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We present the serendipitous discovery of a large double radio relic associated with the merging galaxy cluster PSZ2 G277.93+12.34 and a new odd radio circle, ORC J1027-4422, both found in deep MeerKAT 1.3 GHz wide-band data. The angular separation of the two arc-shaped cluster relics is 16 arcmin or 2.6 Mpc for a cluster redshift of z = 0.158. The thin southern relic, which shows a number of ridges/shocks including one possibly moving inwards, has a linear extent of 1.64 Mpc. In contrast, the northern relic is about twice as wide, twice as bright, but only has a largest linear size of 0.66 Mpc. Complementary SRG/eROSITA X-ray images reveal extended emission from hot intracluster gas between the two relics and around the narrow-angle tail (NAT) radio galaxy PMN J1033-4335 (z = 0.153) located just east of the northern relic. No radio halo associated with the PSZ2 cluster is detected. The radio morphologies of the NAT galaxy and the northern relic, which are also detected with the Australian Square Kilometer Array Pathfinder at 887.5 MHz, suggest both are moving in the same outward direction. The discovery of ORC J1027-4422 in a different part of the MeerKAT image makes it the 4th known single ORC. It has a diameter of 90" corresponding to 400 kpc at a tentative redshift of z = 0.3 and remains undetected in X-ray emission. We discuss similarities between galaxy and cluster mergers as the formation mechanisms for ORCs and radio relics, respectively., 14 pages, 10 figures, submitted to MNRAS

There is a known tension between cosmological parameter constraints obtained from the primary CMB and those from galaxy cluster samples. One possible explanation could be certain types of groups or clusters of galaxy have been missed in the past. We aim to search for galaxy groups and clusters with particularly extended surface brightness distributions, by creating a new X-ray selected catalog of extended galaxy clusters from the ROSAT All-Sky Survey, using a dedicated algorithm optimized for extended sources. Through extensive simulations, the detection efficiency and sample purity are investigated. Previous cluster catalogs in X-ray and other wave-bands, as well as spectroscopic and photometric redshifts of galaxies are used for the cluster identification. We report a catalog of galaxy clusters at high galactic latitude based on the ROSAT All-sky Survey, named as RXGCC, which includes 944 groups and clusters. Out of it, 641 clusters have been identified through ICM emission previously (Bronze), 154 known optical and infrared clusters are detected as X-ray clusters for the first time (Silver), and 149 identified as clusters for the first time (Gold). Based on 200 simulations, the contamination ratio of the detections which were identified as clusters by ICM emission, and the detections which were identified as optical and infrared clusters in previous work is 0.008 and 0.100, respectively. Compared with Bronze sample, the Gold+Silver sample is less luminous, less massive, and has a flatter surface brightness profile. Specifically, the median flux in [0.1-2.4]keV band for Gold+Silver and Bronze sample is 2.496e-12 erg/s/cm^2 and 4.955e-12 erg/s/cm^2, respectively. The median slope of cluster profile is 0.76 and 0.83 for Gold+Silver and Bronze sample, respectively. This whole sample is available at https://github.com/wwxu/rxgcc.github.io/blob/master/table_rxgcc.fits (Abridged), 18 pages, 17 figures, accepted by A&A

Monthly Notices of the Royal Astronomical Society, 422 (1), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

It is believed that the global baryon content of clusters of galaxies is representative of the matter distribution of the universe, and can, therefore, be used to reliably determine the matter density parameter Omega_m. This assumption is challenged by the growing evidence from optical and X-ray observations that the total baryon mass fraction increases towards rich clusters. In this context, we investigate the dependence of stellar, and total baryon mass fractions as a function of mass. To do so, we used a subsample of nineteen clusters extracted from the X-ray flux limited sample HIFLUGCS that have available DR-7 Sloan Digital Sky Survey (SDSS) data. From the optical analysis we derived the stellar masses. Using XMM-Newton we derived the gas masses. Then, adopting a scaling relation we estimate the total masses. Adding the gas and the stellar mass fractions we obtain the total baryonic content that we find to increase with cluster mass, reaching 7-year Wilkinson Microwave Anisotropy Probe (WMAP-7) prediction for clusters with M_500 = 1.6 x 10^{15} M_sun. We observe a decrease of the stellar mass fraction (from 4.5% to ~1.0%) with increasing total mass where our findings for the stellar mass fraction agree with previous studies. This result suggests a difference in the number of stars formed per unit of halo mass, though with a large scatter for low-mass systems. That is, the efficiency of star formation varies on cluster scale that lower mass systems are likely to have higher star formation efficiencies. It follows immediately that the dependence of the stellar mass fraction on total mass results in an increase of the mass-to-light ratio from lower to higher mass systems. We also discuss the consequences of these results in the context of determining the cosmic matter density parameter Omega_m., Comment: Accepted for publication in ApJ, 11 pages, 5 figures. http://stacks.iop.org/0004-637X/743/13

