We detect a weak unidentified emission line at E = (3.55-3.57) + or - 0.03 keV in a stacked XMM-Newton spectrum of 73 galaxy clusters spanning a redshift range 0.01-0.35. When the full sample is ...divided into three subsamples (Perseus, Centaurus+Ophiuchus+Coma, and all others), the line is seen at >3sigma statistical significance in all three independent MOS spectra and the PN "all others" spectrum. It is also detected in the Chandra spectra of the Perseus Cluster. However, it is very weak and located within 50-110 eV of several known lines. The detection is at the limit of the current instrument capabilities. We argue that there should be no atomic transitions in thermal plasma at this energy. An intriguing possibility is the decay of sterile neutrino, a long-sought dark matter particle candidate. Assuming that all dark matter is in sterile neutrinos with m sub(s) = 2E = 7.1 keV, our detection corresponds to a neutrino decay rate consistent with previous upper limits. However, based on the cluster masses and distances, the line in Perseus is much brighter than expected in this model, significantly deviating from other subsamples. This appears to be because of an anomalously bright line at E = 3.62 keV in Perseus, which could be an Ar XVII dielectronic recombination line, although its emissivity would have to be 30 times the expected value and physically difficult to understand. Another alternative is the above anomaly in the Ar line combined with the nearby 3.51 keV K line also exceeding expectation by a factor of 10-20. Confirmation with Astro-H will be critical to determine the nature of this new line.
Abstract
A dissociative merger is formed by the interplay of ram pressure and gravitational forces, which can lead to a spatial displacement of the dark matter and baryonic components of the recently ...collided subclusters. CIZA J0107.7+5408 is a nearby (
z
= 0.105) dissociative merger that hosts two X-ray brightness peaks and a bimodal galaxy distribution. Analyzing MMT/Hectospec observations, we investigate the line-of-sight and spatial distribution of cluster galaxies. Utilizing deep, high-resolution Hubble Space Telescope Advanced Camera for Surveys imaging and large field-of-view Subaru Hyper-Suprime-Cam observations, we perform a weak-lensing analysis of CIZA J0107.7+5408. Our weak-lensing analysis detects a bimodal mass distribution that is spatially consistent with the cluster galaxies but significantly offset from the X-ray brightness peaks. Fitting two Navarro–Frenk–White halos to the lensing signal, we find an equal-mass merger with subcluster masses of
M
200
,
NE
=
2.8
−
1.1
+
1.1
×
10
14
M
⊙
and
M
200
,
SW
=
3.1
−
1.2
+
1.2
×
10
14
M
⊙
. Moreover, the mass-to-light ratios of the subclusters,
(
M
/
L
)
NE
=
571
−
91
+
89
M
☉
/
L
☉
,
B
and
(
M
/
L
)
SW
=
564
−
89
+
87
M
☉
/
L
☉
,
B
, are found to be consistent with each other and within the range of mass-to-light ratios found for galaxy clusters.
We compare recent results from X-ray, strong lensing, weak lensing, and optical observations with numerical simulations of the merging galaxy cluster 1E 0657-56. X-ray observations reveal a ...bullet-like subcluster with a prominent bow shock, which gives an estimate for the merger velocity of 4700 km s super(-1), while lensing results show that the positions of the total mass peaks are consistent with the centroids of the collisionless galaxies (and inconsistent with the X-ray brightness peaks). Previous studies, based on older observational data sets, have placed upper limits on the self- interaction cross section of dark matter per unit mass, image, using simplified analytic techniques. In this work, we take advantage of new, higher quality observational data sets by running full N-body simulations of 1E 0657-56 that include the effects of self-interacting dark matter, and comparing the results with observations. Furthermore, the recent data allow for a new independent method of constraining image, based on the nonobservation of an offset between the bullet subcluster mass peak and galaxy centroid. This new method places an upper limit (68% confidence) of image cm super(2) g super(-1). If we make the assumption that the subcluster and the main cluster had equal mass-to-light ratios prior to the merger, we derive our most stringent constraint of image cm super(2) g super(-1), which comes from the consistency of the subcluster's observed mass-to-light ratio with the main cluster's, and with the universal cluster value, ruling out the possibility of a large fraction of dark matter particles being scattered away due to collisions. Our limit is a slight improvement over the previous result from analytic estimates, and rules out most of the 0.5-5 cm super(2) g super(-1) range invoked to explain inconsistencies between the standard collisionless cold dark matter model and observations.
