Minor Merger-induced Cold Fronts in Abell 2142 and RXJ1720.1+2638 (original) (raw)
Related papers
Substructure in the cold front cluster Abell 3667
The Astrophysical Journal, 2009
We present evidence for the existence of significant substructure in the cold front cluster Abell 3667 based on multi-object spectroscopy taken with the 3.9m Anglo Australian Telescope. This paper is the second in a series analyzing the relationship between cold fronts observed in Chandra X-ray images and merger activity observed at optical wavelengths. We have obtained 910 galaxy redshifts in the field of Abell 3667 out to 3.5 Mpc, of which 550 are confirmed cluster members, more than doubling the number of spectroscopically confirmed members previously available and probing some 3 mag down the luminosity function. From this sample, we derive a cluster redshift of z = 0.0553 ± 0.0002 and velocity dispersion of 1056 ± 38 km s −1 and use a number of statistical tests to search for substructure. We find significant evidence for substructure in the spatial distribution of member galaxies and also in the localized velocity distributions and, in spite of this evidence, find the global velocity distribution does not deviate significantly from a Gaussian. Using combined spatial and velocity information, we find the cluster can be separated into two major structures, with roughly equal velocity dispersions, but offset in peculiar velocity from each other by ∼ 500 km s −1 , and a number of minor substructures. We propose two scenarios which explain the radio and X-ray observations. Our data show the cold front is directly related to cluster merger activity, and also highlights the extent of optical data required to unambiguously detect the presence of substructure.
Monthly Notices of the Royal Astronomical Society, 2010
By analysing the Chandra and XMM-Newton archived data of the nearby galaxy cluster Abell 3158, which was reported to possess a relatively regular, relaxed morphology in the X-ray band in previous works, we identify a bow edge-shaped discontinuity in the X-ray surface brightness distribution at about 120h −1 71 kpc west of the X-ray peak. This feature is found to be associated with a massive, off-centre cool gas clump, and actually forms the west boundary of the cool clump. By calculating the thermal gas pressures in the cool clump and in the freestream region, we determine that the cool gas clump is moving at a subsonic velocity of 700 +140 −340 km s −1 (M = 0.6 +0.1 −0.3) toward west on the sky plane. We exclude the possibility that this cool clump was formed by local inhomogeneous radiative cooling in the intra-cluster medium, due to the effectiveness of the thermal conduction on the timescale of ∼ 0.3 Gyr. Since no evidence for central AGN activity has been found in Abell 3158, and this cool clump bears many similarities to the off-centre cool gas clumps detected in other merging clusters in terms of their mass, size, location, and thermal properties (e.g. lower temperature and higher abundance as compared with the environment), we speculate that the cool clump in Abell 3158 was caused by a merger event, and is the remnant of the original central cool-core of the main cluster or the infalling sub-cluster. This idea is supported not only by the study of line-of-sight velocity distribution of the cluster member galaxies, but also by the study of gas entropy-temperature correlation. This example shows that the appearance of such massive, off-centre cool gas clumps can be used to diagnose the dynamical state of a cluster, especially when prominent shocks and cold fronts are absent.
Chandra Observation of the Merging Cluster Abell 2034
2003
We present an analysis of a Chandra observation of Abell 2034. The cluster has multiple signatures of an ongoing merger, including a cold front and probable significant heating of the intracluster medium above its equilibrium temperature. We find no evidence for the large cooling rate previously determined for the cluster, and in fact find it to be roughly isothermal, though with numerous small-scale inhomogeneities, out to a radius of ~700 kpc. The cold front appears to be in the process of being disrupted by gas dynamic instability and perhaps by shock heating. We find weak evidence for Inverse Compton hard X-ray emission from the radio relic suspected to be associated with the cold front. Finally, we study the emission to the south of the cluster, which was previously thought to be a merging subcluster. We find no evidence that this "subcluster" is interacting with the main Abell 2034 cluster. On the other hand, the properties of this region are inconsistent with an equilibrium cluster at the redshift of Abell 2034 or less. We explore the possibility that it is a disrupted merging subcluster, but find its luminosity to be significantly lower than expected for such a scenario. We suggest that the emission to the south of the cluster may actually be a moderate to high redshift (0.3 < z < 1.25) background cluster seen in projection against Abell 2034.
