arXiv subjects

Yoshiaki Ono

Publications and source records attributed to Yoshiaki Ono.

At least 91 records · Page 5Linked to original sources

arXiv2021

Subaru/FOCAS IFU revealed the metallicity gradient of a local extremely metal-poor galaxy

We present the first measurement of the metallicity gradient in extremely metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph (FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG, HSC J1631+4426, whose oxygen abundance and stellar mass are known to be 12+log(O/H) $=6.9$ and $\log_{10}(M_*/{\rm M}_\odot)=5.8$, respectively. The measured metallicity gradient is $-0.36 \pm 0.04$ dex kpc$^{-1}$ corresponding to $-0.049 \pm 0.006$ dex R$_\mathrm{e}^{-1}$ for the continuum effective radius of $R_\mathrm{e} = 0.14$ kpc. Our observation has successfully demonstrated that three-dimensional spectroscopy with 8m-class telescopes is powerful enough to reveal the metallicity distribution in local EMPGs, providing precious information of the baryon cycle in local analogs of primordial galaxies in the early Universe.

astro-ph.GA↗

arXiv2021

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections

We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Ly$α$ emitting galaxies between 1.88<z<3.52, in a 540 deg^2 area encompassing a co-moving volume of 10.9 Gpc^3. No pre-selection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project's observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the COSMOS, Extended Groth Strip, and GOODS-N fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.

astro-ph.IM↗

arXiv2021

Third Data Release of the Hyper Suprime-Cam Subaru Strategic Program

The paper presents the third data release of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), a wide-field multi-band imaging survey with the Subaru 8.2m telescope. HSC-SSP has three survey layers (Wide, Deep, and UltraDeep) with different area coverages and depths, designed to address a wide array of astrophysical questions. This third release from HSC-SSP includes data from 278 nights of observing time and covers about 670 square degrees in all five broad-band filters at the full depth ($\sim26$~mag at $5σ$) in the Wide layer. If we include partially observed area, the release covers 1,470 square degrees. The Deep and UltraDeep layers have $\sim80\%$ of the originally planned integration times, and are considered done, as we have slightly changed the observing strategy in order to compensate for various time losses. There are a number of updates in the image processing pipeline. Of particular importance is the change in the sky subtraction algorithm; we subtract the sky on small scales before the detection and measurement stages, which has significantly reduced false detections. Thanks to this and other updates, the overall quality of the processed data has improved since the previous release. However, there are limitations in the data (for example, the pipeline is not optimized for crowded fields), and we encourage the user to check the quality assurance plots as well as a list of known issues before exploiting the data. The data release website is https://hsc-release.mtk.nao.ac.jp/.

astro-ph.IM↗

arXiv2021

SILVERRUSH. XI. Intensity Mapping for Lya Emission Extending over $100-1000$ comoving kpc around $z\sim2-7$ LAEs with Subaru HSC-SSP and CHORUS Data

We conduct intensity mapping to probe for extended diffuse Ly$α$ emission around Ly$α$ emitters (LAEs) at $z\sim2-7$, exploiting very deep ($\sim26$ mag at $5σ$) and large-area ($\sim4.5$ deg$^2$) Subaru/Hyper Suprime-Cam narrow-band (NB) images and large LAE catalogs consisting of a total of 1781 LAEs at $z=2.2$, $3.3$, $5.7$, and $6.6$ obtained by the HSC-SSP SILVERRUSH and CHORUS projects. We calculate the spatial correlations of these LAEs with $\sim1-2$ billion pixel flux values of the NB images, deriving the average Ly$α$ surface brightness (${\rm SB_{Lyα}}$) radial profiles around the LAEs. By carefully estimating systematics such as fluctuations of sky background and point spread functions, we detect diffuse Ly$α$ emission ($\sim10^{-20}-10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$) at $100-1000$ comoving kpc around $z=3.3$ LAEs at the $4.1σ$ level and tentatively ($\sim2σ$) at the other redshifts, beyond the virial radius of a dark-matter halo with a mass of $10^{11}\ M_\odot$. While the observed ${\rm SB_{Lyα}}$ profiles have similar amplitudes at $z=2.2-6.6$ within the uncertainties, the intrinsic ${\rm SB_{Lyα}}$ profiles (corrected for the cosmological dimming effect) increase toward high redshifts. This trend may be explained by increasing hydrogen gas density due to the evolution of the cosmic volume. Comparisons with theoretical models suggest that extended Ly$α$ emission around a LAE is powered by resonantly scattered Ly$α$ photons in the CGM and IGM that originates from the inner part of the LAE, and/or neighboring galaxies around the LAE.

