the scatter on the T-F relation is significantly diminished.

Note that the lowest-mass HCG members deviate from the T-F relation in the opposite sense of those gas-rich galaxies studied by McGaugh et al. (2000) for which a “baryonic correction” (to take into account the gas mass into the “luminosity” of the galaxy) was necessary.

Fraction of HCG galaxies with peculiar velocity fields
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In the last column of Table 1 we marked with a $P$ the galaxies whose velocity fields were considered highly disturbed either by Amram et al. (2003), Plana et al. (2003) or Mendes de Oliveira et al. (1998). A total of 17 from 24 galaxies (all in Table 1 but HCG 87a, which could not be classified) are marked peculiar. If we add to this sample those that were not included in the Tully-Fisher analysis because of their strong peculiarities or short gas extension, we find that 22 out of 29 galaxies, or 75% of the sample of studied galaxies have highly disturbed velocity fields. With this high rate of peculiar kinematics, it is striking that the corresponding rotation curves were possible to be obtained and that, on average, galaxies in compact groups follow the T-F relation.