Abell 1201: The anatomy of a cold front cluster from combined optical and X-ray data
The Astrophysical …, 2009
We present a combined X-ray and optical analysis of the cold front cluster Abell 1201 using archival Chandra data and multi-object spectroscopy taken with the 3.9 m Anglo-Australian and 6.5 m Multiple Mirror Telescopes. This paper represents the first in a series presenting a study of a sample of cold front clusters selected from the Chandra archives with the aim of relating cold fronts to merger activity, understanding the dynamics of mergers and their effect on the cluster constituents. The Chandra X-ray imagery of Abell 1201 reveals two conspicuous surface brightness discontinuities that are shown to be cold fronts, and a remnant core structure. Temperature maps reveal a complex multiphase temperature structure with regions of hot gas interspersed with fingers of cold gas. Our optical analysis is based on a sample of 321 confirmed members, whose mean redshift is z = 0.1673 ± 0.0002 and velocity dispersion is 778 ± 36 km s-1. We search for dynamical substructure and find clear evidence for multiple localized velocity substructures coincident with overdensities in the galaxy surface density. Most notably, we find the structure coincident with the remnant X-ray core. Despite the clear evidence for dynamical activity, we find the peculiar velocity distribution does not deviate significantly from Gaussian. We apply two-body dynamical analyses in order to assess which of the substructures are bound, and thus dynamically important in terms of the cluster merger history. We propose that the cold fronts in Abell 1201 are a consequence of its merger with a smaller subunit, which has induced gas motions that gave rise to "sloshing" cold fronts. Abell 1201 illustrates the value of combining multiwavelength data and multiple substructure detection techniques when attempting to ascertain the dynamical state of a cluster.
A High Fidelity Sample of Cold Front Clusters from the Chandra Archive
The Astrophysical …, 2009
This paper presents a sample of "cold front" clusters selected from the Chandra archive. The clusters are selected based purely on the existence of surface brightness edges in their Chandra images which are modeled as density jumps. A combination of the derived density and temperature jumps across the fronts is used to select nine robust examples of cold front clusters: 1ES0657-558, 3667. This sample is the subject of an ongoing study aimed at relating cold fronts to cluster merger activity, and understanding how the merging environment affects the cluster constituents. Here, temperature maps are presented along with the Chandra X-ray images. A dichotomy is found in the sample in that there exists a subsample of cold front clusters which are clearly mergers based on their X-ray morphologies, and a second subsample which harbor cold fronts, but have surprisingly relaxed X-ray morphologies, and minimal evidence for merger activity at other wavelengths. For this second subsample, the existence of a cold front provides the sole evidence for merger activity at X-ray wavelengths. We discuss how cold fronts can provide additional information which may be used to constrain merger histories, and also the possibility of using cold fronts to distinguish major and minor mergers.
ChandraObservation of the Merging Cluster A2034
The Astrophysical Journal, 2003
We present an analysis of a Chandra observation of Abell 2034. The cluster has multiple signatures of an ongoing merger, including a cold front and probable significant heating of the intracluster medium above its equilibrium temperature. We find no evidence for the large cooling rate previously determined for the cluster, and in fact find it to be roughly isothermal, though with numerous small-scale inhomogeneities, out to a radius of ∼700 kpc. The cold front appears to be in the process of being disrupted by gas dynamic instability and perhaps by shock heating. We find weak evidence for Inverse Compton hard X-ray emission from the radio relic suspected to be associated with the cold front. Finally, we study the emission to the south of the cluster, which was previously thought to be a merging subcluster. We find no evidence that this "subcluster" is interacting with the main Abell 2034 cluster. On the other hand, the properties of this region are inconsistent with an equilibrium cluster at the redshift of Abell 2034 or less. We explore the possibility that it is a disrupted merging subcluster, but find its luminosity to be significantly lower than expected for such a scenario. We suggest that the emission to the south of the cluster may actually be a moderate to high redshift (0.3 z 1.25) background cluster seen in projection against Abell 2034.
