138 research outputs found
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
Subaru FOCAS survey of z=7-7.1 Ly{\alpha} emitters: a test for z >~ 7 Ly{\alpha} photometric luminosity functions
Recent observations of z >~ 7 Ly{\alpha} emitters (LAEs) have derived a
variety of Ly{\alpha} luminosity functions (LFs) with contradictory results,
evolution or non-evolution from z <~ 6, the epoch after reionization. This
could be because most of z >~ 7 LFs comprise photometric candidates and might
include some contaminations. We conducted the Subaru Telescope Faint Object
Camera And Spectrograph narrowband NB980 ({\lambda}c ~ 9800A, FWHM ~ 100A)
imaging and spectroscopy survey of z=7-7.1 LAEs to compare its
"contamination-free" result with z >~ 7 photometric Ly{\alpha} LFs previously
derived. We imaged the Subaru Deep Field and the sky around a cluster MS
1520.1+3002 and found one LAE candidate, but spectroscopy did not reveal
Ly{\alpha} though deep enough to detect it. We calculated the expected number
of LAEs in our survey, using five z=7 and three z=7.7 Ly{\alpha} LFs from
recent surveys. Seven of them are consistent with null detection
(0.1^{+1.8}_{-0.1}-1.1^{+2.2}_{-1.0} LAEs) within errors including Poisson
statistics and cosmic variance, but average values (0.7-1.1 LAEs) predicted
from one z=7 and two z=7.7 LFs among the seven indicate nearly a single
detection. The remaining one z=7 LF predicts 3.0^{+3.2}_{-2.0} LAEs. As to z=7,
the discrepancy likely comes from different LAE selection criteria. For z=7.7,
there are two possibilities; (1) If z=7.7 LAEs are somehow brighter in
Ly{\alpha} luminosity than lower redshift LAEs, z=7.7 LF is observed to be
similar to or higher than lower redshift LFs even if attenuated by neutral
hydrogen. (2) All/most of the z=7.7 candidates are not LAEs. This supports the
decline of LF from z ~ 6 to 7.7 and reionization at z ~ 6-7.7.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society, 2012 March 0
Dust Attenuation and H(alpha) Star Formation Rates of Z Approx. 0.5 Galaxies
Using deep narrow-band and broad-band imaging, we identify 401 z approximately 0.40 and 249 z approximately 0.49 H-alpha line-emitting galaxies in the Subaru Deep Field. Compared to other H-alpha surveys at similar redshifts, our samples are unique since they probe lower H-alpha luminosities, are augmented with multi-wavelength (rest-frame 1000AA--1.5 microns) coverage, and a large fraction (20%) of our samples has already been spectroscopically confirmed. Our spectra allow us to measure the Balmer decrement for nearly 60 galaxies with H-beta detected above 5-sigma. The Balmer decrements indicate an average extinction of A(H-alpha)=0.7(uparrow){+1.4}_{-0.7} mag. We find that the Balmer decrement systematically increases with higher H-alpha luminosities and with larger stellar masses, in agreement with previous studies with sparser samples. We find that the SFRs estimated from modeling the spectral energy distribution (SED) is reliable---we derived an "intrinsic" H-alpha luminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted H-alpha luminosity agrees with H-alpha narrow-band measurements over 3 dex (rms of 0.25 dex). We then use the SED SFRs to test different statistically-based dust corrections for H-alpha and find that adopting one magnitude of extinction is inappropriate: galaxies with lower luminosities are less reddened. We find that the luminosity-dependent dust correction of Hopkins et al. yields consistent results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by assuming that stellar reddening is roughly half of nebular reddening. The strong correspondence argue that with SED modeling, we can derive reliable intrinsic SFRs even in the absence of H-alpha measurements at z approximately 0.5
Discovery of Protoclusters at z∼3.7 and 4.9: Embedded in Primordial Superclusters
We have carried out follow-up spectroscopy on three overdense regions of -
and -dropout galaxies in the Canada-France-Hawaii Telescope Legacy Survey
Deep Fields, finding two new protoclusters at , 3.721 and a possible
protocluster at . The protocluster overlaps with a
previously identified protocluster at . The redshift separation
between these two protoclusters is , which is slightly larger
than the size of typical protoclusters. Therefore, if they are not the
progenitors of a halo, they would grow into
closely-located independent halos like a supercluster. The other protocluster
at is also surrounded by smaller galaxy groups. These systems
including protoclusters and neighboring groups are regarded as the early phase
of superclusters. We quantify the spatial distribution of member galaxies of
the protoclusters at and 3.721 by fitting triaxial ellipsoids,
finding a tentative difference: one has a pancake-like shape while the other is
filamentary. This could indicate that these two protoclusters are in different
stages of formation. We investigate the relation between redshift and the
velocity dispersion of protoclusters, including other protoclusters from the
literature, in order to compare their dynamical states. Although there is no
significant systematic trend in the velocity dispersions of protoclusters with
redshift, the distribution is skewed to higher velocity dispersion over the
redshift range of . This could be interpreted as two phases of
cluster formation, one dominated by the steady accretion of galaxies, and the
other by the merging between group-size halos, perhaps depending on the
surrounding large-scale environments.Comment: Accepted for publication in ApJ, 24 pages, 12 figures, 5 table
Keck Spectroscopy of Lyman-break Galaxies and its Implications for the UV-continuum and Ly_alpha Luminosity Functions at z>6
We present Keck spectroscopic observations of z>6 Lyman-break galaxy (LBG)
candidates in the Subaru Deep Field (SDF). The candidates were selected as
i'-dropout objects down to z'=27 AB magnitudes from an ultra-deep SDF z'-band
image. With the Keck spectroscopy we identified 19 LBGs with prominent Ly_alpha
emission lines at 6< z < 6.4. The median value of the Ly_alpha rest-frame
equivalent widths (EWs) is ~50 A, with four EWs >100 A. This well-defined
spectroscopic sample spans a UV-continuum luminosity range of -21.8<
M_{UV}<-19.5 (0.6~5 L*_{UV}) and a Ly_alpha luminosity range of (0.3~3) x
10^{43} erg s^{-1} (0.3~3 L*_ {Ly_alpha}). We derive the UV and Ly_alpha
luminosity functions (LFs) from our sample at ~6.2 after we correct for
sample incompleteness. We find that our measurement of the UV LF is consistent
with the results of previous studies based on photometric LBG samples at 5<z<7.
Our Ly_alpha LF is also generally in agreement with the results of
Ly_alpha-emitter surveys at z~5.7 and 6.6. This study shows that deep
spectroscopic observations of LBGs can provide unique constraints on both the
UV and Ly_alpha LFs at z>6.Comment: 14 pages, 7 figures, accepted for publication in Ap
- …