Surface Brightness Edge Research Articles

A Rare, Strong Shock Front in the Merging Cluster SPT-CLJ 2031-4037

We present our findings from the new deep Chandra observations (256 ks) of the merging galaxy cluster SPT-CLJ 2031-4037 at z = 0.34. Our observations reveal intricate structures seen in a major merger akin to the Bullet Cluster. The X-ray data confirm the existence of two shock fronts, one to the northwest and one to the southeast, by directly measuring the temperature jump of gas across the surface brightness edges. The stronger shock front in the northwest has a density jump of 3.16 ± 0.34 across the sharp surface brightness edge and Mach number M=3.36−0.48+0.87 , which makes this cluster one of the rare merging systems with a Mach number M > 2. We use the northwestern shock to compare two models for shock heating—the instant heating model and the Coulomb collisional heating model—and we determine that the temperatures across the shock front agree with the Coulomb collisional model of heating. For the shock front in the southeastern region, we find a density jump of 1.53 ± 0.14 and a Mach number of M=1.36−0.08+0.09 .

The SRG/eROSITA All-Sky Survey. View of the Virgo Cluster

As the closest galaxy cluster, the Virgo Cluster is an exemplary environment for the study of the large-scale filamentary structure and physical effects that are present in cluster outskirts but absent from the more easily studied inner regions. Here, we present an analysis of the SRG/eROSITA data from five all-sky surveys. eROSITA allows us to resolve the entire Virgo cluster and its outskirts on scales between 1 kpc and 3 Mpc, covering a total area on the sky of about 25$^ by 25$^ We utilized image manipulation techniques and surface brightness profiles to search for extended emission, surface brightness edges, and features in the outskirts. We employed a method of comparing mean and median profiles to measure gas clumping out to and beyond the virial radius. Surface brightness analysis of the cluster and individual sectors of the cluster reveal the full extent of previously identified cold fronts to the north and south. The emissivity bias due to gas clumping, which we quantify over three orders of magnitude in the radial range, is found to be mild, consistent with previous findings. We find uniform clumping measurements in all directions, with no enhancements along candidate filaments. We find an estimated virial gas mass of $M_ gas r<r_ $\,M$_ Through imaging analysis we detect the presence of extended emission spanning 320\,kpc to the southwest of M49. The extension has a significance of 3.15sigma and is coincident with radio emission detected with LOFAR, which could be evidence of an accretion shock or turbulent reacceleration as the M49 group or background W' cloud falls into the cluster and interacts with the intracluster medium.

Abell 746: A Highly Disturbed Cluster Undergoing Multiple Mergers

We present deep XMM-Newton, Karl G. Jansky Very Large Array, and upgraded Giant Metrewave Radio Telescope observations of Abell 746, a cluster that hosts a plethora of diffuse emission sources that provide evidence for the acceleration of relativistic particles. Our new XMM-Newton images reveal a complex morphology of the thermal gas with several substructures. We observe an asymmetric temperature distribution across the cluster: the southern regions exhibit higher temperatures, reaching ∼9 keV, while the northern regions have lower temperatures (≤4 keV), likely due to a complex merger. We find evidence of three surface brightness edges and one candidate edge, of which three are merger-driven shock fronts. Combining our new data with published LOw-Frequency ARray observations has unveiled the nature of diffuse sources in this system. The bright NW relic shows thin filaments and a high degree of polarization with aligned magnetic field vectors. We detect a density jump, aligned with the fainter relic to the north. To the south, we detect high-temperature regions, consistent with the shock-heated regions and a density jump coincident with the northern tip of the southern radio structure. Its integrated spectrum shows a high-frequency steepening. Lastly, we find that the cluster hosts large-scale radio halo emission. A comparison of the thermal and nonthermal emission reveals an anticorrelation between the bright radio and X-ray features at the center. Our findings suggest that Abell 746 is a complex system that involves multiple mergers.

