Title: Radio Exploration of the Host Galaxies of Massive Star Explosions

Bunyo Hatsukade (Institute of Astronomy, Univ. of Tokyo)


I present the results of radio observations of the host galaxies of long
-duration gamma-ray bursts (GRBs) and superluminous supernovae (SLSNe). 
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. 
However, it is still a subject of debate whether they occur in normal 
star-forming environments or not. Observations of molecular gas, the 
fuel of star formation, are essential to understand the properties of 
host galaxies. We conducted ALMA CO observations toward GRB hosts at 0.1 
< z < 2.5 and obtained the largest sample of GRB hosts with molecular 
gas information. We find no systematic offset for the GRB hosts from the 
scaling relation of normal star-forming galaxies in terms of gas 
consumption timescale or gas fraction, suggesting that GRBs occur in 
normal star-forming environments. 
We are also working on radio continuum observations of SLSN hosts to 
constrain the obscured star formation. SLSNe are extremely luminous 
explosions, with peak magnitudes 10–100 times brighter than typical 
Type Ia and core-collapse SNe. The physical nature of SLSNe is still a 
matter of debate, and it is important to study the properties of their 
host galaxies. Our initial study found that four (out of eight) hosts at 
0.01 < z < 0.3 have an excess in radio-derived SFRs compared to 
optically-derived SFRs, suggesting the existence of obscured star 
formation, which cannot be traced by optical studies. This suggests a 
higher fraction of starburst galaxies in SLSN hosts than estimated in 
previous studies. I also present ongoing projects and radio constraints 
on a pulsar-driven SLSN model. 

Host contact: Akihiro Suzuki