A large-scale neutral hydrogen (H i) ring serendipitously found in the Leo I galaxy group is 200 kpc in diameter with MHi ~ 1:67 X 109M⊙, unique in size in the Local Universe. It is still under debate where this Hi ring originated - whether it has formed out of the gas remaining after the formation of a galaxy group (primordial origin) or been stripped during galaxy-galaxy interactions (tidal origin). We are investigating the optical and Hi gas properties of the dwarf galaxies located within the gas ring in order to probe its formation mechanism. In this work, we present the photometric properties of the dwarfs inside the ring using the CFHT MegaCam u*, g', r' and i'-band data. We discuss the origin of the gas ring based on the stellar age and metal abundance of dwarf galaxies contained within it.

We investigate Hi data for a pair of blue compact dwarf galaxies (BCDs), ESO 435-IG20 and ESO 435-IG16, obtained with the Australia Telescope Compact Array. The outer Hi disk is highly disturbed and asymmetric in both galaxies showing a gas tail and/or a broad/extended gas disk on only one side. Based on their low-density surroundings and small projected distance (<80 kpc) at a similar redshift, we conclude that tidal interaction between these two BCDs is responsible for the morphological and kinematical peculiarities in Hi. We also investigate their star formation rates using Hα and UV imaging data to probe their interaction history.

Galaxies can be "pre-processed" in the low-density outskirts by ambient medium in the filaments or tidal interactions with other galaxies while falling into the cluster. In order to probe how early on and by which mechanisms galaxies can be affected before they enter high-density cluster environments, we are carry- ing out an atomic hydrogen (H i) imaging study of a sample of galaxies selected from three filamentary structures around the Virgo cluster. Our sample consists of 14 late-type galaxies, which are potentially interacting with their surroundings. The Hi observations have been done using the Westerbork Synthesis Radio Telescope, the Giant Metrewave Radio Telescope, and the Jansky Very Large Array with column density sensitivity of ≈ 3-5 X 1019 cm-2 in 3σ per channel, which is low enough to detect faint Hi features in the outer disks of galaxies. In this work, we present the Hi data of two galaxies that were observed with GMRT. We examine the Hi morphology and kinematics to find the evidence for gas-gas and/or tidal interactions, and discuss which mechanism(s) could be responsible for pre-processing in these cases.