CHANDRA X-Ray Observations of A119: Cold Fronts and a Shock in an Evolved Off-axis Merger

We present Chandra X-ray observations of the dynamically complex galaxy cluster A119 (z = 0.044). A119 is host to two narrow-angle-tail (NAT) radio sources (0053-015 and 0053-016), whose tails are oriented parallel to each other, despite orthogonally oriented jet axes. Imaging and spectral analysis reveal X-ray emission elongated along the NE–SW axis, along with the presence of complex structures, including surface brightness discontinuities, which suggest possible merger activity along this axis. From radial profiles of the X-ray surface brightness, temperature, pressure, and density, we identify two surface brightness edges that are found to be cold fronts, possibly associated with large-scale sloshing of intracluster medium gas. We also identify a brightness edge to the S that is found to be a shock front with Mach number M = 1.21 ± 0.11, consistent with a merger shock. In addition, previous optical studies show the alignment of optical substructures along the N–S direction. The elongated X-ray emission, orientations of the NAT tails, and alignment of the optical substructure all suggest recent or ongoing merger activity in the NE–SW direction.

Surface brightness discontinuities in radio halos

Context. Dynamical motions in the intra-cluster medium (ICM) can imprint distinctive features on X-ray images that map the thermal bremsstrahlung emission from galaxy clusters, such as sharp surface brightness discontinuities due to shocks and cold fronts. The gas dynamics during cluster mergers may also drive large-scale turbulence in the ICM, which in turn generates extended (megaparsec-scale) synchrontron sources known as radio halos. Aims. Surface brightness edges have been found numerous times in the thermal gas of clusters based on X-ray observations. In contrast, edges in radio halos have only been observed in a handful of cases. Our goal is to search for new radio surface brightness discontinuities in the ICM. Methods. We inspected the images of the Bullet Cluster and the other 25 radio halos reported in the MeerKAT Galaxy Cluster Legacy Survey. To aid the identification of surface brightness discontinuities, we applied a gradient-filtering edge-detection method to the radio images. Results. We find that the adopted filtering technique is helpful in identifying surface brightness edges in radio images, allowing us to identify at least one gradient in half of the radio halos studied. For the Bullet Cluster, we find excellent agreement between the locations of the four radio discontinuities detected and the X-ray edges. This similarity informs us that there is substantial interplay between thermal and nonthermal components in galaxy clusters. This interplay is likely due to the frozen-in ICM magnetic field, which mediates the advection of cosmic rays while being dragged by thermal gas flows. Conclusions. We conclude that radio halos are shaped by dynamical motions in the ICM and that they often display surface brightness discontinuities, which appear to be co-located with edges in the thermal gas emission. Our results demonstrate that new and future generations of radio telescopes will provide an approach to efficiently detecting shocks and cold fronts in the ICM that is complementary to X-rays.

Gas Sloshing and Cold Fronts in Pre-merging Galaxy Cluster A98

We present deep Chandra observations of the pre-merger galaxy cluster Abell 98 (A98). A98 is a complex merging system. While the northern (A98N) and central subclusters (A98S) are merging along the north–south direction, A98S is undergoing a separate late-stage merger, with two distinct X-ray cores. We report the detection of a gas sloshing spiral and two cold front edges in A98N. We find two more surface brightness edges along the east direction of the eastern core and west direction of the western core of A98S. By measuring the gas temperatures and densities across those edges, we confirm that the eastern edge appears to be a cold front while the western edge is a shock front with a Mach number ≈ 1.5. We detect a spiral structure and a “tail” of X-ray emission associated with the eastern core of A98S. Our measurement indicates that the tail is cooler than the surrounding gas at a 4.2σ level. This may suggest that the tail and the spiral structures are the results of ram-pressure stripping, as the eastern core orbits in the main cluster’s gravitational potential.

