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Y. Matsuoka

Publications and source records attributed to Y. Matsuoka.

At least 19 recordsLinked to original sources
arXiv2026

Euclid: Discovery of 31 new quasars at $6.6 < z < 7.8$

We report the discovery of 31 new high-$z$ quasars in the redshift range $6.6 < z < 7.8$. These quasars were selected from approximately 3000 deg$^2$ of sky covered during the first 1.5 years of the Euclid Wide Survey, representing the initial results of the Euclid high-$z$ quasar search. Our candidate selection employed multiple machine-learning and probabilistic techniques applied to the Euclid $I_E$, $Y_E$, $J_E$, and $H_E$ images, supplemented by ancillary $z$-band data when available. Spectroscopic follow-up observations were carried out with Keck, Magellan, and the Large Binocular Telescope (LBT). Among the new discoveries, there are 12 quasars at $z \geq 7$, more than doubling the number of previously known quasars at $z \geq 7$. The newly discovered quasars exhibit $21.2 < J_E < 23.2$ ($-25.5 < M_{1450} < -23.6$), extending quasar studies to the faint end of the quasar luminosity function (QLF) at $z \gtrsim 7$. The quasar with the highest-$z$, EUCL J172902.75+641018.1 at $z \approx 7.77$, sets the new redshift record for the most distant quasar ever reported. These discoveries demonstrate Euclid's transformative role in high-$z$ quasar discovery and set the stage for future follow-up studies of the early galaxies hosting quasars, supermassive black hole growth, and the intergalactic medium in the epoch of reionisation.

astro-ph.GA↗
arXiv2026

Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at $z \approx 7.7$

Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of the $z \approx 7.7$ quasar EUCL\,J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [CII] 158$μ\mathrm{m}$ and cold dust emission in a quasar host to date. The [CII] emission line sets the systemic redshift at $z=7.6980\pm0.0004$. The source exhibits luminosities of $L_{\rm FIR}=3.6\times10^{12}\,L_{\odot}$ and $L_{[CII]}=2\times10^9\,L_{\odot}$, respectively, a dust mass of 1.4$\times 10^{8}\,M_{\odot}$, and a dynamical mass in the range 0.33-1.3$\times10^{10}\,M_{\odot}$. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV ($M_{1450}=-24.06$) than previously known $z\approx7.5$ quasars ( $\sim-$26.5), EUCL\,J125308.55+705432.3 exhibits the brightest [CII] emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate $>250\,M_{\odot}\,\mathrm{yr}^{-1}$, consistent with recent findings that UV-faint quasars at $z>6$ preferentially reside in [CII]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combining Euclid's wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible.

astro-ph.GA↗
arXiv2025

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) XXII. Chandra observations of narrow-line quasar candidates at z>6

We report on Chandra X-ray observations of four narrow-line quasar candidates at z~6, selected from the SHELLQs project, based on the Subaru Hyper Suprime-Cam survey. These objects are characterised by narrow (FWHM<310 km/s), luminous (>1e44 erg/s) Lya and faint UV continuum (M_1450 = -22 - -21), prompting us to examine whether they are obscured luminous AGN at the epoch of reionization. However, none of these objects were detected by Chandra, giving an upper limit to their rest-frame 2-10 keV luminosity (Lx) of 2e44 erg/s (2 sigma), assuming a spectral slope Gamma=2. Subsequent rest-frame optical spectroscopy of these objects by the JWST-NIRSpec, presented in a companion paper, show weak broad Balmer emission at the base of narrow cores. With the scaling relation for low-redshift AGN, the observed strong [OIII]5007 flux of these sources would predict Lx to be around 1e45 erg/s, which is well above the Chandra upper limits. These optical spectra and X-ray quietness are reminiscent of JWST-selected broad-line AGN. We attribute the weak broad Balmer emission to the broad-line regions hidden partially by optically-thick obscuring matter which also hides the optical and X-ray continuum emission from the accretion disc. Compton-thick obscuration, which would strongly suppress X-ray emission, could be due to a dense inter-stellar medium that is often present in galaxies at high redshifts. Alternatively, the same effect could be obtained from an inflated disc at the innermost radii in a supercritical accretion flow, when the disc is viewed at inclined angles.

astro-ph.GA↗
arXiv2025

Euclid: The potential of slitless infrared spectroscopy: A z=5.4 quasar and new ultracool dwarfs

