| Abstract: |
The star-formation activity in the Universe is known to have peaked roughly 8-11 billion years ago, with about half of today's stars born in this period, the "epoch of galaxy assembly". Today, the star-formation activity is lower by more than an order of magnitude; the causes of this decline have been unknown for more than two decades. Addressing this question requires one to understand the evolution of the neutral atomic hydrogen (HI) in galaxies, the primary fuel for star formation. Unfortunately, the weakness of the hyperfine HI 21cm line, the main tracer of the HI content of galaxies, has meant that we know little about the atomic gas mass of high-redshift galaxies and its evolution. ``Stacking'' of the HI 21cm emission signals from a large sample of galaxies, observed simultaneously with a radio interferometer, can allow one to determine the HI properties of the galaxy population. In this talk, I will describe results from our HI 21cm stacking experiments, using the upgraded Giant Metrewave Radio Telescope to measure the average HI properties of star-forming galaxies out to z~1.5. I will discuss the implications of our studies for gas accretion onto galaxies and the decline in the cosmological SFR density towards the end of the epoch of galaxy assembly. Finally, I will discuss connections with the Subaru Prime Focus Spectrograph (PFS) and the importance of PFS spectroscopy for progress in this field over the next decade. |