The NuSTAR and Chandra View of CL 0217+70 and Its Tell-tale Radio Halo

Mergers of galaxy clusters are the most energetic events in the universe, driving shock and cold fronts, generating turbulence, and accelerating particles that create radio halos and relics. The galaxy cluster CL 0217+70 is a remarkable late-stage merger, with a double peripheral radio relic and a giant radio halo. Chandra detects surface brightness (SB) edges that correspond to radio features within the halo. In this work, we present a study of this cluster with Nuclear Spectroscopic Telescope Array and Chandra data using spectro-imaging methods. The global temperature is found to be kT = 9.1 keV. We set an upper limit for the inverse Compton (IC) flux of ∼2.7 × 10−12 erg s−1 cm−2, and a lower limit to the magnetic field of 0.08 μG. Our local IC search revealed a possibility that IC emission may have a significant contribution at the outskirts of the radio halo emission and on/near shock regions within ∼0.6 r 500 of clusters. We detected a “hot spot” feature in our temperature map coincident with an SB edge, but our investigation on its origin is inconclusive. If the “hot spot” is the downstream of a shock, we set a lower limit of kT > 21 keV to the plasma that corresponds to ∼2. We found three shock fronts within 0.5 r 500. Multiple weak shocks within the cluster center hint at an ongoing merger activity and continued feeding of the giant radio halo. CL 0217+70 is the only example hosting these secondary shocks in multiple form.

The eROSITA view of the Abell 3391/95 field: The Northern Clump

Context.Galaxy clusters grow through mergers and the accretion of substructures along large-scale filaments. Many of the missing baryons in the local Universe may reside in such filaments as the warm-hot intergalactic medium (WHIM).Aims.SRG/eROSITA performance verification observations revealed that the binary cluster Abell 3391/3395 and the Northern Clump (the MCXC J0621.7–5242 galaxy cluster) are aligning along a cosmic filament in soft X-rays, similarly to what has been seen in simulations before. We aim to understand the dynamical state of the Northern Clump as it enters the atmosphere (3 ×R200) of Abell 3391.Methods.We analyzed joint eROSITA,XMM-Newton, andChandraobservations to probe the morphological, thermal, and chemical properties of the Northern Clump from its center out to a radius of 988 kpc (R200). We utilized the ASKAP/EMU radio data, the DECam optical image, and thePlanck y-map to study the influence of the wide-angle tail (WAT) radio source on the Northern Clump’s central intracluster medium. Using eROSITA data, we also analyzed the gas properties of the Northern Filament, the region between the virial radii of the Northern Clump and the A3391 cluster. From the Magneticum simulation, we identified an analog of the A3391/95 system along with an infalling group resembling the Northern Clump.Results.The Northern Clump is a weak cool-core cluster centered on a WAT radio galaxy. The gas temperature over 0.2–0.5R500iskBT500=1.99 ± 0.04 keV. We employed the mass-temperature(M – T) scaling relation and obtained a mass estimate ofM500= (7.68 ± 0.43) × 1013M⊙andR500= (63 6 ± 12) kpc. Its X-ray atmosphere has a boxy shape and deviates from spherical symmetry. We identify a southern surface brightness edge, likely caused by subsonic motion relative to the filament gas in the southern direction. At ~R500, the southern atmosphere (infalling head) appears to be 42% hotter than its northern atmosphere. We detect a downstream tail pointing toward the north with a projected length of ~318 kpc, plausibly the result of ram pressure stripping. Through a two-temperature fit, we identify a cooler component in the Northern Filament withkBT= 0.68- 0.64+ 0.38keV andne= 1.99-1.24+0.88× 10-5cm-3, which are consistent within the expected ranges of WHIM properties. The analog group in the Magneticum simulation is experiencing changes in its gas properties and a shift between the position of the halo center and that of the bound gas, while approaching the main cluster pair.Conclusions.The Northern Clump is a dynamically active system and far from being relaxed. Its atmosphere is affected by an interaction with the WAT and by gas sloshing or its infall toward Abell 3391 along the filament, consistent with the analog group-size halo in the Magneticum simulation.

Is There an Enormous Cold Front at the Virial Radius of the Perseus Cluster?

Abstract We present new XMM-Newton observations extending the mosaic of the Perseus cluster out to the virial radius to the west. Previous studies with ROSAT have reported a large excess in surface brightness to the west, possibly the result of large-scale gas sloshing. In our new XMM-Newton observations we have found two X-ray surface brightness edges at 1.2 and 1.7 Mpc to the west. The temperature measurements obtained with Suzaku data indicate that the temperature increases sharply at each edge, consistent with what would be expected from cold fronts. However the the XMM-Newton data are affected by stray light, which at present is a poorly understood source of systematic error that can also lead to curved features in X-ray images. To test our results, we compared our X-ray surface brightness profile with that obtained from ROSAT PSPC data. While the edge at 1.2 Mpc is confirmed by ROSAT PSPC, the ROSAT data quality is insufficient to confirm the outer edge at 1.7 Mpc. Further observations with future X-ray telescopes will be needed to confirm the existence of the outer edge at 1.7 Mpc. By comparing with numerical simulations, we find that these large cold fronts require a large impact parameter, and low-mass ratio mergers that can produce fast gas motions without destroying the cluster core.

