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HCGGALAXY: Help

HCGGALAXY - Hickson's Compact Groups of Galaxies (HCG) Individual Galaxies Data


Overview

The HCGGALAXY database table is based on the Hickson Catalog of Compact Groups, and contains data on 463 galaxies in 100 compact groups of galaxies that were identified by a systematic search of the Palomar Observatory Sky Survey red prints. Each group contains four or more galaxies, has an estimated mean surface brightness brighter than 26.0 magnitude per arcsec^2 and satisfies an isolation criterion. Astrometry, photometry, and morphological types, derived from CCD images, are presented for the 463 galaxies. Radial velocities are given for 457 of the 463 galaxies: more than 84% of the galaxies measured have radial velocities that are within 1000 km/s of the group median velocity. Morphological information derived from either an isophotal analysis or from a visual inspection of images is given for 210 of the 463 galaxies.

This database table essentially contains the information given in Table 2 of Hickson, P. et al. (1989, ApJS, 70, 687), Table 2 of Hickson, P. et al. (1992, ApJ, 399, 353), and Table 2 of Mendes de Oliveira, C. and Hickson, P. (1994, ApJ, 427, 684). Consequently, the information on the properties of the Hickson Compact Groups as units that is also given in some of these references, e.g., in Table 3 of Hickson, P. et al. (1992, ApJ, 399, 353), is not in the HCGGALXY database table; however, the latter data can be found in the related HEASARC database table HCG.


Catalog Bibcode

1989ApJS...70..687H

References

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

Provenance

This database table was created by the HEASARC in August, 1999, based on machine-readable tables obtained from the ADC/CDS data centers (CDS catalog VII/213, files galaxies.dat and morpho.dat). The HEASARC added Galactic coordinates and updated the table's metadata in August, 2005.

Parameters

Name
The full designation of the HCG galaxy in the standard form as recognized by SIMBAD.

HCG
The Hickson Compact Group number.

HCG_Galaxy
The letter designation of the individual galaxy within its HCG group, e.g., 'a', 'b', etc.

RA
The right ascension of the HCG galaxy in the specified equinox. The equinox of the positions in the originating table was B1950, notice, and the RA was given there to a precision of 0.01 seconds. The measurement error is estimated to be approximately 2 arcseconds rms; however, uncertainties in locating the center of a bright galaxy can be as much as 5% of the galaxy diameter.

Dec
The declination of the HCG galaxy in the specified equinox. The equinox of the positions in the originating table was B1950, notice, and the declination was given there to a precision of 0.1 arcseconds. The measurement error is estimated to be approximately 2 arcseconds rms; however, uncertainties in locating the center of a bright galaxy can be as much as 5% of the galaxy diameter.

LII
The galactic longitude of the HCG galaxy.

BII
The galactic latitude of the HCG galaxy.

Semi_Major_Axis
The semi-major axis in arcseconds of the B magnitude = 25.0 mag/arcsec^2 isophote.

Semi_Minor_Axis
The semi-minor axis in arcseconds of the B magnitude = 25.0 mag/arcsec^2 isophote.

Hubble_Type
The Hubble morphological type.

Morph_Type
A numeric morphological type code based on this scheme:

      Hubble      Code     RC2

      E0-E7        0       -4, -5
      S0, SB0      1       -2
      S0a, SB0a    2        0
      Sa, SBa      3        1
      Sab, SBab    4        2
      Sb, SBb      5        3
      Sbc, SBbc    6        4
      Sc, SBc      7        5
      Scd, SBcd    8        6
      Sd, SBd      9        7
      Sdm, SBdm   10        8
      Sm, SDm     11        9
      Im, IBm     12       10
      cI          13       11
  

Morph_Info
A flag that is set to 'Y' when more morphology information for this galaxy is available in the Comments parameter, 'N' when there is not.

Radial_Velocity
The galaxy's heliocentric radial velocity in km/s.

Radial_Velocity_Error
The estimated rms radial velocity error in km/s.

