1. Introduction

Evidence for enhanced star formation in interacting galaxies has been demonstrated by many research groups focusing on different observational techniques. However, when unbiased samples of interacting- and non-interacting galaxies are compared only, a moderate excess of star formation activity in the very centers of interacting galaxies is found (Bergvall et al. 1997). Telles Terlevich (1995) have also argued that even most of the HII galaxies, considered as the best candidates for tidally induced starbursts, are hardly triggered by interactions. Indeed, it seems that special galactic disk and perturbation characteristics are needed for enhanced star formation to be induced by galaxy encounters.

Detailed N-body modelling of galaxy pairs gives valuable information of their probable orbital characteristics. For example, our simulation models for Arp 86 (NGC 7753/7752) (Salo Laurikainen, 1993) and M51 (NGC 5194/5195) (Salo Laurikainen 1997a) suggest that significant mass transfer to the companion can take place, but only in favorable orbital conditions. The mass flow occurs episodically after the crossing of the main galaxy disk, and may subsequently induce a nuclear starburst in the companion if enough mass is accreted. In the case of Arp 86 the low orbital inclination favours mass accretion, whereas the companion of M51, with almost perpendicular orbit, is expected to be inactive. This scenario is consistent with observations showing a recent starburst in NGC 7752, but not in NGC 5195. Our models for both systems predict bound current orbits and several orbital revolutions inside the halo of the main galaxy before the final merger. We propose that most M51-type pairs represent similar gravitationally bound systems, implying that their star formation properties and spiral patterns are continuously evolving during the course of the orbital evolution. In M51 the models suggest that the long term perturbation from the bound orbit may have induced even the tightly wound innermost spiral arms (Salo & Laurikainen 1997b) observed in near-IR (Zaritsky et al. 1993).

In order to study other similar M51-type pairs, and for comparison with somewhat wider pairs, we have obtained deep BVRI images for a sample of galaxy pairs. They were chosen from the "Arp's Atlas of Peculiar Galaxies" (1966) and from the "Catalog of Isolated Pairs of Galaxies in the Northern Hemisphere" by Karachentsev (1972). Deep images enable studies of morphology and stellar distributions both in the inner and outer regions of the galaxies as well as distribution of intermediate age stars. Optical images are especially valuable for detecting the outermost morphology traced by luminous stars. In this paper (Paper I) we present the data reductions and display R, B-V and R-I images. The data analysis is postponed to Paper II (Laurikainen Salo, in preparation). A complete observational analysis including HI Fabry-Perot interferometric observations, low- and high resolution IR-images, as well as N-body models for the most interesting M51-type pairs, will be presented later.

 

Galaxy RA DEC cz Other name

(1950) (1950) [h m s]

