HI asymmetry in the isolated galaxy CIG 85 (UGC 1547)
Résumé
Context. We present the results from the Giant Metrewave Radio Telescope (GMRT) interferometric Hi and 20 cm radio continuum observations of CIG85, an isolated asymmetric galaxy from the AMIGA (Analysis of the Interstellar Medium of Isolated GAlaxies - http://amiga.iaa.es) sample. Aims. Despite being an isolated galaxy, CIG 85 showed an appreciable optical and Hi spectral asymmetry and therefore was an excellent candidate for resolved Hi studies to understand the reasons giving rise to asymmetries in isolated galaxies. Methods. The galaxy was imaged in Hi and 20 cm radio continuum using the GMRT. For a detailed discussion of the results we also made use of multi-wavelength data from archival SDSS, GALEX and H alpha imaging. Results. We find the Hi in CIG 85 to have a clumpy, asymmetric distribution which in the NW part is correlated with optical tail like features, but the Hi velocity field displays a relatively regular rotation pattern. Evaluating all the observational evidence, we come to a conclusion that CIG85 is most likely a case of a disturbed spiral galaxy which now appears to have the morphology of an irregular galaxy. Although it is currently isolated from major companions, the observational evidence is consistent with Hi asymmetries, a highly disturbed optical disk and recent increase in star formation having been caused by a minor merger, remnants of which are now projected in front of the optical disk. If this is correct, the companion will be fully accreted by CIG 85 in the near future.