Takatoshi Shibuya, Nobunari Kashikawa, Kazuaki Ota, Masanori Iye, Masami Ouchi, Hisanori Furusawa, Kazuhiro Shimasaku, Takashi Hattori
We have performed deep imaging surveys for Lyman Alpha emitters (LAEs) at
redshift ~ 7.3 in two blank fields, the Subaru Deep Field (SDF) and the
Subaru/XMM-Newton Deep Field (SXDF), using the Subaru/Suprime-Cam equipped with
new red-sensitive CCDs and a new narrow-band filter, NB1006 (lambda_c=10,052A,
FWHM=214A). By comparing the NB1006 magnitudes of detected objects with those
at other shorter wavelength bands, we identified four objects as LAE candidates
that exhibit luminosity excess in NB1006. By carrying out deep follow-up
spectroscopy for three of them using Subaru/FOCAS and Keck/DEIMOS, a
definitively asymmetric emission line is detected for one of them,
SXDF-NB1006-2. Assuming this line is LyA, this object is a LAE at z=7.215 which
has luminosity of 1.2^{+1.5}_{-0.6} x 10^{43} erg s-1, star formation rate
(SFR) of 11 Mo yr-1 estimated from the LyA emission line, and a weighted
skewness S_w = 4.90+-0.86. Another object, SDF-NB1006-2, shows variable
photometry and is thus probably a quasar (QSO) or an active galactic nucleus
(AGN). It shows an asymmetric emission line at 10,076A which may be due to
either LyA at z=7.288 or [OII] at z=1.703. The third object, SDF-NB1006-1, is
likely a galaxy with temporal luminosity enhancement associated with a
supernova explosion, as the brightness of this object varies between the
observed epochs. Its spectrum does not show any emission lines. The inferred
decreases in the number density of LAEs toward higher redshift are
n_{LyA}^{z=7.3}/n_{LyA}^{z=5.7} = 0.05^{+0.11}_{-0.05} from z=5.7 to 7.3 and
n_{LyA}^{z=7.3}/n_{LyA}^{z=6.6} = 0.16^{+0.38}_{-0.16} from z=6.6 to 7.3 down
to L^{LyA} = 1.0 x 10^{43} erg s-1. The present result is consistent with the
interpretation in previous studies that the neutral hydrogen fraction is
rapidly increasing from z=5.7 to 7.3.
View original:
http://arxiv.org/abs/1112.3997
No comments:
Post a Comment