Galaxy evolution: The atomic hydrogen perspective

As galaxies evolve they convert their gas into stars. On a cosmic scale, it is well established that the high noon of star formation was about 10 billion years  ago and that the average star formation rate has declined sharply since then. Atomic hydrogen is the primary fuel for star formation. Stars form as the gas cools to become molecular hydrogen, which further collapses under self gravity. Understanding the evolution of the atomic hydrogen content of galaxies is key to understanding the evolution of the star formation rate. Unfortunately, because of the difficulties in detecting atomic hydrogen emission, until recently very little was known about the evolution of the gas content of galaxies. I will discuss results from ongoing atomic hydrogen surveys using the upgraded GMRT that have significantly added to our understanding of the evolution of the baryonic content of galaxies.