Cluster Mass

The mass of the clusters from the GMBCG catalog have not been calibrated by using weak lensing techniques. I correlate the richness estimate of the same clusters from GMBCG and MaxBCG and build the following mass ~ richness (GM_Scaled_Ngals) relation for GMBCG clusters: (I use Ngals to denote GM_Scaled_Ngals in the equation)

cluster mass = 8.8e13*((0.66*Ngals+9.567)/20.)^1.28 (h^-1 M_sun)

Clarification of the sky coverage of the public GMBCG catalog for DR7


In the GMBCG public catalog, it does not contain the stripe 44, stripe 79 and partial stripe 38, 39 and partial stripe 9, see the Figure 1. If you compare this with  sdss dr7 footprint Figure 2, http://www.sdss.org/DR7/coverage/, you will see that the public GMBCG catalog coverage is actually almost the same as the legacy spectroscopic footprint. We choose this area eventually because it is supposed to have the best photometry (according to my colleague Brian Yanny). The mask used is the version 7.2 of the vagc lss mask from the NYC group.

We got the number of 8240 deg^2 in our paper from somewhere on the dr7 website. I noticed that now the webpage show the number is 8423 deg^2 that includes the stripe 44 and the complete stripe 38, 39, 9. So, after removing those extra stripes, a better estimate of the area covered by the public GMBCG catalog should be the legacy spectroscopic coverage, i.e., 8032 deg^2. But be aware that due to the complication of the mask, you should probably expect +/- 5% variation of the actual area.

Thanks Dr. Tommaso Giannantonio for raising this question.

Figure 1

Figure 2

Cluster objids and names updated

As we noted before, some of the objids of the BCGs are "shorter" than it should be. This is because part of the DR7 catalogue I was using are from an earlier rerun of the SDSS pipeline (before 1/2009). Although the DR7 is officially released by the end of 2008, some reprocessing was still in progress after 1/2009. Thanks to Brian Yanny who told me that the latest DR7 catalogues all have their final rerun finished and the objids are finalised. Therefore, I updated the BCGs' objids. Note that this only affect a small portion of the BCGs. Also, some spectroscopic redshifts are added to those BCGs after updating the objids.

Per Heinz Andernach's suggestion, I added a "name" column to the cluster catalog. The name is by the convention GMBCG J RA DEC. For the RAs and DECs, I keep both of them to 5 digits.

The new catalogs are ready for downloading from the webpage.

A few updates since the catalog release

I got some feedbacks from the users of GMBCG cluster catalog ever since its public release. Especially, Heinz Andernach has carefully check the catalog and gave back many good suggestions and pointed out several close pair duplicates. Some of the duplicates are due to the input DR7 catalog, where they are just the same object but assigned with different objids. Some others are due to the percolation codes I am using that did not catch the very close pairs. Altogheter, there are 13 such BCGs are "duplicated". I removed them and updates all the catalogs(Fits and ascii). Now, the total # of clusters are 55,424.（The last update is on 11/14/10）

kick off

GMBCG cluster catalog for SDSS DR7 is a large optical galaxy cluster catalog, which is built by identifying the BCG + Red Sequence feature of clusters. It is a kind of continuation of the maxBCG cluster catalog (Koester et al 2007) to red shift range beyond 0.3, but with different algorithm. The two catalogs are in good agreement at low redshift (0.1 - 0.3), about 60% of BCGs identified by maxBCG have been exactly identified as BCGs in the GMBCG catalog.

This blog serves as an interactive platform for users of the GMBCG catalog. Please leave us your comments, suggestions and requests. We will try to make it user friendly as much as possible. You can also "follow" this blog by using the google buzz. Just click the "follow" at the right panel. We will publish our updates of the catalog via this blog in the future.