73 research outputs found
Star Formation Rates and Metallicities of K-selected Star Forming Galaxies at z~2
We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB)<23
in the Subaru Deep Field, for which Halpha and some other emission lines are
detected in 0.9 to 2.3 micron spectra with a resolution of R=500. Using Halpha
luminosities, we obtain star formation rates (SFRs), and then specific SFRs
(SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to
BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have
larger SFRs. A negative correlation is seen between stellar mass and SSFR,
which is consistent with the previous results for z~2 galaxies. This implies
that a larger growth of stellar mass occurs in less massive galaxies. In
addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio
of NII(lambda 6584) to Halpha using the N2 index method. We have found a
correlation between stellar mass and oxygen abundance in the sense that more
massive sBzKs tend to be more metal rich, which is qualitatively consistent
with the relation for UV-selected z~2 galaxies. However, the metallicity of the
sBzKs is ~0.2 dex higher than that of UV-selected galaxies with similar stellar
masses, which is significant considering the small uncertainties. The sBzKs in
our sample have redder R-K colors than the UV-selected galaxies. This galaxy
color-dependence in the oxygen abundance may be caused by older or dustier
galaxies having higher metallicities at z~2.Comment: 20 pages, 13 figures, 2 tables, accepted for publication in The
Astrophysical Journa
Properties of star-forming galaxies in a cluster and its surrounding structure at z=1.46
We conduct a narrow-band imaging survey of [OII] emitters over a 32'x23' area
in and around the XMMXCS J2215.9-1738 cluster at z=1.46 with
Subaru/Suprime-Cam, and select 380 [OII] emitting galaxies down to 1.4E-17
erg/s/cm2. Among them, 16 [OII] emitters in the cluster central region are
confirmed by NIR spectroscopy with Subaru/MOIRCS. We find that [OII] emitters
are distributed along filamentary large-scale structures around the cluster.
The z'-K vs K colour-magnitude diagram shows that a significantly higher
fraction of [OII] emitters is seen on the red sequence in the cluster core than
in other environments we define in this paper. It is likely that these red
galaxies are nearly passively evolving galaxies which host [OII] emitting AGNs,
rather than dust-reddened star-forming galaxies. We argue therefore that AGN
feedback may be one of the critical processes to quench star formation in
massive galaxies in high density regions. We also find that the cluster has
experienced high star formation activities at rates comparable to that in the
field at z=1.46. In addition, a mass-metallicity relation exists in the cluster
at z=1.46, which is similar to that of star-forming galaxies in the field at
z~2. These results all suggest that at z~1.5 star formation activity in the
cluster core becomes as high as those in low density environments and there is
apparently not yet a strong environmental dependence, except for the red
emitters.Comment: 19 pages, 17 figures, 4 tables, accepted for publication in MNRA
EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with (Fe/O) and (O/H) : Possible Traces of Super Massive () Stars in Early Galaxies
We present element abundance ratios and ionizing radiation of local young
low-mass (~ M_sun) extremely metal poor galaxies (EMPGs) with a 2%
solar oxygen abundance (O/H)_sun and a high specific star-formation rate
(sSFR~300 Gyr), and other (extremely) metal poor galaxies, which are
compiled from Extremely Metal-Poor Representatives Explored by the Subaru
Survey (EMPRESS) and the literature. Weak emission lines such as [FeIII]4658
and HeII4686 are detected in very deep optical spectra of the EMPGs taken with
8m-class telescopes including Keck and Subaru (Kojima et al. 2019, Izotov et
al. 2018), enabling us to derive element abundance ratios with photoionization
models. We find that neon- and argon-to-oxygen ratios are comparable to those
of known local dwarf galaxies, and that the nitrogen-to-oxygen abundance ratios
(N/O) are lower than 20% (N/O)_sun consistent with the low oxygen abundance.
