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 (\(\sim\)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 (\({\cal M}_{\rm{W}}\) = 2.8 \(\pm~0.4\)) in the western direction at \(r\sim26\)', derived from a temperature and surface brightness discontinuity across the radio relic. In the East, we detect a weaker shock (\({\cal M}_{\rm{E}}\) = 1.5 \(\pm~0.1\)) at \(r\sim8\)', possibly associated to the 'notch' of eastern relic, and a cold front at \(r\sim3\)'. Based on the shock speed calculated from the Mach numbers, we estimate that the dynamical age of the shock front is \(\sim\)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.
We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, XMM-Newton) and optical (SOAR, HST) ...observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intra-cluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff-Riley Class I (FR I) system, the D configuration image shows two bright, relative to the central region, large (~160 kpc diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance r~>230 kpc. The XMM-Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ~7x10^59 erg and the mechanical power output of the jets is ~10^44 erg/s. The jets are mildly curved and possibly re-brightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm H\alpha+NII nebula and a cold molecular CO disk. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.
Chemical abundances in the X-ray halos (also known as the intracluster medium, ICM) of clusters and groups of galaxies can be measured via prominent emission line features in their X-ray spectra. ...Elemental abundances are footprints of time-integrated yields of various stellar populations that have left their specific abundance patterns prior to and during the cluster and group evolution. We aim to constrain nitrogen abundances in the CHEmical Evolution RGS Sample (CHEERS), which contains 44 nearby groups and clusters of galaxies, in order to have a better understanding of their chemical enrichment. We examine the high-resolution spectra of the CHEERS sample carefully and take into account various systematic effects in the spectral modelling. We compare the observed abundance ratios with those in the Galactic stellar populations, as well as predictions from stellar yields (low- and intermediate-mass stars, massive stars and degenerate stars). The nitrogen abundance can only be well constrained (\(\gtrsim3\sigma\)) in one cluster of galaxies and seven groups of galaxies. The O/Fe -- Fe/H relation of the ICM is comparable to that for the Galaxy, while both N/Fe and N/O ratios of the ICM are higher than in the Galaxy. Future studies on nitrogen radial distributions are required to tell whether the obtained higher N/Fe and N/O ratios are biased due to the small extraction region (\(r/r_{500}\lesssim0.05\)) that we adopt here. Since abundances of odd-\(Z\) elements are more sensitive to the initial metallicity of stellar populations, accurate abundance measurements of N, Na and Al are required to better constrain the chemical enrichment in the X-ray halos of clusters and groups of galaxies.
The M49 group, resident outside the virial radius of the Virgo cluster, is falling onto the cluster from the south. We report results from deep {\sl XMM-Newton} mosaic observations of M49. Its hot ...gas temperature is 0.8\,keV at the group center and rises to 1.5\,keV beyond the brightest group galaxy (BGG). The group gas extends to radii of \(\sim300\)\,kpc to the north and south. The observations reveal a cold front \(\sim20\)\,kpc north of the BGG center and an X-ray bright stripped tail 70\,kpc long and 10\,kpc wide to the southwest of the BGG. We argue that the atmosphere of the infalling group was slowed by its encounter with the Virgo cluster gas, causing the BGG to move forward subsonically relative to the group gas. We measure declining temperature and metallicity gradients along the stripped tail. The tail gas can be traced back to the cooler and enriched gas uplifted from the BGG center by buoyant bubbles, implying that AGN outbursts may have intensified the stripping process. We extrapolate to a virial radius of 740\,kpc and derive a virial mass of \(4.6\times10^{13}\,M_\odot\) for the M49 group. Its group atmosphere appears truncated and deficient when compared with isolated galaxy groups of similar temperatures. If M49 is on its first infall to Virgo, the infall region of a cluster could have profound impacts on galaxies and groups that are being accreted onto galaxy clusters. Alternatively, M49 may have already passed through Virgo once.
We report on the results of a $Suzaku$ observation of the plasma in the
filament located between the two massive clusters of galaxies Abell 399 and
Abell 401. Abell 399 ($z$=0.0724) and Abell 401 ...($z$=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
$kT\sim$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
$kT\sim$6-7 keV within 10' or $\sim$0.8 Mpc. Across $r$=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 ${\cal M}\sim$1.3. We also successfully
determined the abundance profile up to 15' (1.3 Mpc), showing an almost
constant value ($Z$=0.3 solar) at the cluster outskirt. We estimated the
Compton $y$-parameter to be $\sim$14.5$\pm1.3\times10^{-6}$, which is in
agreement with $Planck$'s results (14-17$\times10^{-6}$ on the filament). The
line of sight depth of the filament is $l\sim$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 $\sim$7.7$\times10^{13}~\rm
M_{\odot}$. 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.
We present the results of $Suzaku$ and $XMM-Newton$ X-ray observations of the
cluster pair 1E2216.0-0401 and 1E2215.7-0404. We discover an X-ray bridge
between the clusters. $Suzaku$ and $XMM-Newton$ ...observations revealed that each
cluster hosts gas with moderate temperature of $kT_{1E2216.0-0401}=$4.8$\pm$0.1
keV and $kT_{1E2215.7-0404}=$5.8$\pm$0.2 keV, respectively. On the other hand,
the bridge region shows a remarkably high temperature ({\it kT}=6.6$\pm$0.5
keV). Furthermore, at the position of the bridge, we detected an enhancement in
the wavelet-decomposed soft-band (0.5-4.0 keV) $XMM-Newton$ image at 3 sigma
significance, this is most likely due to a compression of the intracluster
medium (ICM) as a consequence of the merging activity. This X-ray intensity and
temperature enhancement are not consistent with those expected from a late
phase, but are in agreement with the predictions by numerical simulations of an
early phase merger. From the temperature jump at the location of the bridge,
the Mach number is estimated to be ${\cal M}=1.4\pm0.1$, which corresponds to a
shock propagation velocity of about 1570 km/s. From the shock properties, we
estimate that core-passage will occur in 0.3-0.6 Gyr and that the age of the
shock structure is 50--100 Myr. Based on the measured properties of the ICM at
the bridge and estimation of timescales, we find indications for
non-equilibrium ionization. We also discover possible diffuse radio emission
located between the merging clusters. Combining the radio, X-ray, and optical
image data, we speculate that the detected radio sources are most likely
related to the merger event. Thus, 1E2216.0-0401 and 1E2215.7-0404 is a new
example of an early phase cluster merger with remarkable characteristics.
