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Linhua Jiang,
Eiichi Egami,
Matthew Mechtley,
Xiaohui Fan,
Seth H. Cohen,
Rogier A. Windhorst,
Romeel Dave,
Kristian Finlator, Nobunari Kashikawa,
Masami Ouchi,
Kazuhiro Shimasaku
[show abstract]
[hide abstract]
ABSTRACT: We present deep HST near-IR and Spitzer mid-IR observations of a large sample
of spectroscopically-confirmed galaxies at z >= 6. The sample consists of 51
Lyman-alpha emitters (LAEs) at z ~ 5.7, 6.5, and 7.0, and 16 Lyman-break
galaxies (LBGs) at 5.9 < z < 6.5. The majority of them were discovered in the
Subaru Deep Field. They have extremely deep optical imaging data in a series of
broad and narrow bands taken with Subaru Suprime-Cam. The near-IR images were
mostly obtained from WFC3 with a typical depth of two HST orbits in the F125W
and F160W bands. The Spitzer mid-IR images have a depth of 3 ~ 6 hrs in IRAC
channels 1 and 2. We utilize the wealth of the multi-band data and the secure
redshifts to derive the properties of their rest-frame UV continuum and
Lyman-alpha emission. These galaxies have steep UV continuum slopes roughly
between beta ~ -1.5 and -3.5, with a median value of beta ~ -2.3, which is
slightly steeper than the slopes of photometrically-selected LBGs reported in
previous studies. The slope shows little dependence on UV continuum luminosity
except for a few of the brightest galaxies. We find a statistically significant
excess of galaxies with slopes around beta ~ -3, suggesting the existence of
very young stellar populations with extremely low metallicity and dust content.
Our galaxies have moderately strong rest-frame Lyman-alpha equivalent width
(EW) in a range of ~10 to ~300 \AA. The star-formation rates derived from the
Lyman-alpha and UV continuum luminosities are also moderate, from a few to a
few tens solar masses per year. The LAEs and LBGs in this sample share many
common properties, implying that LAEs represent a subset of LBGs with strong
Lyman-alpha emission. Finally, we derive the UV luminosity functions (LFs) of
LAEs with EW > 20 \AA\ at z ~ 5.7 and 6.5, and compare them with the UV LFs of
LBGs at similar redshifts. [abridged].
02/2013;
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Linhua Jiang,
Eiichi Egami,
Xiaohui Fan,
Rogier A. Windhorst,
Seth H. Cohen,
Romeel Dave,
Kristian Finlator, Nobunari Kashikawa,
Matthew Mechtley,
Masami Ouchi,
Kazuhiro Shimasaku
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed structural and morphological study of a large sample of
spectroscopically-confirmed galaxies at z>=6, using deep HST near-IR broad-band
images and Subaru optical narrow-band images. The galaxy sample consists of 51
Lyman-alpha emitters (LAEs) at z~5.7, 6.5, and 7.0, and 16 Lyman-break galaxies
(LBGs) at 5.9<z<6.5. These galaxies exhibit a wide range of rest-frame UV
continuum morphology in the HST images, from compact features to multiple
component systems. The fraction of merging/interacting galaxies reaches 40~50%
at M_UV<-20.5 mag, suggesting hierarchical build-up of the brightest galaxies
at high redshift. We use half-light radius to describe the galaxy sizes, and
find that the intrinsic radii r_{hl,in}, after correction for PSF broadening,
are roughly between 0.05" and 0.3", with a median value of 0.13" (~0.75 kpc).
This is consistent with the sizes of bright LAEs and LBGs at z>6 in previous
studies. In addition, more luminous galaxies tend to have larger physical
sizes, exhibiting a size-luminosity relation r_{hl,in} \propto L^0.2. The slope
0.2 is significantly flatter than those in previous fainter LBG samples. We for
the first time characterize the morphology of z>6 galaxies using nonparametric
methods, including the CAS system, the Gini and M_{20} parameters. Compared to
low-redshift galaxies, our galaxies appear in slightly different locations in
the parameter space, mainly due to their small sizes in the HST images.
However, we find strong correlations between the measured parameters, as
expected from their definitions. This implies that these nonparametric methods
could be still applicable for z>=6 galaxies, if used with caution. We search
for extended Lyman-alpha emission halos around LAEs at z~5.7 and 6.5, by
stacking a number of narrow-band images. We do not find evidence of extended
halos predicted. [abridged].
