of galaxy clusters. In this work, we utilize
XMM-Newton X-ray observations of five galaxy clusters to map the morphology of
the intracluster medium (ICM), characterize the galaxy clusters, determine the
position of the cluster center, and measure the offset between the cluster
center and the superluminous disk galaxies. We demonstrate that one
superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center
of a low-mass () galaxy cluster. This
represents the first conclusive evidence that a superluminous disk galaxy is
the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX
J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed
due to the merger of galaxies. We exclude the possibility that the other four
superluminous disk galaxies reside at the center of galaxy clusters, as their
projected distance from the cluster center is kpc, which corresponds
to . We conclude that these clusters host quiescent
massive elliptical galaxies at their center.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059
Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we
investigate the temperature structure (kT and sigma_T ) and the abundances of 9
elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium
(ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a
deep analysis of the cluster core, a careful modelling of the EPIC background
allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably
because of projection effects, the temperature ICM is found not to be in single
phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar,
Ca and Fe, but also O are peaked towards the core. Fe and O are still
significantly detected in the outermost annuli; suggesting that the enrichment
by both type Ia and core-collapse SNe started in the early stages of the
cluster formation. However, the particularly high Ca/Fe ratio that we find in
the core is not well reproduced by the standard SNe yield models. Finally, 2-D
maps of temperature and Fe abundance are presented and confirm the existence of
a denser, colder, and Fe-rich ridge southwest of the core, previously observed
by Chandra. The origin of this asymmetry in the hot gas of the cluster core is
still unclear, but might be explained by a past intense ram-pressure stripping
event near the central cD galaxy.Comment: 17 pages, 13 figures, accepted for publication in A&
METALS IN THE ICM: WITNESSES OF CLUSTER FORMATION AND EVOLUTION
The baryonic composition of galaxy clusters and groups is dominated by a hot, X-ray emitting Intra-Cluster Medium (ICM). The mean metallicity of the ICM has been found to be roughly 0.3 ÷ 0.5 times the solar value, therefore a large fraction of this gas cannot be of purely primordial origin. Indeed, the distribution and amount of metals in the ICM is a direct consequence of the past history of star formation in the cluster galaxies and of the processes responsible for the injection of enriched material into the ICM. We here shortly summarize the current views on the chemical enrichment, focusing on the observational evidence in terms of metallicity measurements in clusters, spatial metallicity distribution and evolution, and expectations from future missions
The thermalisation of massive galaxy clusters
In the hierarchical scenario of structure formation, galaxy clusters are the
ultimate virialised products in mass and time. Hot baryons in the intracluster
medium (ICM) and cold baryons in galaxies inhabit a dark matter dominated halo.
Internal processes, accretion, and mergers can perturb the equilibrium, which
is established only at later times. However, the cosmic time when
thermalisation is effective is still to be assessed. Here we show that massive
clusters in the observed universe attained an advanced thermal equilibrium
ago, at redshift , when the universe was
old. Hot gas is mostly thermalised after the time when
cosmic densities of matter and dark energy match. We find in a statistically
nearly complete and homogeneous sample of 120 clusters from the {\it Planck}
Early Sunyaev-Zel'dovich (ESZ) sample that the kinetic energy traced by the
galaxy velocity dispersion is a faithful probe of the gravitational energy
since a look back time of at least , whereas the efficiency
of hot gas in converting kinetic to thermal energy, as measured through X-ray
observations in the core-excised area within , steadily increases with
time. The evolution is detected at the per cent probability level.
Our results demonstrate that halo mass accretion history plays a larger role
for cluster thermal equilibrium than radiative physics. The evolution of hot
gas is strictly connected to the cosmic structure formation
Outskirts of Galaxy Clusters
Until recently, only about 10% of the total intracluster gas volume had been
studied with high accuracy, leaving a vast region essentially unexplored. This
is now changing and a wide area of hot gas physics and chemistry awaits
discovery in galaxy cluster outskirts. Also, robust large-scale total mass
profiles and maps are within reach. First observational and theoretical results
in this emerging field have been achieved in recent years with sometimes
surprising findings. Here, we summarize and illustrate the relevant underlying
physical and chemical processes and review the recent progress in X-ray,
Sunyaev--Zel'dovich, and weak gravitational lensing observations of cluster
outskirts, including also brief discussions of technical challenges and
possible future improvements.Comment: 52 pages. Review paper. Accepted for publication in Space Science
Reviews (eds: S. Ettori, M. Meneghetti). This is a product of the work done
by an international team at the International Space Science Institute (ISSI)
in Bern on "Astrophysics and Cosmology with Galaxy Clusters: the X-ray and
Lensing View
CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck
Pressure profiles are sensitive probes of the thermodynamic conditions and
the internal structure of galaxy clusters. The intra-cluster gas resides in
hydrostatic equilibrium within the Dark Matter gravitational potential.
However, this equilibrium may be perturbed, e.g. as a consequence of thermal
energy losses, feedback and non-thermal pressure supports. Accurate measures of
the gas pressure over the cosmic times are crucial to constrain the cluster
evolution as well as the contribution of astrophysical processes. In this work
we presented a novel algorithm to derive the pressure profiles of galaxy
clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of
Planck and South Pole Telescope (SPT) observations. The synergy of the two
instruments made it possible to track the profiles on a wide range of spatial
scales. We exploited the sensitivity to the larger scales of the Planck
High-Frequency Instrument to observe the faint peripheries, and the higher
spatial resolution of SPT to solve the innermost regions. We developed a
two-step pipeline to take advantage of the specifications of each instrument.
We first performed a component separation on the two data-sets separately to
remove the background (CMB) and foreground (galactic emission) contaminants.
Then we jointly fitted a parametric pressure profile model on a combination of
Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE
clusters detected by SPT. We compare the results of the SZ analysis with
profiles derived from X-ray observations with XMM-Newton. We find an excellent
agreement between these two independent probes of the gas pressure structure.Comment: 19 pages, 13 figures, submitted to A&
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