We present some recent highlights and prospects for the study of hot astrophysical plasmas. Hot plasmas can be studied primarily through their X-ray emission and absorption. Most astrophysical ...objects, from solar system objects to the largest scale structures of the Universe, contain hot gas. In general we can distinguish collisionally ionised gas and photoionised gas. We introduce several examples of both classes and show where the frontiers of this research in astrophysics can be found. We put this also in the context of the current and future generation of X-ray spectroscopy satellites. The data coming from these missions challenge the models that we have for the calculation of the X-ray spectra.
High-resolution spectroscopy of the core of the Perseus Cluster of galaxies, using the \(Hitomi\) satellite above 2 keV and the \(XMM\)-\(Newton\) Reflection Grating Spectrometer at lower energies, ...provides reliable constraints on the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni. Accounting for all known systematic uncertainties, the Ar/Fe, Ca/Fe, and Ni/Fe ratios are determined with a remarkable precision of less than 10%, while the constraints on Si/Fe, S/Fe, and Cr/Fe are at the 15% level, and Mn/Fe is measured with a 20% uncertainty. The average biases in determining the chemical composition using archival CCD spectra from \(XMM\)-\(Newton\) and \(Suzaku\) range typically from 15-40%. A simple model in which the enrichment pattern in the Perseus Cluster core and the proto-solar nebula are identical gives a surprisingly good description of the high-resolution X-ray spectroscopy results, with \(\chi^2=10.7\) for 10 d.o.f. However, this pattern is challenging to reproduce with linear combinations of existing supernova nucleosynthesis calculations, particularly given the precise measurements of intermediate \(\alpha\)-elements enabled by \(Hitomi\). We discuss in detail the degeneracies between various supernova progenitor models and explosion mechanisms, and the remaining uncertainties in these theoretical models. We suggest that including neutrino physics in the core-collapse supernova yield calculations may improve the agreement with the observed pattern of \(\alpha\)-elements in the Perseus Cluster core. Our results provide a complementary benchmark for testing future nucleosynthesis calculations required to understand the origin of chemical elements.
The chemical yields of supernovae and the metal enrichment of the hot intra-cluster medium (ICM) are not well understood. This paper introduces the CHEmical Enrichment RGS Sample (CHEERS), which is a ...sample of 44 bright local giant ellipticals, groups and clusters of galaxies observed with XMM-Newton. This paper focuses on the abundance measurements of O and Fe using the reflection grating spectrometer (RGS). The deep exposures and the size of the sample allow us to quantify the intrinsic scatter and the systematic uncertainties in the abundances using spectral modeling techniques. We report the oxygen and iron abundances as measured with RGS in the core regions of all objects in the sample. We do not find a significant trend of O/Fe as a function of cluster temperature, but we do find an intrinsic scatter in the O and Fe abundances from cluster to cluster. The level of systematic uncertainties in the O/Fe ratio is estimated to be around 20-30%, while the systematic uncertainties in the absolute O and Fe abundances can be as high as 50% in extreme cases. We were able to identify and correct a systematic bias in the oxygen abundance determination, which was due to an inaccuracy in the spectral model. The lack of dependence of O/Fe on temperature suggests that the enrichment of the ICM does not depend on cluster mass and that most of the enrichment likely took place before the ICM was formed. We find that the observed scatter in the O/Fe ratio is due to a combination of intrinsic scatter in the source and systematic uncertainties in the spectral fitting, which we are unable to disentangle. The astrophysical source of intrinsic scatter could be due to differences in AGN activity and ongoing star formation in the BCG. The systematic scatter is due to uncertainties in the spatial line broadening, absorption column, multi-temperature structure and the thermal plasma models. (Abbreviated).
We present the results of deep Chandra, XMM-Newton and Suzaku observations of the nearby galaxy cluster Abell 85, which is currently undergoing at least two mergers, and in addition shows evidence ...for gas sloshing which extends out to r ~ 600 kpc. One of the two infalling subclusters, to the south of the main cluster center, has a dense, X-ray bright cool core and a tail extending to the southeast. The northern edge of this tail is strikingly smooth and sharp (narrower than the Coulomb mean free path of the ambient gas) over a length of 200 kpc, while toward the southwest the boundary of the tail is blurred and bent, indicating a difference in the plasma transport properties between these two edges. The thermodynamic structure of the tail strongly supports an overall northwestward motion. We propose, that a sloshing-induced tangential, ambient, coherent gas flow is bending the tail eastward. The brightest galaxy of this subcluster is at the leading edge of the dense core, and is trailed by the tail of stripped gas, suggesting that the cool core of the subcluster has been almost completely destroyed by the time it reached its current radius of r ~ 500 kpc. The surface-brightness excess, likely associated with gas stripped from the infalling southern subcluster, extends toward the southeast out to at least r_500 of the main cluster, indicating that the stripping of infalling subclusters may seed gas inhomogeneities. The second merging subcluster appears to be a diffuse non-cool core system. Its merger is likely supersonic with a Mach number of ~ 1.4.
