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The X-ray telescope eROSITA onboard the newly launched SRG mission serendipitously observed the galaxy cluster A3408 ($z=0.0420$) 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 ($z=0.0428$), appears to be close at least in projection ($sim 1.7$ 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 $1.4r_{500}$. 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 ${rm k_B}T_{500}=(2.23pm0.09)$ keV. The T-profile reveals a hot core within $2$ of the emission peak, ${rm k_B}T=3.04^{+0.29}_{-0.25}$ keV. Employing a M-T relation, we obtain $M_{500}=(9.27pm0.75)times 10^{13}M_{odot}$ iteratively. The $r_{200}$ 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.
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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$_{200}$=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$pm$ 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 1058$pm$41 km s$^{-1}$. The total mass was determined as $M_{200}$=1.38$pm$ 0.25x10$^{15}$ $M_{odot}$. The mass estimate from the M-T relation is significantly lower at M$_{200}$=5.09$pm$ 0.59x10$^{14}M_{odot}$. 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.
The galaxy cluster Abell 3266 is one of the X-ray brightest in the sky and is a well-known merging system. Using the ability of the eROSITA telescope onboard SRG (Spectrum Rontgen Gamma) to observe a wide field with a single pointing, we analyse a new observation of the cluster out to a radius of R_200. The X-ray images highlight substructures present in the cluster, including the northeast-southwest merger seen in previous ASCA, Chandra and XMM-Newton data, a merging group towards the northwest and filamentary structures between the core and one or more groups towards the west. We compute spatially-resolved spectroscopic maps of the thermodynamic properties of the cluster, including the metallicity. The merging subclusters are seen as low entropy material within the cluster. The filamentary structures could be the rims of a powerful AGN outburst, or most likely material stripped from the western group(s) as they passed through the cluster core. Seen in two directions is a pressure jump at a radius of 1.1 Mpc consistent with a shock with a Mach number of ~1.5-1.7. The eROSITA data confirm that the cluster is not a simple merging system, but is made up of several subclusters which are merging or will shortly merge. For the first time we find a radio halo associated with the system detected in GLEAM data. We compute a hydrostatic mass from the eROSITA data, finding good agreement with a previous XMM-Newton result. With this pointing we detect several extended sources, where we find for seven of them secure associations between z=0.36-1.0; i.e., background galaxy groups and clusters, highlighting the power of eROSITA to find such systems.
We used the APEX-SZ and LABOCA bolometer cameras on the APEX telescope to map the decrement of the Sunyaev-Zeldovich effect at 150 GHz and the increment at 345 GHz toward the galaxy cluster Abell 2163. The SZE images were used to model the radial density and temperature distribution of the ICM, and to derive the gas mass fraction in the cluster under the assumption of hydrostatic equilibrium. We used the isothermal beta model to fit the SZE decrement/increment radial profiles. We performed a simple, non-parametric de-projection of the radial density and temperature profiles, in conjunction with XMM-Newton X-ray data, under the simplifying assumption of spherical symmetry. We combined the peak SZE signals derived in this paper with published SZE measurements of this cluster to derive the cluster line-of-sight bulk velocity and the central Comptonization, using priors on the ICM temperature. We find that the best-fit isothermal model to the SZE data is consistent with the ICM properties implied by the X-ray data, particularly inside the central 1 Mpc radius. Although the assumptions of hydrostatic equilibrium and spherical symmetry may not be optimal for this complex system, the results obtained under these assumptions are consistent with X-ray and weak-lensing measurements. This shows the applicability of the simple joint SZE and X-ray de-projection technique described in this paper for clusters with a wide range of dynamical states. (Abridged)
Diffuse radio emission in galaxy clusters, and their connection with cluster mergers, are still debated. We seek to explore the internal dynamics of the radio halo cluster Abell 545. This cluster is also peculiar for hosting in its center a very bright, red, diffuse intracluster light due to an old, stellar population, so bright to be named as star pile. Our analysis is based on redshift data for 110 galaxies. We identify 95 cluster members and analyze the cluster internal dynamics by combining galaxy velocities and positions. We also use both photometric and X-ray data. We estimate the cluster redshift, z=0.1580, a velocity dispersion of 1200 km/s, and ICM temperature kT_X~8 keV. Our optical and X-ray analyses detect substructures. Optical data reveal three main galaxy clumps (center, NNW, and NE), and possibly a fourth clump at South. There is not a dominant galaxy and the four brightest galaxies avoid the cluster core (>~0.4h distant from the cluster center) and are >~1500 km/s far from the mean cluster velocity. The analysis of the X-ray surface brightness distribution provides us evidence of a disturbed dynamical phase. Located in the star pile region there is the brightest galaxies of the cluster core (CBCG) and a very compact elliptical galaxy. We show that the star pile has a similar redshift to that of the CBCG. Both the star pile and the CBCG are at rest in the cluster rest frame. The emerging picture of Abell 545 is that of a massive, M(R<1.6 h_70^-1 Mpc)=1.1-1.8x10^15 h_70^-1 Msun, very complex cluster with merging occurring along two directions. A545 gives another proof in the favor of the connection between cluster merger and extended, diffuse radio emission. The star pile, likely due to the process of a brightest galaxy forming in the cluster core. A545 represents a textbook cluster where to study the simultaneous formation of a galaxy system and its brightest galaxy.
Cosmological simulations are fundamental tools to study structure formation and the astrophysics of evolving structures, in particular clusters of galaxies. While hydrodynamical simulations cannot sample efficiently large volumes and explore different cosmologies at the same time, N-body simulations lack the baryonic physics that is crucial to determine the observed properties of clusters. One solution is to use (semi-)analytical models to implement the needed baryonic physics. In this way, we can generate the many mock universes that will be required to fully exploit future large sky surveys, such as that from the upcoming eROSITA X-ray telescope. We developed a phenomenological model based on observations of clusters to implement gas density and temperature information on the dark-matter-only halos of the MultiDark simulations. We generate several full-sky mock light-cones of clusters for the WMAP and Planck cosmologies, adopting different parameters in our phenomenological model of the intra-cluster medium. For one of these simulations and models, we also generate 100 light-cones corresponding to 100 random observers and explore the variance among them in several quantities. In this first paper on MultiDark mock galaxy cluster light-cones, we focus on presenting our methodology and discuss predictions for eROSITA, in particular, exploring the potential of angular power spectrum analyses of its detected (and undetected) cluster population to study X-ray scaling relations, the intra-cluster medium, and the composition of the cosmic X-ray background. We make publicly available on-line more than 400 GB of light-cones, which include the expected eROSITA count rate, on Skies & Universes (http://www.skiesanduniverses.org).
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