astro-ph.GA↗

arXiv2021

First HETDEX Spectroscopic Determinations of Ly$α$ and UV Luminosity Functions at $z=2-3$: Bridging a Gap Between Faint AGN and Bright Galaxies

We present Ly$α$ and ultraviolet-continuum (UV) luminosity functions (LFs) of galaxies and active galactic nuclei (AGN) at $z=2.0-3.5$ determined by the un-targetted optical spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We combine deep Subaru imaging with HETDEX spectra resulting in $11.4$ deg$^2$ of fiber-spectra sky coverage, obtaining $18320$ galaxies spectroscopically identified with Ly$α$ emission, $2126$ of which host type 1 AGN showing broad (FWHM$~>1000$ km s$^{-1}$) Ly$α$ emission lines. We derive the Ly$α$ (UV) LF over 2 orders of magnitude covering bright galaxies and AGN in $\log L_\mathrm{Lyα}/\mathrm{[erg~s^{-1}]}=43.3-45.5$ ($-27 -21$) type 1 AGN increases from $z\sim2$ to $z\sim0$ as opposed to the evolution of bright ($M_\mathrm{UV}<-21$) type 1 AGN, suggesting the AGN downsizing in the rest-frame UV luminosity.

astro-ph.GA↗

arXiv2021

EMPRESS. III. Morphology, Stellar Population, and Dynamics of Extremely Metal Poor Galaxies (EMPGs): Are EMPGs Local Analogs of High-$z$ Young Galaxies?

We present the morphology and stellar population of 27 extremely metal poor galaxies (EMPGs) at $z\sim0$ with metallicities of 0.01--0.1 Z$_{\odot}$. We conduct multi-component surface brightness (SB) profile fitting for the deep Subaru/HSC $i$-band images of the EMPGs with the {\sc Galfit} software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of $\log(M_{*}/{\rm M}_{\odot})=6.0$ have a median S{é}rsic index of $n=1.1$ and a median effective radius of $r_{\rm e}=200$ pc, suggesting that typical EMPGs have very compact disk. We compare the EMPGs with $z\sim6$ galaxies and local galaxies on the size-mass ($r_{\rm e}$-$M_*$) diagram, and identify that the majority of the EMPGs have a $r_{\rm e}$-$M_*$ relation similar to $z\sim0$ star-forming galaxies rather than $z\sim6$ galaxies. Not every EMPG is a local analog of high-$z$ young galaxies in the $r_{\rm e}$-$M_*$ relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of $ΔV=101\pm32$ km s$^{-1}$. This moderately-large $ΔV$ cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail.

astro-ph.GA↗

arXiv2021

SILVERRUSH. IX. Lya Intensity Mapping with Star-Forming Galaxies at z=5.7 and 6.6: A Possible Detection of Extended Lya Emission at $\gtrsim$100 comoving kpc around and beyond the Virial-Radius Scale of Galaxy Dark Matter Halos

We present results of the cross-correlation Ly$α$ intensity mapping with Subaru/Hyper Suprime-Cam (HSC) ultra-deep narrowband images and Ly$α$ emitters (LAEs) at $z=5.7$ and $6.6$ in a total area of $4$ deg$^2$. Although overwhelming amount of data quality controls have been performed for the narrowband images, we further conduct extensive analysis evaluating systematics of large-scale point-spread-function wings, sky subtractions, and unknown errors based on physically uncorrelated signals and sources found in real HSC images and object catalogs, respectively. Removing the systematics, we carefully calculate cross-correlations between Ly$α$ intensity of the narrowband images and the LAEs. We tentatively identify very diffuse Ly$α$ emission with the $\simeq 3σ$ ($\simeq 2σ$) significance at $\gtrsim$ 100 comoving kpc (ckpc) far from the LAEs at $z=5.7$ ($6.6$), around and probably even beyond a virial radius of star-forming galaxies with $M_\mathrm{h}\sim10^{11}M_\odot$. The diffuse Ly$α$ emission possibly extends up to $1$,$000$ ckpc with the surface brightness of $10^{-20}$-$10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. We confirm that the small-scale ($<150$ ckpc) Ly$α$ radial profiles of LAEs are consistent with those obtained by recent MUSE observations. Comparisons with numerical simulations suggest that the large-scale ($\sim150$-$1$,$000$ ckpc) Ly$α$ emission are not explained by unresolved faint neighboring galaxies including satellites, but by a combination of Ly$α$ photons emitted from the central LAE and other unknown sources, such as cold-gas streams and galactic outflow. We find no evolution in the Ly$α$ radial profiles of our LAEs from $z=5.7$ to $6.6$, where theoretical models predict a flattening of the profile slope made by cosmic reionization, albeit with our moderately large observational errors.

