50 research outputs found
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
ALMA Observations for CO Emission from Luminous Lyman-break Galaxies at -
We present our new Atacama Large Millimeter/submillimeter Array (ALMA)
observations targeting CO(6-5) emission from three luminous Lyman break
galaxies (LBGs) at - found in the Subaru/Hyper
Suprime-Cam survey, whose [OIII]m and [CII]m emission have been
detected with ALMA. We find a marginal detection of the CO(6-5) line from one
of our LBGs, J0235-0532, at the significance level and obtain
upper limits for the other two LBGs, J1211-0118 and J0217-0208. Our
luminous LBGs are consistent with the previously found correlation between the
CO luminosity and the infrared luminosity. The unique ensemble of the multiple
far-infrared emission lines and underlying continuum fed to a photodissociation
region model reveal that J0235-0532 has a relatively high hydrogen nucleus
density that is comparable to those of low- (U)LIRGs, quasars, and Galactic
star-forming regions with high values, while the other two LBGs
have lower consistent with local star-forming galaxies. By
carefully taking account of various uncertainties, we obtain total gas mass and
gas surface density constraints from their CO luminosity measurements. We find
that J0235-0532 locates below the Kennicutt-Schmidt (KS) relation, comparable
to the previously CO(2-1) detected LBG, HZ10. Combined with previous
results for dusty starbursts at similar redshifts, the KS relation at -
is on average consistent with the local one.Comment: 33 pages, 12 figures, accepted for publication in Ap
Subaru high-z exploration of low-luminosity quasars (SHELLQs). I. Discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9
We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9.
This is the initial result from the Subaru High-z Exploration of Low-Luminosity
Quasars (SHELLQs) project, which exploits the exquisite multiband imaging data
produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The
candidate selection is performed by combining several photometric approaches
including a Bayesian probabilistic algorithm to reject stars and dwarfs. The
spectroscopic identification was carried out with the Gran Telescopio Canarias
and the Subaru Telescope for the first 80 deg2 of the survey footprint. The
success rate of our photometric selection is quite high, approaching 100 % at
the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the
known high-z quasars on the HSC images. Among the 15 discovered objects, six
are likely quasars, while the other six with interstellar absorption lines and
in some cases narrow emission lines are likely bright Lyman-break galaxies. The
remaining three objects have weak continua and very strong and narrow Ly alpha
lines, which may be excited by ultraviolet light from both young stars and
quasars. These results indicate that we are starting to see the steep rise of
the luminosity function of z > 6 galaxies, compared with that of quasars, at
magnitudes fainter than M1450 ~ -22 mag or zAB ~24 mag. Follow-up studies of
the discovered objects as well as further survey observations are ongoing.Comment: Published in ApJ (828:26, 2016
Discovery of the First Low-Luminosity Quasar at z > 7
We report the discovery of a quasar at z = 7.07, which was selected from the
deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru
Strategic Program survey. This quasar, HSC J124353.93+010038.5, has an order of
magnitude lower luminosity than do the other known quasars at z > 7. The
rest-frame ultraviolet absolute magnitude is M1450 = -24.13 +/- 0.08 mag and
the bolometric luminosity is Lbol = (1.4 +/- 0.1) x 10^{46} erg/s. Its spectrum
in the optical to near-infrared shows strong emission lines, and shows evidence
for a fast gas outflow, as the C IV line is blueshifted and there is indication
of broad absorption lines. The Mg II-based black hole mass is Mbh = (3.3 +/-
2.0) x 10^8 Msun, thus indicating a moderate mass accretion rate with an
Eddington ratio 0.34 +/- 0.20. It is the first z > 7 quasar with sub-Eddington
accretion, besides being the third most distant quasar, known to date. The
luminosity and black hole mass are comparable to, or even lower than, those
measured for the majority of low-z quasars discovered by the Sloan Digital Sky
Survey, and thus this quasar likely represents a z > 7 counterpart to quasars
commonly observed in the low-z universe.Comment: Accepted for publication in ApJ Letter
Current Performance and On-Going Improvements of the 8.2 m Subaru Telescope
An overview of the current status of the 8.2 m Subaru Telescope constructed
and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of
Japan is presented. The basic design concept and the verified performance of
the telescope system are described. Also given are the status of the instrument
package offered to the astronomical community, the status of operation, and
some of the future plans. The status of the telescope reported in a number of
SPIE papers as of the summer of 2002 are incorporated with some updates
included as of 2004 February. However, readers are encouraged to check the most
updated status of the telescope through the home page,
http://subarutelescope.org/index.html, and/or the direct contact with the
observatory staff.Comment: 18 pages (17 pages in published version), 29 figures (GIF format),
This is the version before the galley proo
Dual supermassive black holes at close separation revealed by the Hyper Suprime-Cam Subaru Strategic Program
The unique combination of superb spatial resolution, wide-area coverage, and
deep depth of the optical imaging from the Hyper Suprime-Cam (HSC) Subaru
Strategic Program is utilized to search for dual quasar candidates. Using an
automated image analysis routine on 34,476 known SDSS quasars, we identify
those with two (or more) distinct optical point sources in HSC images covering
796 deg^2. We find 421 candidates out to a redshift of 4.5 of which one hundred
or so are more likely after filtering out contaminating stars. Angular
separations of 0.6 - 4.0" correspond to projected separations of 3 - 30 kpc, a
range relatively unexplored for population studies of luminous dual quasars.
Using Keck-I/LRIS and Gemini-N/NIFS, we spectroscopically confirm three dual
quasar systems at z < 1, two of which are previously unknown out of eight
observed, based on the presence of characteristic broad emission lines in each
component, while highlighting that the continuum of one object in one of the
pairs is reddened. In all cases, the [OIII]5007 emission lines have mild
velocity offsets, thus the joint [OIII] line profile is not double-peaked. We
find a dual quasar fraction of 0.26+/-0.18% and no evidence for evolution. A
comparison with the Horizon-AGN simulation seems to support the case of no
evolution in the dual quasar fraction when broadly matching the quasar
selection. These results may indicate a scenario in which the frequency of the
simultaneous triggering of luminous quasars is not as sensitive as expected to
the cosmic evolution of the merger rate or gas content of galaxies.Comment: 11 pages; 12 figures; Accepted for publication in The Astrophysical
Journa
First Data Release of the Hyper Suprime-Cam Subaru Strategic Program
The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered
imaging survey aimed at addressing some of the most outstanding questions in
astronomy today, including the nature of dark matter and dark energy. The
survey has been awarded 300 nights of observing time at the Subaru Telescope
and it started in March 2014. This paper presents the first public data release
of HSC-SSP. This release includes data taken in the first 1.7 years of
observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers
covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and
~27.0 mag, respectively (5sigma for point sources). All the layers are observed
in five broad bands (grizy), and the Deep and UltraDeep layers are observed in
narrow bands as well. We achieve an impressive image quality of 0.6 arcsec in
the i-band in the Wide layer. We show that we achieve 1-2 per cent PSF
photometry (rms) both internally and externally (against Pan-STARRS1), and ~10
mas and 40 mas internal and external astrometric accuracy, respectively. Both
the calibrated images and catalogs are made available to the community through
dedicated user interfaces and database servers. In addition to the pipeline
products, we also provide value-added products such as photometric redshifts
and a collection of public spectroscopic redshifts. Detailed descriptions of
all the data can be found online. The data release website is
https://hsc-release.mtk.nao.ac.jp/.Comment: 34 pages, 20 figures, 7 tables, moderate revision, accepted for
publication in PAS