SDSS_DR8.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
the group/cluster id
ngalintmeta.numberrichness (number of members) of the group
zcmbdoublesrc.redshiftCMB-corrected redshift of group, calculated as an average over all group/cluster members
groupdistdoublepos.distanceMpc/hcomoving distance to the group centre
raj2000doublepos.eq.radegright ascension of the group centre
dej2000doublepos.eq.decdegdeclination of the group centre
glondoublepos.galactic.londeggalactic longitude
glatdoublepos.galactic.latdeggalactic latitude
etadoubleposdegthe SDSS survey coordinates eta
lamdoubleposdegthe SDSS survey coordinates lambda
crd_xdoublepos.cartesian.xCartesian coordinate along the x-axis defined by eta and lambda
crd_ydoublepos.cartesian.yCartesian coordinate along the y-axis defined by eta and lambda
crd_zdoublepos.cartesian.zCartesian coordinate along the z-axis defined by eta and lambda
r_maxfloatstat.max
phys.size.radius
Mpc/hmaximum radius of the group/cluster
r_virfloatphys.size.radius
phys.virial
Mpc/hvirial radius (the projected harmonic mean)
sigma_skyfloatstat.stdev
pos.distance
Mpc/hrms deviation of the projected distance in the sky from the group centre; sigma_sky defines the extent of the group in the sky
sigma_vfloatstat.stdev
phys.veloc
km/srms radial velocity deviation
lum_r_groupfloatphys.luminosity10+10Lsun/h2observed luminosity, i.e. the sum of the luminosities of the galaxies in the group/cluster
weightfloatstat.weightweight factor for the group at the mean distance of the group
dlinkfloatpos.distanceMpc/hthe co-moving linking length used to define the group (Mpc/h)
den1floatsrc.densitythe environmental density of the group for the smoothing scale of 1 Mpc/h
den2floatsrc.densitythe environmental density of the group for the smoothing scale of 2 Mpc/h
den4floatsrc.densitythe environmental density of the group for the smoothing scale of 4 Mpc/h
den8floatsrc.densitythe environmental density of the group for the smoothing scale of 8 Mpc/h
den16floatsrc.densitythe environmental density of the group for the smoothing scale of 16 Mpc/h
dist_edgefloatpos.distanceMpc/hthe minimum co-moving distance of group galaxies from the edge of the survey mask; zero, if at least one member is outside the survey mask
flag_fctinyintmeta.codeif greater than zero, indicates that the group contains potentially missing (with unknown redshift) galaxies due to the fibre collisions