astro-ph.GA↗

arXiv2021

Optical Spectroscopy of Dual Quasar Candidates from the Subaru HSC-SSP program

We report on a spectroscopic program to search for dual quasars using Subaru Hyper Suprime-Cam (HSC) images of SDSS quasars which represent an important stage during galaxy mergers. Using Subaru/FOCAS and Gemini-N/GMOS, we identify three new physically associated quasar pairs having projected separations less than 20 kpc, out of 26 observed candidates. These include the discovery of the highest redshift ($z=3.1$) quasar pair with a separation $<$ 10 kpc. Based on the sample acquired to date, the success rate of identifying physically associated dual quasars is $19\%$ when excluding stars based on their HSC colors. Using the full sample of six spectroscopically confirmed dual quasars, we find that the black holes in these systems have black hole masses ($M_{BH} \sim 10^{8-9}M_{\odot}$) similar to single SDSS quasars as well as their bolometric luminosities and Eddington ratios. We measure the stellar mass of their host galaxies based on 2D image decomposition of the five-band ($grizy$) optical emission and assess the mass relation between supermassive black holes (SMBHs) and their hosts. Dual SMBHs appear to have elevated masses relative to their host galaxies. Thus mergers may not necessarily align such systems onto the local mass relation, as suggested by the Horizon-AGN simulation. This study suggests that dual luminous quasars are triggered prior to the final coalescence of the two SMBHs, resulting in early mass growth of the black holes relative to their host galaxies.

astro-ph.GA↗

arXiv2021

SILVERRUSH X: Machine Learning-Aided Selection of $9318$ LAEs at $z=2.2$, $3.3$, $4.9$, $5.7$, $6.6$, and $7.0$ from the HSC SSP and CHORUS Survey Data

We present a new catalog of $9318$ Ly$α$ emitter (LAE) candidates at $z = 2.2$, $3.3$, $4.9$, $5.7$, $6.6$, and $7.0$ that are photometrically selected by the SILVERRUSH program with a machine learning technique from large area (up to $25.0$ deg$^2$) imaging data with six narrowband filters taken by the Subaru Strategic Program with Hyper Suprime-Cam (HSC SSP) and a Subaru intensive program, Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). We construct a convolutional neural network that distinguishes between real LAEs and contaminants with a completeness of $94$% and a contamination rate of $1$%, enabling us to efficiently remove contaminants from the photometrically selected LAE candidates. We confirm that our LAE catalogs include $177$ LAEs that have been spectroscopically identified in our SILVERRUSH programs and previous studies, ensuring the validity of our machine learning selection. In addition, we find that the object-matching rates between our LAE catalogs and our previous results are $\simeq 80$-$100$% at bright NB magnitudes of $\lesssim 24$ mag. We also confirm that the surface number densities of our LAE candidates are consistent with previous results. Our LAE catalogs will be made public on our project webpage.

astro-ph.GA↗

arXiv2021

EMPRESS. II. Highly Fe-Enriched Metal-poor Galaxies with $\sim 1.0$ (Fe/O)$_\odot$ and $0.02$ (O/H)$_\odot$ : Possible Traces of Super Massive ($>300 M_{\odot}$) Stars in Early Galaxies

We present element abundance ratios and ionizing radiation of local young low-mass (~$10^{6}$ 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$^{-1}$), 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$β$ 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$β$ ratios are explained by the past existence of super massive ($>$300 M_sun) stars, which may evolve into intermediate-mass black holes ($\gtrsim$100 M_sun).

astro-ph.GA↗

arXiv2021

ALMA Lensing Cluster Survey: Bright [CII] 158 $μ$m Lines from a Multiply Imaged Sub-$L^{\star}$ Galaxy at $z=6.0719$

