4. Data analysis

Table 2 lists the data for 14 Karachentsev's pairs observed. Column (1) gives the identification in Karachentsev's catalog of isolated pairs, Col. (2) gives other identifications, Col. (3) gives the pair position (1950.0). Columns (4) to (6) give the integrated magnitudes in B, V, I calculated as described in the previous section. (7) and (8) give the colors B-V and V-I. Column (9) gives the morphology of each galaxy obtained from NED ( gives the new morphology found from the radial profiles). Column (10) gives the radial velocities (km s^-1 obtained from NED).

 

Name Id. B V I B-V V-I Morph.

CPG018a UGC 00496 00 45 54 +01 05.0 15.11 14.15 12.71 0.96 1.44 E 18648

CPG018b UGC 00496 00 45 54 +01 05.0 14.78 13.80 12.57 0.98 1.23 E 19003

CPG069a IC0233 02 29 03 +02 35.5 14.24 14.15 13.44 0.09 0.71 dIn 8266

CPG069b CGCG388-036 02 29 03 +02 35.5 15.82 15.59 14.63 0.23 0.96 Sab 8303

CPG083a NGC1143 02 52 39 -00 23.0 14.20 13.29 12.03 0.91 1.26 8514

CPG083b NGC1144 02 52 39 -00 23.0 13.23 12.14 11.20 1.14 0.94 Sring 8714

CPG091a CGCG391-011 03 32 45 -01 23.5 15.26 14.55 13.35 0.71 1.20 Sa 10674

CPG091b CGCG391-012 03 32 45 -01 23.5 14.82 13.78 12.47 1.04 1.31 Edust 11086

CPG099a NGC1587 04 28 06 +00 33.0 12.29 11.50 10.25 0.79 1.25 E 3800

CPG099b NGC1588 04 28 06 +00 33.0 13.35 12.46 11.11 0.89 1.35 3495

CPG545a UGC11567 20 25 42 +00 19.5 14.08 13.12 11.94 0.96 1.18 SB? 5762

CPG545b CGCG373-015 20 25 42 +00 19.5 13.85 12.69 11.19 1.16 1.50 Sb 5732

CPG547a UGC11593 20 32 12 +07 48.0 14.68 14.11 12.90 0.57 1.21 E 7856

CPG547b UGC11593 20 32 12 +07 48.0 12.67 12.48 11.45 0.19 1.03 Sc 7887

CPG548a NGC6962 20 44 51 +00 07.5 11.07 10.58 0.48 SAB(r)ab 4419

CPG548b NGC6964 20 44 51 +00 07.5 12.20 10.88 1.32 E 4032

CPG551a UGC11657 20 57 12 -02 04.0 14.00 13.49 12.40 0.51 1.09 Pec 6033

CPG551b UGC11658 20 57 12 -02 04.0 14.50 13.84 13.02 0.56 1.09 SAB(rs)s 6025

CPG575a NGC7469 23 00 46 +08 36.9 12.86 12.65 12.56 0.21 0.29 SAB(rs)s 5083

CPG575b IC5283 23 00 46 +08 36.9 13.72 12.98 11.71 0.74 1.27 SA(r)cdpec 5220

CPG577a CGCG406-013 23 08 18 +08 52.0 14.92 14.18 12.95 0.74 1.23 E 11646

CPG577b CGCG406-013 23 08 18 +08 52.0 14.94 14.01 12.74 0.93 1.27 11762

CPG580a NGC7587 23 15 24 +09 23.5 13.35 12.06 10.92 1.29 1.14 SBab 8819

CPG580b CGCG406-051 23 15 24 +09 23.5 14.53 14.03 12.55 0.50 1.48 S 8508

CPG583a CGCG380-058 23 24 00 +02 02.5 14.46 13.54 12.23 0.92 1.31 5876

CPG583b CGCG380-059 23 24 00 +02 02.5 14.46 13.54 12.23 0.92 1.31 Sa 5561

CPG587a NGC7714 23 33 45 +01 52.7 11.86 11.99 11.99 -0.13 1.16 SB(s)b 2980

CPG587b NGC7715 23 33 45 +01 52.7 11.81 12.14 10.22 -0.33 1.92 Impec 2933

4.1. Morphological properties

CPG018 is a very interesting EE pair with a common envelope. Elliptical models were fitted and surface brightness profiles follow an r^1/4 law, however the ellipticity of the isophotal contours vary from 0 to 0.4 outside 10 arcsec.

