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RASSSDSSGC - ROSAT All-Sky Survey and Sloan Digital Sky Survey DR7 Galaxy Clusters

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Overview

The authors use ROSAT All-Sky Survey (RASS) broad-band X-ray images and the optical clusters identified from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) to estimate the X-ray luminosities around ~65,000 candidate galaxy clusters with masses >~1013 h-1 Msun based on an optical to X-ray (OTX) code that they developed. They obtain a catalog with X-ray luminosities for all 64,646 clusters. A total of 34,522 (~53%) of these clusters have a signal-to-noise ratio S/N > 0 after subtracting the background signal. According to the reference paper (but see HEASARC Caveats section below), this catalog contains 817 clusters (473 at redshift z <= 0.12) with S/N > 3 for their X-ray detections (an additional 12,629 clusters have 3 >= S/N > 1 and 21,076 clusters have 1 >= S/N > 0). The authors find about 65% of these X-ray clusters have their most massive member located near the X-ray flux peak; for the remaining 35%, the most massive galaxy is separated from the X-ray peak, with the separation following a distribution expected from a Navarro-Frenk-White profile. In the reference paper, the authors investigate a number of correlations between the optical and X-ray properties of these X-ray clusters, and find that the cluster X-ray luminosity is correlated with the stellar mass (luminosity) of the clusters, as well as with the stellar mass (luminosity) of the central galaxy and the mass of the halo, although the scatter in these correlations is large. Comparing the properties of X-ray clusters of similar halo masses but having different X-ray luminosities, they find that massive haloes with masses >~1014 h-1 Msun contain a larger fraction of red satellite galaxies when they are brighter in X-ray. An opposite trend is found in central galaxies in relative low-mass haloes with masses <~1014 h-1 Msun where X-ray brighter clusters have smaller fraction of red central galaxies. Clusters with masses >~1014 h-1 Msun that are strong X-ray emitters contain many more low-mass satellite galaxies than weak X-ray emitters. These results are also confirmed by checking X-ray clusters of similar X-ray luminosities but having different characteristic stellar masses. The cluster catalog containing the optical properties of member galaxies and the X-ray luminosity is also available at http://gax.shao.ac.cn/data/Group.html.

The optical data used in this analysis are taken from the SDSS galaxy group catalogs of Yang et al. (2007, ApJ, 671, 153), constructed using the adaptive halo-based group finder of Yang et al. (2005, MNRAS, 356, 1293), here updated to DR7. The parent galaxy catalog is the New York University Value-Added Galaxy Catalog (NYU-VAGC; Blanton et al. 2005, AJ, 129, 2562) based on the SDSS DR7 (Abazajian et al. 2009, ApJS, 182, 543), which contains an independent set of significantly improved reductions.

In this study, the authors adopt a Lambda cold dark matter cosmology whose parameters are consistent with the 7-year data release of the WMAP mission: Omegam = 0.275, OmegaLambda = 0.725, h = H0/(100 km s-1 Mpc-1) = 0.702, and sigma8 = 0.816.


Catalog Bibcode

2014MNRAS.439..611W

References

Measuring the X-ray luminosities of SDSS DR7 clusters from ROSAT All Sky Survey.
    Wang L., Yang X., Shen S., Mo H.J., Van Den Bosch F.C., Luo W., Wang Y.,
    Lau E.T., Wang Q.D., Kang X., Li R.
   <Mon. Not. R. Astron. Soc., 439, 611-622 (2014)>
   =2014MNRAS.439..611W    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in June 2017 based upon the CDS Catalog J/MNRAS/439/611 file catalog.dat.

HEASARC Caveats

Only a small fraction (1.4%) of the clusters in this catalog have been detected with high significance (S/N > 3) and can thus be considered bona fide detected X-ray emitters. The HEASARC has discovered that the S/N numbers quoted in the reference paper are somewhat inconsistent with the actual values in this table, as shown below:
  S/N          Number of entries     Actual number of
               given in paper        entries in this table

  All values    64,646                64,646
  > 3              817                   931
  > 1 & <= 3    12,629                13,295
  > 0 & <= 1    21,076                20,297

Parameters

Name
The optical group identification: this is taken from the SDSS galaxy group catalogs of Yang et al. (2007, ApJ, 671, 153), and thus the HEASARC has added the prefix of '[YMV2007]' (for Yang, Mo, van den Bosch 2007) to the identification number given in the original reference to construct this name parameter.

Central_Galaxy_ID
The identification of the central galaxy of the specified group. The authors identify the central galaxy of the X-ray cluster from the four most massive galaxies (MMGs). If the values of LX are different for the four MMGs, the central galaxy is defined to be the one that has a signal-to-noise ratio (S/N) > 1.0 and with the maximum LX. If more than one MMG has S/N > 1.0 and the difference of their LX is less than the minimum of their LX errors, the authors select the one that has the maximum M_*_^(1/3)/Dp as the central galaxy, where M* is the stellar mass of the candidate and Dp is the projected distance between the candidate and the X-ray center.