THE EFFECTS OF MERGING AND ENVIRONMENT ON GALAXIES AND CLUSTERS OF GALAXIES
Galaxy Clusters: Observations, Physics and …, 2008
the intracluster medium and a clear detection of cooler gas being associated with the gas on the denser side of the front. From this sample, the clusters Abell 1201, Abell 2163, RXJ1720.1+2638 and Abell 3667 were taken as the initial test cases for establishing whether cold fronts are a signpost of ongoing or recent major merger activity. They were targeted for comprehensive spectroscopic follow-up at optical wavelengths using the 3.9m Anglo Australian and 6.5m Multiple Mirror Telescopes.
Chandra observation of the multiple merger cluster Abell 521
Astronomy and Astrophysics, 2006
We present the Chandra analysis of the rich galaxy cluster Abell 521 (z=0.247). The high resolution of the Chandra observation has allowed us to refine the original merging scenario proposed for A521, and to reveal new features in its X-ray emission. A521 has strongly substructured ICM density and temperature maps. Its X-ray diffuse emission is elongated along a NW/SE direction (SX2) and shows two major components, a main cluster and a northern group of galaxies. This latter is in turn substructured, showing a clump of cold and very dense gas centred on the Brightest Cluster Galaxy (BCG), and a northern tail aligned in the SX2 direction. A compression of the X-ray isophotes is also observed South of the BCG. We conclude that the northern group is infalling onto the main cluster along the NW/SE direction. This hypothesis is corroborated by the presence of a hot bar in the ICM temperature map located between the southern and northern regions, as the gas could be compressionally heated due to the subclusters' collision. The hot region corresponds to the eastern part of an over-dense ridge of galaxies, along which it was originally suggested that a merging of subclusters has recently occurred along the line of sight. An alternative hypothesis about the origin of the hot central bar is that we could observe in projection the shock fronts due to this older cluster-cluster collision. However, the two hypothesis do not exclude each other. Two other structures possibly interacting with the main cluster are detected on the West and North-East sides of the BCG. We also uncover the presence of two northern edges in the ICM density, which could be due to the ongoing merging events observed in the central field of the cluster, or even in its outer regions. A521 is a spectacular example of a multiple merger cluster made up by several substructures converging at different epochs towards the centre of the system. The very pertubed dynamical state of this cluster is also confirmed by our discovery of a radio relic in its South-East region.
A Chandrastudy of the Core of the Nearby Cluster Abell 576
We present data from a Chandra observation of the nearby cluster of galaxies Abell 576. The core of the cluster shows a significant departure from dynamical equilibrium. We show that this core gas is most likely the remnant of a merging subcluster, which has been stripped of much of its gas, depositing a stream of gas behind it in the main cluster. The unstripped remnant of the subcluster is characterized by a different temperature, density and metalicity than that of the surrounding main cluster, suggesting its distinct origin. Continual dissipation of the kinetic energy of this minor merger may be sufficient to counteract most cooling in the main cluster over the lifetime of the merger event.
Chandra Observation of Abell 2065: An Unequal Mass Merger?
The Astrophysical Journal
We present an analysis of a 41 ks Chandra observation of the merging cluster Abell 2065 with the ACIS-I detector. Previous observations with ROSAT and ASCA provided evidence for an ongoing merger, but also suggested that there were two surviving cooling cores, which were associated with the two cD galaxies in the center of the cluster. The Chandra observation reveals only one X-ray surface brightness peak, which is associated with the more luminous, southern cD galaxy. The gas related with that peak is cool and displaced slightly from the position of the cD. The data suggest that this cool material has formed a cold front. On the other hand, in the higher spatial resolution Chandra image, the second feature to the north is not associated with the northern cD; rather, it appears to be a trail of gas behind the main cD. We argue that only one of the two cooling cores has survived the merger, although it is possible that the northern cD may not have possessed a cool core prior to the m...