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.
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
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
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:
Other papers that use data from these catalogs include:
... and papers by other authors using these data: