68 research outputs found
Possible depletion of metals into dust grains in the core of the Centaurus cluster of galaxies
We present azimuthally averaged metal abundance profiles from a full,
comprehensive, and conservative re-analysis of the deep (800 ks total net
exposure) \textit{Chandra}/ACIS-S observation of the Centaurus cluster core
(NGC\,4696). After carefully checking various sources of systematic
uncertainties, including the choice of the spectral deprojection method,
assumptions about the temperature structure of the gas, and uncertainties in
the continuum modeling, we confirm the existence of a central drop in the
abundances of the `reactive' elements Fe, Si, S, Mg, and Ca, within
10 kpc. The same drops are also found when analyzing the
\textit{XMM-Newton}/EPIC data (150 ks). Adopting our most conservative
approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca,
the abundance of the `nonreactive' element Ar is fully consistent with showing
no central drop. This is further confirmed by the significant ()
central radial increase of the Ar/Fe ratio. Our results corroborate the
previously proposed `dust depletion scenario' , in which central metal
abundance drops are explained by the deposition of a significant fraction of
centrally cooled reactive metals into dust grains present in the central
regions of the Centaurus cluster. This is also supported by the previous
findings that the extent of the metal abundance drops in NGC\,4696 broadly
coincides with the infrared dust emission.Comment: Accepted for publication in A&A; 12 pages, 5 figures, 2 table
Properties of the cosmological filament between two clusters: A possible detection of a large-scale accretion shock by
We report on the results of a observation of the plasma in the
filament located between the two massive clusters of galaxies Abell 399 and
Abell 401. Abell 399 (=0.0724) and Abell 401 (=0.0737) are expected to be
in the initial phase of a cluster merger. In the region between the two
clusters, we find a clear enhancement in the temperature of the filament plasma
from 4 keV (expected value from a typical cluster temperature profile) to
6.5 keV. Our analysis also shows that filament plasma is present out to
a radial distance of 15' (1.3 Mpc) from a line connecting the two clusters. The
temperature profile is characterized by an almost flat radial shape with
6-7 keV within 10' or 0.8 Mpc. Across =8'~from the axis, the
temperature of the filament plasma shows a drop from 6.3 keV to 5.1 keV,
indicating the presence of a shock front. The Mach number based on the
temperature drop is estimated to be 1.3. We also successfully
determined the abundance profile up to 15' (1.3 Mpc), showing an almost
constant value (=0.3 solar) at the cluster outskirt. We estimated the
Compton -parameter to be 14.5, which is in
agreement with 's results (14-17 on the filament). The
line of sight depth of the filament is 1.1 Mpc, indicating that the
geometry of filament is likely a pancake shape rather than cylindrical. The
total mass of the filamentary structure is 7.7. We discuss a possible interpretation of the drop of X-ray emission
at the rim of the filament, which was pushed out by the merging activity and
formed by the accretion flow induced by the gravitational force of the
filament.Comment: 8 pages, 8 figures, accepted for publication in A&
Enrichment of the hot intracluster medium: observations
Four decades ago, the firm detection of an Fe-K emission feature in the X-ray
spectrum of the Perseus cluster revealed the presence of iron in its hot
intracluster medium (ICM). With more advanced missions successfully launched
over the last 20 years, this discovery has been extended to many other metals
and to the hot atmospheres of many other galaxy clusters, groups, and giant
elliptical galaxies, as evidence that the elemental bricks of life -
synthesized by stars and supernovae - are also found at the largest scales of
the Universe. Because the ICM, emitting in X-rays, is in collisional ionisation
equilibrium, its elemental abundances can in principle be accurately measured.
