Projection effects in galaxy cluster samples: insights from X-ray redshifts

Presently, 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 of the ROSAT satellite limits the attainable amount of spatial information for 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: RXC J2306.6−1319, ZwCl 1665, and RXC J0034.6−0208, 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 (fX, 500 ≥ 5 × 10−12 erg s−1 cm−2 in the 0.1−2.4 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 seven, rather than three. 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 ZwCl 1665 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.

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The 3XMM/SDSS Stripe 82 Galaxy Cluster Survey – II. X-ray and optical properties of the cluster sample

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1097 ◽

2019 ◽

Vol 486 (4) ◽

pp. 4863-4879 ◽

Cited By ~ 2

Author(s):

Ali Takey ◽

Florence Durret ◽

Isabel Márquez ◽

Amael Ellien ◽

Mona Molham ◽

...

Keyword(s):

Optical Properties ◽

Galaxy Cluster ◽

X Rays ◽

Present Sample ◽

X Ray ◽

Cluster Galaxies ◽

Cluster Survey ◽

Cluster Sample ◽

Cluster Mass ◽

First Time

ABSTRACT We present X-ray and optical properties of the optically confirmed galaxy cluster sample from the 3XMM/SDSS Stripe 82 cluster survey. The sample includes 54 galaxy clusters in the redshift range of 0.05–1.2, with a median redshift of 0.36. We first present the X-ray temperature and luminosity measurements that are used to investigate the X-ray luminosity–temperature relation. The slope and intercept of the relation are consistent with those published in the literature. Then, we investigate the optical properties of the cluster galaxies including their morphological analysis and the galaxy luminosity functions (GLFs). The morphological content of cluster galaxies is investigated as a function of cluster mass and distance from the cluster centre. No strong variation of the fraction of early- and late-type galaxies with cluster mass is observed. The fraction of early-type galaxies as a function of cluster radius varies as expected. The individual GLFs of red sequence galaxies were studied in the five ugriz bands for 48 clusters. The GLFs were then stacked in three mass bins and two redshift bins. Twenty clusters of the present sample are studied for the first time in X-rays, and all are studied for the first time in the optical range. Altogether, our sample appears to have X-ray and optical properties typical of ‘average’ cluster properties.

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Interaction of the massive cluster system Abell 3016/3017 embedded in a cosmic filament

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833068 ◽

2019 ◽

Vol 621 ◽

pp. A77 ◽

Cited By ~ 1

Author(s):

Gayoung Chon ◽

Hans Böhringer ◽

Sarthak Dasadia ◽

Matthias Kluge ◽

Ming Sun ◽

...

Keyword(s):

Large Scale ◽

Galaxy Cluster ◽

Cluster System ◽

X Rays ◽

X Ray ◽

Filament Axis ◽

Main Cluster ◽

Abell Clusters ◽

The Galaxy ◽

Massive Cluster

The galaxy cluster system RXCJ0225.9-4154 with the two sub-clusters A3016 and A3017 is embedded in a large-scale structure filament with signatures of filamentary accretion. In a Chandra observation of this system at a redshift of z = 0.2195 we detect both clusters in X-rays. In addition we detect a filament of X-ray emission connecting the two clusters and a galaxy group therein. The main cluster, A3017, shows indications of shocks most probably from a recent interaction with cluster components along the filament axis as well as a cold front at about 150 kpc from the cluster centre. The filament between the two clusters is likely to be heated by the accretion shocks of the clusters. We discuss two scenarios for the origin of the X-ray filament between the two clusters. In the first scenario the material of the filament has been ripped off of A3017 during the fly-by of A3016 and is now trailing the latter sub-cluster. Support for this scenario is a gas deficit on the eastern side of A3017. In the second scenario the filament between the two clusters does not come from either of them, but a significant contribution could come from the galaxy group located inside and the entire structure is on its first collapse. We favour the second explanation as the gas mass in the filament seems to be too large to be supplied by the interaction of the two Abell clusters. The paper describes many properties of the components of this cluster merger system that are used to assist the interpretation of the observed configuration.

