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