ABSTRACT We perform a detailed study of the stacked Suzaku observations of 47 galaxy clusters, spanning a redshift range of 0.01-0.45, to search for the unidentified 3.5 keV line. This sample ...provides an independent test for the previously detected line. We detect a -significant spectral feature at 3.5 keV in the spectrum of the full sample. When the sample is divided into two subsamples (cool-core and non-cool core clusters), the cool-core subsample shows no statistically significant positive residuals at the line energy. A very weak ( confidence) spectral feature at 3.5 keV is permitted by the data from the non-cool-core clusters sample. The upper limit on a neutrino decay mixing angle of from the full Suzaku sample is consistent with the previous detections in the stacked XMM-Newton sample of galaxy clusters (which had a higher statistical sensitivity to faint lines), M31, and Galactic center, at a 90% confidence level. However, the constraint from the present sample, which does not include the Perseus cluster, is in tension with previously reported line flux observed in the core of the Perseus cluster with XMM-Newton and Suzaku.
ABSTRACT The intracluster medium (ICM), as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics under extreme conditions that cannot be achieved on Earth. NGC ...1404 is a bright elliptical galaxy that is being gas stripped as it falls through the ICM of the Fornax Cluster. We use the new Chandra X-ray observations of NGC 1404 to study ICM microphysics. The interstellar medium of NGC 1404 is characterized by a sharp leading edge, 8 kpc from the Galaxy center, and a short downstream gaseous tail. Contact discontinuities are resolved on unprecedented spatial scales (0 5 = 45 pc) due to the combination of the proximity of NGC 1404, the superb spatial resolution of Chandra, and the very deep (670 ks) exposure. At the leading edge, we observe sub-kiloparsec-scale eddies generated by Kelvin-Helmholtz instability (KHI) and put an upper limit of 5% Spitzer on the isotropic viscosity of the hot cluster plasma. We also observe mixing between the hot cluster gas and the cooler galaxy gas in the downstream stripped tail, which provides further evidence of a low viscosity plasma. The assumed ordered magnetic fields in the ICM ought to be smaller than 5 G to allow KHI to develop. The lack of an evident magnetic draping layer just outside the contact edge is consistent with such an upper limit.
We present Chandra and XMM-Newton X-ray observations of the Abell 3391/Abell 3395 intercluster filament. It has been suggested that the galaxy clusters Abell 3395, Abell 3391, and the galaxy group ...ESO-161 -IG 006 located between the two clusters, are in alignment along a large-scale intercluster filament. We find that the filament is aligned close to the plane of the sky, in contrast to previous results. We find a global projected filament temperature kT = keV, electron density cm−3, and M . The thermodynamic properties of the filament are consistent with that of the intracluster medium (ICM) of Abell 3395 and Abell 3391, suggesting that the filament emission is dominated by ICM gas that has been tidally disrupted during an early stage merger between these two clusters. We present temperature, density, entropy, and abundance profiles across the filament. We find that the galaxy group ESO-161 may be undergoing ram-pressure-stripping in the low-density environment at or near the virial radius of both clusters, due to its rapid motion through the filament.
We present new weak-lensing observations of 1E 0657-558 (z = 0.296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the ...gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray-emitting plasma are spatially segregated. By using both wide-field ground-based images and HST/ACS images of the cluster cores, we create gravitational lensing maps showing that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8 ssignificance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law and thus proves that the majority of the matter in the system is unseen.
ABSTRACT We present results from recent Suzaku and Chandra X-ray and Multiple Mirrior Telescope optical observations of the strongly merging "double cluster" A1750 out to its virial radius, both ...along and perpendicular to a putative large-scale structure filament. Some previous studies of individual clusters have found evidence for ICM entropy profiles that flatten at large cluster radii, as compared with the self-similar prediction based on purely gravitational models of hierarchical cluster formation, and gas fractions that rise above the mean cosmic value. Weakening accretion shocks and the presence of unresolved cool gas clumps, both of which are expected to correlate with large-scale structure filaments, have been invoked to explain these results. In the outskirts of A1750, we find entropy profiles that are consistent with self-similar expectations, and gas fractions that are consistent with the mean cosmic value, both along and perpendicular to the putative large-scale filament. Thus, we find no evidence for gas clumping in the outskirts of A1750, in either direction. This may indicate that gas clumping is less common in lower temperature (kT 4 keV), less massive systems, consistent with some (but not all) previous studies of low-mass clusters and groups. Cluster mass may, therefore, play a more important role in gas clumping than dynamical state. Finally, we find evidence for diffuse, cool (<1 keV) gas at large cluster radii (R200) along the filament, which is consistent with the expected properties of the denser, hotter phase of the warm-hot intergalactic medium.
Background Aortic syndromes (ASs), including aortic dissection, intramural hematoma, and penetrating aortic ulcer, carry significant acute and long-term morbidity and mortality. However, the ...contemporary incidence and outcomes of AS are unknown. Methods and Results We used the Rochester Epidemiology Project record linkage system to identify all Olmsted County, MN, residents with AS (1995-2015). Diagnostic imaging, medical records, and death certificates were reviewed to confirm the diagnosis and AS subtype. Age- and sex-adjusted incidence rates were estimated using annual county-level census data. Survival for patients with AS was compared with age- and sex-matched controls using Cox regression to adjust for comorbid conditions. We identified 133 patients with AS (77, aortic dissection; 21, intramural hematoma; and 35, penetrating aortic ulcer). Average age was 71.8 years (SD=14.1), and 57% were men. The age- and sex-adjusted incidence was 7.7 per 100 000 person-years, was higher for men than women (10.2 versus 5.7 per 100 000 person-years), and increased with age. Among subtypes, the incidence of aortic dissection was highest (4.4 per 100 000 person-years), whereas the incidence of penetrating aortic ulcer and intramural hematoma was lower (2.1 and 1.2 per 100 000 person-years). Overall, the incidence of AS was stable over time ( P trend=0.33), although the incidence of penetrating aortic ulcer seemed to increase from 0.6 to 2.6 per 100 000 person-years ( P=0.008) with variability over the study interval. Patients with AS had more than twice the mortality rate at 5, 10, and 20 years when compared with population-based controls (5-, 10-, and 20-year mortality 39%, 57%, and 91% versus 18%, 41%, and 66%; overall adjusted mortality hazards ratio=2.1; P<0.001). Survival was lower than expected up to 90 days after AS diagnosis and did not differ significantly by subtype or by 5-year strata of diagnosis. Conclusions Overall, the incidence of aortic dissection and intramural hematoma has remained stable since 1995, despite the decline noted for other cardiovascular disease. AS confers increased early and long-term mortality that has not changed. These data highlight the need to improve long-term care to impact the prognosis of this patient group.
We present results of a joint Chandra and XMM-Newton analysis of the Fornax Cluster, the nearest galaxy cluster in the southern sky. Signatures of merger-induced gas sloshing can be seen in the X-ray ...image. We identify four sloshing cold fronts in the intracluster medium, residing at radii of 3 kpc (west), 10 kpc (northeast), 30 kpc (southwest), and 200 kpc (east). Despite spanning over two orders of magnitude in radius, all four cold fronts fall onto the same spiral pattern that wraps around the BCG NGC 1399, likely all initiated by the infall of NGC 1404. The most evident front is to the northeast, 10 kpc from the cluster center, which separates low-entropy high-metallicity gas and high-entropy low-metallicity gas. The metallicity map suggests that gas sloshing, rather than an AGN outburst, is the driving force behind the redistribution of the enriched gas in this cluster. The innermost cold front resides within the radius of the strong cool core. The sloshing timescale within the cooling radius, calculated from the Brunt-Väsälä frequency, is an order of magnitude shorter than the cooling time. It is plausible that gas sloshing is contributing to the heating of the cool core, provided that gas of different entropies can be mixed effectively via Kelvin-Helmholtz instability. The estimated age of the outermost front suggests that this is not the first infall of NGC 1404.
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