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The great Kite in the sky: A LOFAR observation of the radio source in Abell 2626

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039056 ◽

2020 ◽

Vol 643 ◽

pp. A172

Author(s):

A. Ignesti ◽

T. Shimwell ◽

G. Brunetti ◽

M. Gitti ◽

H. Intema ◽

...

Keyword(s):

Radio Source ◽

Spatial Correlation ◽

Thermal Plasma ◽

Low Frequency ◽

Galaxy Cluster ◽

Nonthermal Plasma ◽

X Ray ◽

New Radio ◽

Sky Survey ◽

The Galaxy

Context. The radio source at the center of the galaxy cluster Abell 2626, also known as the Kite, stands out for its unique morphology composed of four symmetric arcs. Previous studies have probed the properties of this source at different frequencies and its interplay with the surrounding thermal plasma, but the puzzle of its origin is still unsolved. Aims. We use a new LOw-Frequency ARray (LOFAR) observation from the LOFAR Two-meter Sky Survey at 144 MHz to investigate the origin of the Kite. Methods. We present a detailed analysis of the new radio data, which we combined with archival radio and X-ray observations. We produced a new, resolved spectral index map of the source with a resolution of 7″ and we studied the spatial correlation of radio and X-ray emission to investigate the interplay between thermal and nonthermal plasma. Results. The new LOFAR data changed our view of the Kite because we discovered two steep-spectrum (α < −1.5) plumes of emission connected to the arcs. The spectral analysis shows, for the first time, a spatial trend of the spectrum along the arcs with evidence of curved synchrotron spectra and a spatial correlation with the X-ray surface brightness. On the basis of our results, we propose that the Kite was originally an X-shaped radio galaxy whose fossil radio plasma, after the end of the activity of the central active galactic nucleus, has been compressed as a consequence of motions of the thermal plasma encompassing the galaxy. The interplay between the compression and advection of the fossil plasma, with the restarting of the nuclear activity of the central galaxy, could have enhanced the radio emission of the fossil plasma producing the arcs of the Kite. We also present the first, low-frequency observation of a jellyfish galaxy in the same field, in which we detect extended, low-frequency emission without a counterpart at higher frequencies.

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A2241: Clusters with Head-Tails at X-Rays

Symposium - International Astronomical Union ◽

10.1017/s0074180900081110 ◽

1996 ◽

Vol 175 ◽

pp. 361-362

Author(s):

L. Norci ◽

L. Feretti ◽

E.J.A. Meurs

Keyword(s):

Galaxy Cluster ◽

Radio Galaxies ◽

Brightness Distribution ◽

Radio Sources ◽

X Rays ◽

Intracluster Medium ◽

X Ray ◽

Physical Conditions ◽

The Galaxy ◽

Energy Equipartition

A ROSAT PSPC image of the galaxy cluster Abell 2241 has been obtained, showing X-ray emission from the intracluster medium and from individual objects. The brightness distribution of the cluster gas is used to assess the physical conditions at the location of two tailed radio galaxies (in A2241E and A2241W, at different redshifts). Together with radio and X-ray information on the two galaxies themselves the results are of relevance to the question of energy equipartition in radio sources.

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The role of AGN activity in the building up of the BCG at z ∼ 1.6

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320003105 ◽

2019 ◽

Vol 15 (S356) ◽

pp. 280-284

Author(s):

Angela Bongiorno ◽

Andrea Travascio

Keyword(s):