Radial_Velocity_Qual
A confidence code for the radial velocity, with values ranging from 0 to 2 (only 3 galaxies have a value of 2), as follows:

  the confidence code is
       0 = highest confidence: spectral features clearly visible
       1 = lower confidence: spectral features not clearly visible
       2 = lowest confidence: very noisy spectra with no obvious features.
  

Bmag
The B magnitude of the galaxy within the 24.5 mag/square arcsec isophote.

Bmag_Qual
A confidence level for the B magnitude parameter bmag, with values ranging from 0 to 4, as follows:

  confidence levels are:
       0 = good
       1 = uncertain due to overlapping isophotes
       2 = uncertain due to contamination
       3 = uncertain due to poor calibration
       4 = uncertain due to clouds.
       (the value of 5 for HCG 64c is unexplained in the references)
  

Diameter_Bmag
The diameter in arcseconds of the B=24.5 mag/square arcsec isophote, defined as the square root of A/{pi}, where A is the area of the isophote.

Rmag
The R magnitude of the galaxy within the 24.0 mag/square arcsec isophote.

Rmag_Qual
A confidence level for the R magnitude parameter rmag, with values ranging from 0 to 4, as follows:

  confidence levels are:
       0 = good
       1 = uncertain due to overlapping isophotes
       2 = uncertain due to contamination
       3 = uncertain due to poor calibration
       4 = uncertain due to clouds.
       (the value of 5 for HCG 64c is unexplained in the references)
  

Diameter_Rmag
The diameter in arcseconds of the R=24.0 mag/square arcsec isophote, defined as the square root of A/{pi}, where A is the area of the isophote.

Br_Color
The (B-R) color within the 24.5 mag/arcsec^2 isophote.

Bt_Asympt_Mag
The total asymptotic B_T magnitude derived by fitting the observed intensity profile to the standard profiles published in the RC2.

Corr_Bt_Asympt_Mag
The total asymptotic B_T magnitude corrected for internal and external extinction using the procedure described in the RC2. No K-corrections were included.

Bt_Asympt_Mag_Error
The mean (1-sigma) error in the B_T asymptotic magnitude.

Abs_Bmag
The absolute B_T asymptotic magnitude M(B_T) of the galaxy, assuming a Hubble Constant Ho of 100 km/sec/Mpc, or, in more general terms, the function M(B_T) + 5 log h, where h=Ho/100 km/sec.

Alt_Name1
An alternate name taken from the UGC (U), NGC (N), Index (I), Markarian (MK), or MCG Catalogs.

Alt_Name2
A second alternate name taken from the UGC (U), NGC (N), Index (I), Markarian (MK), or MCG Catalogs.

Alt_Name3
A third alternate name taken from the UGC (U), NGC (N), Index (I), Markarian (MK), or MCG Catalogs.

Comments
Comments about the morphological evidence that the galaxies may be interacting and/or other information about them taken by the catalog's authors from the literature. Galaxies marked with an (I) are thought to be interacting, while galaxies marked with an (M) are thought to be merging. The explanation for other abbreviations used in the comments is as follows (notice that the string 'ANSAC' in the comments for HCG 58A is probably a typographical error in the original table for 'ANSAE'):

    ASYM.    = asymmetric
    EMISSION = galaxy with emission lines in its nuclear spectrum
    IR       = infrared emitter (Hickson et al. 1989ApJ...341..679H,
               Sulentic & de Mello Rabaca 1993ApJ...410..520S)
    MORPHO   = morphology
    N.C.I.   = nonconcentric isophotes
    R.C.     = rotation curve
    RADIO    = radio-loud galaxies (Menon & Hickson 1985; Menon 1993)
    TAIL-LIKE= galaxy has tail-like features
    VEL.     = velocity
    WR       = galaxy exhibits Wolf-Rayet spectral features
  

Class
The (crude) Browse object classification, derived from the listed Hubble type for each galaxy.


Contact Person

Questions regarding the HCGGALAXY database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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