02/2013;
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Yuji Urata,
Patrick P. Tsai,
Kuiyun Huang,
Tomoki Morokuma,
Naoki Yasuda,
Masaomi Tanaka,
Kentaro Motohara,
Masao Hayashi, Nobunari Kashikawa,
Chun Ly,
Matthew A. Malkan
[show abstract]
[hide abstract]
ABSTRACT: We present observations of SDF-05M05, an unusual optical transient discovered
in the Subaru Deep Field (SDF). The duration of the transient is > ~800 d in
the observer frame, and the maximum brightness during observation reached
approximately 23 mag in the i' and z' bands. The faint host galaxy is clearly
identified in all 5 optical bands of the deep SDF images. The photometric
redshift of the host yields z~0.6 and the corresponding absolute magnitude at
maximum is ~-20. This implies that this event shone with an absolute magnitude
brighter than -19 mag for approximately 300 d in the rest frame, which is
significantly longer than a typical supernova and ultra-luminous supernova. The
total radiated energy during our observation was 1x10^51 erg. The light curves
and color evolution are marginally consistent with some of luminous IIn
supernova. We suggest that the transient may be a unique and peculiar supernova
at intermediate redshift.
10/2012;
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Nobunari Kashikawa,
Tohru Nagao,
Jun Toshikawa,
Yoshifumi Ishizaki,
Eiichi Egami,
Masao Hayashi,
Chun Ly,
Matthew A. Malkan,
Yuichi Matsuda,
Kazuhiro Shimasaku,
Masanori Iye,
Kazuaki Ota,
Takatoshi Shibuya,
Linhua Jiang,
Yoshiaki Taniguchi,
Yasuhiro Shioya
[show abstract]
[hide abstract]
ABSTRACT: We have identified a very interesting Ly-alpha emitter, whose Ly-alpha
emission line has an extremely large observed equivalent width of
EW_0=436^{+422}_{-149}A, which corresponds to an extraordinarily large
intrinsic rest-frame equivalent width of EW_0^{int}=872^{+844}_{-298}A after
the average intergalactic absorption correction. The object was
spectroscopically confirmed to be a real Ly-alpha emitter by its apparent
asymmetric Ly-alpha line profile detected at z=6.538. The continuum emission of
the object was definitely detected in our deep z'-band image; thus, its EW_0
was reliably determined. Follow-up deep near-infrared spectroscopy revealed
emission lines of neither He II lambda1640 as an apparent signature of
Population III, nor C IV lambda1549 as a proof of active nucleus. No detection
of short-lived He II lambda1640 line is not necessarily inconsistent with the
interpretation that the underlying stellar population of the object is
dominated by Population III. We found that the observed extremely large EW_0 of
the Ly-alpha emission and the upper limit on the EW_0 of the He II lambda1640
emission can be explained by population synthesis models favoring a very young
age less than 2-4Myr and massive metal-poor (Z<10^{-5}) or even metal-free
stars. The observed large EW_0 of Ly-alpha is hardly explained by Population
I/II synthesis models with Z>10^{-3}. However, we cannot conclusively rule out
the possibility that this object is composed of a normal stellar population
with a clumpy dust distribution, which could enhance the Ly-alpha EW_0, though
its significance is still unclear.
10/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present the first detailed study of the stellar populations of
star-forming galaxies at z~1.5, which are selected by their [O II] emission
line, detected in narrow-band surveys. We identified ~1,300 [O II] emitters at
z=1.47 and z=1.62 in the Subaru Deep Field with rest-frame EWs above 13\AA.
Optical and near-infrared spectroscopic observations for ~10% of our samples
show that our separation of [O II] from [O III] emission-line galaxies in
two-color space is 99% successful. We analyze the multi-wavelength properties
of a subset of ~1,200 galaxies with the best photometry. They have average
rest-frame EW of 45\AA, stellar mass of 3 x 10^9 M_sun, and stellar age of 100
Myr. In addition, our SED fitting and broad-band colors indicate that [O II]
emitters span the full range of galaxy populations at z~1.5. We also find that
80% of [O II] emitters are also photometrically classified as "BX/BM" (UV)
galaxies and/or the star-forming "BzK" (near-IR) galaxies. Our [O II] emission
line survey produces a far more complete, and somewhat deeper sample of z~1.5
galaxies than either the BX/BM or sBzK selection alone. We constructed average
SEDs and find that higher [O II] EW galaxies have somewhat bluer continua. SED
model-fitting shows that they have on average half the stellar mass of galaxies
with lower [O II] EW. The observed [O II] luminosity is well-correlated with
the far-UV continuum with a logarithmic slope slightly 0f 0.89\pm0.22. The
scatter of the [O II] luminosity against the far-UV continuum suggests that [O
II] can be used as a SFR indicator with a reliability of 0.23 dex.