X-ray study of the merging galaxy cluster Abell 3411-3412 with XMM-Newton and Suzaku

Context. Previous Chandra observations of the Abell 3411-3412 merging galaxy cluster system revealed an outbound bullet-like sub-cluster in the northern part and many surface brightness edges at the southern periphery, where multiple diffuse sources are also reported from radio observations. Notably, a southeastern radio relic associated with fossil plasma from a radio galaxy and with a detected X-ray edge provides direct evidence of shock re-acceleration. The properties of the reported surface brightness features have yet to be constrained from a thermodynamic viewpoint. Aims. We use the XMM-Newton and Suzaku observations of Abell 3411-3412 to reveal the thermodynamical nature of the previously reported re-acceleration site and other X-ray surface brightness edges. We also aim to investigate the temperature profile in the low-density outskirts with Suzaku data. Methods. We performed both imaging and spectral analysis to measure the density jump and the temperature jump across multiple known X-ray surface brightness discontinuities. We present a new method to calibrate the vignetting function and spectral model of the XMM-Newton soft proton background. Archival Chandra, Suzaku, and ROSAT data are used to estimate the cosmic X-ray background and Galactic foreground levels with improved accuracy compared to standard blank sky spectra. Results. At the southeastern edge, temperature jumps revealed by both XMM-Newton and Suzaku point to a ℳ ∼ 1.2 shock, which agrees with the previous result from surface brightness fits with Chandra. The low Mach number supports the re-acceleration scenario at this shock front. The southern edge shows a more complex scenario, where a shock and the presence of stripped cold material may coincide. There is no evidence for a bow shock in front of the northwestern “bullet” sub-cluster. The Suzaku temperature profiles in the southern low-density regions are marginally higher than the typical relaxed cluster temperature profile. The measured value kT500 = 4.84 ± 0.04 ± 0.19 keV with XMM-Newton and kT500 = 5.17 ± 0.07 ± 0.13 keV with Suzaku are significantly lower than previously inferred from Chandra.

NGC 4869 in the Coma Cluster: Twist, Wrap, Overlap, and Bend

Abstract The upgraded Giant Metrewave Radio Telescope (GMRT) has been used to image the head–tail radio galaxy NGC 4869 in the Coma cluster with an angular resolution of 6.″26 at 250–500 MHz and 2.″18 at the 1050–1450 MHz bands. The archival legacy GMRT data have also been used to image the source with angular resolutions from 4.″9 to 21.″8 at 610 MHz, 325 MHz, 240 MHz, and 150 MHz. We find that the ∼200 kpc scale radio morphology consists of five distinct regions with the clear presence of a pinch at ≈1.′4 (=38.8 kpc) and a ridge at ≈3.′4 (=94.2 kpc) from the head. The sharp bend by ∼70° at ∼3.′5 (=97 kpc) from the head is possibly due to projection effects. The radio spectra show progressive spectral steepening as a function of distance from the head and there is possibly re-acceleration of the synchrotron electrons and perhaps also magnetic field regeneration in the 6″–208″ (=2.8–96.1 kpc) region of the jet. We report a steep spectrum sheath layer enveloping a flat spectrum spine, hinting at a transverse velocity structure with a fast-moving spine surrounded by a slow-moving sheath layer. We also derive the lifetimes of the radiating electrons and equipartition parameters. A plausible explanation for the characteristic feature, a ridge of emission perpendicular to the direction of tail is the flaring of a straight, collimated radio jet as it crosses a surface brightness edge due to Kelvin–Helmholtz instabilities.

