SDSS_DR12.GalGroup table

The GalGroup table contains galaxy groups and clusters that are extracted from the Galaxy table using the FoF method.

Table structure

ColumnTypeUCDUnitDescription
groupidintmeta.id
meta.main
group/cluster id
ngalintmeta.numberrichness (number of members) of the group
raj2000doublepos.eq.radegright ascension of the group centre
dej2000doublepos.eq.decdegdeclination of the group centre
lamdoubleposdegSDSS survey coordinate lambda of the group centre
etadoubleposdegSDSS survey coordinate eta of the group centre
crd_xdoublepos.cartesian.xCartesian coordinate of the group centre along the x-axis
crd_ydoublepos.cartesian.yCartesian coordinate of the group centre along the y-axis
crd_zdoublepos.cartesian.zCartesian coordinate of the group centre along the z-axis
zcmbdoublesrc.redshiftCMB-corrected redshift of group, calculated as an average over all group/cluster members
groupdistdoublepos.distanceMpccomoving distance to the group centre
sigma_vfloatstat.stdev
phys.veloc
km/srms radial velocity deviation (in physical coordinates)
sigma_skyfloatstat.stdev
pos.distance
Mpcrms deviation of the projected distance in the sky from the group centre (in physical coordinates); sigma_sky defines the extent of the group in the sky
r_maxfloatstat.max
phys.size.radius
Mpcmaximum radius of the group/cluster in the plane of the sky
mass_200floatphys.mass10+12Msunestimated mass of the group assuming the NFW density profile
r_200floatphys.size.radius
phys.virial
Mpcradius in which the group mean density is 200 times higher than the average density of the Universe; radius of the group that contains the mass mass_200
lum_r_groupfloatphys.luminosity10+10Lsunobserved luminosity, i.e. the sum of luminosities of the galaxies in the group/cluster
weightfloatstat.weightweight factor for the group at the mean distance of the group
den1_5floatsrc.densitynormalized environmental density (mean of group galaxy densities) of the group for the smoothing scale of 1.5 Mpc
den3floatsrc.densitynormalized environmental density (mean of group galaxy densities) of the group for the smoothing scale of 3 Mpc
den6floatsrc.densitynormalized environmental density (mean of group galaxy densities) of the group for the smoothing scale of 6 Mpc
den10floatsrc.densitynormalized environmental density (mean of group galaxy densities) of the group for the smoothing scale of 10 Mpc
dist_nearest_clfloatpos.distanceMpcdistance to the nearest cluster in comoving coordinates
id_nearest_clintmeta.idgroupid of the nearest cluster
id_mergerintmeta.idid of the merging system, zero otherwise