125 research outputs found
Re-calibration of SDF/SXDS Photometric Catalogs of Suprime-Cam with SDSS Data Release 8
We present photometric recalibration of the Subaru Deep Field (SDF) and
Subaru/XMM-Newton Deep Survey (SXDS). Recently, Yamanoi et al. (2012) suggested
the existence of a discrepancy between the SDF and SXDS catalogs. We have used
the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8) catalog and compared
stars in common between SDF/SXDS and SDSS. We confirmed that there exists a
0.12 mag offset in B-band between the SDF and SXDS catalogs. Moreover, we found
that significant zero point offsets in i-band (~ 0.10 mag) and z-band (~ 0.14
mag) need to be introduced to the SDF/SXDS catalogs to make it consistent with
the SDSS catalog. We report the measured zero point offsets of five filter
bands of SDF/SXDS catalogs. We studied the potential cause of these offsets,
but the origins are yet to be understood.Comment: 36 pages, 19 figures(128 EPS files), PASJ accepte
The First Systematic Survey for Lyman Alpha Emitters at z=7.3 with Red-sensitive Subaru/Suprime-Cam
We have performed deep imaging surveys for LyA emitters (LAEs) at redshift
~7.3 in two blank fields, the Subaru Deep Field (SDF) and the Subaru/XMM-Newton
Deep survey Field (SXDF), using the Subaru/Suprime-Cam equipped with new
red-sensitive CCDs and a new narrow-band filter, NB1006 (lambda_c=10052 Ang,
FWHM=214 Ang). 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] 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 10076
Ang, 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 decrease in the number density of LAEs toward higher redshift is
n_LyA(z=7.3)/n_LyA(z=5.7) = 0.05^+0.11_-0.05 from z=5.7 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.Comment: 12 pages, 11 figures, Accepted to Ap
The Subaru/XMM-Newton Deep Survey (SXDS) -VII. Clustering Segregation with Ultraviolet and Optical Luminosities of Lyman-Break Galaxies at z~3
We investigate clustering properties of Lyman-break galaxies (LBGs) at z~3
based on deep multi-waveband imaging data from optical to near-infrared
wavelengths in the Subaru/XMM-Newton Deep Field. The LBGs are selected by U-V
and V-z' colors in one contiguous area of 561 arcmin^2 down to z'=25.5. We
study the dependence of the clustering strength on rest-frame UV and optical
magnitudes, which can be indicators of star formation rate and stellar mass,
respectively. The correlation length is found to be a strong function of both
UV and optical magnitudes with brighter galaxies being more clustered than
faint ones in both cases. Furthermore, the correlation length is dependent on a
combination of UV and optical magnitudes in the sense that galaxies bright in
optical magnitude have large correlation lengths irrespective of UV magnitude,
while galaxies faint in optical magnitude have correlation lengths decreasing
with decreasing UV brightness. These results suggest that galaxies with large
stellar masses always belong to massive halos in which they can have various
star formation rates, while galaxies with small stellar masses reside in less
massive halos only if they have low star formation rates. There appears to be
an upper limit to the stellar mass and the star formation rate which is
determined by the mass of hosting dark halos.Comment: 16 pages, 15 figures, accepted for publication in Ap
The Subaru high-z quasar survey: discovery of faint z~6 quasars
We present the discovery of one or two extremely faint z~6 quasars in 6.5
deg^2 utilizing a unique capability of the wide-field imaging of the
Subaru/Suprime-Cam. The quasar selection was made in (i'-z_B) and (z_B-z_R)
colors, where z_B and z_R are bandpasses with central wavelengths of 8842A and
9841A, respectively. The color selection can effectively isolate quasars at z~6
from M/L/T dwarfs without the J-band photometry down to z_R<24.0, which is 3.5
mag. deeper than SDSS. We have selected 17 promising quasar candidates. The
follow-up spectroscopy for seven targets identified one apparent quasar at
z=6.156 with M_1450=-23.10. We also identified one possible quasar at z=6.041