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We derived the luminosity function (LF) of dwarf galaxies in the Coma Cluster
down to M_R=-10 at three fields located at the center, intermediate, and
outskirt. The LF (-19<M_R<-10) shows no significant differences among the three
fields. It shows a clear dip at M_R\sim-13, and is composed of two distinct
components of different slopes; the bright component with -19<M_R<-13 has a
flatter slope than the faint component with -13<M_R<-10 which has a steep
slope. The bright component (-19<M_R<-13) consists of mostly red extended
galaxies including few blue galaxies whose colors are typical of late-type
galaxies. On the other hand, the faint component (-13<M_R<-10) consists of
largely PSF-like compact galaxies. We found that both these compact galaxies
and some extended galaxies are present in the center while only compact
galaxies are seen in the outskirt. In the faint component, the fraction of blue
galaxies is larger in the outskirt than in the center. We suggest that the
dwarf galaxies in the Coma Cluster, which make up the two components in the LF,
are heterogeneous with some different origins.
05/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We searched for z=7.3 Lya emitters (LAEs) behind two lensing clusters, Abell
2390 and CL 0024, with the Subaru Telescope Suprime-Cam and a narrowband NB1006
(FWHM ~ 21 nm centered at 1005 nm). We investigated if there exist objects
consistent with the color of z=7.3 LAEs behind the clusters but could not
detect any LAEs to the unlensed line limit F(Lya) ~ 6.9 x 10^{-18} erg/s/cm^2.
Using several z=7 Lya luminosity functions (LFs) from the literature, we
estimated and compared the expected detection numbers of z ~ 7 LAEs in lensing
and blank field surveys in the case of using an 8m class ground based
telescope. Given the steep bright-end slope of the LFs, when the detector
field-of view (FOV) is comparable to the angular extent of a massive lensing
cluster, imaging cluster(s) is more efficient in detecting z ~ 7 LAEs than
imaging a blank field. However, the gain is expected to be modest, a factor of
two at most and likely much less depending on the adopted LFs. The main
advantage of lensing-cluster survey, therefore, remains to be the gain in depth
and not necessarily in detection efficiency. For much larger detectors, the
lensing effect becomes negligible and the efficiency of LAE detection is
proportional to the instrumental FOV. We also inspected NB1006 images of three
z ~ 7 z-dropouts previously detected in Abell 2390 and found that none of them
are detected in NB1006. Two of them are consistent with predictions from the
previous studies that they would be at lower redshifts. The other one has a
photometric redshift of z ~ 7.3, and if it is at z=7.3, its unlensed Lya line
flux would be very faint: F(Lya) < 4.4 x 10^{-18} erg/s/cm^2 (1 sigma upper
limit) or rest frame equivalent width of W(Lya) < 26A. Its Lya emission might
be attenuated by neutral hydrogen, as recent studies show that the fraction of
Lyman break galaxies displaying strong Lya emission is lower at z ~ 7 than at z
<~ 6.
04/2012;
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Jun Toshikawa, Nobunari Kashikawa,
Kazuaki Ota,
Tomoki Morokuma,
Takatoshi Shibuya,
Masao Hayashi,
Tohru Nagao,
Linhua Jiang,
Matthew A. Malkan,
Eiichi Egami,
Kazuhiro Shimasaku,
Kentaro Motohara,
Yoshifumi Ishizaki
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a protocluster at z~6 containing at least eight
cluster member galaxies with spectroscopic confirmations in the wide-field
image of the Subaru Deep Field (SDF). The overdensity of the protocluster is
significant at the 6 sigma level, based on the surface number density of
i'-dropout galaxies. The overdense region covers ~36 sq. arcmin, and includes
30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are
real z~6 galaxies (5.7 < z < 6.3). Eight of the 15 are clustering in a narrow
redshift range centered at z=6.01, corresponding to a seven-fold increase in
number density over the average in redshift space. We found no significant
difference in the observed properties, such as Ly-alpha luminosities and UV
continuum magnitudes, between the eight protocluster members and the seven
non-members. The velocity dispersion of the eight protocluster members is 647
km/s, which is about three times higher than that predicted by the standard
cold dark matter model. This discrepancy could be attributed to the
distinguishing three-dimensional distribution of the eight protocluster
members. We discuss two possible explanations for this discrepancy: either the
protocluster is already mature, with old galaxies at the center, or it is still
immature and composed of three subgroups merging to become a larger cluster. In
either case, this concentration of z=6.01 galaxies in the SDF may be one of the
first sites of formation of a galaxy cluster in the universe.
