ESGC (G0): South Equatorial Galaxy Catalog (19921128)
FILE: esgc.g0 (3244 galaxies)
CONTENTS: South Equatorial Galaxy Catalog: -21<Dec<5
DATASET: This file is part of HyperSky dataset G-2 (G-2.2), version 19921128 Availability on HyperSky CD-ROM: Vol. 1 (1993)
DESCRIPTION: This datafile is taken from preliminary version 1.1 of the ESGC by Harold G. Corwin, Jr., prepared in collaboration with G. and A. de Vaucouleurs, and Brian A. Skiff. It is nominally complete to a limiting diameter of 2.0 arcmin, but includes many smaller galaxies as well. All RC2 objects are included, as are all NGC (but not all IC) galaxies. The survey's declination limits are approximately +3 deg to -21 deg in its original 1950 equinox; it covers the 0, -6, -12, and -18 degree zones of the Palomar Sky Survey. Glass copies of the 103a-O blue plates were used for the survey.
One of the functions of the ESGC is to fill the gap between the northern Uppsala Galaxy Catalog and the Southern Galaxy Catalog. Two of the main purposes of the catalog are to provide morphological type and luminosity class data; galaxy magnitudes were not determined for this catalog.
DATA: The HyperSky datafile contains the following data from the catalog:
MAG: Magnitudes are not provided in the ESGC. WARNING! Since magnitudes are not provided, all galaxies in this file will disappear if HyperSky's faint limiting faint galaxy magnitude is raised above its default. This is because HyperSky assigns the default faint limit to any galaxy without a magnitude.
IDENTIFICATION: Each galaxy name begins with a prefix indicating the associated catalog identification:
NGC: New General Catalog
IC: Index Catalog
UGC: Uppsala General Catalog of Galaxies
M: Morphological Catalog of Galaxies
A: Anonymous RC2 (Second Reference Catalog of Bright Galaxies) name.
SE: Arbitrary ESGC designation built on 1950 RA and declination.
Many NGC identifications are new. They are based on the original publications that were used by Dreyer to assemble the NGC, or -- in some cases -- on copies of the unpublished discovery drawings made at Leander McCormick Observatory in the 1880's by Stone, Leavenworth, and Muller. About 200 objects are new to the ESGC, not having appeared previously in a major galaxy catalog. These have not been named.
COMMENTS: The comment lines contain the following additional information, provided if available for each galaxy:
* Alternate identifications.
* Galaxy type in the revised Hubble system (de Vaucouleurs 1959, 1963). This is a purely morphological classification; there was no reliable way to distinguish between elliptical galaxies and early lenticulars without detailed photometric and/or kinematic/dynamic studies. Uncertainty symbols (: and ?) are used to indicate a classification parameter of half- or quarter-weight when necessary.
* Luminosity classes in the van den Bergh (1960a,b) system (Roman numerals) are provided for later-type spirals and irregular galaxies where possible.
The van den Bergh luminosity classes give an indication of the absolute magnitude of a spiral galaxy. In general, the more luminous a galaxy is, the better developed its spiral structure will be. For irregular galaxies without spiral structure, the average surface brightness is an indicator of absolute magnitude. The galaxies with the strongest, most coherent spiral structure are assigned luminosity classes of "I", and typically have absolute magnitudes around -21 (this varies somewhat with morphological type). Faint, low surface brightness irregular galaxies are assigned luminosity classes of "V". Their average absolute magnitudes are around -15, but the range in this figure is large. Spirals of intermediate brightness are assigned luminosity classes of II, II-III, III and so on. M51 is a good example of a giant spiral with a luminosity class of "I". IC 1613, a dwarf irregular in the Local Group, has a luminosity class of "V".
Surface brightness is just as important a criterion for luminosity classification here as is the degree of development of spiral structure. This means that obscured galaxies near the galactic plane will generally be given too large a luminosity class, unless their spiral structure is very apparent. These low-latitude objects always have their luminosity classes marked uncertain ":" or doubtful "?".
[References: vdB 1960a: Ap. J. 131, 215; vdB 1960b: Publ. David Dunlap Obs., II, No. 6]
* The length of the major and minor galactic axes, in the form Dxd', in arc minutes. These dimensions are converted from the ESGC values logD (log of the major diameter) and logR (log of the axis ratio).