We demonstrate the potential of Euclid's slitless spectroscopy to discover high-redshift (z>5) quasars and their main photometric contaminant, ultracool dwarfs. Sensitive infrared spectroscopy from space is able to efficiently identify both populations, as demonstrated by Euclid Near-Infrared Spectrometer and Photometer Red Grism (NISP RGE) spectra of the newly discovered z=5.404 quasar EUCL J181530.01+652054.0, as well as several ultracool dwarfs in the Euclid Deep Field North and the Euclid Early Release Observation field Abell 2764. The ultracool dwarfs were identified by cross-correlating their spectra with templates. The quasar was identified by its strong and broad CIII] and MgII emission lines in the NISP RGE 1206-1892 nm spectrum, and confirmed through optical spectroscopy from the Large Binocular Telescope. The NISP Blue Grism (NISP BGE) 926-1366 nm spectrum confirms CIV and CIII] emission. NISP RGE can find bright quasars at z~5.5 and z>7, redshift ranges that are challenging for photometric selection due to contamination from ultracool dwarfs. EUCL J181530.01+652054.0 is a high-excitation, broad absorption line quasar detected at 144 MHz by the LOw-Frequency Array (L144=4e25 W/Hz). The quasar has a bolometric luminosity of 3e12 Lsun and is powered by a 3.4e9 Msun black hole. The discovery of this bright quasar is noteworthy as fewer than one such object was expected in the ~20 deg2 surveyed. This finding highlights the potential and effectiveness of NISP spectroscopy in identifying rare, luminous high-redshift quasars, previewing the census of these sources that Euclid's slitless spectroscopy will deliver over about 14,000 deg2 of the sky.

astro-ph.GA↗
arXiv2024

Demonstration of logical qubits and repeated error correction with better-than-physical error rates

The promise of quantum computers hinges on the ability to scale to large system sizes, e.g., to run quantum computations consisting of more than 100 million operations fault-tolerantly. This in turn requires suppressing errors to levels inversely proportional to the size of the computation. As a step towards this ambitious goal, we present experiments on a trapped-ion QCCD processor where, through the use of fault-tolerant encoding and error correction, we are able to suppress logical error rates to levels below the physical error rates. In particular, we entangled logical qubits encoded in the [[7,1,3]] code with error rates 9.8 times to 500 times lower than at the physical level, and entangled logical qubits encoded in a [[12,2,4]] code based on Knill's C4/C6 scheme with error rates 4.7 times to 800 times lower than at the physical level, depending on the judicious use of post-selection. Moreover, we demonstrate repeated error correction with the [[12,2,4]] code, with logical error rates below physical circuit baselines corresponding to repeated CNOTs, and show evidence that the error rate per error correction cycle, which consists of over 100 physical CNOTs, approaches the error rate of two physical CNOTs. These results signify a transition from noisy intermediate scale quantum computing to reliable quantum computing, and demonstrate advanced capabilities toward large-scale fault-tolerant quantum computing.

quant-ph↗
arXiv2024

High-fidelity and Fault-tolerant Teleportation of a Logical Qubit using Transversal Gates and Lattice Surgery on a Trapped-ion Quantum Computer

Quantum state teleportation is commonly used in designs for large-scale fault-tolerant quantum computers. Using Quantinuum's H2 trapped-ion quantum processor, we implement the first demonstration of a fault-tolerant state teleportation circuit for a quantum error correction code - in particular, the planar topological [[7,1,3]] color code, or Steane code. The circuits use up to 30 trapped ions at the physical layer qubits and employ real-time quantum error correction - decoding mid-circuit measurement of syndromes and implementing corrections during the protocol. We conduct experiments on several variations of logical teleportation circuits using both transversal gates and lattice surgery protocols. Among the many measurements we report on, we measure the logical process fidelity of the transversal teleportation circuit to be 0.975(2) and the logical process fidelity of the lattice surgery teleportation circuit to be 0.851(9). Additionally, we run a teleportation circuit that is equivalent to Knill-style quantum error correction and measure the process fidelity to be 0.989(2).

quant-ph↗
arXiv2022

Analytical Study of Anomalous Diffusion by Randomly Modulated Dipole

This paper derives the Fokker-Planck (FP) equation for a particle moving in potential by a randomly modulated dipole. The FP equation describes the anomalous diffusion observed in the companion paper [1] and breaks the conservation of the total probability at the singularity by the dipole. It also shows anisotropic diffusion, which is typical in fluid turbulence. We need to modify the probability density by introducing a mechanism to recover the particle. After the modification, the latent fractal dimension matches with the results of the companion paper. We hope that our model gives a new example of fractional diffusion, where the random singularity triggers fractionality.

math-ph↗
arXiv2021

The eROSITA Final Equatorial-Depth Survey (eFEDS): The first archetypal Quasar in the feedback phase discovered by eROSITA

