We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the interacting pair Arp 202 (NGC 2719 and NGC 2719A). Earlier deep UV(GALEX) observations of this system revealed a tidal tail like extension with a diffuse object
towards its end, proposed as a tidal dwarf galaxy (TDG) candidate. We detect HI emission from the Arp 202 system, including HI counterparts for the tidal tail and the TDG candidate. Our GMRT HI morphological and kinematic results clearly link the HI tidal tail and the HI TDG counterparts to the interaction between NGC 2719 and NGC 2719A, thus strengthening the case for the TDG. The Arp 202 TDG candidate belongs to a small group of TDG candidates with extremely blue colours. In order to gain a better understanding of this group we carried out a comparative study of their properties from the available data. We find that HI (and probably stellar) masses of this extremely blue group are similar to the lowest HI mass TDGs in the literature. However the number of such blue TDG candidates examined so far is too small to conclude whether or not their properties justify them to be considered as a subgroup of TDGs.
We present results from GMRT HI 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 HI (90%) displaced well beyond the optical disks of the pair with the highest densi
ty HI located ~70 kpc west of the pair. An HI bridge extending between the optical pair and the bulk of the HI together with their HI deficiencies provide strong evidence that the interaction between the pair has removed most of their HI to the current projected position. HI to the west of the pair has two approximately equal intensity peaks. The HI intensity maximum furthest to the west coincides with a small spiral companion SDSS J102726.32+794911.9 which shows enhanced mid-infrared (Spitzer), UV (GALEX) and H alpha emission indicating intense star forming activity. The HI 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 HI tidal tails originating at NGC 3212 and, previously proposed to be a tidal dwarf galaxy in formation. Future sensitive HI surveys by telescopes like ASKAP 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.
