44 research outputs found
GRB 100418A: a Long GRB without a Bright Supernova in a High-Metallicity Host Galaxy
We present results of a search for a supernova (SN) component associated with
GRB 100418A at the redshift of 0.624. The field of GRB 100418A was observed
with FOCAS on Subaru 8.2m telescope under a photometric condition (seeing
0.3"-0.4") on 2010 May 14 (UT). The date corresponds to 25.6 days after the
burst trigger (15.8 days in the restframe). We did imaging observations in V,
Rc, and Ic bands, and two hours of spectrophotometric observations. We got the
resolved host galaxy image which elongated 1.6" (= 11 kpc) from north to south.
No point source was detected on the host galaxy. The time variation of Rc-band
magnitude shows that the afterglow of GRB 100418A has faded to Rc \sim > 24
without SN like rebrightening, when we compare our measurement to the reports
in GCN circulars. We could not identify any SN feature such as broad
emission-lines or bumps in our spectrum. Assuming the SN is fainter than the
3{\sigma} noise spectrum of our observation, we estimate the upper limit on the
SN absolute magnitude MIc,obs > -17.2 in observer frame Ic-band. This magnitude
is comparable to the faintest type Ic SNe. We also estimate host galaxy
properties from the spectrum. The host galaxy of GRB 100418A is relatively
massive (log M_{star}/M_{sun} = 9.54) compared to typical long GRB host
galaxies, and has 12+log(O/H) = 8.75.Comment: 8 pages, 8 figures, accepted for publication in PASJ, changed figure
8 and related tex
The Redshift Evolution of the Relation between Stellar Mass, Star Formation Rate, and Gas Metallicity of Galaxies
We investigate the relation between stellar mass (), star formation
rate (SFR), and metallicity () of galaxies, so called the fundamental
metallicity relation, in the galaxy sample of the Sloan Digital Sky Survey Data
Release 7. We separate the galaxies into narrow redshift bins and compare the
relation at different redshifts, and find statistically significant (%)
evolution. We test various observational effects that might cause seeming
evolution, and find it difficult to explain the evolution of the relation only
by the observational effects. In the current sample of low redshift galaxies,
galaxies with different and SFR are sampled from different redshifts,
and there is degeneracy between /SFR and redshift. Hence it is not
straightforward to distinguish a relation between and SFR from a relation
between and redshift. The separation of the intrinsic relation from the
redshift evolution effect is a crucial issue to understand evolution of
galaxies.Comment: 8 pages, 12 figures, 1 table, accepted for publication in ApJ, added
discussions about the noise in the galaxy spectr