Chandra and XMM–Newton observations of A2256: cold fronts, merger shocks, and constraint on the IC emission

ABSTRACT We present the results of deep Chandra and XMM–Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic (RR). The temperature and metallicity maps show clear evidence of a merger between the western subcluster (SC) and the primary cluster (PC). We detect five X-ray surface brightness edges. Three of them near the cluster centre are cold fronts (CFs): CF1 is associated with the infalling SC; CF2 is located in the east of the PC; and CF3 is located to the west of the PC core. The other two edges at cluster outskirts are shock fronts (SFs): SF1 near the RR in the NW has Mach numbers derived from the temperature and the density jumps, respectively, of MT = 1.62 ± 0.12 and Mρ = 1.23 ± 0.06; SF2 in the SE has MT = 1.54 ± 0.05 and Mρ = 1.16 ± 0.13. In the region of the RR, there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse-Compton emission, and therefore set a lower limit on the magnetic field (∼ 450 kpc from PC centre) of B > 1.0 μG for a single power-law electron spectrum or B > 0.4 μG for a broken power-law electron spectrum. We propose a merger scenario including a PC, an SC, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.

Chandra observation of a cold front in Abell 2554

Abstract We present the evidence for the existence of sub-structure in the cold front cluster A2554 based on a 20.14 ks Chandra observation. Using centroid shift and X-ray brightness concentration parameters, we confirm that A2554 is a dynamically disturbed system. We detect two dominant structures: a main cluster at z = 0.1108 and a foreground northern sub-structure at z = 0.1082. The analysis reveals an X-ray surface brightness edge at r ≃ 60 h−1 kpc from the cluster core. The thermodynamical profiles across the edge are ruling out the shock scenario. The temperature jump (from ∼6 keV to ∼10 keV), and pressure equilibrium (P0/P1 = 1.01 ± 0.23) across the edge, are consistent with the definition of a cold front with a Mach number $\mathcal {M}_1=0.94^{+0.13}_{-0.17}$. We also observed a weak bow-shock at ∼100 kpc in front of the cold cloud, corresponding an upper limit to the Mach number $\mathcal {M}_1$ ∼1.1. If the northern sub-structure was not related to the cold front, we conclude that the transonic motion of the cloud is caused by a merger, which was weak or occurred long ago.

AGN Feedback in Galaxy Groups: A Detailed Study of X-Ray Features and Diffuse Radio Emission in IC 1262

Abstract This paper reports a systematic search of X-ray cavities, density jumps, and shocks in the intergalactic environment of the galaxy group IC 1262 using Chandra, GMRT, and Very Large Array archival observations. The X-ray imaging analysis reveals a pair of X-ray cavities to the north and south of the X-ray peak, at projected distances of 6.48 kpc and 6.30 kpc respectively. Total mechanical power contained in both of these cavities is found to be ∼12.37 × 1042 erg s−1, and compares well with the X-ray luminosity, within the cooling radius, measured to be ∼3.29 × 1042 erg s−1, suggesting that the mechanical power injected by the central AGN efficiently balances the radiative loss. We detect a previously unknown X-ray cavity at the position of the southern radio lobe in the intra-group medium and find a loop of excess X-ray emission extending ∼100 kpc southwest from the central galaxy. The X-ray cavity at the position of the southern radio lobe probably represents a first generation X-ray cavity. Two surface brightness edges are evident to the west and northeast of the center of this group. The radio galaxy at the core of the IC 1262 group is a rare low-redshift ultra-steep radio galaxy, its spectral index being α ∼ −1.73 (including the central AGN) and α ∼ −2.08 (excluding the central AGN). We detect a radio phoenix embedded within the southern radio lobe, for the first time in a poor group, with a spectral index (α ≤ −1.92). The spectral index distribution across the phoenix steepens with increasing distance from its intensity peak.

