61 research outputs found
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
Minor Contribution of Quasars to Ionizing Photon Budget at z~6: Update on Quasar Luminosity Function at the Faint-end with Subaru/Suprime-Cam
We constrain the quasar contribution to cosmic reionization based on our deep
optical survey of z~6 quasars down to z_R=24.15 using Subaru/Suprime-Cam in
three UKIDSS-DXS fields covering 6.5 deg^2. In Kashikawa et al. (2015), we
select 17 quasar candidates and report our initial discovery of two
low-luminosity quasars (M_1450~ -23) from seven targets, one of which might be
a Lyman alpha emitting galaxy. From an additional optical spectroscopy, none of
the four candidates out of the remaining ten turn out to be genuine quasars.
Moreover, the deeper optical photometry provided by the Hyper Suprime-Cam
Subaru Strategic Program (HSC-SSP) shows that, unlike the two already-known
quasars, the i-z and z-y colors of the last six candidates are consistent with
M- or L-type brown dwarfs. Therefore, the quasar luminosity function (QLF) in
the previous paper is confirmed. Compiling QLF measurements from the literature
over a wide magnitude range, including an extremely faint AGN candidate from
Parsa et al. (2017}, to fit them with a double power-law, we find that the
best-fit faint-end slope is alpha=-2.04^+0.33_-0.18 (-1.98^+0.48_-0.21) and
characteristic magnitude is M_1450^*=-25.8^+1.1_-1.9 (-25.7^+1.0_-1.8) in the
case of two (one) quasar detection. Our result suggests that, if the QLF is
integrated down to M_1450=-18, quasars produce ~1-12% of the ionizing photons
required to ionize the whole universe at z~6 with 2sigma confidence level,
assuming that the escape fraction is f_esc=1 and the IGM clumpy factor is C=3.
Even when the systematic uncertainties are taken into account, our result
supports the scenario that quasars are the minor contributors of reionization.Comment: 8 pages, 3 figures, ApJL accepte
The Subaru HSC Galaxy Clustering with Photometric Redshift. I. Dark Halo Masses versus Baryonic Properties of Galaxies at 0.3≤z≤ 1.4
We present the clustering properties of low- galaxies
selected by the Hyper Suprime-Cam Subaru Strategic Program Wide layer over
deg. The wide-field and multi-wavelength observation yields
galaxies at with photometric redshifts and
physical properties. This enables the accurate measurement of angular
correlation functions and subsequent halo occupation distribution (HOD)
analysis allows the connection between baryonic properties and dark halo
properties. The fraction of less-massive satellite galaxies at is
found to be almost constant at , but it gradually decreases beyond
. However, the abundance of satellite
galaxies at is quite small even for less-massive galaxies due to the
rarity of massive centrals at high-. This decreasing trend is connected to
the small satellite fraction of Lyman break galaxies at . The
stellar-to-halo mass ratios at are almost consistent with
the predictions obtained using the latest empirical model; however, we identify
small excesses from the theoretical model at the massive end. The pivot halo
mass is found to be unchanged at at , and we systematically show that is a
universal pivot halo mass up to that is derived using only the
clustering/HOD analyses. Nevertheless, halo masses with peaked instantaneous
baryon conversion efficiencies are much smaller than the pivot halo mass
regardless of a redshift, and the most efficient stellar-mass assembly is
thought to be in progress in dark haloes.Comment: 33 pages, 16 figures, submitted to Ap
Statistical Correlation between the Distribution of Lyα Emitters and Intergalactic Medium Hi at z∼2.2 Mapped by the Subaru/Hyper Suprime-Cam
The correlation between neutral Hydrogen (HI) in the intergalactic medium
(IGM) and galaxies now attracts great interests. We select four fields which
include several coherently strong Ly absorption systems at
detected by using background quasars from the whole SDSS/(e)BOSS database. Deep
narrow-band and -band imaging are performed using the Hyper Suprime-Cam on
the Subaru Telescope. We select out 2,642 Ly emitter (LAE) candidates
at down to the Ly luminosity of
to construct the
galaxy overdensity maps, covering an effective area of 5.39 deg. Combining
the sample with the Ly absorption estimated from 64 (e)BOSS quasar
spectra, we find a moderate to strong correlation between the LAE overdensity
and the effective optical depth in
line-of-sights, with -value () when the field that
contains a significant quasar overdensity is in(ex)cluded. The
cross-correlation analysis also clearly suggests that up to pMpc, LAEs
tend to cluster in the regions rich in HI gas, indicated by the high , and avoid the low region where the HI gas is deficient.