We report on the status of our effort to constrain the nature of dark energy through the evolution of the cluster mass function. Chandra temperature profiles for 31 clusters from a local cluster sample are shown. The X-ray appearance of the proto supermassive binary black hole at the center of the cluster Abell 400 is described. Preliminary weak lensing results obtained with Megacam@MMT for a redshift z=0.5 cluster from a distant cluster sample are given., Comment: 5 pages, to appear in: Aschenbach, B., Burwitz, V., Hasinger, G., Leibundgut, B. (eds.), Relativistic Astrophysics and Cosmology - Einstein's Legacy. ESO Astrophysics Symposia, Springer Verlag, Berlin, Germany

The original abstract significantly exceeds the space available here, so here's a brief summary. The abstract is similar to the abstract of astro-ph/0111285 (ApJ, 567, 716) which describes the X-ray galaxy cluster sample HIFLUGCS, the X-ray luminosity--gravitational mass relation, the cluster mass function, and the derived cosmological constraints. Additionally, the fraction of the total gravitating mass in the universe which is contained in intracluster gas is quantified. Furthermore, physical properties of the cluster sample have been studied and analyses of relations between different cluster parameters (including the gas mass fraction, gas temperature, X-ray luminosity, gas mass, gravitational mass, beta, and core radius) are discussed. Also, results from an analysis of XMM-Newton performance verification phase data of Abell 1835 are described., Comment: 143 pages; Ph.D. thesis, Ludwig-Maximilians-Universitaet Muenchen (2001); thesis was submitted on July 27, 2001 (i.e., it took me two years to get around to submit it to astro-ph); the abstract -Chapter 0- is in German, the rest in English (the summary -Chapter 9- is pretty much a translation of Chapter 0 into English); also available at http://www.reiprich.net

The cosmological implications from a new estimate of the local X-ray galaxy cluster abundance are summarized. The results are then compared to independent observations. It is suggested that `low' values for the mean cosmic matter density and the amplitude of mass density fluctuations currently do not appear unreasonable observationally., Comment: 6 pages; to be published in the Proceedings of the Conference on Matter and Energy in Clusters of Galaxies, Chung-Li (2002), editors: S. Bowyer and C.-Y. Hwang; also available at http://www.reiprich.net

It is shown that galaxy cluster surveys selecting clusters by their X-ray luminosity effectively select by cluster mass. It is shown that a selection based solely on Abell galaxy richness is less efficient in terms of mass. Furthermore the empirical X-ray luminosity - gravitational mass relation and its scatter is quantified and the relation is compared to predicted relations., Comment: 3 pages; to be published in the Proceedings of the Workshop on Mining the Sky, Garching (2000); also available at http://www.xray.mpe.mpg.de/~reiprich/act/publi.html

One hundred and six galaxy clusters have been studied in detail using X-ray data and important global physical properties have been determined. Correlations between these properties are studied with respect to the description of clusters as a self-similar class of objects. The results support the self-similar picture only partly and significant deviations are found for some correlations., Comment: 4 pages; to be published in the Proceedings of the Ringberg Workshop on Diffuse Thermal and Relativistic Plasma in Galaxy Clusters, Ringberg Castle (1999); also available at http://www.xray.mpe.mpg.de/~reiprich/act/publi.html

The majority of the ordinary matter in the local Universe has been heated by strong structure formation shocks and resides in a largely unexplored hot, diffuse, X-ray emitting plasma that permeates the halos of galaxies, galaxy groups and clusters, and the cosmic web. We propose a next-generation "Cosmic Web Explorer" that will permit a complete and exhaustive understanding of these unseen baryons. This will be the first mission capable to reach the accretion shocks located several times farther than the virial radii of galaxy clusters, and reveal the out-of-equilibrium parts of the intra-cluster medium which are live witnesses to the physics of cosmic accretion. It will also enable a view of the thermodynamics, kinematics, and chemical composition of the circumgalactic medium in galaxies with masses similar to the Milky Way, at the same level of detail that $Athena$ will unravel for the virialized regions of massive galaxy clusters, delivering a transformative understanding of the evolution of those galaxies in which most of the stars and metals in the Universe were formed. Finally, the proposed X-ray satellite will connect the dots of the large-scale structure by mapping, at high spectral resolution, as much as 100% of the diffuse gas hotter than $10^6$ K that fills the filaments of the cosmic web at low redshifts, down to an over-density of 1, both in emission and in absorption against the ubiquitous cosmic X-ray background, surveying at least 1600 square degrees over 5 years in orbit. This requires a large effective area (~10 m$^2$ at 1 keV) over a large field of view ($\sim1$ deg$^2$), a megapixel cryogenic microcalorimeter array providing integral field spectroscopy with a resolving power $E/\Delta E$ = 2000 at 0.6 keV and a spatial resolution of 5 arcsec in the soft X-ray band, and a low and stable instrumental background ensuring high sensitivity to faint, extended emission., Comment: White paper submitted in response to ESA's Voyage 2050 Call. Accepted for publication in Experimental Astronomy