with a faint continuum of M_1450=-22.58 and a narrow Lyman-alpha emission with
HWHM=427 km/s, which cannot be distinguished from Lyman-alpha emitters. We
derive the quasar luminosity function at z~6 by combining our faint quasar
sample with the bright quasar samples by SDSS and CFHQS. Including our data
points invokes a higher number density in the faintest bin of the quasar
luminosity function than the previous estimate employed. This suggests a
steeper faint-end slope than lower-z, though it is yet uncertain based on a
small number of spectroscopically identified faint quasars and several quasar
candidates are still remain to be diagnosed. The steepening of the quasar
luminosity function at the faint-end does increase the expected emission rate
of the ionizing photon, however, it only changes by a factor of ~2-6. This was
found to be still insufficient for the required photon budget of reionization
at z~6.Comment: 10 pages, 8 figures. Accepted for publication in Ap
New Improved Photometric Redshifts of Galaxies in the HDF
We report new improved photometric redshifts of 1048 galaxies in the Hubble
Deep Field (HDF). A standard chi^2 minimizing method is applied to seven-color
UBVIJHK photometry by Fernandez-Soto, Lanzetta, & Yahil (1999). We use 187
template SEDs representing a wide variety of morphology and age of observed
galaxies based on a population synthesis model by Kodama & Arimoto (1997). We
introduce two new recipes. First, the amount of the internal absorption is
changed as a free parameter in the range of E(B-V)=0.0 to 0.5 with an interval
of 0.1. Second, the absorption due to intergalactic HI clouds is also changed
by a factor of 0.5, 1.0, and 1.5 around the opacity given by Madau (1995). The
total number of template SEDs is thus 187x6x3=3,366, except for the redshift
grid. The dispersion sigma_z of our photometric redshifts with respect to
spectroscopic redshifts is sigma_z=0.08 and 0.24 for z2, respectively,
which are smaller than the corresponding values (sigma_z=0.09 and 0.45) by
Fernandez-Soto et al. Improvement is significant, especially in z>2. This is
due to smaller systematic errors which are largely reduced mainly by including
three opacities due to intergalactic HI clouds. We discuss redshift
distribution N(z) and cosmic star formation rate based on our new photometric
redshifts.Comment: 24 pages including 16 eps figures; accepted for publication in Ap
A New Constraint on the Ly Fraction of UV Very Bright Galaxies at Redshift 7
We study the extent to which very bright (-23.0 < MUV < -21.75) Lyman-break
selected galaxies at redshifts z~7 display detectable Lya emission. To explore
this issue, we have obtained follow-up optical spectroscopy of 9 z~7 galaxies
from a parent sample of 24 z~7 galaxy candidates selected from the 1.65 sq.deg
COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared
public survey data, and new ultra-deep Subaru z'-band imaging (which we also
present and describe in this paper). Our spectroscopy has yielded only one
possible detection of Lya at z=7.168 with a rest-frame equivalent width EW_0 =
3.7 (+1.7/-1.1) Angstrom. The relative weakness of this line, combined with our
failure to detect Lya emission from the other spectroscopic targets allows us
to place a new upper limit on the prevalence of strong Lya emission at these
redshifts. For conservative calculation and to facilitate comparison with
previous studies at lower redshifts, we derive a 1-sigma upper limit on the
fraction of UV bright galaxies at z~7 that display EW_0 > 50 Angstrom, which we
estimate to be < 0.23. This result may indicate a weak trend where the fraction
of strong Lya emitters ceases to rise, and possibly falls between z~6 and z~7.
Our results also leave open the possibility that strong Lya may still be more
prevalent in the brightest galaxies in the reionization era than their fainter
counterparts. A larger spectroscopic sample of galaxies is required to derive a
more reliable constraint on the neutral hydrogen fraction at z~7 based on the
Lya fraction in the bright galaxies.Comment: 20 pages, 7 figures, accepted for publication in Ap
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