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

Abstract

We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift $z\sim 0.07$ that show extended and diffuse X-ray emission in the ROSAT All Sky Survey (RASS) images. The targets were selected from a previous catalog of 303 newly-identified cluster candidates with the similar properties using the intra-cluster medium emission. Using the new MMT Hectospec data and SDSS archival spectra, we identify a number of member galaxies for the two targets and confirm that they are galaxy clusters at $z=0.079$ and 0.067, respectively. The size of the two clusters, calculated from the distribution of the member galaxies, is roughly 2 Mpc in radius. We estimate cluster masses using three methods based on their galaxy number overdensities, galaxy velocity dispersions, and X-ray emission. The overdensity-based masses are $(6\sim 8)\times 10^{14}{\mathrm{M}}_{\odot }$, comparable to the masses of large clusters at low redshift. The masses derived from velocity dispersions are significantly lower, likely due to their diffuse and low concentration features. Our result suggests the existence of a population of large clusters with very diffuse X-ray emission that have been missed by most previous searches using the RASS images. If most of the 303 candidates in the previous catalog are confirmed to be real clusters, this may help to reduce the discrepancy of cosmological results between the CMB and galaxy cluster measurements.

arXiv comment12 pages, 7 figures, 1 table

References in corpus (41)

• The Case for a Positive Cosmological Lambda-term
• Profiles of dark haloes: evolution, scatter, and environment
• Observational evidence for self-interacting cold dark matter
• Galaxy Harassment and the Evolution of Clusters of Galaxies
• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data
• Cosmological Parameters from Observations of Galaxy Clusters
• Analytic model for galaxy and dark matter clustering
• Chandra Cluster Cosmology Project III: Cosmological Parameter Constraints
• Formation of Galaxy Clusters
• The ROSAT-ESO Flux Limited X-ray (REFLEX) Galaxy Cluster Survey. V. The cluster catalogue
• Chandra X-ray Observations of the Hydra A Cluster: An Interaction Between the Radio Source and the X-Ray-Emitting Gas
• Galaxy Clustering in Early SDSS Redshift Data
• The MCXC: a Meta-Catalogue of X-ray detected Clusters of galaxies
• The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey I: X-ray Properties of Clusters Detected as Extended X-ray Sources
• A Spectroscopic Catalog of 10 Distant Rich Clusters of Galaxies
• K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
• Properties of the X-ray brightest Abell-type clusters of galaxies (XBACs) from ROSAT All-Sky Survey data --- I. The sample
• Second ROSAT all-sky survey (2RXS) source catalogue
• A catalog of 132,684 clusters of galaxies identified from Sloan Digital Sky Survey III
• Hectospec, the MMT's 300 Optical Fiber-Fed Spectrograph
• Virial Scaling of Massive Dark Matter Halos: Why Clusters Prefer a High Normalization Cosmology
• The ROSAT Brightest Cluster Sample (BCS) - IV. The extended sample
• The Dark Matter Distribution in the Central Regions of Galaxy Clusters: Implications for CDM
• The Dark Matter Distribution in the Central Regions of Galaxy Clusters
• Cluster Lenses
• The relation between velocity dispersion and mass in simulated clusters of galaxies: dependence on the tracer and the baryonic physics
• 2MASS Photometric Redshift catalog: a comprehensive three-dimensional census of the whole sky
• The EMSS catalog of X-ray-selected clusters of galaxies. I. An atlas of CCD images of 41 distant clusters
• The Half Million Quasars (HMQ) Catalogue
• Brightest Cluster Galaxies at the Present Epoch
• The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) IV. X-ray Luminosity Function and First Constraints on Cosmological Parameters
• Galaxy clustering, photometric redshifts and diagnosis of systematics in the DES Science Verification data
• The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 Ster around the South Galactic Pole
• The ROSAT North Ecliptic Pole Survey: The X-ray Catalog
• A catalogue of clusters of galaxies identified from all sky surveys of 2MASS, WISE, and SuperCOSMOS
• Galaxy Clusters from the DESI Legacy Imaging Surveys. I. Cluster Detection
• The extended Northern ROSAT Galaxy Cluster Survey (NORAS II) I. Survey Construction and First Results
• An X-ray selected catalog of extended galaxy clusters from the ROSAT All-Sky Survey (RXGCC)
• A New X-ray Selected Sample of Very Extended Galaxy Groups from the ROSAT All-Sky Survey
• SPIDERS: An Overview of The Largest Catalogue of Spectroscopically Confirmed X-ray Galaxy Clusters
• Optically-detected galaxy cluster candidates in the $AKARI$ North Ecliptic Pole field based on photometric redshift from Subaru Hyper Suprime-Cam