Aditya Chowdhury

Neutral Atomic Hydrogen (HI) is the dominant component in the interstellar medium of star-forming galaxies and is the primary fuel for star-formation. Understanding galaxy evolution thus critically requires measurements of the HI mass of galaxies at different cosmological epochs. We have used the upgraded Giant Metrewave Radio Telescope (GMRT) to carry out the first measurement of the HI mass of galaxies at a redshift of one. In this talk, I will describe our survey, the stacking analysis used to carry out the first detection of 21 cm emission at z~1, and how our measurement of the HI mass of galaxies at z~1 provides a plausible explanation to the long-standing puzzle of why the star-formation activity of the Universe declined rapidly after its peak at z~1-3. I will also describe our immediate plans which involve using the upgraded GMRT to push HI 21 cm emission studies out to z~2-3. These GMRT observations are providing us with an understanding of the build-up of HI in galaxies and its connection to the star formation history over the past 11 billion years.