03/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of deep imaging and spectroscopic observations of very
extended ionized gas (EIG) around four member galaxies of the Coma cluster of
galaxies: RB199, IC4040, GMP2923 and GMP3071. The EIGs were serendipitously
found in an H-alpha narrow band imaging survey of the central region of the
Coma cluster. The relative radial velocities of the EIGs with respect to the
systemic velocities of the parent galaxies from which they emanate increase
almost monotonically with the distance from the nucleus of the respective
galaxies, reaching -400 - -800 km/s at around 40 - 80 kpc from the galaxies.
The one-sided morphologies and the velocity fields of the EIGs are consistent
with the predictions of numerical simulations of ram pressure stripping. We
found a very low-velocity filament (v_rel = -1300 km/s) at the southeastern
edge of the disk of IC4040. Some bright compact knots in the EIGs of RB199 and
IC4040 exhibit blue continuum and strong H-alpha emission. The equivalent
widths of the H-alpha emission exceed 200 A, and are greater than 1000 A for
some knots. The emission line intensity ratios of the knots are basically
consistent with those of sub-solar abundance HII regions. These facts indicate
that intensive star formation occurs in the knots. Some filaments, including
the low velocity filament of the IC4040 EIG, exhibit shock-like emission line
spectra, suggesting that shock heating plays an important role in ionization
and excitation of the EIGs.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: Using deep narrow-band and broad-band imaging, we identify 401 z~0.40 and 249
z~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^{+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~0.5.
02/2012;
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[show abstract]
[hide abstract]
ABSTRACT: 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.
12/2011;
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Yoshiaki Ono,
Masami Ouchi,
Bahram Mobasher,
Mark Dickinson,
Kyle Penner,
Kazuhiro Shimasaku,
Benjamin J. Weiner,
Jeyhan S. Kartaltepe,
Kimihiko Nakajima,
Hooshang Nayyeri,
Daniel Stern, Nobunari Kashikawa,
and Hyron Spinrad
[show abstract]
[hide abstract]
ABSTRACT: We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at ~1 μm with a signal-to-noise ratio of ~10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Lyα, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Lyα emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Lyα fluxes of 3 × 10–17 erg s–1 cm–2 and rest-frame equivalent widths EWLyα 0 = 33-43 Å. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Lyα-emitting galaxies (EWLyα 0 > 25 Å) is low at z ~ 7; 17% ± 10% and 24% ± 12% for bright (M UV –21) and faint (M UV –19.5) galaxies, respectively. The fractions of Lyα-emitting galaxies drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ~ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.
The Astrophysical Journal 12/2011; 744(2):83. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report a search for z=7 Ly-alpha emitters (LAEs) using a custom-made
Narrow-Band filter, centered at 9755 Angstroms, with the instrument Suprime-Cam
installed at the Subaru telescope. We observed two different fields and
obtained two sample of 7 Ly-alpha emitters of which 4 are robust in each field.
We are covering the luminosity range of 9.10^{42} - 2.10^{43} erg/s in comoving
volumes of ~ 4.10^{5} and 4.3.10^{5} Mpc^{3}. From this result, we derived
possible z~7 Ly-alpha luminosity functions for the full samples and for a
subsample of 4 objects in each field. We do not observe, in each case, any
strong evolution between the z=6.5 and z~7 Ly-alpha luminosity functions.
Spectroscopic confirmation for these candidate samples is required to establish
a definitive measure of the luminosity function at z~7.
09/2011;
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[show abstract]
[hide abstract]
ABSTRACT: 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.
