There is no clear definition of such companions. They are simply "close'' to a UGC galaxy. Nilson did not measure the equatorial coordinates for these galaxies but instead made an identification in polar coordinates with respect to the central UGC galaxy. This relative position is given by the position angle (measured in degrees from north through east) and the angular separation (measured in arcminute from the center of the parent UGC galaxy). In addition, Nilson gives major and minor axes (in arcminute) of these small companions.
This catalogue of UGC companions was keypunched by one of us (CP) ten years ago. This was a difficult task because of the very compact printing format of this catalogue. If the coordinates of these companion galaxies had been deduced at that time from the polar coordinates, any deplacement of the parent galaxy would have completely distorted the look of the field. Of course this could have been solved by moving the companions at the same time but it is not obvious to know which galaxy is a companion and which is not. Our catalogue remained ten years on our computer disk.
Today, thanks to the remarkable work by Cotton et al. (1999), all UGC galaxies have accurate equatorial coordinates. This suggested to us that we use this catalogue as a source of equatorial coordinates for the central UGC galaxies. However, instead of calculating the equatorial coordinates from the polar ones we prefered to use the plate solution given by the Digitized Sky Survey. The first reason is that the accuracy of the measurements of position angle and angular separation is not good enough to provide us with accurate equatorial coordinates. The position angle is known with an accuracy of one or two degrees and the angular separation is known with an accuracy of 6'' to 10'' leading to an uncertainty of 14'' at a distance of 5' from the center of the parent galaxy. The second reason is that the uncertainties on both axes (R.A. and DEC.) would have been correlated in a complicated manner.
Instead, the polar coordinates are used for an easy identification of companion galaxies by displaying simultaneously the DSS image, centered on the parent UGC galaxy, and the location of companions. In Fig. 1 we present such a display.
|Figure 1: A typical image from the Digitized Sky Survey got from ESO. The frame is . North is on the upper side, East is on the left side. The large galaxy in the center is the parent UGC galaxy (UGC 5). The companion is the small galaxy at the end of the line. The diameter of the companion is drawn according to twice the Nilson's measurements|
The coordinates are obtained by clicking on the center of the companion. This is done with special routines developed from the PGPLOT package. The center is estimated visually.
|Figure 2: Histogram of angular separations of parent galaxy and companions. We considered only companions with a separation smaller or equal to 5'|
The coordinates of the UGC galaxies are taken from the LEDA database. For efficiencies sake we loaded all DSS images (i.e. about 2600 images) from the ESO facility.
Then, the measurements were done. Sometimes, the identification is not possible either because we have a choice between two companions or because of an error in the input catalogue. These cases were treated individually by refering to the original UGC catalogue or by analysing the field carefully.
This work results in 3301 new accurate coordinates for companions of 2597 UGC galaxies. Most of these companions are not available in large databases. For each companion we give the major axis and minor axis diameters as measured by Nilson.
|h min sec deg ' ''||'||'|
|0000037||MCG 4- 1- 9||000031.6+261819||0.25||0.15||12896|
|0000089||MCG 2- 1- 9||000113.3+130836||0.80||0.30||12906|
|0000092||MCG 2- 1- 10||000115.1+130647||0.50||0.15||12906|
|0000252||CGCG 408- 17||000337.7+083810||0.70||0.30||00010|
The following data are given:
Column 1: PGC number according to LEDA database (Paturel et al. 1989).
Column 2: Name according to some well-known catalogues, if applicable. In Table 3 we give the acronyms used for these catalogues.
Column 3: Right Ascension and Declination for equinox 2000 (in hours, minutes, seconds and tenths and degrees, arcminutes and arcseconds).
Column 4: Major axis diameter in arcminute measured by Nilson (1973).
Column 5: Minor axis diameter in arcminute measured by Nilson.
Column 6: UGC Name of the parent galaxy.
|h min sec deg ' ''|
|0000027||MCG -1- 1- 18||000023.3-065612|
|0000036||IC 5373||000029.0+324656 *|
|0000037||MCG 4- 1- 9||000031.6+261819|
|0000040||MCG 0- 1- 17||000035.6-014550|
|0000122||MCG -7- 1- 7||000130.9-404912|
|0000152||MCG -5- 1- 25||000205.4-303709|
|CGMW||Catalogue of Galaxies Behind the Milky Way; Saito et al., 1990-1991;|
|Roman et al., 1996-1998|
|DRCG||Dressler Catalogue of Cluster of Galaxies; Dressler, 1980|
|ESO||European Southern Observatory catalogue; Lauberts, 1982|
|FAIR||Fairall lists; Fairall; 1977-1988|
|HICK||Compact Groups of Galaxies; Hickson, 1993|
|NGC||New General Catalogue; Dreyer, 1889|
|IC||Index Catalogue; Dreyer, 1895-1910|
|CGCG||Catalogue of Galaxies and Cluster of Galaxies; Zwicky et al. 1961-1968|
|nZW||Catalogue of Selected Compact and Post-eruptive Galaxies; Zwicky, 1971;|
|Zwicky et al., 1975 (n is the number of the list from 1 to 8)|
|nSZW||Zwicky Compact Galaxies in two southern fields; Rodgers et al., 1978|
|(n is the number of the list from 1 to 2)|
|IRAS||IRAS Point Source Catalogue, 1988|
|KAZA||Kazaryan lists; Kazaryan, 1979-1983|
|KCPG||Karachentsev Catalogue of Pair of Galaxies; Karachentsev 1972|
|KUG||Kiso Survey of Ultraviolet Excess Galaxies: Takase and Miyauchi-Isobe, 1993|
|MCG||Morphological Catalogue of Galaxies: Vorontsov-Vel'jaminov et al. 1963-1974|
|MK||Markaryan lists; Markarian 1967-1981 (list 1-15)|
|POX||Catalogue of active galaxies; Kunth; 1981|
|RB||Rood and Baum Catalogue: Rood and Baum, 1967|
|UGC||Uppsala General Catalogue; Nilson, 1973|
|UGCA||Catalogue of Selected non-UGC Galaxies; Nilson, 1974|
|UM||University of Michigan lists; Mac Alpine et al., 1977-1981|
|VCC||Virgo Cluster Catalogue; Bingelli et al., 1985|
|WEIN||Galaxies behind the Milky Way; Weinberger et al., 1980|
It is to be noted that two galaxies are companion of two different UGC galaxies. (PGC 12267 is compan- ion of UGC 2639 and UGC 2651; PGC 212567 is companion of UGC 408 and UGC 423. In the catalogue they are given on the same line).
Copyright The European Southern Observatory (ESO)