Catalog of X-ray-selected extended galaxy clusters from the ROSAT All-Sky Survey (RXGCC)

Abstract

Context. There is a known tension between cosmological parameter constraints obtained from the primary cosmic microwave background and those drawn from galaxy cluster samples. One possible explanation for this discrepancy may be that the incomplete character of detected clusters is higher than estimated and, as a result, certain types of groups or galaxy clusters have been overlooked in the past. Aims. 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 (RASS), based on a dedicated source detection and characterization algorithm that is optimized for extended sources. Methods. Our state-of-the-art algorithm includes multi-resolution filtering, source detection, and characterization. On the basis of extensive simulations, we investigated the detection efficiency and sample purity. We used previous cluster catalogs in X-ray and other bands, as well as spectroscopic and photometric redshifts of galaxies to identify clusters. Results. We report a catalog of galaxy clusters at high galactic latitude based on the ROSAT All-sky Survey, known as the RASS-based extended X-ray Galaxy Cluster Catalog, which includes 944 groups and clusters. Of this number, 641 clusters have been previously identified based on intra-cluster medium (ICM) emission (Bronze), 154 known optical and infrared clusters are detected as X-ray clusters for the first time (Silver) and 149 are identified as clusters for the first time (Gold). Based on 200 simulations, the contamination ratio of the detections that were identified as clusters by ICM emission and the detections that were identified as optical and infrared clusters in previous work is 0.008 and 0.100, respectively. Compared with the Bronze sample, the Gold+Silver sample is less luminous, less massive, and exhibits a flatter surface brightness profile. Specifically, the median flux in [0.1−2.4] keV band for Gold+Silver and Bronze sample is 2.496 × 10−12 erg s−1 cm−2 and 4.955 × 10−12 erg s−1 cm−2, respectively. The median value of β (the slope of cluster surface brightness profile) is 0.76 and 0.83 for the Gold+Silver and Bronze sample, respectively.

Spectroscopic Confirmation of Two X-Ray Diffuse and Massive Galaxy Clusters at Low Redshift

“…We selected our targets from the RXGCC catalog by Xu et al (2021). The basic procedure of detecting extended clusters using X-ray images in Xu et al (2021) is summarized below.…”

“…We selected our targets from the RXGCC catalog by Xu et al (2021). The basic procedure of detecting extended clusters using X-ray images in Xu et al (2021) is summarized below. The algorithm includes a multiresolution wavelet filtering of the RASS image at [0.5-2.0] keV, a source extraction, and a maximum likelihood fitting to characterize detections.…”

“…We selected two newly ICM-identified, very extended cluster candidates from the RXGCC catalog of Xu et al (2021). The brief selection procedure is as follows.…”

“…The two quasars are included in the ROSAT X-ray Source Catalog (Voges et al 1999(Voges et al , 2000Boller et al 2016) and Half-Million Quasar catalog (Flesch 2015). The existence of the two quasars has affected the determination of the X-ray center in the work of Xu et al (2021). Thus, we masked out the two quasars in the RASS image and the newly determined X-ray center is shown in Table 1.…”

“…Recently, Xu et al (2018Xu et al ( , 2021 reanalyzed the ROSAT All-Sky Survey (RASS) images using a combination of wavelet filtering, source extraction, and maximum likelihood fitting. They identified 944 very extended galaxy clusters, and constructed an X-ray selected catalog of extended clusters from RASS (referred to as the RXGCC catalog).…”