08/2011;
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Yoshiaki Ono,
Masami Ouchi,
Bahram Mobasher,
Mark Dickinson,
Kyle Penner,
Kazuhiro Shimasaku,
Benjamin J. Weiner,
Jeyhan S. Kartaltepe,
Kimihiko Nakajima,
Hooshang Nayyeri,
Daniel Stern, Nobunari Kashikawa,
Hyron Spinrad
[show abstract]
[hide abstract]
ABSTRACT: We present the results of our ultra-deep Keck/DEIMOS spectroscopy of
z-dropout galaxies in the SDF and GOODS-N. For 3 out of 11 objects, we detect
an emission line at ~ 1um with a signal-to-noise ratio of ~ 10. The lines show
asymmetric profiles with high weighted skewness values, consistent with being
Lya, yielding redshifts of z=7.213, 6.965, and 6.844. Specifically, we confirm
the z=7.213 object in two independent DEIMOS runs with different spectroscopic
configurations. The z=6.965 object is a known Lya emitter, IOK-1, for which our
improved spectrum at a higher resolution yields a robust skewness measurement.
The three z-dropouts have Lya fluxes of 3 x 10^-17 erg s^-1 cm^-2 and
rest-frame equivalent widths EW_0^Lya = 33-43A. Based on the largest
spectroscopic sample of 43 z-dropouts that is the combination of our and
previous data, we find that the fraction of Lya-emitting galaxies (EW_0^Lya >
25A) is low at z ~ 7; 17 +- 10% and 24 +- 12% for bright (Muv ~= -21) and faint
(Muv ~= -19.5) galaxies, respectively. The fractions of Lya-emitting galaxies
drop from z ~ 6 to 7 and the amplitude of the drop is larger for faint galaxies
than for bright galaxies. These two pieces of evidence would indicate that the
neutral hydrogen fraction of the IGM increases from z ~ 6 to 7, and that the
reionization proceeds from high- to low-density environments, as suggested by
an inside-out reionization model.
07/2011;
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[show abstract]
[hide abstract]
ABSTRACT: Several UV and near-infrared color selection methods have identified galaxies at z = 1-3. Since each method suffers from selection biases, we have simultaneously applied three leading techniques (Lyman break, BX/BM, and BzK selection) in the Subaru Deep Field. This field has reliable (Δz/(1 + z) = 0.02-0.09) photometric redshifts for ~53,000 galaxies from 20 bands (1500 Å-2.2 μm). The BzK, LBG, and BX/BM samples suffer contamination from z < 1 interlopers of 6%, 8%, and 20%, respectively. Around the redshifts where it is most sensitive (z ~ 1.9 for star-forming BzK, z ~ 1.8 for z ~ 2 LBGs, z ~ 1.6 for BM, and z ~ 2.3 for BX), each technique finds 60%-80% of the census of the three methods. In addition, each of the color techniques shares 75%-96% of its galaxies with another method, which is consistent with previous studies that adopt identical criteria on magnitudes and colors. Combining the three samples gives a comprehensive census that includes 90% of z phot = 1-3 galaxies, using standard magnitude limits similar to previous studies. In fact, we find that among z = 1-2.5 galaxies in the color selection census, 81%-90% of them can be selected by just combining the BzK selection with one of the UV techniques (z ~ 2 LBG or BX and BM). The average galaxy stellar mass, reddening, and star formation rates (SFRs) all decrease systematically from the sBzK population to the LBGs, and to the BX/BMs. The combined color selections yield a total cosmic SFR density of 0.18 ± 0.03 M ☉ yr–1 Mpc–3 for K AB 24. We find that 65% of the star formation is in galaxies with E(B – V) > 0.25 mag, even though they are only one-fourth of the census by number.
The Astrophysical Journal 06/2011; 735(2):91. · 6.02 Impact Factor
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Nobunari Kashikawa,
Kazuhiro Shimasaku,
Yuichi Matsuda,
Eiichi Egami,
Linhua Jiang,
Tohru Nagao,
Masami Ouchi,
Matthew A. Malkan,
Takashi Hattori,
Kazuaki Ota,
Yoshiaki Taniguchi,
Sadanori Okamura,
Chun Ly,
Masanori Iye,
Hisanori Furusawa,
Yasuhiro Shioya,
Takatoshi Shibuya,
Yoshifumi Ishizaki,
and Jun Toshikawa
[show abstract]
[hide abstract]
ABSTRACT: We carried out extended spectroscopic confirmations of Lyα emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Lyα luminosity, both photometrically and spectroscopically, to accurately determine the Lyα and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Lyα LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Lyα LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Lyα LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Lyα LF.