Nyuvagc_Name
The name of the central galaxy in the New York University Value-Added Galaxy Catalog (NYU-VAGC; Blanton et al. 2005, AJ, 129, 2562). See Yang et al. (2007, ApJ, 671, 153; 2008, ApJ, 676, 248; 2009, ApJ, 695, 900) for more details.

Multi_Z_B1_Flag
This parameter contains the multiple redshift (multi-z) flag, b1, where a value of b1 of 0 means a clean (or isolated) detection, with the value of the multi_flux_fraction parameter, fmulti, being 1.0, meaning that the nearest neighbor detection is farther away than 0.5 * r200, r200 being the radius within which the average mass density is 200 times the critical mass density of the Universe. Values of b1 of 1,2,3...n mean that there are nearest neighbor detections within 0.5 * r200, ordered by their redshift z.

Multi_Z_B2_Flag
This parameter contains the multiple redshift (multi-z) flag, b2, which is described in the CDS documentation thus: "multi-z flag b2: for the i-th cluster (or group or detection) with b1=j+1, if b2/=0 then the former (i-1)th cluster (has lower redshift) with b1=j locate in 0.5*r200 of the i-th cluster."

Multi_Z_B3_Flag
This parameter contains the multiple redshift (multi-z) flag, b3, which is described in the CDS documentation thus: "multi-z flag b3: b3(i+1)=1 means the i-th cluster has larger min{Rx,0.5*r200} than the former (i-1)th cluster (has lower redshift)."

Mass_Sequence_ID
The mass sequence identification for the central, the k-th most massive galaxy in the group, where k <= 4.

Offset
The angular offset, in arcminutes, between the optical galaxy and the center of the X-ray cluster.

RA
The Right Ascension of the center of the X-ray cluster in the selected equinox. This was given in decimal degrees to a precision of 10-5 degrees in the original table.

Dec
The Declination of the center of the X-ray cluster in the selected equinox. This was given in decimal degrees to a precision of 10-5 degrees in the original table.

LII
The Galactic Longitude of the center of the X-ray cluster.

BII
The Galactic Latitude of the center of the X-ray cluster.

Count_Rate
The background-subtracted X-ray count rate in the 0.1-2.4 keV energy range, in counts s-1, within the detection radius of 0.5 * r200 centered on the cluster position.

Count_Rate_Error
The error in the background-subtracted X-ray count rate in the 0.1-2.4 keV energy range, in counts s-1.

Angular_Radius
The X-ray extension radius of the cluster, rX, set by the authors to be 0.5 * r200.

Flux
The X-ray flux of the cluster in the 0.1-2.4 keV energy range, in erg s-1 cm-2. The authors integrated the source count rate profile inside rX to get the total source count rate of the cluster. They then assumed that the X-ray emission has a thermal spectrum with a temperature T and a gas metal abundance of one-third of the solar value to make a conversion from the source count rates to X-ray fluxes.

Lx
The X-ray luminosity of the cluster in the 0.1-2.4 keV energy range, in erg s-1, calculated from the X-ray flux and the redshift according to the cosmological assumptions outlined in the Overview section above, and using a beta-profile extension correction to compensate for the X-ray luminosity missed in the range rX < r < r200.

Lbol
The bolometric luminosity of the cluster (derived from its soft X-ray luminosity, LX), in erg s-1.

Beta_Model_Cor_Fac
The beta model correction factor that was used to compensate for the X-ray luminosity that was missed in the projected range rX < r < r200.

Sigma_Velocity
The velocity dispersion, sigma, of the cluster derived from the optical halo mass, in km s-1. See Yang et al. (2007, ApJ, 671, 153), equation (6).

Number_Galaxies
The number of galaxies in the cluster.

T_Gas
The gas temperature of the group derived from the velocity dispersion, in keV. See White et al. (1997MNRAS, 292, 419); or Shen et al. (2008, MNRAS, 389, 1074), Eq. 2.

Log_NH_Gal
The Galactic Hydrogen column density in the direction of the cluster, in H atoms cm-2.

Exposure
The average RASS exposure time in the direction of the cluster, in seconds.

Redshift
The optical spectroscopic redshift of the central galaxy of the cluster.

R500_Aperture
The radius within which the average mass density is 500 times the critical mass density of the Universe, r500 , in arcminutes.

SNR
The signal-to-noise ratio S/N of the X-ray detection of the cluster.

Multi_Flux_Fraction
For multi-cluster systems, the authors add up all the 'expected' X-ray fluxes and obtain a contribution fraction for each cluster, 'i', in the system, fmult,i = FX,i/ [Sum over i of (FX,i)]. This parameter is then applied to each cluster in the multi-cluster system to partly take into account the projection effects when quantities such as LX and S/N are calculated.


Contact Person

Questions regarding the RASSSDSSGC database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 13-Jun-2017