Oral Presentation
ALMA Observations of Molecular Gas in the Host Galaxies of Long-duration Gamma-ray Bursts
Presenter: Bunyo Hatsukade (The University of Tokyo)
Long-duration gamma-ray bursts (GRBs) are associated with the explosion of massive stars. Because GRBs are bright enough to be observable in the cosmological distances, they are expected to be a new tool to probe the cosmic star-formation history (SFH). However, it is still a subject of debate whether they occur in normal star-forming environments and can be used as an unbiased tracer of SFH. It is important to understand the environment of GRBs by comparing with those of normal star-forming galaxies. Observations of molecular gas, the fuel of star formation, is essential to understand the properties of host galaxies. We conducted an ALMA CO survey toward 14 GRB hosts at 0.1 < z < 2.5 and obtained the largest sample of GRB hosts with molecular gas information, allowing for statistical studies in terms of molecular gas for the first time. We find that the GRB hosts follow the same scaling relation as other normal star-forming galaxy populations in the plot of gas depletion timescale or gas fraction as a function of the offset from main-sequence line. This suggests that galaxies traced by GRBs are no different from other star-forming galaxies in terms of molecular gas.