By averaging the as a function of the projected distance ()
to LAEs, we find a excess signal at level at pkpc,
indicating the dense HI in circumgalactic medium, and a tentative excess at
pkpc in IGM regime, corroborating the cross-correlation signal
detected at about pMpc. These statistical analyses indicate that
galaxyIGM HI correlations exist on scales ranging from several hundred pkpc
to several pMpc at .Comment: 27 pages, 15 figures; Resubmitted to ApJ after the first referee's
report. Comments are welcom
The Hyper Suprime-Cam SSP Survey: Overview and Survey Design
Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of
the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of
scientists from Japan, Taiwan and Princeton University is using HSC to carry
out a 300-night multi-band imaging survey of the high-latitude sky. The survey
includes three layers: the Wide layer will cover 1400 deg in five broad
bands (), with a point-source depth of . The
Deep layer covers a total of 26~deg in four fields, going roughly a
magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter
still in two pointings of HSC (a total of 3.5 deg). Here we describe the
instrument, the science goals of the survey, and the survey strategy and data
processing. This paper serves as an introduction to a special issue of the
Publications of the Astronomical Society of Japan, which includes a large
number of technical and scientific papers describing results from the early
phases of this survey.Comment: 14 pages, 7 figures, 5 tables. Corrected for a typo in the
coordinates of HSC-Wide spring equatorial field in Table
A new portable monitor for measuring odorous compounds in oral, exhaled and nasal air
<p>Abstract</p> <p>Background</p> <p>The B/B Checker<sup>®</sup>, a new portable device for detecting odorous compounds in oral, exhaled, and nasal air, is now available. As a single unit, this device is capable of detecting several kinds of gases mixed with volatile sulfur compounds (VSC) in addition to other odorous gasses. The purpose of the present study was to evaluate the effectiveness of the B/B Checker<sup>® </sup>for detecting the malodor level of oral, exhaled, and nasal air.</p> <p>Methods</p> <p>A total of 30 healthy, non-smoking volunteers (16 males and 14 females) participated in this study. The malodor levels in oral, exhaled, and nasal air were measured using the B/B Checker<sup>® </sup>and by organoleptic test (OT) scores. The VSCs in each air were also measured by gas chromatography (GC). Associations among B/B Checker<sup>® </sup>measurements, OT scores and VSC levels were analyzed using Spearman correlation coefficients. In order to determine the appropriate B/B Checker<sup>® </sup>level for screening subjects with malodor, sensitivity and specificity were calculated using OT scores as an identifier for diagnosing oral malodor.</p> <p>Results</p> <p>In oral and nasal air, the total VSC levels measured by GC significantly correlated to that measured by the B/B Checker<sup>®</sup>. Significant correlation was observed between the results of OT scores and the B/B Checker<sup>® </sup>measurements in oral (r = 0.892, p < 0.001), exhaled (r = 0.748, p < 0.001) and nasal air (r = 0.534, p < 0.001). The correlation between the OT scores and VSC levels was significant only for oral air (r = 0.790, p < 0.001) and nasal air (r = 0.431, p = 0.002); not for exhaled air (r = 0.310, p = 0.096). When the screening level of the B/B Checker<sup>® </sup>was set to 50.0 for oral air, the sensitivity and specificity were 1.00 and 0.90, respectively. On the other hand, the screening level of the B/B Checker<sup>® </sup>was set to 60.0 for exhaled air, the sensitivity and specificity were 0.82 and 1.00, respectively.</p> <p>Conclusion</p> <p>The B/B Checker<sup>® </sup>is useful for objective evaluation of malodor in oral, exhaled and nasal air and for screening subjects with halitosis.</p> <p>Trial registration</p> <p>ClinicalTrials.gov: <a href="http://www.clinicaltrials.gov/ct2/show/NCT01139073">NCT01139073</a></p
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