3. Observations and data reduction

Table 2 (click here) summarizes the observing parameters for each object in the sample: date of observations, telescope and instrument used, spatial or spectral resolution and exposure time.

 

Optical imaging Optical spectroscopy Infrared imaging

s Å/px s s

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)

00199-7426 07/94 3.5 m NTT 0.27 300 12/95 D1.5 m ESO 2.9 2700 02/96 2.2 m ESO 0.51 480

06035-7102 08/89 3.5 m NTT 0.25 20 07/89 4 m CTIO 5.7 600 02/96 2.2 m ESO 0.51 480

06206-6315 08/89 3.5 m NTT 0.25 60 07/89 4 m CTIO 5.7 600 - - - -

09061-1248 02/93 3.5 m NTT 0.44 60 02/93 3.5 m NTT 4.5 1800 02/96 2.2 m ESO 0.51 480

09111-1007 02/93 3.5 m NTT 0.44 60 02/92 3.5 m NTT 4.5 1800 02/96 2.2 m ESO 0.51 480

11095-0238 02/93 3.5 m NTT 0.44 120 07/89 4 m CTIO 5.7 600 06/93 2.2 m ESO 0.49 300

14348-1447 08/89 3.5 m NTT 0.25 120 - - - - - - - -

14378-3651 08/89 3.5 m NTT 0.25 180 07/88 4 m CTIO 5.7 1200 06/93 2.2 m ESO 0.27 300

15462-0450 07/94 3.5 m NTT 0.27 600 02/93 3.5 m NTT 3.7 900 06/93 2.2 m ESO 0.27 300

16090-0139 07/94 3.5 m NTT 0.27 300 - - - - - - - -

17208-0014 08/89 3.5 m NTT 0.25 130 07/89 4 m CTIO 5.7 1200 06/93 2.2 m ESO 0.49 300

19254-7245 06/92 3.6 m ESO 0.81 600 07/88 4 m CTIO 5.7 1200 06/92 2.2 m ESO 0.49 900

20046-0623 07/94 3.5 m NTT 0.27 300 - - - - - - - -

20087-0308 07/94 3.5 m NTT 0.27 300 07/89 4 m CTIO 5.7 1200 06/93 2.2 m ESO 0.49 300

20100-4156 08/89 3.5 m NTT 0.25 180 07/88 4 m CTIO 5.7 1200 06/92 2.2 m ESO 0.49 300

20414-1651 08/89 3.5 m NTT 0.25 180 07/89 4 m CTIO 5.7 600 06/92 2.2 m ESO 0.49 300

20551-4250 08/89 3.5 m NTT 0.25 180 07/88 4 m CTIO 5.7 600 06/92 2.2 m ESO 0.49 300

21130-4446 08/89 3.5 m NTT 0.25 180 07/89 4 m CTIO 5.7 720 06/92 2.2 m ESO 0.27 300

21504-0628 07/94 3.5 m NTT 0.27 300 - - - - - - - -

22491-1808 06/92 3.6 m ESO 0.81 600 - - - - - - - -

23128-5919 08/89 3.5 m NTT 0.25 180 07/89 4 m CTIO 5.7 600 06/92 2.2 m ESO 0.49 300

23230-6926 07/94 3.5 m NTT 0.27 300 07/88 4 m CTIO 5.7 1200 07/94 2.2 m ESO 0.27 900

23389-6139 07/94 3.5 m NTT 0.27 300 07/89 4 m CTIO 5.7 900 07/94 2.2 m ESO 0.49 200

 

3.1. Optical imaging

Optical images from the Melnick & Mirabel (1990) sample have been obtained in September 1989 during the commissioning period of the NTT, at the European Southern Observatory. R band observations were carried out with the EFOSC2 camera. Due to guiding and rotating problems, the exposure time had to be limited to 2 min. Optical data have been complemented in June 1992, February 1993 and July 1994 with images obtained using the EFOSC camera on the ESO 3.6 m, and the EMMI camera on the NTT. They have been reduced with standard procedures using the IRAF CCDRED package.

