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3 Results

FIR sources were reliably detected at the positions of 24 out of the considered 367 SCGGs. Data for the detected FIR sources is presented in Table 1. Column 1 lists the Shakhbazian designation of the group in the first row. In the second row of Col. 1 the identification number of the galaxy (as labeled on the original SCGG finding charts) which is within the 60 $\mu$m IRAS beam and is suspected to be the dominant FIR emitter, based on proximity to the IRAS source position and optical brightness, is given. Column 2 gives the diameter of the group in arcminutes. In Cols. 3 and 4 the right ascension and declination (J2000.0) of the IRAS source are listed in the first row; the coordinates of the suspected dominant FIR-emitting galaxy are listed below. In Cols. 5, 6, and 7 the flux densities at 25 $\mu$m, 60 $\mu$m and 100 $\mu$m are presented together with their SNR (in parentheses). The fluxes determined by the SCANPI method in some cases differ from that given in the IRAS catalogs. This is generally due to underestimates of flux densities in the IRAS catalogs for sources which are slightly resolved by the IRAS beam.

Isophotes of the detected FIR sources at 60 $\mu$m overlaid on POSS[*] E (red) images of the groups are presented in Fig. 2. To produce these plots, the IRAS FRESCO/HIRES images in cartesian (nearly orthographic) B1950 coordinates were contoured into "vector files'' in the B1950 system. Then the AGRA package developed at IPAC was used to project the contour vectors point-by point into the J2000 "plate'' projection system of the DSS images. The reprojected contours were then overlayed on a grayscale of the J2000 DSS image, and a coordinate grid and scale were added using the IPAC Skyview image analysis package.

As mentioned above, the angular sizes of SCGGs are very small and in many cases they are of the order of 1-2 arcmin. This is smaller than the angular resolution (beam size) of IRAS at 60 $\mu$m, which is nominally $5\hbox{$^\prime$}\times 2\hbox{$^\prime$}$ FWHM. Hence usually it is impossible to determine which galaxy of the group might be the dominant FIR emitter. It is likely, as suggested by Sulentic & De Mello Rabaça (1993) for HCGs, that more than one galaxy in the group contributes to the total observed FIR emission. In some cases, such as Shkh 22, 176 and 243, the FIR source is extended, providing evidence that more than one galaxy contributes to the FIR emission. The second IRAS source within the boundaries of Shkh 22 may be associated with galaxies No. 2 and/or 3. Thus, it is possible that in some cases IRAS has detected the integral FIR emission of a few galaxies in the groups.

Several IRAS sources were detected in the vicinity of SCGGs, but with positions and uncertainty ellipses centered outside the group boundaries. Most of these have been identified with galaxies or stars that are merely projected near the corresponding SCGGs. For 10 remaining SCGGs, IRAS sources were found close to the groups, but SCGG galaxy members could not be confidently identified as the FIR source for various reasons. The 10 SCGGs with possible IRAS detections are presented in Table 2, where the columns contain the same parameters as the first row in Table 1. Since the IRAS detector in-scan and cross-scan widths at 60 $\mu$m were $\sim\! 2.5$ and $\sim\! 4$ arcmin respectively, it is possible that these IRAS sources may be associated with members of the galaxy groups. However, confusion with foreground Galactic cirrus, lack of FSC or FSCR counterparts, or location near the edge of the IRAS beam make the identification very uncertain. The remarks following Table 2 indicate why each IRAS source has an uncertain association with the corresponding galaxy group. Figure 3 presents IRAS isophotes overlayed on visual DSS fields for the sources in Table 2.


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Up: Far-infrared emission from Shakhbazian Groups

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