A combined X-ray, optical, and radio view of the merging galaxy cluster MACS J0417.5–1154

We present a comprehensive multi-wavelength analysis of the merging galaxy cluster MACS~J0417.5-1154 at a redshift of $z=0.44$, using available images red obtained with \chandra\ in X-ray, {\it Subaru}, {\it Hubble Space Telescope} (HST) in optical, {\it Giant Metrewave Radio Telescope} (GMRT) in radio and {\it Bolocam} at 2.1~mm wavelength. This is an example of a complex merging galaxy cluster also hosting a steep-spectrum Mpc scale radio halo. The mass distribution obtained by weak lensing reconstruction shows that MACS~J0417.5-1154 belongs to the dissociative class of mergers, where one of its substructures has had its gas content detached after the pericentric passage. We find the main cluster mass $M_{200}~=~11.5^{+3.0}_{-3.5} \times 10^{14}\ M_\odot$ and the smaller second (sub)cluster mass to be $M_{200}~=~1.96^{+1.60}_{-0.95} \times 10^{14}\ M_\odot$, leading to a large total mass of $M_{200}~=~13.8^{+2.6}_{-2.8} \times 10^{14}\ M_\odot$. The overall structure, surface brightness profile, temperature and metal abundance of the intra-cluster medium (ICM) all point towards the presence of a cold front and merger induced gas-sloshing motion near the core. We detect a surface brightness edge to the south$-$east direction at a projected distance of $\sim$45 arcsec ($\sim$255\,kpc) from the centre of this cluster. The X-ray spectral analysis across the inner and outer edge allows us to confirm the detected edge as a cold front. The GMRT 235\,MHz observation shows a comet$-$like extended sychrotron radio halo emission trailing behind the cold front. The peak of the Sunyaev-Zel'dovich decrement is found displaced from the centre of X-ray emission, which is interpreted as consequence of the merger dynamics.

Suzaku and Chandra observations of the galaxy cluster RXC J1053.7+5453 with a radio relic

Abstract We present the results of Suzaku and Chandra observations of the galaxy cluster RXC J1053.7+5453 (z = 0.0704), which contains a radio relic. The radio relic is located at a distance of ∼540 kpc from the X-ray peak toward the west. We measured the temperature of this cluster for the first time. The resultant temperature in the center is ∼1.3 keV, which is lower than the value expected from the X-ray luminosity–temperature and the velocity dispersion–temperature relations. Though we did not find a significant temperature jump at the outer edge of the relic, our results suggest that the temperature decreases outward across the relic. Assuming the existence of the shock at the relic, its Mach number becomes M ≃ 1.4. A possible spatial variation of Mach number along the relic is suggested. Additionally, a sharp surface brightness edge is found at a distance of ∼160 kpc from the X-ray peak toward the west in the Chandra image. We performed X-ray spectral and surface brightness analyses around the edge with the Suzaku and Chandra data, respectively. The obtained surface brightness and temperature profiles suggest that this edge is not a shock but likely a cold front. Alternatively, it cannot be ruled out that thermal pressure is really discontinuous across the edge. In this case, if the pressure across the surface brightness edge is in equilibrium, other forms of pressure sources, such as cosmic-rays, are necessary. We searched for the non-thermal inverse Compton component in the relic region. Assuming a photon index Γ = 2.0, the resultant upper limit of the flux is 1.9 × 10−14 erg s−1 cm−2 for a 4.50 × 10−3 deg2 area in the 0.3–10 keV band, which implies that the lower limit of magnetic field strength becomes 0.7 μG.

MACS J0553.4−3342: a young merging galaxy cluster caught through the eyes of Chandra and HST

We present a detailed analysis of a young merging galaxy cluster \mac~(z=0.43), from {\it Chandra} X-ray and {\it Hubble Space Telescope} archival data. X-ray observations confirm that the X-ray emitting intra-cluster medium (ICM) in this system is among the hottest (average $T=12.1 \pm 0.6$ keV) and most luminous known. Comparison of X-ray and optical images confirm that this system hosts two merging subclusters SC1 and SC2, separated by a projected distance of about 650\,kpc. The subcluster SC2 is newly identified in this work, while another subcluster (SC0), previously thought to be part of this merging system, is shown to be possibly a foreground object. Apart from two subclusters, we find a tail-like structure in the X-ray image, extending to a projected distance of $\sim$1\,Mpc, along the north-east direction of the eastern subcluster (SC1). From a surface brightness analysis, we detect two sharp surface brightness edges at $\sim$40$\arcsec$ ($\sim$320\,kpc) and $\sim$80$\arcsec$ ($\sim$640\,kpc) to the east of SC1. The inner edge appears to be associated with a merger-driven cold front, while the outer one is likely to be due to a shock front, the presence of which, ahead of the cold front, makes this dynamically disturbed cluster interesting. Nearly all the early-type galaxies belonging to the two subclusters, including their BCGs, are part of a well-defined red sequence.

