(Proposal ID) S17B-070

(PI) Morokuma, Tomoki

(Proposal Title)
Tidal Disruption Event Rate Measurement at z~0.5

(Abstract)
We propose 1-night optical spectroscopic observations with FOCAS to 
(i) determine the redshifts of 4 tidal disruption event (TDE) candidates, 
(ii) measure the TDE rate at high redshifts ($z\sim0.5$), and (iii) study the 
host galaxies and black hole-host galaxy relations in the low-mass regime. 
TDEs, in general, are preferably hosted by lower-mass black holes (BHs; ~10^{6}
M_sun) and a useful tool to study BH-host galaxy relation without being 
affected by luminous AGN. The TDE candidates here  are selected using 
transient survey data from Nov. 2016 in five optical bands (grizy) in the 
COSMOS field in the Hyper Suprime-Cam Strategic Survey Program. The light 
curves of the TDE candidates are roughly characterized by power-law decay 
(f proportion t^{-5/3}) and the colors are bluer than supernovae showing 
similar decays. The photometric redshifts of these host galaxies indicate 
that they are at higher redshifts, z~0.5, than previously studies TDEs without 
relativistic jets. This makes our TDE sample the highest redshift and most 
uniformly selected one, which enables us to derive the TDE rate at z~0.5 for 
the first time. In addition, the host galaxy spectra will be examined and 
compared with previous results indicating that TDEs are preferably hosted 
by post-starburst or ultra-luminous infrared galaxies.