Galaxy Cluster ◽

Cluster Galaxy ◽

X Ray ◽

Groups Of Galaxies ◽

Star Forming ◽

The Core ◽

The Galaxy ◽

Multi Wavelength

AbstractXDCPJ0044.0-2033 is one of the most massive galaxy cluster at z ∼1.6, for which a wealth of multi-wavelength photometric and spectroscopic data have been collected during the last years. I have reported on the properties of the galaxy members in the very central region (∼ 70kpc × 70kpc) of the cluster, derived through deep HST photometry, SINFONI and KMOS IFU spectroscopy, together with Chandra X-ray, ALMA and JVLA radio data.In the core of the cluster, we have identified two groups of galaxies (Complex A and Complex B), seven of them confirmed to be cluster members, with signatures of ongoing merging. These galaxies show perturbed morphologies and, three of them show signs of AGN activity. In particular, two of them, located at the center of each complex, have been found to host luminous, obscured and highly accreting AGN (λ = 0.4−0.6) exhibiting broad Hα line. Moreover, a third optically obscured type-2 AGN, has been discovered through BPT diagram in Complex A. The AGN at the center of Complex B is detected in X-ray while the other two, and their companions, are spatially related to radio emission. The three AGN provide one of the closest AGN triple at z > 1 revealed so far with a minimum (maximum) projected distance of 10 kpc (40 kpc). The discovery of multiple AGN activity in a highly star-forming region associated to the crowded core of a galaxy cluster at z ∼ 1.6, suggests that these processes have a key role in shaping the nascent Brightest Cluster Galaxy, observed at the center of local clusters. According to our data, all galaxies in the core of XDCPJ0044.0-2033 could form a BCG of M* ∼ 1012Mȯ hosting a BH of 2 × 108−109Mȯ, in a time scale of the order of 2.5 Gyrs.

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Anisotropy of the galaxy cluster X-ray luminosity–temperature relation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731222 ◽

2018 ◽

Vol 611 ◽

pp. A50 ◽

Cited By ~ 5

Author(s):

Konstantinos Migkas ◽

Thomas H. Reiprich

Keyword(s):

Galaxy Clusters ◽

Statistical Significance ◽

Cosmological Parameters ◽

Galaxy Cluster ◽

Luminosity Distance ◽

Temperature Relation ◽

X Ray ◽

Two Samples ◽

The Galaxy ◽

Group A

We introduce a new test to study the cosmological principle with galaxy clusters. Galaxy clusters exhibit a tight correlation between the luminosity and temperature of the X-ray-emitting intracluster medium. While the luminosity measurement depends on cosmological parameters through the luminosity distance, the temperature determination is cosmology-independent. We exploit this property to test the isotropy of the luminosity distance over the full extragalactic sky, through the normalization a of the LX–T scaling relation and the cosmological parameters Ωm and H0. To this end, we use two almost independent galaxy cluster samples: the ASCA Cluster Catalog (ACC) and the XMM Cluster Survey (XCS-DR1). Interestingly enough, these two samples appear to have the same pattern for a with respect to the Galactic longitude. More specifically, we identify one sky region within l ~ (−15°, 90°) (Group A) that shares very different best-fit values for the normalization of the LX–T relation for both ACC and XCS-DR1 samples. We use the Bootstrap and Jackknife methods to assess the statistical significance of these results. We find the deviation of Group A, compared to the rest of the sky in terms of a, to be ~2.7σ for ACC and ~3.1σ for XCS-DR1. This tension is not significantly relieved after excluding possible outliers and is not attributed to different redshift (z), temperature (T), or distributions of observable uncertainties. Moreover, a redshift conversion to the cosmic microwave background (CMB) frame does not have an important impact on our results. Using also the HIFLUGCS sample, we show that a possible excess of cool-core clusters in this region, is not able to explain the obtained deviations. Furthermore, we tested for a dependence of the results on supercluster environment, where the fraction of disturbed clusters might be enhanced, possibly affecting the LX–T relation. We indeed find a trend in the XCS-DR1 sample for supercluster members to be underluminous compared to field clusters. However, the fraction of supercluster members is similar in the different sky regions, so this cannot explain the observed differences, either. Constraining Ωm and H0 via the redshift evolution of LX–T and the luminosity distance via the flux–luminosity conversion, we obtain approximately the same deviation amplitudes as for a. It is interesting that the general observed behavior of Ωm for the sky regions that coincide with the CMB dipole is similar to what was found with other cosmological probes such as supernovae Ia. The reason for this behavior remains to be identified.