MERGER HYDRODYNAMICS OF THE LUMINOUS CLUSTER RX J1347.5–1145

ABSTRACT We present an analysis of the complex gas hydrodynamics in the X-ray-luminous galaxy cluster RX J1347.5–1145 caught in the act of merging with a subcluster to its southeast using a combined 186 ks Chandra exposure, 2.5 times greater than previous analyses. The primary cluster hosts a sloshing cold front spiral traced by four surface brightness edges west, southeast, east, and northeast from the primary central dominant galaxy, suggesting that the merger is in the plane of the sky. We measure temperature and density ratios across these edges, confirming that they are sloshing cold fronts. We observe the eastern edge of the subcluster infall shock, confirming that the observed subcluster is traveling from the southwest to the northeast in a clockwise orbit. We measure a shock density contrast of and infer a Mach number of 1.25 ± 0.08 and a shock velocity of km s−1. Temperature and entropy maps show cool, low-entropy gas trailing the subcluster in a southwestern tail, consistent with core shredding. Simulations suggest that a perturber in the plane of the sky on a clockwise orbit would produce a sloshing spiral winding counterclockwise, opposite to that observed. The most compelling solution to this discrepancy is that the observed southeastern subcluster is on its first passage, shock-heating gas during its clockwise infall, while the main cluster’s clockwise cold front spiral formed from earlier encounters with a second perturber orbiting counterclockwise.

Applications for edge detection techniques usingChandraandXMM–Newtondata: galaxy clusters and beyond

The unrivalled spatial resolution of the Chandra X-ray observatory has allowed many breakthroughs to be made in high energy astrophysics. Here we explore applications of Gaussian Gradient Magnitude (GGM) filtering to X-ray data, which dramatically improves the clarity of surface brightness edges in X-ray observations, and maps gradients in X-ray surface brightness over a range of spatial scales. In galaxy clusters, we find that this method is able to reveal remarkable substructure behind the cold fronts in Abell 2142 and Abell 496, possibly the result of Kelvin Helmholtz instabilities. In Abell 2319 and Abell 3667, we demonstrate that the GGM filter can provide a straightforward way of mapping variations in the widths and jump ratios along the lengths of cold fronts. We present results from our ongoing programme of analysing the Chandra and XMM-Newton archives with the GGM filter. In the Perseus cluster we identify a previously unseen edge around 850 kpc from the core to the east, lying outside a known large scale cold front, which is possibly a bow shock. In MKW 3s we find an unusual 'V' shape surface brightness enhancement starting at the cluster core, which may be linked to the AGN jet. In the Crab nebula a new, moving feature in the outer part of the torus is identified which moves across the plane of the sky at a speed of ~0.1c, and lies much further from the central pulsar than the previous motions seen by Chandra.

FRONTIER FIELDS CLUSTERS: DEEP CHANDRA OBSERVATIONS OF THE COMPLEX MERGER MACS J1149.6+2223

ABSTRACT The Hubble Space Telescope Frontier Fields cluster MACS J1149.6+2223 is one of the most complex merging clusters, believed to consist of four dark matter halos. We present results from deep (365 ks) Chandra observations of the cluster, which reveal the most distant cold front (z = 0.544) discovered to date. In the cluster outskirts, we also detect hints of a surface brightness edge that could be the bow shock preceding the cold front. The substructure analysis of the cluster identified several components with large relative radial velocities, thus indicating that at least some collisions occur almost along the line of sight. The inclination of the mergers with respect to the plane of the sky poses significant observational challenges at X-ray wavelengths. MACS J1149.6+2223 possibly hosts a steep-spectrum radio halo. If the steepness of the radio halo is confirmed, then the radio spectrum, combined with the relatively regular ICM morphology, could indicate that MACS J1149.6+2223 is an old merging cluster.