The Astrophysical Journal 06/2011; 734(2):119. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Faint Object Camera and Spectrograph (FOCAS) is a versatile common-use
optical instrument for the 8.2m Subaru Telescope, offering imaging and
spectroscopic observations. FOCAS employs grisms with resolving powers ranging
from 280 to 8200 as dispersive optical elements. A grism is a direct-vision
grating composed of a transmission grating and prism(s). FOCAS has five grisms
with replica surface-relief gratings including an echelle-type grism, and eight
grisms with volume-phase holographic (VPH) gratings. The size of these grisms
is 110 mm X 106 mm in aperture with a maximum thickness of 110 mm. We employ
not only the dichromated gelatin, but also the hologram resin as a recording
material for VPH gratings. We discuss the performance of these FOCAS grisms
measured in the laboratory, and verify it by test observations, and show
examples of astronomical spectroscopic observations.
05/2011;
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Noboru Ebizuka,
Kotaro Ichiyama,
Toru Yamada,
Chihiro Tokoku,
Masato Onodera,
Mai Hanesaka,
Kashiko Kodate,
Yuka Katsuno Uchimoto,
Miyoko Maruyama,
Kazuhiro Shimasaku,
Ichi Tanaka,
Tomohiro Yoshikawa, Nobunari Kashikawa,
Masanori Iye,
Takashi Ichikawa
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ABSTRACT: We have developed high dispersion VPH (volume phase holographic) grisms with
zinc selenide (ZnSe) prisms for the cryogenic optical system of MOIRCS
(Multi-Object near InfraRed Camera and Spectrograph) for Y-, J-, H- and K- band
observations. We fabricated the VPH gratings using a hologram resin. After
several heat cycles at between room temperature and 120 K, the VPH gratings
were assembled to grisms by gluing with two ZnSe prisms. Several heat cycles
were also carried out for the grisms before being installed into MOIRCS. We
measured the efficiencies of the VPH grisms in a laboratory, and found them to
be 70% - 82%. The performances obtained by observations of MOIRCS with the 8.2
m Subaru Telescope have been found to be very consistent with the results in
the laboratory test. This is the first astronomical application of cryogenic
VPH grisms.
05/2011;
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Nobunari Kashikawa,
Kazuhiro Shimasaku,
Yuichi Matsuda,
Eiichi Egami,
Linhua Jiang,
Tohru Nagao,
Masami Ouchi,
Matthew A. Malkan,
Takashi Hattori,
Kazuaki Ota,
Yoshiaki Taniguchi,
Sadanori Okamura,
Chun Ly,
Masanori Iye,
Hisanori Furusawa,
Yasuhiro Shioya,
Takatoshi Shibuya,
Yoshifumi Ishizaki,
Jun Toshikawa
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ABSTRACT: We carried out extended spectroscopic confirmations of Ly-alpha emitters
(LAEs) at z=6.5 and 5.7 in the Subaru Deep Field. Now, the total number of
spectroscopically confirmed LAEs is 45 and 54 at z=6.5 and 5.7, respectively,
and at least 81% (70%) of our photometric candidates at z=6.5 (5.7) have been
spectroscopically identified as real LAEs. We made careful measurements of the
Ly-alpha luminosity, both photometrically and spectroscopically, to accurately
determine the Ly-alpha and rest-UV luminosity functions (LFs). The
substantially improved evaluation of the Ly-alpha LF at z=6.5 shows an apparent
deficit from z=5.7 at least at the bright end, and a possible decline even at
the faint end, though small uncertainties remain. The rest-UV LFs at z=6.5 and
5.7 are in good agreement, at least at the bright end, in clear contrast to the
differences seen in the Ly-alpha LF. These results imply an increase in the
neutral fraction of the intergalactic medium from z=5.7 to 6.5. The rest-frame
equivalent width (EW_0) distribution at z=6.5 seems to be systematically
smaller than z=5.7, and it shows an extended tail toward larger EW_0. The
bright end of the rest-UV LF can be reproduced from the observed Ly-alpha LF
and a reasonable EW_0-UV luminosity relation. Integrating this rest-UV LF
provides the first measurement of the contribution of LAEs to the photon budget
required for reionization. The derived UV LF suggests that the fractional
contribution of LAEs to the photon budget among Lyman break galaxies
significantly increases towards faint magnitudes. Low-luminosity LAEs could
dominate the ionizing photon budget, though this inference depends strongly on
the uncertain faint-end slope of the Ly-alpha LF.
04/2011;