However, the iron-to-oxygen abundance ratios (Fe/O) of the EMPGs are generally
high; the EMPGs with the 2%-solar oxygen abundance show high Fe/O ratios of
~90-140% (Fe/O)_sun, which are unlikely explained by suggested scenarios of
Type Ia supernova iron productions, iron's dust depletion, and metal-poor gas
inflow onto previously metal-riched galaxies with solar abundances. Moreover,
these EMPGs have very high HeII4686/H ratios of ~1/40, which are not
reproduced by existing models of high-mass X-ray binaries whose progenitor
stellar masses are less than 120 M_sun. Comparing stellar-nucleosynthesis and
photoionization models with a comprehensive sample of EMPGs identified by this
and previous EMPG studies, we propose that both the high Fe/O ratios and the
high HeII4686/H ratios are explained by the past existence of super
massive (300 M_sun) stars, which may evolve into intermediate-mass black
holes (100 M_sun).Comment: ApJ in press. 23 pages, 7 Figures, 6 Table
Extremely Metal-Poor Representatives Explored by the Subaru Survey (EMPRESS). I. A Successful Machine Learning Selection of Metal-Poor Galaxies and the Discovery of a Galaxy with M*<10^6 M_sun and 0.016 Z_sun
We have initiated a new survey for local extremely metal-poor galaxies
(EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (~500 deg^2) optical
images reaching a 5 sigma limit of ~26 magnitude, about 100 times deeper than
the Sloan Digital Sky Survey (SDSS). To select Z/Z_sun<0.1 EMPGs from ~40
million sources detected in the Subaru images, we first develop a
machine-learning (ML) classifier based on a deep neural network algorithm with
a training data set consisting of optical photometry of galaxy, star, and QSO
models. We test our ML classifier with SDSS objects having spectroscopic
metallicity measurements, and confirm that our ML classifier accomplishes
86%-completeness and 46%-purity EMPG classifications with photometric data.
Applying our ML classifier to the photometric data of the Subaru sources as
well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG
candidates from the Subaru and SDSS photometric data, respectively. We conduct
optical follow-up spectroscopy for 10 out of our EMPG candidates with
Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS, and find that the 10 EMPG
candidates are star-forming galaxies at z=0.007-0.03 with large H_beta
equivalent widths of 104-265 A, stellar masses of log(M*/M_sun)=5.0-7.1, and
high specific star-formation rates of ~300 Gyr^{-1}, which are similar to those
of early galaxies at z>6 reported recently. We spectroscopically confirm that 3
out of 10 candidates are truly EMPGs with Z/Z_sun<0.1, one of which is HSC
J1631+4426, the most metal-poor galaxy with Z/Z_sun=0.016 reported ever.Comment: 30 pages, 26 figures, and 8 tables; (Revision: metallicities changed
due to the use of a more pricise dust correction method, but conclusion does
not change, Minor: a table, some figures, and sentences are added for a clear
explanation.
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
A multi-ethnic meta-analysis identifies novel genes, including ACSL5, associated with amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS) is a devastating progressive motor neuron disease that affects people of all ethnicities. Approximately 90% of ALS cases are sporadic and thought to have multifactorial pathogenesis. To understand the genetics of sporadic ALS, we conducted a genome-wide association study using 1,173 sporadic ALS cases and 8,925 controls in a Japanese population. A combined meta-analysis of our Japanese cohort with individuals of European ancestry revealed a significant association at the ACSL5 locus (top SNP p = 2.97 × 10−8). We validated the association with ACSL5 in a replication study with a Chinese population and an independent Japanese population (1941 ALS cases, 3821 controls; top SNP p = 1.82 × 10−4). In the combined meta-analysis, the intronic ACSL5 SNP rs3736947 showed the strongest association (p = 7.81 × 10−11). Using a gene-based analysis of the full multi-ethnic dataset, we uncovered additional genes significantly associated with ALS: ERGIC1, RAPGEF5, FNBP1, and ATXN3. These results advance our understanding of the genetic basis of sporadic ALS
下顎側切歯と下顎犬歯の癒合歯
We observed four fused teeth of the mandibular lateral incisor and the mandibular canine on three patients. In Case 1, both sides of the teeth were fused to the tooth crown and root. From observation of dental radiography, we were able to confirm that the fusion area of these teeth reached to the dentin. In Case 2, the tooth crown was divided into two parts, mesial and distal, and was fused to the tooth root. From observation of dental radiography, the fusion area of the tooth was confirmed to reach to the dentin. In Case 3, we were able to confirm from observation of plaster model that the tooth crown was fused completely. The appearance rate of fused permanent teeth was 0.3%. We thought that the abnormal cases appeared as a result of many embryological phenomena. We propose that the abnormal cases should be reported along with the detail data, and not thought to be rare
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