Theoretical models of galaxy-AGN co-evolution ascribe an important role for the feedback process to a short, luminous, obscured, and dust-enshrouded phase during which the accretion rate of the SMBH is expected to be at its maximum and the associated AGN-driven winds are also predicted to be maximally developed. To test this scenario, we have isolated a text-book candidate from the eROSITA Final Equatorial-Depth Survey (eFEDS) obtained within the Performance and Verification program of the eROSITA telescope on board Spectrum Roentgen Gamma. From an initial catalog of 246 hard X-ray selected sources matched with the photometric and spectroscopic information available within the eROSITA and Hyper Suprime-Cam consortia, three candidates Quasars in the feedback phase have been isolated applying the diagnostic proposed in Brusa et al. (2015). Only one source (eFEDSU J091157.5+014327) has a spectrum already available (from SDSS-DR16, z=0.603) and it unambiguously shows the presence of a broad component (FWHM~1650 km/s) in the [OIII]5007 line. The associated observed L_[OIII] is ~2.6x10^{42} erg/s, one to two orders of magnitude larger than that observed in local Seyferts and comparable to those observed in a sample of z~0.5 Type 1 Quasars. From the multiwavelength data available we derive an Eddington Ratio (L_bol/L_Edd) of ~0.25, and a bolometric correction in the hard X-ray of k_bol~10, lower than those observed for objects at similar bolometric luminosity. The presence of an outflow, the high X-ray luminosity and moderate X-ray obscuration (L_X~10^44.8 erg/s, N_H~2.7x10^22 cm^-2) and the red optical color, all match the prediction of quasars in the feedback phase from merger driven models. Forecasting to the full eROSITA all-sky survey with its spectroscopic follow-up, we predict that by the end of 2024 we will have a sample of few hundreds such objects at z=0.5-2.

astro-ph.HE↗
arXiv2018

Performance test of the MAIKo active target

A new active target named MAIKo (Mu-PIC based Active target for Inverse Kinematics$_{\circ}$) has been developed at Kyoto University and Research Center for Nuclear Physics (RCNP), Osaka University. MAIKo is suited for missing-mass spectroscopy of unstable nuclei at forward scattering angles in inverse kinematics. MAIKo consists of a time projection chamber (TPC), which incorporates a micro-pixel chamber ($μ$-PIC) as the electron multiplication and collection system. In MAIKo, the medium gas also plays the role of a reaction target, thus allowing detection of low-energy recoil particles with high position resolution. The MAIKo TPC was commissioned with He(93%)+iso-C$_{4}$H$_{10}$(7%) and He(93%)+CO$_{2}$(7%) mixture gasses at 430 hPa. The gas gain and the angular resolution of MAIKo were evaluated with an alpha source and a $^{4}$He beam at 56 MeV. The TPC was stably operated up to 1000-kcps beam intensity. A tracking algorithm using the Hough transform method has been developed to analyze scattering events. An angular resolution of 1.3$^{\circ}$ was achieved for scattered $^{4}$He particles.

physics.ins-det↗
arXiv2018

Zodiacal Light Beyond Earth Orbit Observed with Pioneer 10

We reanalyze the Imaging Photopolarimeter data from Pioneer 10 to study the zodiacal light in the B and R bands beyond Earth orbit, applying an improved method to subtract integrated star light (ISL) and diffuse Galactic light (DGL). We found that there exists a significant instrumental offset, making it difficult to examine the absolute sky brightness. Instead, we analyzed the differential brightness, i.e., the difference in sky brightness from the average at high ecliptic latitude, and compared with that expected from the model zodiacal light. At a heliocentric distance of r<2 au, we found a fairly good correlation between the J-band model zodiacal light and the residual sky brightness after subtracting the ISL and DGL. The reflectances of the interplanetary dust derived from the correlation study are marginally consistent with previous works. The zodiacal light is not significantly detectable at r>3 au, as previously reported. However, a clear discrepancy from the model is found at r=2.94 au which indicates the existence of a local dust cloud produced by the collision of asteroids or dust trail from active asteroids (or main-belt comets). Our result confirms that the main component of the zodiacal light (smooth cloud) is consistent with the model even beyond the earth orbit, which justifies the detection of the extragalactic background light after subtracting the zodiacal light based on the model.

astro-ph.EP↗
arXiv2018

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 < z < 6.9

We report discovery of 41 new high-z quasars and luminous galaxies, which were spectroscopically identified at 5.7 < z < 6.9. This is the fourth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates by a Bayesian probabilistic algorithm, and then carried out follow-up spectroscopy with the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous papers, we have now spectroscopically identified 137 extremely-red HSC sources over about 650 deg2, which include 64 high-z quasars, 24 high-z luminous galaxies, 6 [O III] emitters at z ~ 0.8, and 43 Galactic cool dwarfs (low-mass stars and brown dwarfs). The new quasars span the luminosity range from M1450 ~ -26 to -22 mag, and continue to populate a few magnitude lower luminosities than have been probed by previous wide-field surveys. In a companion paper, we derive the quasar luminosity function at z ~ 6 over an unprecedentedly wide range of M1450 ~ -28 to -21 mag, exploiting the SHELLQs and other survey outcomes.

