Unusual displacement of HI due to tidal interaction in Arp 181

Abstract

We present results from Giant Metrewave Radio Telescope H i 21 cm line observations of the interacting galaxy pair Arp 181 (NGC 3212 and NGC 3215) at z = 0.032. We find almost all of the detected H i (90 per cent) is displaced well beyond the optical discs of the pair with the highest density H i located ∼70 kpc west of the pair. An H i bridge extending between the optical pair and the bulk of H i together with their H i deficiencies provide strong evidence that the interaction between the pair has removed most of their H i to the current projected position. H i to the west of the pair has two approximately equal intensity peaks. The H i intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), ultraviolet (UV; GALEX) and Hα emission indicating intense star-forming activity. The H i intensity maximum close to the Arp 181 pair, coincides with a diffuse optical cloud detected in UV (GALEX) at the end of the stellar and H i tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive H i surveys by telescopes like Australian Square Kilometre Array Pathfinder should prove to be powerful tools for identifying tidal dwarfs at moderate to large redshifts to explore in detail the evolution of dwarf galaxies in the Universe.