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Astron. Astrophys. 344, 421-432 (1999)

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2. The sample of isolated galaxies

In configuring our sample of isolated spiral galaxies, the first step was to select all the spirals brighter than [FORMULA] = 13 mag with [FORMULA] in the CfA catalogue (Huchra et al. 1983). For practical reasons only galaxies with diameters smaller than 4´ were retained. To minimize inclination corrections for both photometric and kinematical data, we only considered objects with inclinations between 32o and 73o (i.e., catalogued [FORMULA] in the range 0.8[FORMULA] 0.3). The sample selected in that way is magnitude and size limited.

After that we defined a criterion for isolation. We first excluded all the galaxies that are in the catalogues by Karachentsev (1972), Turner (1976) or Soares (1989), that is to say, well characterized members of isolated pairs or small groups. Then, a galaxy was considered isolated when the nearest neighbor found in the CfA catalogue was outside the volume defined by a projected distance of 0.5 Mpc (we adopt here H0 = 75 km s-1 Mpc-1) and a redshift difference of 500 km s-1. To eliminate the possibility of having small companions fainter than the limit of the CfA catalogue, that could be still very efficient in producing dynamical or morphological perturbations in the main galaxy (see quoted references and Márquez et al. 1996), we also excluded galaxies with optical companions in the Palomar Sky Survey Prints. The final sample contains 22 galaxies defined as isolated (see Table 1 in Paper I). It is found that all of them have [FORMULA] 6000 km s-1.

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© European Southern Observatory (ESO) 1999

Online publication: March 18, 1999