Astron. Astrophys. 353, 92-96 (2000)

3. Characteristics of tidal tails

To be sure that our selected galaxies possess true tidal tails, we performed photometric measurements in the I passband using circular apertures centered on the brightest regions of the suspected tails. For the measurements, we retrieved the HDF-S images (version 1) from the ST ScI web site and processed them in the ESO-MIDAS environment. The results of these measurements are summarized in Table 1 (Column 5). The observed surface brightness of the tails has been converted to a rest-frame B by applying the cosmological dimming term and a k-correction color term:  - 2.5 log(1+z)³ + () + 0.17 (Lilly et al. 1998). General photometric characteristics of the local tidal tails are close to those for late-type spiral galaxies (Sb-Sc) (Schombert et al. 1990, Reshetnikov 1998) and we used color term for Sbc galaxy (Lilly et al. 1995) in our calculations. The results are presented in the last column of Table 1 and in Fig. 2.

Fig. 2. The distribution of surface brightnesses of tidal tails. Top : solid line - distribution for local galaxies in the B band according to Reshetnikov (1998), dashed line - distribution for objects in the HDF-N and HDF-S in the I filter. Bottom : distribution of the B band rest-frame surface brightnesses for HDF tails (calculated from observed I band distribution). Dashed line shows galaxies with .

The mean rest-frame surface brightness of the tidal structures in the joint (HDF-N plus HDF-S) sample is (tail) = 23.41.1, in full agreement with our results for the local sample of interacting galaxies (obtained by analogous manner) - (tail) = 23.80.8 (Reshetnikov 1998).

Fig. 2 (top) presents the observed distribution of the values of the suspected HDF tails (dashed line) in comparison with the distribution for local objects in the B passband. The bottom part of the figure shows converted to a rest-frame, B distribution for HDF tails. It is evident that tails of distant galaxies demonstrate a distribution of values close to that for local interacting galaxies. Fig. 2 illustrates clearly the influence of observational selection on the recognition of tidal structures - we are able to detect relatively faint tails among the galaxies with but among objects we can see only very bright tails. Therefore, our sample of galaxies with extended tidal tails is sufficiently incomplete for . Thus, objects with will give a more reasonable estimation of m in comparison with the total sample.

© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999
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