CPG069 is a late-type pair with the two galaxies showing tidal effects in their shapes. CPG069a is a warm IRAS galaxy with flux ratio F₆₀/F₃₀ = 2.86 and its spectra is typical of an HII region galaxy (Kailey & Lebofsky 1988). CPG069a surface brightness profile in the central regions are not well fitted.

CPG083 is a strongly interacting mixed pair also known as Arp 118 or VV331. Both galaxies, NGC 1143(E) and NGC 1144 (S), show starburst activities and signs of tidal distortion. The spiral galaxy presents a knotty ring with a peculiar structure which can be interpreted as the product of an interaction of two disk galaxies (Hippelein 1989). From the surface brightness profile it is clear that NGC 1143 is in fact a lenticular galaxy.

CPG091 is a mixed pair with moderate signs of interaction. The elliptical galaxy presents a strong dust lane and its surface brightness profile follows an r^1/4 law. The ellipticity of the isophotal contours is 0.4 outside 10 arcsec.

CPG099 is an early-type pair strongly interacting. The two early-type galaxies (NGC 1587/88) show isophotal distortion and asymmetric light distribution. See Borne & Hoessel (1988) for a simulation of this pair. From the surface brightness profile it is clear that NGC 1588 is in fact a lenticular galaxy. For NGC 1587 the ellipticity of the isophotal contours is 0.3 outside 15 arcsec.

CPG545 is a late-type pair composed by a barred spiral and an Sb galaxy. Photometry of this pair is affected by bright stars in the field.

CPG547 is a mixed pair in close contact. The barred spiral galaxy is edge-on and overlaps the elliptical (Keel 1993). The surface brightness profiles of the elliptical galaxy follow an r^1/4 law. The ellipticity of the isophotal contours is quite irregular varying from 0 to 0.2 outside 10 arcsec.

CPG548 is a mixed pair. The spiral galaxy has two long symmetric arms and a weak central bar and the elliptical has an elongated shape. The surface brightness profiles follow an r^1/4 law. Rampazzo et al. (1995) studied its kinematics and found signs of interaction. The ellipticity of the isophotal contours of NGC 6964 is 0.3 outside 20 arcsec.

CPG551 is a late-type pair strongly disturbed by tidal effects.

CPG575 is a late-type pair of galaxy with one galaxy (IC 5283) very disturbed by tidal effects and the other one (NGC 7469) with an outer and an inner ring (Buta & Crocker 1993; Marquez & Moles 1994). Structures can be seen in their surface brightness profiles. Seyfert activity is present (Marquez & Moles 1994).

CPG577 is an early-type pair. No common halo was found. The surface brightness profiles show that CPG577b is a lenticular galaxy. The surface brightness profiles of CPG577a follow an r^1/4 law. The ellipticity of the isophotal contours is quite irregular, varying from 0.4 to 0.2 in the inner region between 6 to 10 arcsec, and from 0.2 to 0.4 outside 10 arcsec.

CPG580 is a late-type pair with one of the galaxies very disturbed and with a barred spiral with a dust lane and a warped disk (NGC 7587).

CPG583 is a mixed pair, with a spiral and a lenticular without any clear peculiarity.

CPG587 is a late-type pair with two very disturbed late-type galaxies. NGC 7715 has an irregular shape and NGC 7714 has a bar and a peculiar ring.

We have classified these pairs according to the degree of distortion that each galaxy presents. We used a slightly modified version of the classification scheme proposed by Dahari (1985). Pairs with galaxies that showed strong signs of interaction were called which corresponds to classes 4, 5 and 6 of Dahari. Pairs with moderate signs of interaction were called (2 and 3 in Dahari's scheme) and pairs with weak or no sign of interaction were called . Pairs that had one galaxy disturbed and one normal were classified as M-W. In Table 3 we present the classification of the peculiarities according to this scheme, the angular separation ((')), the projected separation (in kpc) and the radial velocity difference (in km s^-1).