astro-ph.GA↗
arXiv2018

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$^2$ in five broad bands ($grizy$), with a $5\,σ$ point-source depth of $r \approx 26$. The Deep layer covers a total of 26~deg$^2$ 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$^2$). 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.

astro-ph.IM↗
arXiv2017

Ultraviolet to optical diffuse sky emission as seen by the Hubble Space Telescope Faint Object Spectrograph

We present an analysis of the blank sky spectra observed with the Faint Object Spectrograph on board the Hubble Space Telescope. We study the diffuse sky emission from ultraviolet to optical wavelengths, which is composed of the zodiacal light (ZL), diffuse Galactic light (DGL), and residual emission. The observations were performed toward 54 fields distributed widely over the sky, with the spectral coverage from 0.2 to 0.7 um. In order to avoid contaminating light from the earthshine, we use the data collected only in orbital nighttime. The observed intensity is decomposed into the ZL, DGL, and residual emission, in eight photometric bands spanning our spectral coverage. We found that the derived ZL reflectance spectrum is flat in the optical, which indicates major contribution of C-type asteroids to the interplanetary dust (IPD). In addition, the ZL reflectance spectrum has an absorption feature at ~0.3 um. The shape of the DGL spectrum is consistent with those found in earlier measurements and model predictions. While the residual emission contains a contribution from the extragalactic background light, we found that the spectral shape of the residual looks similar to the ZL spectrum. Moreover, its optical intensity is much higher than that measured from beyond the IPD cloud by Pioneer10/11, and also than that of the integrated galaxy light. These findings may indicate the presence of an isotropic ZL component, which is missed in the conventional ZL models.

astro-ph.GA↗
arXiv2015

Measurements of Diffuse Sky Emission Components in High Galactic Latitudes at 3.5 and 4.9 um Using DIRBE and WISE Data

Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.

astro-ph.GA↗
arXiv2015

Thermal Conductivity in the Frustrated Two-Leg Spin-Ladder System BiCu2PO6

We have measured temperature and magnetic-field dependences of the thermal conductivity of single crystals of the frustrated two-leg spin-ladder system BiCu2PO6 in magnetic fields up to 14 T. It has been found that the temperature dependence of the thermal conductivity along every principal crystallographic axis shows two peaks in zero field but that the magnitude of the thermal conductivity along the b-axis parallel to spin ladders, $κ$b, is significantly larger than those of the thermal conductivity along the a-axis, $κ$a, and along the c-axis, $κ$c, at high temperatures above 7 K. These results suggest that the thermal conductivity due to spins probably exists only in $κ$b. Furthermore, it has been found that both magnetic-field dependences of $κ$a and $κ$b at 3 K show kinks at ~ 7 T and ~ 10 T, where the spin state may change.

cond-mat.str-el↗
arXiv2015

Thermal Conductivity of the S = 1/2 Quasi-One-Dimensional Ferromagnetic Spin System CsCuCl3

We have measured the thermal conductivity along the c-axis, \k{appa}||c, parallel to ferromagnetic spin-chains of single crystals of the S = 1/2 quasi-one-dimensional spin system CsCuCl3 in magnetic fields up to 14 T, in order to investigate the thermal conductivity due to spins, \k{appa}spin, and the change of thermal conductivity corresponding to the change of the spin state. In the temperature dependence of \k{appa}||c, no contribution of \k{appa}spin has been observed, while a dip has been observed at the antiferromagnetic phase transition temperature, TN. Furthermore, it has been found that \k{appa}||c at a low temperature of 5.1 K below TN changes with increasing field perpendicular to the c-axis in good correspondence to the field-induced change of the spin state.

cond-mat.str-el↗
arXiv2015

Thermal Conductivity in the Triangular-Lattice Antiferromagnet Ba3CoSb2O9

We have measured the thermal conductivity in the ab-plane, $κ$ab, and along the c-axis, $κ$c, of single crystals of the S = 1/2 triangular-lattice antiferromagnet Ba3CoSb2O9 in zero field and magnetic fields. In zero field, it has been found that both $κ$ab and $κ$c show a similar broad peak around 40 K, suggesting that the thermal conductivity due to phonons is dominant in this compound and that the mean free path of phonons is suppressed so much by strong magnetic-fluctuations due to the magnetic frustration. It has also been found that both $κ$ab and $κ$c show a kink at the antiferromagnetic transition temperature TN. In magnetic fields parallel to the ab-plane up to 14 T, magnetic-field dependences of both $κ$ab and $κ$c at temperatures below and above TN have been found to be understood taking into account the phonon-magnon scattering in the so-called 120$°$ structure phase and the up-up-down (UUD) phase, while the minima of $κ$ab and $κ$c observed in the middle of the UUD phase have not been understood. This suggests the occurrence of some change of the magnetic state in the middle of the UUD phase.

cond-mat.str-el↗