分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： 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)
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Weiwei Xu
Huanyuan Shan
Ran Li
Chunxiang Wang
Linhua Jiang
Eric Jullo
Ginevra Favole
Jean-Paul Kneib
Chaoli Zhang
摘要： The concentration-mass (c-M) relation encodes the key information of the assembly history of the dark matter halos, however its behavior at the high mass end has not been measured precisely in observations yet. In this paper, we report the measurement of halo c-M relation with galaxy-galaxy lensing method, using shear catalog of the Dark Energy Camera Legacy Survey (DECaLS) Data Release 8, which covers a sky area of 9500 deg^2. The foreground lenses are selected from redMaPPer, LOWZ, and CMASS catalogs, with halo mass range from 10^{13} to 10^{15} M_sun and redshift range from z=0.08 to z=0.65. We find that the concentration decreases with the halo mass from 10^{13} to 10^{14} M_sun, but shows a trend of upturn after the pivot point of ~10^{14} M_sun. We fit the measured c-M relation with the concentration model c(M)=C_0 (M/(10^{12} M_sun/h)^{-\gamma} [1+(M/M_0)^{0.4}], and get the values (C_0, \gamma, log(M_0) = (5.119_{-0.185}^{0.183}, 0.205_{-0.010}^{0.010}, 14.083_{-0.133}^{0.130}), and (4.875_{-0.208}^{0.209}, 0.221_{-0.010}^{0.010}, 13.750_{-0.141}^{0.142}) for halos with 0.08<=z<0.35 and 0.35<=z<0.65, respectively. We also show that the model including an upturn is favored over a simple power-law model. Our measurement provides important information for the recent argument of massive cluster formation process.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift $z\sim0.07$ 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 $(6\sim8) \rm \times10^{14}\ M_\odot$, 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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present MMT spectroscopic observations of two massive galaxy cluster candidates at redshift $z\sim0.07$ 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 $(6\sim8) \rm \times10^{14}\ M_\odot$, 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.
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