Figure 3 (click here) presents for each system in the sample (except IRAS 05189-2524; an image of this object can be found in Sanders et al. 1988a), a greyscale large field image and a contour map of the central region in a logarithm scale. The images obtained during the 1989 run had already been published in Melnick & Mirabel (1990). They have however been reprocessed and reproduced here to emphasize the central regions; they also have been rotated so that the orientation is the same for all objects. For comparison purposes, an angular and linear scale are indicated in each image.

The photometry has been done with the APPHOT package within IRAF. The derived R band magnitudes can be found in Table 3 (click here). Since, during the 1989 and 1992 runs, no standard photometric stars had been observed, we could only obtain a rough estimate of the R magnitude (with an error of 0.3 mag) by calibrating the data with published magnitudes. The 1993 and 1994 observations were done under photometric conditions, and Landolt standards stars have been observed (Landolt 1992). The error for these objects is typically 0.1 mag. A polygonal aperture was used to derive the total magnitude because of the peculiar morphology of ULIRGs. The limiting isophote corresponds roughly to 25 mag arcsec^-2. If several objects are present in the IRAS field, the data are given for each of them. For multi nucleated systems, the magnitude of the whole system and of the nuclei are mentioned. For these, a circular aperture was used. The corresponding radius is indicated in Col. 3 of Table 3 (click here).

3.2. Near infrared imaging

Near infrared imaging was mainly carried out in June 1992 and June 1993 with the IRAC 2 camera, installed on the ESO/MPI 2.2-meter telescope. Additional observations with an upgraded version of the instrument, IRAC 2B, were done in July 1994 and February 1996. The detector was a HgCdTe NICMOS 3 array. According to the seeing conditions, we have either used the 0.27 or 0.5 arcsec/pixel objectives with the J, H and K filters. The individual exposures ranged between 1 s and 20 s depending on the filter and on the background level. The number of individual frames taken for one position was adjusted to reach an integration time of 1 min. For sky acquisition the telescope was offset by typically 30 in each direction around the central position, with most of the time the object still in the field, so that no observing time was lost. The images were sky subtracted using a sky obtained by median filtering the images of the different positions. The final frame was obtained by a shift and add method on the individual images. To increase the signal to noise, the images were smoothed with a flat-topped rectangular kernel. The total on-source integration time for the K band is given in Table 2 (click here).

 

Optical Infrared

IRAS name R Apert Ref J H K Apert Ref

mag mag mag mag

(1) (2) (3) (4) (5) (6) (7) (8) (9)