These abundance measurements, in turn, are valuable to constrain the physics
and environmental conditions of the Type Ia and core-collapse supernovae that
exploded and enriched the ICM over the entire cluster volume. On the other
hand, the spatial distribution of metals across the ICM constitutes a
remarkable signature of the chemical history and evolution of clusters, groups,
and ellipticals. Here, we summarise the most significant achievements in
measuring elemental abundances in the ICM, from the very first attempts up to
the era of XMM-Newton, Chandra, and Suzaku and the unprecedented results
obtained by Hitomi. We also discuss the current systematic limitations of these
measurements and how the future missions XRISM and Athena will further improve
our current knowledge of the ICM enrichment.Comment: 49 pages. Review paper. Accepted for publication on Space Science
Reviews. This is the companion review of "Enrichment of the hot intracluster
medium: numerical simulations
Origin of central abundances in the hot intra-cluster medium - I. Individual and average abundance ratios from XMM-Newton EPIC
The hot intra-cluster medium (ICM) is rich in metals, which are synthesized
by supernovae (SNe) explosions and accumulate over time into the deep
gravitational potential well of clusters of galaxies. Since most of the
elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse
(SNcc) supernovae, measuring their abundances gives us direct information on
the nucleosynthesis products of billions of SNe since the epoch of the star
formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments
onboard XMM-Newton to measure the abundances of 9 elements (O, Ne, Mg, Si, S,
Ar, Ca, Fe and Ni) from a sample of 44 nearby cool-core galaxy clusters,
groups, and elliptical galaxies. We find that the Fe abundance shows a large
scatter (~20-40%) over the sample, within 0.2 and, especially,
0.05. Unlike the absolute Fe abundance, the abundance ratios (X/Fe)
are quite uniform over the considered temperature range (~0.6-8 keV), and with
a limited scatter. In addition to a unprecedented treatment of systematic
uncertainties, we provide the most accurate abundance ratios measured so far in
the ICM, including Cr/Fe and Mn/Fe that we firmly detect (>4{\sigma} with MOS
and pn independently). We find that Cr/Fe, Mn/Fe and Ni/Fe, differ
significantly from the proto-solar values. However, the large uncertainties in
the proto-solar abundances prevent us from making a robust comparison between
the local and the intra-cluster chemical enrichments. We also note that,
interestingly, and despite the large net exposure time (~4.5 Ms) of our
dataset, no line emission feature is seen around ~3.5 keV.Comment: 17 pages, 9 figures, accepted for publication in A&
Magnetic fields and extraordinarily bright radio emission in the X-ray faint galaxy group MRC 0116+111
MRC 0116+111 is a nearby () poor galaxy group, which was previously
known for exhibiting a bright diffuse radio emission with no central point-like
source, presumably related to a past activity of the active galactic nucleus
(AGN) in its central cD galaxy. Here, we present an X-ray observation (30
ks of cleaned XMM-Newton/EPIC exposure) of this system, allowing us for the
first time a detailed comparison between the thermal and non-thermal components
of its intragroup medium (IGrM). Remarkably, we find that the radio-to-X-ray
luminosity ratio is among the highest ever observed for a diffuse extragalactic
source so far, while the extent of the observed radio emission is about three
times larger than its observed soft X-ray emission. Although powerful AGN
activity may have disturbed the dynamics of the thermal IGrM in the form of
turbulence, possibly re-energising part of the relativistic electron
population, the gas properties lie within the - scaling relation
established previously for other groups. The upper limit we find for the
non-thermal inverse-Compton X-ray emission translates into a surprisingly high
lower limit for the volume-averaged magnetic field of the group (4.3
G). Finally, we discuss some interesting properties of a distant () galaxy cluster serendipitously discovered in our EPIC field of
view.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Iron abundance distribution in the hot gas of merging galaxy clusters
We present XMM-Newton/EPIC observations of six merging galaxy clusters and
study the distributions of their temperature, iron (Fe) abundance and
pseudo-entropy along the merging axis. For the first time, we focus
simultaneously, and in a comprehensive way, on the chemical and thermodynamic
properties of the freshly collided intracluster medium (ICM). The Fe
distribution of these clusters along the merging axis is found to be in good
agreement with the azimuthally-averaged Fe abundance profile in typical
non-cool-core clusters out to . In addition to showing a moderate
central abundance peak, though less pronounced than in relaxed systems, the Fe
abundance flattens at large radii towards 0.2-0.3 . Although
this shallow metal distribution is in line with the idea that disturbed,
non-cool-core clusters originate from the merging of relaxed, cool-core
clusters, we find that in some cases, remnants of metal-rich and low entropy
cool cores can persist after major mergers. While we obtain a mild
anti-correlation between the Fe abundance and the pseudo-entropy in the (lower
entropy, = 200-500 keV cm) inner regions, no clear correlation is found
at (higher entropy, = 500-2300 keV cm) outer radii. The apparent
spatial abundance uniformity that we find at large radii is difficult to
explain through an efficient mixing of freshly injected metals, particularly in
systems for which the time since the merger is short. Instead, our results
provide important additional evidence in favour of the early enrichment
scenario - in which the bulk of the metals are released outside galaxies at
> 2-3 - and extend it from cool-core and (moderate) non-cool-core clusters to a
few of the most disturbed merging clusters as well. These results constitute a
first step towards a deeper understanding of the chemical history of merging
clusters.Comment: Accepted for publication in A&A, 21 pages with 17 figures and 19
table
X-ray study of the double radio relic Abell 3376 with Suzaku
We present an X-ray spectral analysis of the nearby double radio relic merging cluster Abell 3376 ( z = 0.046), observed with the Suzaku XIS instrument. These deep (similar to 360 ks) observations cover the entire double relic region in the outskirts of the cluster. These diffuse radio structures are amongst the largest and arc-shaped relics observed in combination with large-scale X-ray shocks in a merging cluster. We confirm the presence of a stronger shock (M-W = 2.8 +/- 0.4) in the western direction at r similar to 26 0, derived from a temperature and surface brightness discontinuity across the radio relic. In the east, we detect a weaker shock ( M-E = 1.5 +/- 0.1) at r similar to 8', possibly associated with the "notch" of the eastern relic, and a cold front at r similar to 3'. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is similar to 0.6 Gyr after core passage, indicating that Abell 3376 is still an evolving merging cluster and that the merger is taking place close to the plane of the sky. These results are consistent with simulations and optical and weak lensing studies from the literature
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