COSMOS Galaxy and X-ray Group Membership Catalogs

Contact: Matt George (UC Berkeley/LBL)


This page is a repository for files and information about the X-ray selected galaxy group catalogs in the COSMOS field. The group catalogs are publicly available, and contain 189 groups out to z=1 with halo masses in the range ~1013-1014 solar masses, determined with weak lensing. 4631 member galaxies down to a flux limit iF814W<24.2 have been assigned to these groups using photometric and spectroscopic redshifts, out of >105 galaxies in this field. The membership algorithm has been extensively tested using mock catalogs from simulations and the group member properties are well-studied.

See the references below for more details.


IRSA hosts the official versions of these catalogs, where they will be available for the long term.

Older versions are available here.


Below are some plots showing the colors, morphologies, and stellar masses of the group member galaxies. The first two are summary figures from our recent paper (George et al. 2013 - arXiv:1302.6620). Please refer to this paper when using any of the following figures.
Caption: Illustrations of our main results and interpretation. Left panel shows the projected positions of satellites in an ensemble group with stellar mass of 109.8-1010.3 solar masses and redshifts z=0.2-0.5 with only the blue late disks (which dominate the outskirts) and red bulge+disks (which dominate the interior) displayed. The schematic diagram at right shows the effects of various physical mechanisms on color and morphology; the large arrow indicates the observed transformation from blue late disks to red bulge+disks, suggesting a combination of processes.

Next is Figure 1 from the same paper, introducing the data.

Caption: Group members as a function of stellar mass and distance from the group center. Colors for each galaxy represent the average unextincted rest-frame template NUV-R color, with shading proportional to the logarithmic surface brightness mu. The gray band at the bottom of the high-redshift panels shows the stellar mass completeness limit for a passive population calculated with our flux limits F814W=24.2 and K=24 following the approach of Bundy et al. 2010 (see also Figure 1 of George et al. 2011). Central galaxies in these groups are shown in the light gray band on the left side of each of the outer panels. The middle frame shows morphological classifications for a random sample of galaxies chosen to span the range of colors observed; objects in this panel are sorted vertically by color and horizontal offsets within each classification are arbitrary.

The plots below show the individual redshift slices in more detail. You can also download each of these images in a multi-page pdf.
Alternatively, these presentation slides may be useful: Keynote, PPT, PDF

Another visualization of these galaxies was displayed at the Berkeley Arts Festival Gallery for the Art in Science Gala.

Caption: "Nature versus nurture" is not only a question for understanding human traits, but those of galaxies as well. In this image of a composite galaxy cluster, blue galaxies near the outskirts are actively forming stars and often show clumps and spiral features, while those in the dense inner regions tend to be redder and rounder with mostly older stars. You can see that the characteristics of galaxies are sensitive to their environment, as well as other intrinisic properties not shown, like their mass. These images were taken by the Hubble Space Telescope as part of the COSMOS survey over an area of the sky about nine times the size of the full moon, and ground-based telescopes were used to determine measure galaxy colors, which are related to the rate of star formation. The galaxies are a bit less massive than our Milky Way and were selected from groups and clusters at distances of 2.5 to 7 billion light years away.

Finally, for fun, some of these images have been used to illustrate an adapted poem (with apologies to Dr. Seuss). [html, PDF]


If you use these group catalogs please refer to the following paper which describes them:

  • Galaxies in X-Ray Groups. I. Robust Membership Assignment and the Impact of Group Environments on Quenching
    George, M.R., et al. 2011, ApJ, 742, 125. ADS arXiv:1109.6040

    You may also wish to read these papers describing the groups, which focus on determining halo centers with weak lensing and on the colors and morphologies of satellite galaxies:

  • Galaxies in X-Ray Groups. II. A Weak Lensing Study of Halo Centering
    George, M.R., et al. 2012, ApJ, 757, 2. ADS arXiv:1205.4262
  • Galaxies in X-ray Groups. III. Satellite Color and Morphology Transformations
    George, M.R., et al. 2013, ApJ in press. arXiv:1302.6620

    Other papers that use data from these catalogs include:

  • A Weak Lensing Study of X-ray Groups in the Cosmos Survey: Form and Evolution of the Mass-Luminosity Relation
    Leauthaud, A., et al. 2010, ApJ, 709, 97. ADS arXiv:0910.5219
  • A Detection of Weak-lensing Magnification Using Galaxy Sizes and Magnitudes
    Schmidt, F., et al. 2012, ApJ, 744, 22. ADS arXiv:1111.3679
  • New Constraints on the Evolution of the Stellar-to-dark Matter Connection: A Combined Analysis of Galaxy-Galaxy Lensing, Clustering, and Stellar Mass Functions from z=0.2 to z=1
    Leauthaud, A., et al. 2012, ApJ, 744, 159. ADS arXiv:1104.0928
  • The Integrated Stellar Content of Dark Matter Halos
    Leauthaud, A., et al. 2012, ApJ, 746, 95. ADS arXiv:1109.0010
  • Measuring the Geometry of the Universe from Weak Gravitational Lensing behind Galaxy Groups in the HST COSMOS Survey
    Taylor, J., et al. 2012, ApJ, 749, 127. ADS arXiv:1111.3370
  • Magnification by Galaxy Group Dark Matter Halos
    Ford, J., et al. 2012, ApJ, 754, 143. ADS arXiv:1111.3698
  • The Correlated Formation Histories of Massive Galaxies and Their Dark Matter Halos
    Tinker, J.L., et al. 2012, ApJ, 755, 5. ADS arXiv:1205.4245
  • Occupation of X-Ray-selected Galaxy Groups by X-Ray Active Galactic Nuclei
    Allevato, V., et al. 2012, ApJ, 758, 47. ADS arXiv:1209.2420

    ... and papers by other authors using these data:

  • The evolution of the mass-size relation for early-type galaxies from z~1 to the present: dependence on environment, mass range and detailed morphology
    Huertas-Company, M., et al. 2013, MNRAS, 428, 1715. ADS arXiv:1207.5793
  • Efficient satellite quenching at z~1 from the GEEC2 spectroscopic survey of galaxy groups
    Mok, A., et al., 2013, MNRAS ADS arXiv:1302.2562

    Last updated 2013 February 26