We present bright [CII] 158 $μ$m line detections from a strongly magnified and multiply-imaged ($μ\sim20-160$) sub-$L^{*}$ ($M_{\rm UV}$ = $-19.75^{+0.55}_{-0.44}$) Lyman-break galaxy (LBG) at $z=6.0719\pm0.0004$ from the ALMA Lensing Cluster Survey (ALCS). Emission lines are identified at 268.7 GHz at $\geq$ 8$σ$ exactly at positions of two multiple images of the LBG behind the massive galaxy cluster RXCJ0600$-$2007. Our lens models, updated with the latest spectroscopy from VLT/MUSE, indicate that a sub region of the LBG crosses the caustic and is lensed into a long ($\sim6''$) arc with a local magnification of $μ\sim 160$, for which the [CII] line is also significantly detected. The source-plane reconstruction resolves the interstellar medium (ISM) structure, showing that the [CII] line is co-spatial with the rest-frame UV continuum at the scale of $\sim$300 pc. The [CII] line properties suggest that the LBG is a rotation-dominated system whose velocity gradient explains a slight difference of redshifts between the whole LBG and its sub region. The star formation rate (SFR)-$L_{\rm [CII]}$ relations from the sub to the whole regions of the LBG are consistent with those of local galaxies. We evaluate the lower limit of the faint-end of the [CII] luminosity function at $z=6$, and find that it is consistent with predictions from semi analytical models and from the local SFR-$L_{\rm [CII]}$ relation with a SFR function at $z=6$. These results imply that the local SFR-$L_{\rm [CII]}$ relation is universal for a wide range of scales including the spatially resolved ISM, the whole region of galaxy, and the cosmic scale, even in the epoch of reionization.

astro-ph.GA↗

arXiv2020

Observations of the Lyman-$α$ Universe

Hydrogen Lyman-$α$ (Ly$α$) emission has been one of the major observational probes for the high redshift universe, since the first discoveries of high-$z$ Ly$α$ emitting galaxies in the late 1990s. Due to the strong Ly$α$ emission originated by resonant scattering and recombination of the most-abundant element, Ly$α$ observations witness not only HII regions of star formation and AGN but also diffuse HI gas in the circum-galactic medium (CGM) and the inter-galactic medium (IGM). Here we review Ly$α$ sources, and present theoretical interpretations reached to date. We conclude that: 1) A typical Ly$α$ emitter (LAE) at $z\gtrsim 2$ with a $L^*$ Ly$α$ luminosity is a high-$z$ counterpart of a local dwarf galaxy, a compact metal-poor star-forming galaxy (SFG) with an approximate stellar (halo) mass and star-formation rate of $10^{8-9} M_\odot$ ($10^{10-11} M_\odot$) and $1-10 M_\odot$ yr$^{-1}$, respectively; 2) High-$z$ SFGs ubiquitously have a diffuse Ly$α$ emitting halo in the CGM extending to the halo virial radius and beyond; 3) Remaining neutral hydrogen at the epoch of reionization makes a strong dimming of Ly$α$ emission for galaxies at $z>6$ that suggest the late reionization history. The next generation large telescope projects will combine Ly$α$ emission data with HI Ly$α$ absorptions and 21cm radio data that map out the majority of hydrogen (HI+HII) gas, uncovering the exchanges of i) matter by outflow/inflow and ii) radiation, relevant to cosmic reionization, between galaxies and the CGM/IGM.

astro-ph.GA↗

arXiv2020

CHORUS. I. Cosmic HydrOgen Reionization Unveiled with Subaru: Overview

To determine the dominant sources for cosmic reionization, the evolution history of the global ionizing fraction, and the topology of the ionized regions, we have conducted a deep imaging survey using four narrow-band (NB) and one intermediate-band (IB) filters on the Subaru/Hyper Suprime-Cam (HSC), called Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS). The central wavelengths and full-widths-at-half-maximum of the CHORUS filters are, respectively, 386.2 nm and 5.5 nm for NB387, 526.0 nm and 7.9 nm for NB527, 717.1 nm and 11.1 nm for NB718, 946.2 nm and 33.0 nm for IB945, and 971.2 nm and 11.2 nm for NB973. This combination, including NB921 (921.5 nm and 13.5 nm) from the Subaru Strategic Program with HSC (HSC SSP), are carefully designed, as if they were playing a chorus, to observe multiple spectral features simultaneously, such as Lyman continuum, Ly$α$, C~{\sc iv}, and He~{\sc ii} for $z=2$--$7$. The observing field is the same as that of the deepest footprint of the HSC SSP in the COSMOS field and its effective area is about 1.6 deg$^2$. Here, we present an overview of the CHORUS project, which includes descriptions of the filter design philosophy, observations and data reduction, multiband photometric catalogs, assessments of the imaging quality, measurements of the number counts, and example use cases of the data. All the imaging data, photometric catalogs, masked pixel images, data of limiting magnitudes and point spread functions, results of completeness simulations, and source number counts are publicly available through the HSC SSP database.

