Dr. Yogesh Chandola

Hydrogen is the most abundant element in the Universe and exists in different forms and scales. In the interstellar medium (ISM) of galaxies, cold (~100 K) neutral atomic hydrogen (HI) acts as a fuel reservoir for the star-formation activity. Hence, it is important to study this phase of gas in different types of galaxies. In the radio bands, it can be traced using the 21-cm (1420.405 MHz) spectral line through absorption or emission. In this presentation, I will discuss 21-cm absorption in the host galaxies of radio active galactic nuclei (AGNs) and 21-cm emission in the nearby young starburst dwarf galaxies. While cold gas in the host galaxies provides fuel for the AGN as well as star formation activity, radio AGNs through mechanical feedback may also affect the gas properties and star formation in host galaxies. Associated HI 21-cm absorption can trace the cold gas in the interstellar medium and circumnuclear regions of the radio AGN hosts and help understand the fueling and feedback processes. In this talk, I will briefly give an overview of HI absorption towards radio AGNs in the literature and present our recent work on HI absorption towards radio AGNs with the Five-hundred-metre Aperture Spherical radio Telescope (FAST) where we discovered 5 new HI absorbers including 4 towards lowest radio luminosity radio sources in the redshift range 0.25-0.4. Blue compact dwarf galaxies (BCDs) and recently discovered Green Peas and Blueberry galaxies with very young starbursts (specific star formation rate ¿ 10^-8 yr^-1) act as a local laboratory to understand the star-formation process in the early primordial Universe in the reionization era. In this talk, I will present our work on HI in selected mid-infrared bright BCDs with the Arecibo telescope and Giant Metrewave Radio Telescope (GMRT) where we find that these systems have very short HI depletion time scales of ~0.3 Gyr, and present recent results on HI in Blueberry galaxies with FAST. I will conclude with a brief overview of the prospects of HI studies with Square Kilometre Array (SKA) pathfinders such as FAST, GMRT, ASKAP, MeerKAT, and SKA in future.