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2 Catalogue of UGC galaxy companions

Many years ago Peter Nilson (1973) produced his famous UGC catalogue with nearly 13000 galaxies larger than one arcminute. This catalogue was integrated a long time ago in general extragalactic databases like NED or LEDA. At the end of the UGC catalogue Nilson gave many additional pieces of information about the UGC galaxies and their environment. For instance, small galaxies surrounding a UGC galaxy and listed in the CGCG catalogue (Zwicky et al. 1961-1968) are given with their original CGCG coordinates. Further, Nilson identified many small companions around his UGC galaxies.

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 $\beta$ (measured in degrees from north through east) and the angular separation $\rho$ (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.

  \begin{figure}\rotatebox{-90}{\resizebox{\hsize}{!}{\includegraphics{image.eps}}}\end{figure} Figure 1: A typical image from the Digitized Sky Survey got from ESO. The frame is $10' \times 10'$. 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.

2.1 Treatment of images

We selected first UGC galaxies with companions and made the histogram of the radial vectors of their companions. This histogram is given in Fig. 2.

  \begin{figure}\resizebox{\hsize}{!}{\includegraphics{historho.eps}}\end{figure} 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.


Table 1: Catalogue of UGC galaxy companions. The full list is availbale in electronic form
PGC Name R.A.2000 DEC2000 D d ugc-parent
    h min sec deg ' '' ' '  
0000037 MCG 4- 1- 9 000031.6+261819 0.25 0.15 12896
0215025   000047.8+285602 0.30 0.10 12901
0000089 MCG 2- 1- 9 000113.3+130836 0.80 0.30 12906
0215026   000114.1+344059 0.20 0.10 12904
0000092 MCG 2- 1- 10 000115.1+130647 0.50 0.15 12906
0215027   000129.5+130551 0.50 0.40 12906
1422918   000145.3+130601 0.40 0.40 12906
0215028   000211.2+173337 0.50 0.30 12916
0215029   000212.8+125643 0.40 0.40 12919
0215030   000216.3+125501 0.30 0.20 12919
0212450   000227.4+445333 0.35 0.25 00002
0000185 IC 5379 000240.7+163602 0.70 0.35 00001
0212451   000253.6+185041 0.50 0.30 00003
0212453   000308.0+155836 0.40 0.20 00007
0212452   000313.6-015809 0.30 0.15 00005
0212454   000318.0+083641 0.60 0.20 00010
0000234 KUG 0000+271 000325.0+272412 0.30 0.30 00013
0212457   000329.1+041747 0.30 0.20 00015
0212455   000334.4+220456 0.50 0.35 00011
0000252 CGCG 408- 17 000337.7+083810 0.70 0.30 00010

2.2 The final catalogue

The catalogue is now loaded in LEDA but it will be distributed in an electronic form via the Astronomy and Astrophysics archives. Here we simply reproduce a sample page (Table 1). This table gives measurements for 3301 galaxies (539 were already known).

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.


Table 2: New measurements of equatorial coordinates. The full table is available in electronic form
PGC Name R.A.2000 DEC2000
    h min sec deg ' ''
0089489   000008.4-603304
0141432   000009.8-633540
0089490   000018.2-605343
0000027 MCG -1- 1- 18 000023.3-065612
0165937 IRAS 23578-5307 000023.8-525031
0000041   000025.8-054640
0000036 IC 5373 000029.0+324656 *
0000046   000029.7-054636
0000037 MCG 4- 1- 9 000031.6+261819
0000040 MCG 0- 1- 17 000035.6-014550
0097568 IRAS 23583+1813 000054.2+183022
0141433   000058.8-604956
0000079 IC 5374 000104.6+043006
0097569 IRAS 23586-0116 000113.3-005937
0000122 MCG -7- 1- 7 000130.9-404912
0141435   000137.7+172919
0100354   000201.2+145837
0000152 MCG -5- 1- 25 000205.4-303709
0000150 FAIR 1065 000205.4-512056


Table 3: Acronyms used in Tables 1 and 2 for galaxy identification
Acronym Reference
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).

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