00199-7426 15.0 tot a 14.1 13.2 12.5 5.0 a

06035-7102 15.6 tot b 13.3 12.6 12.0 13 a

06035-7102W 16.8 3 b 14.9 14.2 13.6 3 a

06035-7102E 17.0 3 b 14.4 13.6 12.8 3 a

06206-6315 16.3 tot b - - - - -

09061-1248 15.8 tot a 14.0 13.2 12.6 7.5 a

09061-1248S 17.0 2.5 a 14.9 14.0 13.2 2.5 a

09061-1248N 17.3 2.5 a 15.5 14.7 14.2 2.5 a

09111-1007W 15.7 tot a 13.3 12.4 11.9 15 a

09111-1007E 14.8 tot a 13.0 12.4 12.0 15 a

11095-0238 16.8 tot a 16.1 15.6 14.7 5 a

14348-1447 15.8 tot b 15.0 14.1 13.3 5 b

14348-1447S 16.9 2.5 b 15.6 14.7 13.7 2.5 b

14348-1447N 18.2 2.5 b 16.1 15.1 14.3 2.5 b

14378-3651 16.3 tot b 14.5 13.9 12.8 5 a

15462-0450/N 16.6 tot a 14.8 13.6 12.2 5 a

15462-0450/S 17.3 tot a - - - - -

16090-0139 16.7 tot a - - - - c

17208-0014 14.8 tot a 14.0 12.9 12.4 13 a

19254-7245 14.7 - b 14.0 12.7 11.6 15 a

19254-7245/S 15.8 8 b 14.7 13.5 12.2 8 a

19254-7245/N 16.2 8 b 15.4 14.3 13.1 8 a

20046-0623 16.2 tot a - - - - c

20088-0308 15.9 tot a 14.7 13.6 12.8 5 a

20100-4156 16.5 tot b 15.0 14.3 13.7 7.5 a

20100-4156/S 18.2 1.2 b 16.6 15.6 15.8 1.2 a

20100-4156/N 18.6 1.2 b 17.4 16.7 16.7 1.25 a

20414-1651 16.9 tot a 15.4 14.2 13.3 5 a

20551-4250 14.2 31 a 13.4 12.2 12.0 13 a

21130-4446 16.1 tot b 15.3 14.1 13.5 9 a

21130-4446/S 17.9 1.5 b 17.1 16.0 15.3 1.5 a

21130-4446/N 17.6 1.5 b 16.6 15.3 14.8 1.5 a

21504-0628 15.6 tot a - - - - -

22491-1808 15.4 tot b 14.7 14.0 13.6 5 b

23128-5919 14.1 tot b 13.4 12.3 11.8 10 a

23128-5919/S 15.7 2.5 b 14.3 13.4 12.6 2.5 a

23128-5919/N 15.9 2.5 b 14.7 13.7 13.3 2.5 a

23230-6926 16.6 tot a 15.4 14.2 13.6 5 a

23389-6139 16.4 tot a 15.0 14.2 13.5 8 a

23389-6139/S 17.6 3 a 15.5 14.3 13.7 3 a

23389-6139/N 18.5 3 a 16.8 16.5 15.8 3 a

 

The photometry has been done with circular apertures centered on each nucleus. For flux calibration, faint stars from the IRIS list of SAAO standard stars (Carter & Meadows 1995) have been observed. However, during our 1992 run, the weather conditions have not been photometric. Nevertheless, for the few objects that we have observed during both our 1992 and 1993 runs, we did not find any significant discrepancy within the data. The magnitude difference is less than 0.1 mag. Photometric data are given in Table 3 (click here).

Figure 4 (click here) presents the K band calibrated contour maps of the 17 galaxies that we have observed. The angular and linear scales are indicated. Contour maps of the three SULIRGs belonging to the BGS can be found in Carico et al. (1988) and Murphy et al. (1996) have published an uncalibrated K image of IRAS 20046-0623.

3.3. Optical spectroscopy

Low and high resolution spectra have mostly been obtained in July 1988 and July 1989 during two observing runs with the 4-meter telescope at Cerro Tololo Inter-American Observatory. Two gratings were used, one covering the spectral range 4400-7700 Å with a pixel resolution of 5.7 Å; the other covering 6500-7500 Å with a pixel resolution of 1.8 Å. The spatial resolution along the slit was 0 4/px. Its width was 1 3. For three objects, we have obtained in February 1994 low resolution spectra with the EMMI instrument installed on the ESO NTT. The grism used had a pixel resolution of 4.5 Å. The spectrum of IRAS 00199-7426 was taken in December 1995, with the DFOSC instrument installed at the Danish 1.5 m telescope at La Silla Observatory. In total, spectroscopic data for 18 galaxies have been collected. Three more, IRAS 05189-2524, IRAS 14348-1447 and IRAS 22491-1808 have spectra published in Sanders et al. (1988a).

The data reduction was carried out with the LONGSLIT package within IRAF. The spectra of the galactic nuclei were extracted from the 2D spectra. The angular size over which the extraction was done depended on the distance of the objects, and on the nuclei separation for interacting objects. It ranged between . Standard stars from the list of Stone & Baldwin (1983) have been observed for flux calibration. The calibrated low and high resolution spectra are displayed in Fig. 5 (click here). For the galaxies observed with the NTT, a close-up of the low resolution spectrum in the red wavelength range is shown instead of the high resolution spectrum. The spectrophotometry of the main optical, low resolution lines, is presented in Table 4 (click here). The fluxes and equivalent widths have been directly measured with the SPLOT task. The flux uncertainty, estimated from successive line measurements, is typically 10%, for bright lines with fluxes higher than . It may be higher in the case of the H line, strongly contaminated in some galaxies by stellar absorption. It is indicated in Col. 3, whether the H line is seen in emission, in absorption, or in emission within an absorption line. Another uncertainty affecting the spectrophotometry comes from the differential atmospheric refraction (Filippenko 1982). For interacting galaxies, the slit was preferentially put along the double nuclei, and therefore was not oriented along the parallactic angle. Since most of our objects (60%) have been observed with airmasses below 1.4, the differential refraction within our spectral range was less than 0 5, which is small compared to our slit width. For 15% of them however, observed with an airmass greater than 2, and for which the differential refraction might have been, in the worst cases, as high as 1 0, spectrophotometric errors might have been significant. In Table 4 (click here), uncertain fluxes and equivalent width measurements, with errors greater than 10%, are marked with a ":''.

