GMRT Stacking Detects 15.5 Billion Solar Mass Average HI Reservoir in 8122 COSMOS Galaxies at z=1.081

The upgraded GMRT observed seven pointings in the COSMOS field at 550-850 MHz, delivering 90 kpc resolution stacks. On-source integration reached 67 hours in the central field and 89 hours across the outer six, allowing the team to co-add the faint HI signals while simultaneously extracting the median 680 MHz continuum to derive a weighted-median SFR of 8.90 ± 0.92 solar masses per year. The resulting HI-to-stellar mass ratio of 1.15 ± 0.27 and depletion timescale of 1.74 ± 0.45 Gyr match earlier DEEP2 results at the same epoch. These numbers indicate that atomic gas supply is already insufficient to sustain the observed star-formation rate density below z=1. The measurement constitutes only the second direct average HI census for any z≈1 population and strengthens the case that declining cosmic star formation is driven by reduced intergalactic accretion rather than exhaustion of molecular reservoirs. Future wide-field 21 cm surveys with MeerKAT and the SKA will test whether this shortfall grows monotonically toward the present day or exhibits environment-dependent scatter.