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Radio and X-ray Observations of the Restarted Radio Galaxy in the Galaxy Cluster CL 0838+1948

Galaxies ◽

10.3390/galaxies9040108 ◽

2021 ◽

Vol 9 (4) ◽

pp. 108

Author(s):

Simona Giacintucci ◽

Tracy Clarke ◽

Namir E. Kassim ◽

Wendy Peters ◽

Emil Polisensky

Keyword(s):

Radio Source ◽

Survey Data ◽

Radio Galaxy ◽

Galaxy Cluster ◽

Gas Emission ◽

Low Frequencies ◽

Nuclear Activity ◽

X Ray ◽

Hot Gas ◽

The Galaxy

We present VLA Low-band Ionosphere and Transient Experiment (VLITE) 338 MHz observations of the galaxy cluster CL 0838+1948. We combine the VLITE data with Giant Metrewave Radio Telescope 610 MHz observations and survey data. The central galaxy hosts a 250 kpc source whose emission is dominated by two large lobes at low frequencies. At higher frequencies, a pair of smaller lobes (∼30 kpc) is detected within the galaxy optical envelope. The observed morphology is consistent with a restarted radio galaxy. The outer lobes have a spectral index αout=1.6, indicating that they are old, whereas the inner lobes have αinn=0.6, typical for an active source. Spectral modeling confirms that the outer emission is a dying source whose nuclear activity switched off not more than 110 Myr ago. Using archival Chandra X-ray data, we compare the radio and hot gas emission. We find that the active radio source is contained within the innermost and X-ray brightest region, possibly a galactic corona. Alternatively, it could be the remnant of a larger cool core whose outer layers have been heated by the former epoch of activity that has generated the outer lobes.

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Absorption and Production of Soft X-Rays in the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900100427 ◽

1973 ◽

Vol 55 ◽

pp. 235-249

Author(s):

S. Hayakawa

Keyword(s):

Emission Lines ◽

Interstellar Matter ◽

X Rays ◽

Diffuse Component ◽

Number Density ◽

High Number Density ◽

Hard Component ◽

X Ray ◽

Cygnus Loop ◽

The Galaxy

The column densities of interstellar hydrogen to X-ray sources derived from their spectra are compared with those obtained from 21 cm radio observations. Referring to several observed results on Cyg X-2, Cygnus Loop etc., the interpretation of the low energy cut-off of the spectrum in terms of the interstellar absorption is subject to ambiguities due to a modification of the emission spectrum by Compton scattering in the sources and the contribution of emission lines.The result of soft X-ray sky surveys indicates that the diffuse component of soft X-rays consists of the extragalactic and the galactic components. The former has a hard component with a power law spectrum and a soft component which may be represented by an exponential spectrum. The galactic component is so soft that its spectrum may also be explained by thermal bremsstrahlung of temperature of about 0.1 keV. Its generation rate may account for the heating and ionization of interstellar matter. It is suggested that galactic diffuse soft X-rays are produced by active stars of a rather high number density.

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Soft X-rays from the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900004605 ◽

1970 ◽

Vol 37 ◽

pp. 406-407

Author(s):

M. J. Rees

Keyword(s):

Galactic Plane ◽

Galactic Latitude ◽

X Rays ◽

Indirect Methods ◽

X Ray ◽

Background Data ◽

Diffuse Background ◽

The Galaxy ◽

X Ray Background ◽

Significant Flux

Below 1 keV, analyses of X-ray background data are complicated by galactic absorption effects, which cause the received intensity to vary with galactic latitude. Bowyer et al. (1968) observed that the diffuse background did not fall off as rapidly as was expected towards the galactic plane. One plausible interpretation of their data would be to suppose that a significant flux of soft X-rays emanates from the disc itself. I wish to discuss what could be inferred about the latter component from improved observations of its latitude-dependence, and by indirect methods.

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