 

4861 4959 5007 6300 6563 6584 6717/31 4861 5173 5890 6300 6563

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

00199-7426 1.00 em - 1.51 - - - - 5.68 0.53 8.98 - -

06035-7102/W 1.62 em 1.35: 2.72 2.39 21.66 9.92 11.07 4.64 - 0.35 4.76 48.01

06035-7102/E 2.17 em 1.55: 2.04 1.12 18.54 7.66 5.15 5.98 - 1.01 3.75 40.46

06206-6315 0.26: abs/em - 1.36 - 6.31 4.45 4.86 1.18: 2.31 2.63 - 13.82

09061-1248/S 0.61: abs/em - 0.53: 0.71: 7.09 4.51 3.94 3.44: 0.55 1.13 2.75: 26.54

09061-1248/N 1.95 em 0.25: 0.74: 0.75: 12.67 8.01 4.74 9.29 0.18 2.23 2.63: 43.44

09111-1007/W 0.14 em - - 0.32: 6.70 4.87 1.60 2.38 0.49 15.50 2.28: 43.35

09111-1007/E 4.10 em 5.64 16.15 2.97 43.73 32.54 15.63 17.98 0.49 - 9.10 138.80

11095-0238 1.35 em 0.72 2.29 1.46 13.38 8.15 6.66 10.76 - 1.48 17.38 88.43

14378-3651 - - 0.59: 1.76 0.69: 13.71 7.28 3.57 - 1.02 6.20 3.63: 39.77

15462-0450/S 2.86 em 0.38: 1.76 - 18.29 7.16 5.72 17.70 0.37 3.08 - 99.16

15462-0450/N ^* 19.45: em 10.67: 16.17: 1.04: 55.09: 23.20: 5.66 49.63: - - 2.67: 120.40:

17208-0014 0.59: abs/em - 0.65: 1.40 16.59 10.30 5.23 1.64: 0.45 6.11 3.90 28.09

19254-7245/S 2.03 em 4.55 15.72 10.02 117.10 - 19.70 9.02 - 5.13 30.15 218.10

19254-7245/N -0.37: abs - - - 5.74 4.22 2.10 1.47: 2.83 4.80 2.47 10.13

20087-0308 -0.93 abs - - - 6.32 4.72 2.53 7.02 2.06 7.34 4.64 23.40

20100-4156 1.86 em 0.89: 2.79 1.00 16.08 7.02 2.74 10.51 0.11 3.06 7.93 56.82

20414-1651 0.93: abs/em 0.71: 1.33 0.86: 9.76 4.73 4.21 6.46: 1.32 2.19 6.46: 41.18

20551-4250 6.39 em 2.57 6.78 4.58 61.44 24.47 23.71 8.70 1.12 0.99 4.77 42.91

21130-4446 9.68 em 4.27 13.11 1.09 45.05 11.57 13.63 29.75 0.87 - 5.56 130.00

23128-5919/N 8.86 em 5.54 14.48 3.09 82.99 19.76 23.72 20.45 - 1.31 5.91 115.30

23128-5919/S 13.32 em 13.60 40.09 4.54 93.35 29.50 25.61 20.68 - 1.64 8.35 131.70

23230-6926 1.08 em 1.04: 1.71 1.10 13.51 5.83 6.32 8.06 - 2.32 5.89 71.67

23389-6139 0.34: em 1.74 4.29 - 22.58 - 3.59 2.55: 1.92 2.59 4.62 108.40