Arp 70 01:20:41 30:31:25 10494¹ .S?.... PGC 5085

Arp 74 02:05:17 41:14:33 5543¹ .SXT5.. PGC 8161

Kar 64 A 02:18:24 39:08:51 7465 .SAS3P. PGC 8961, Arp 273

Kar 64 B 02:18:27 39:07:43 7335 .SBS1P. PGC 8970

Kar 125 A 07:06:14 20:40:58 5227¹ .P..... PGC 20259, NGC 2341

Kar 125 B 07:06:21 20:43:03 5276¹ .S...P. PGC 20265, NGC 2342

Arp 82 08:08:13 25:21:19 4079 .SAR5P. PGC 22957, NGC 2535

08:08:16 25:19:46 4142 .SBT5P. PGC 22958, NGC 2536

Kar 168 A 08:39:53 14:27:58 1988 .S..1.. PGC 24464, Arp 89, NGC 2648

Kar 168 B 08:40:00 14:27 2166 PGC 24469

Kar 179 A 08:53:06 52:17:51 4098 .S?.... PGC 25130

Kar 179 B 08:53:22 52:15:33 3778 .SB.2*. PGC 25142, NGC 2692

Kar 203 A 09:23:30 68:37:43 3698 .SBS8P. Arp 300a, Mrk 111,PGC 26849

Kar 203 B 09:23:43 68:38:21 3874 .SXS5. Arp 300b,PGC 26864

Kar 296 A 11:37:33 15:36:17 3299¹ .SXT3*P PGC 36197,Arp 83a, NGC 3800

Kar 296 B 11:37:37 15:37:11 3312¹ .SBS3*P PGC 36193,Arp 83b, NGC 3799

Arp 87 11:38:08 22:42:18 7050 .SXT5*P PGC 36227, NGC 3808

11:38:08 22:43:22 7189 .I.O.SP PGC 36228, NGC 3808A

Kar 302 A 11:46:01 48:59:20 944 .SXT5*. PGC 36875, NGC 3893

Kar 302 B 11:46:19 48:57:10 869 .SB.O*P PGC 36897, NGC 3896

Kar 331 A 12:18:55 06:55:53 4227 .L..... NGC 4296,PGC 39943

Kar 331 B 12:18:54 06:56 4046 SO

Arp 183 13:32:38 31:39:00 4962¹ .S..3.. PGC 47867

Arp 36 13:31:57 31:40:53 5017¹ .SB?... PGC 47808

Kar 404 A 13:56:25 37:41:51 3427 .SBS3P. PGC 49739, NGC 5394

Kar 404 B 13:56:30 37:40:05 3505 .SAS3P. PGC 49747, NGC 5395

NGC 5905 15:14:03 55:42:06 3390¹ .SBR3.. PGC 54445

NGC 5908 15:15:23 55:35:37 3306¹ .SAS3*/ PGC 54522

Kar 471 A 15:42:36 41:15:00 9480 .S..... PGC 55913,Mrk 489,NGC 5992

Kar 471 B 15:42:43 41:16:33 9565 .SBR3*. PGC 55918, NGC 5993

Arp 218 15:51:18 18:45 .SXS4.. PGC 56314

Kar 523 A 17:44:18 35:35 7081

Kar 523 B 17:44:30 35:35:20 6734 .SB?... PGC 60829, NGC 6447

Kar 538 A 19:11:53 73:19:30 7510 .SB?... PGC 62864, NGC 6786

Kar 538 B 19:12:00 73:19 7555 .S?.... PGC 62867

Arp 298 23:00:44 08:36:19 4846 .PSXT1. PGC 70348, NGC 7469

23:00:47 08:37:26 4894 .SAR6P PGC 70350

Arp 86 23:44:33 29:12:22 5163¹ .SXT4.. PGC 72387,NGC7753

23:44:27 29:10:52 5072¹ .I.O*. PGC 72382,NGC7752, Mrk1134

The radial velocities are from optical measurements, but while marked with superscript they are from
21 cm line measurements.

is mean revised morphological type in the RC2 system.

 

Date Telescope Pix. size/chip size seeing Comment

1990 Jan. 1-5 NOT, 2.5 m 0.9-1.4 photometric

1990 Feb. 24-27 NOT, 2.5 m 0.7-2.4 photometric

1991 Jan. 7 JKT, 1.0 m partly photom.

1991 July 16-18 NOT, 2.5 m 0.6-1.0 non-photom.

1991 Aug. 31, Sep 5 Calar Alto, 1.5 m 1.4-2.2 photometric

1992 Feb. 5-12 Calar Alto, 1.5 m 1.1-1.7 partly photom.

1993 Apr. 13-14 NOT, 2.5 m 0.6-1.3 partly photom.

1993 Nov. 18-20 NOT, 2.5 m 1.0-4.0 non-photom.

1995 Jan. 31 SPM, 2.1 m photometric

 

Galaxy Filters Rebin Telescope

Arp 70 BVRIbl 1 NOT, Nov. 1993

Arp 74 BVRIbl 1 NOT, Nov. 1993

Kar 64 AB VRI 3 Calar Alto, Feb. 1992

Kar 64 A,B B 1 NOT, Nov. 1993

Kar 125 AB BVRI 4 NOT, July 1991

Arp 82 AB BVRIbl 1 SPM, Jan. 1995

Kar 168 AB BVRI 2 Calar Alto, Feb. 1992

Kar 179 A BVRI 1 NOT, Nov. 1993

Kar 179 B BVRIbl 1

Kar 203 A 1 JKT, Jan. 1991

Kar 203 B V 1

Kar 296 AB BVRI 3 NOT, Jan. 1990

Arp 87 BVRI 3 Calar Alto, Feb. 1992

Kar 302 A RI 4 Calar Alto, Feb. 1992

Kar 302 B BVRI 3

Kar 331 A 2 NOT, July 1991

Kar 331 B 2

Arp 183 2 NOT, Apr. 1993

Arp 36 1 NOT, Apr. 1993

Kar 404 AB BVRI 4 Calar Alto, Feb. 1992

NGC 5905 BVRI 3 Calar Alto, Aug. 1991

NGC 5908 BVRI 1

Kar 471 A 2 NOT, July 1991

Kar 471 B 1

Arp 218 AB 2 NOT, Apr. 1993

Kar 523 A 2 NOT, July 1991

Kar 523 B 2

Kar 538 A 5 NOT, July 1991

Kar 538 B 7

Arp 298 AB BVR 2 Calar Alto, Aug. 1991