 

Name Type Int.Class Sep.

(') (km s^-1)

CPG 018 EE 0.34 18.6 355

CPG 069 SS 0.70 16.9 37

CPG 083 ES 0.71 17.8 200

CPG 091 ES 0.72 22.8 412

CPG 099 EE 0.97 10.3 305

CPG 545 SS 0.34 05.7 30

CPG 547 ES 0.67 15.3 31

CPG 548 ES 1.76 21.6 387

CPG 551 SS 0.98 17.2 8

CPG 575 SS 1.32 19.8 137

CPG 577 EE 0.47 16.0 116

CPG 580 SS 0.82 20.7 311

CPG 583 ES 1.00 16.6 315

CPG 587 SS 1.88 16.2 47

We have looked for star formation regions in the galaxies of our sample. Color maps (B-V and V-I) were used to identify these regions. Blue regions, blue tails, bars, patchy and knotty features were identified in most of the late-type galaxies. The strongest tidal damage and star formation regions are found in CPG083 and CPG551. CPG083 is a mixed pair with late-type galaxy completely disrupted and with prominent blue star formation regions (see also Hippelein 1989). CPG551a presents several blue knots typical of star formation activity and CPG551b presents a blue tail and a blue central bar. We have used color maps in order to identify dust regions and found clear signs of dust in early and late-type galaxies. CPG091b has the strongest equatorial dust lane of our sample. The warped galaxy CPG580a also shows a strong dust feature. Another interesting result is the number of barred galaxies found in our sample. Six late-type galaxies are barred, however no late-type pair was found to have two barred galaxies. Reduzzi & Rampazzo (1996) also found a frequent presence of bars in pairs and suggested that bars would be an efficient transient mechanism to transfer gas to the nuclear region and produce nuclear activity.

We have also looked for inner substructures in the early-type galaxies in our sample following the same procedure used in de Mello et al. (1995, 1996) and Reduzzi et al. (1994). Elliptical models were subtracted from the images and residual images were created using the ELLIPSE task (IRAF). In this procedure the residual intensity along each ellipse are parametrized in terms of harmonic components. The deviations from a pure ellipse are expressed as a Fourier series such that the fourth cosine term (C4) describes whether the isophotes are pointy (positive) or boxy (negative). After careful residual images analysis we verify that six early-type galaxies show residual features indicating deviations from elliptical isophotes. On the other hand, for the remaining five early-type galaxies in our sample (CPG018b, CPG083a, CPG099a, CPG547a and CPG548b) no substructure is observed, and the residual images of these galaxies are very similar to E506-01 shown in Reduzzi et al. (1994).

The images of CPG018a, CPG091b and CPG577a, after subtraction, show ripples and asymmetries like AM2312-511 (Reduzzi et al. 1994). The model-subtracted image of CPG099b presents a substructure, like a cross, elongated towards the tidal deformation (south) of the galaxy, similar to the E5720420 (Reduzzi et al. 1996). They classified this residual feature as "discy isophotes". According to Reduzzi et al. (1996b), after model subtraction, discy ellipticals show a filament of light which corresponds to the area where the model underestimates the light. The filament could be real or artificial; the later produced by the combined effects of pointy isophotes and twisting of the isophotes. The calculated average value of the coefficient C4 between 10'' and 20'' for this galaxy is -0.02. The residual images of the CPG577b and CPG583a show the most interesting inner features in our sample. CPG577b have inner shells like the residual map of NGC 2300 (Forbes & Thomson 1992, Plate 2a) and CPG583a shows an X-structure similar to the E556-130 (Reduzzi et al. 1994). Deviations, such as X-structures, could be associated to the fact that we were adjusting an elliptical model to a boxy galaxy. Reduzzi et al. (1996b) concluded that in E556-130 (NGC 2211), the X-structure is described by sudden variation in the trend of C4 from a boxiness of up to -1.6 percent to a diskiness which reaches 2 percent. However, Forbes & Thomson (1992) have suggested that a variety of phenomena could be responsible for the boxy isophotes. We verified a similar variation of C4 as a function of semi-major axis for both CPG577b (-0.007 inner 15'' to 0.02 out) and CPG583a (-0.01 inner 12'' to 0.03 out).