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## HCG - Hickson's Compact Groups of Galaxies (HCG) Catalog |
HEASARC Archive |

This database table essentially contains the information given in Table 1 of Hickson, P. (1982, ApJ, 255, 382) and Table 3 of Hickson, P. et al. (1992, ApJ, 399, 353). Consequently, the information on individual galaxies in the Hickson groups that is also given in these references, e.g., in Table 2 of Hickson, P. et al. (1992, ApJ, 399, 353), is not in the HCG database table; however, the latter data can be found in the related HEASARC database table HCGGALAXY.

Systematic Properties of Compact Groups of Galaxies Hickson P. <Astrophys. J. 255, 382 + Erratum 259, 930 (1982)> =1982ApJ...255..382H A photometric catalog of compact groups of galaxies. Hickson P., Kindl E., Auman J.R. <Astrophys. J. Suppl. Ser. 70, 687 (1989)> =1989ApJS...70..687H The luminosity function of compact groups of galaxies Mendes de Oliveira C., Hickson P. <Astrophys. J. 380, 30 (1991)> =1991ApJ...380...30M Dynamical properties of compact groups of galaxies. Hickson P., Mendes de Oliveira C., Huchra J.P., Palumbo G.G.C. <Astrophys. J. 399, 353 (1992)> =1992ApJ...399..353H Morphology of galaxies in compact groups. Mendes de Oliveira C., Hickson P. <Astrophys. J., 427, 684 (1994)> =1994ApJ...427..684M

**HCG**

The HCG catalog entry number, ranging from 1 to 100, for the compact group.

**Name**

The HCG catalog compact group designation.

**RA**

The right ascension in the specified equinox. The position given for the
group is actually the center of the circle that encloses the group. The
equinox of the positions in the originating table was B1950, notice, and the
RA was given to a precision of 1 second.

**Dec**

The declination in the specified equinox. The position given for the
group is actually the center of the circle that encloses the group. The
equinox of the positions in the originating table was B1950, notice, and the
declination was given to a precision of 1 arcsecond.

**LII**

The galactic longitude of the center of the circle that encloses the
compact group.

**BII**

The galactic latitude of the center of the circle that encloses the
compact group.

**Dynamics_Flag**

A flag that is set to 'Y' if dynamical parameter information
is available for the particular compact group.

**Group_Type**

A two-character code (a letter followed by a number) classifying
the group type, based on its two brightest members, according to the following
scheme:

S The brightest galaxy is a spiral galaxy. E The brightest galaxy is not a spiral galaxy. 1 m(b) - m(a) >= 1.0 2 0.5 <= m(b) - m(a) < 1.0 3 m(b) - m(a) < 0.5 where m(a) and m(b) are the estimated red magnitudes of the brightest and second brightest members, respectively, of the cluster.

**Member_Count**

The total number of galaxies in the compact group that are
within 3 magnitudes of the brightest galaxy.

**Angular_Size**

The angular diameter, in arcminutes, of the smallest circle
containing the geometric centers of all group members.

**Tot_Mag_Group**

The total estimated red magnitude of those galaxies
counted as group galaxies, i.e., those with individual magnitudes within
3 magnitudes of the brightest galaxy.

**Brightest_Mag**

The estimated red magnitude of the brightest galaxy in
the compact group.

**Brightest_Redshift**

The corrected redshift of the brightest galaxy in
the compact group. In all but ten cases this parameter is blank, and the
ADC/CDS documentation recommends that that the value of the group redshift
(the parameter 'redshift' in the HEASARC database) derived from the median
galaxy heliocentric velocity be preferred.

**Alt_Name1**

An alternate designation for the compact group.

**Alt_Name2**

An alternate designation for the compact group.

**Alt_Name3**

An alternate designation for the compact group.

**Alt_Name4**

An alternate designation for the compact group.

**Redshift**

The group redshift derived from the median galaxy heliocentric
velocity.

**Number_Galaxies**

The number of galaxies in the group with accordant
velocities, i.e., that have individual velocities that are within 1000
km/sec of the group median velocity, and are thus assumed to be physically
associated with the group.

**Log_Sigma_Vrad**

The logarithm (base 10) of the radial velocity dispersion,
in km/sec, of the accordant galaxies.

**Log_Vel_Dispersion**

The logarithm (base 10) of the estimated intrinsic
three-dimensional velocity dispersion, in km/sec, corrected for measurement
errors.

**Log_Median_Sep**

The logarithm (base 10) of the median projected separation,
in kpc.

**Log_Crossing_Time**

The logarithm (base 10) of the dimensionless crossing
time parameter, which is the ratio of the crossing time to the approximate
age of the universe, and is independent of the choice of Hubble constant.

**Log_Virial_Mass**

The logarithm (base 10) of the virial mass of the group,
in grams.

**Log_Projected_Mass**

The logarithm (base 10) of the projected mass of the
group, in grams.

**Log_Average_Mass**

The logarithm (base 10) of the average mass of the group,
in grams.

**Log_Median_Mass**

The logarithm (base 10) of the median mass of the group,
in grams.

**Log_Adopted_Mass**

The logarithm (base 10) of the adopted mass of the group,
in grams. The adopted mass for the group is the median of the nonzero mass
estimates given in the four parameters log_virial_mass, log_projected_mass,
log_average_mass, and log_median_mass.

**Log_Tot_Luminosity**

The logarithm (base 10) of the total blue luminosity of
the accordant galaxies, in units of Watts (=10^7 erg/sec).

**Log_Mass_To_Light**

The logarithm (base 10) of the mass to light (M/L) ratio,
in solar units, i.e., solar mass/solar luminosity.

**Log_Mass_Density**

The logarithm (base 10) of the mass density, in gm/cm^3.