24 research outputs found
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
X-ray studies of the Abell 3158 galaxy cluster with eROSITA
Context. The most nearby clusters are the best places for studying physical and enrichment effects in the faint cluster outskirts. The Abell 3158 cluster (A3158), located at z = 0.059, is quite extended with a characteristic radius r = 23.95 arcmin. The metal distribution in the outskirts of this cluster has previously been studied with XMM-Newton. In 2019, A3158 was observed as a calibration target in a pointed observation with the eROSITA telescope on board the Spektrum-Roentgen-Gamma mission. Bright large clusters, such as A3158, are ideal for studying the metal distribution in the cluster outskirts, along with the temperature profile and morphology. With the deeper observation time of the eROSITA telescope, these properties can now be studied in greater detail and at larger radii. Furthermore, bright nearby clusters are ideal X-ray instrumental cross-calibration targets as they cover a large fraction of the detector and do not vary in time.
Aims. We first compare the temperature, metal abundance, and normalisation profiles of the cluster from eROSITA with previous XMM-Newton and Chandra data. Following this calibration work, we investigate the temperature and metallicity of the cluster out to almost r, measure the galaxy velocity dispersion, and determine the cluster mass. Furthermore, we search for infalling clumps and background clusters in the field.
Methods. We determined 1D temperature, abundance, and normalisation profiles from both eROSITA and XMM-Newton data as well as 2D maps of temperature and metal abundance distribution from eROSITA data. The velocity dispersion was determined and the cluster mass was calculated from the mass–velocity dispersion (M−σ) relation. Galaxy density maps were created to enable a better understanding of the structure of the cluster and the outskirts.
Results. The overall (i.e. in the range 0.2−0.5r) temperature was measured to be 5.158 ± 0.038 keV. The temperature, abundance, and normalisation profiles of eROSITA all agree to within a confidence level of about 10% with those we determined using XMM-Newton and Chandra data, and they are also consistent with the profiles published previously by the X-COP project. The cluster morphology and surface brightness profile of cluster Abell 3158 appear to be regular at a first glance. Clusters that have such profiles typically are relaxed and host cool cores. However, the temperature profile and map show that the cluster lacks a cool core, as was noted before. Instead, an off-centre cool clump lies to the west of the central cluster region, as reported previously. These are indications that the cluster may be undergoing some sloshing and merger activity. Furthermore, there is a bow-shaped edge near the location of the cool gas clump west of the cluster centre. Farther out west of the X-ray images of A3158, an extension of gas is detected. This larger-scale extension is described here for the first time. The gas metallicity (~0.2 solar) measured in the outskirts (»r) is consistent with an early-enrichment scenario. The velocity dispersion of the cluster member galaxies is measured to be 1058 ± 41 kms based on spectroscopic redshifts of 365 cluster member galaxies and the total mass is determined as M,c = 1.38 ± 0.25 × 10 M⊙. The mass estimate based on the X-ray temperature is significantly lower at M200 = 6.20 ± 0.75 × 10 M⊙, providing further indications that merger activity boosts the velocity dispersion and/or biases the temperature low. An extended X-ray source located south of the field of view also coincides with a galaxy overdensity with spectroscopic redshifts in the range 0.05 < z < 0.07. This source further supports the idea that the cluster is undergoing merger activity. Another extended source located north of the field of view is detected in X-rays and coincides with an overdensity of galaxies with spectroscopic redshifts in the range of 0.070 < z < 0.077. This is likely a background cluster that is not directly related to A3158. Additionally, the known South Pole Telescope cluster SPT-CL J0342-5354 at z = 0. 53 was detected
X-Ray Studies of the Abell 3158 Galaxy Cluster with eROSITA
The most nearby clusters are the best places to study physical and enrichment
effects in the faint cluster outskirts. A3158 located at z=0.059 is quite
extended with a characteristic radius r=23.95 arcmin. In 2019, A3158
was observed as a calibration target in a pointed observation with the eROSITA
telescope onboard the SRG mission.
We determined 1d temperature, abundance and normalisation profiles from
eROSITA and XMM-Newton and Chandra data as well as 2d maps of temperature
distribution from eROSITA data. The velocity dispersion was determined and the
cluster mass was calculated.
The overall temperature was measured to be 4.725 0.035 keV. The profiles
of eROSITA all agree on a ~10% level with those determined with XMM-Newton and
Chandra data. From the temperature map we see that the cluster lacks a cool
core, as noted before. The presence of a previously detected off-centre cool
clump West of the central cluster region is observed. Furthermore there is a
bow shaped edge near the location of the cool gas clump West of the cluster
centre. An extension of gas is detected for the first time further out in the
West. The velocity dispersion of the cluster was measured to be 105841 km
s. The total mass was determined as =1.38 0.25x10
. The mass estimate from the M-T relation is significantly lower at
M=5.09 0.59x10. An extended X-ray source located
South of the cluster also coincides with a galaxy overdensity with redshifts in
the range 0.05<z<0.07. These are indications that the cluster may be undergoing
merger activity. Another extended source located North of the cluster is
detected in X-rays and coincides with an overdensity of galaxies with redshifts
in the range of 0.070<z<0.077. This is likely a background cluster not related
to A3158. Additionally a known SPT cluster at z=0.53 was detected.Comment: 14 pages, 17 figures in the main text, and 3 figures in the appendix.
Accepted by A&A for the Special Issue: The Early Data Release of eROSITA and
Mikhail Pavlinsky ART-XC on the SRG Missio
EROSITA Spectro-Imaging Analysis of the Abell 3408 Galaxy Cluster
The X-ray telescope eROSITA onboard the newly launched SRG mission
serendipitously observed the galaxy cluster A3408 () during the PV
observation of the AGN 1H0707-495. Despite its brightness and large extent, it
has not been observed by any modern X-ray observatory. A neighbouring cluster
in NW direction, A3407 (), appears to be close at least in projection
( Mpc). This cluster pair could be in a pre- or post-merger state.
We perform a detailed X-ray analysis of A3408. We construct particle
background subtracted and exposure corrected images and surface brightness
profiles in different sectors. The spectral analysis is performed out to
. Additionally, a temperature map is presented depicting the
distribution of the ICM temperature. Furthermore, we make use of data from the
RASS to estimate some bulk properties of A3408 and A3407, using the growth
curve analysis method and scaling relations.
The imaging analysis shows a complex morphology of A3408 with a strong
elongation in SE-NW direction. This is quantified by comparing the surface
brightness profiles of the NW, SW, SE and NE directions, where the NW and SE
directions show a significantly higher surface brightness compared to the other
directions. We determine a gas temperature
keV. The T-profile reveals a hot core within of the emission peak, keV. Employing a M-T relation, we obtain
iteratively. The of
A3407 and A3408 are found to overlap in projection which makes ongoing
interactions plausible. The 2d T-map reveals higher temperatures in W than in E
direction.
A3407 and A3408 are likely in a pre-merger state, affecting the ICM
properties, i.e., increased temperatures in the direction of A3407 indicate
adiabatic compression or shocks due to the interaction.Comment: 10 pages, 7 figures (main text), 2 figures (appendix). Submitted to
A&A for the Special Issue: The Early Data Release of eROSITA and Mikhail
Pavlinsky ART-XC on the SRG Missio