astro-ph.GA↗

arXiv2020

Cosmological 3D HI Gas Map with HETDEX Ly$α$ Emitters and eBOSS QSOs at $z=2$: IGM-Galaxy/QSO Connection and a $\sim$ 40-Mpc Scale Giant HII Bubble Candidate

We present cosmological ($30-400$ Mpc) distributions of neutral hydrogen (HI) in the inter-galactic medium (IGM) traced by Ly$α$ Emitters (LAEs) and QSOs at $z=2.1-2.5$, selected with the data of the on-going Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the eBOSS survey. We investigate spatial correlations of LAEs and QSOs with HI tomography maps reconstructed from HI Ly$α$ forest absorption in the spectra of background galaxies and QSOs obtained by the CLAMATO survey and this study, respectively. In the cosmological volume far from QSOs, we find that LAEs reside in regions of strong HI absorption, i.e. HI rich, which is consistent with results of previous galaxy-background QSO pair studies. Moreover, there is an anisotropy in the HI-distribution plot of transverse and line-of-sight distances; on average the HI absorption peak is blueshifted by $\sim 200$ km s$^{-1}$ from the LAE Ly$α$ redshift, reproducing the known average velocity offset between the Ly$α$ emission redshift and the galaxy systemic redshift. We have identified a $\sim$ 40-Mpc scale volume of HI underdensity that is a candidate for a giant HII bubble, where six QSOs and an LAE overdensity exist at $\left < z \right > =2.16$. The coincidence of the QSO and LAE overdensities with the HI underdensity indicates that the ionizing photon radiation of the QSOs has created a highly ionized volume of multiple proximity zones in a matter overdensity. Our results suggest an evolutionary picture where HI gas in an overdensity of galaxies becomes highly photoionized when QSOs emerge in the galaxies.

astro-ph.GA↗

arXiv2020

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.

astro-ph.GA↗

arXiv2020

Electronic States of Al-Mg-Zn Quasicrystal and Its Approximant based on the First-Principles Calculations

First-principles calculations are performed to investigate the electronic states of 1/1 and 2/1 approximants with the composition Al$_{15}$Zn$_{40}$Mg$_{45}$ which is close to the quasicrystal (QC) Al$_{14.9}$Zn$_{41.0}$Mg$_{44.1}$ in which the superconductivity is recently discovered. The density of states for the 1/1 approximant shows a wide pseudogap structure near the Fermi level as commonly observed in various approximants of the QCs, whereas those for the 2/1 approximant do not show such a wide pseudogap. Instead of the wide pseudogap, the 2/1 approximant shows a remarkable narrow pseudogap at the Fermi level in contrast to the 1/1 approximant, which shows a shallow hump at the Fermi level within the wide pseudogap. This seems to be consistent with the experimental observation of the electrical resistivity, which increases with decreasing temperature from the room temperature down to around the superconducting transition temperature for the 2/1 approximant together with the QC, whereas it monotonically decreases for the 1/1 approximant.

cond-mat.supr-con↗

arXiv2020

Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with Lyman Break Technique

We report a discovery of $z = 4.72$ radio galaxy, HSC J083913.17+011308.1, by using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for VLA FIRST radio sources. The number of known high-$z$ radio galaxies (HzRGs) at $z > 3$ is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected $r$-band dropouts with a radio detection, a follow-up optical spectroscopy with GMOS/Gemini has been performed. The obtained spectrum presents a clear Ly$α$ emission line redshifted to $z=4.72$. The SED fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with $\log{M_*/M_{\odot}} = 11.4$. The small equivalent width of Ly$α$ and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum: $α^{325}_{1400}$ of $-1.1$ and $α^{150}_{1400}$ of $-0.9$, demonstrating that the HSC-SSP survey compensates for a sub-population of HzRGs which are missed in surveys focusing on an ultra-steep spectral index.

astro-ph.GA↗

arXiv2020

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.

astro-ph.GA↗