arXiv subjects

K. Ito

Publications and source records attributed to K. Ito.

At least 19 recordsLinked to original sources

arXiv2026

Extended [CII] gas emission in and around a massive quiescent galaxy at z=7.3

We report the discovery of [CII] 158 micron emission in and around the most distant known massive quiescent galaxy RUBIES-UDS-QG-z7 at z = 7.27. Observed with ALMA in band 6, the [CII] line independently confirms the spectroscopic redshift from JWST/NIRSpec spectra at low and medium resolution. The emission extends over an effective radius R_eff,[CII] = 8 +/- 3 kpc, well beyond the compact stellar body traced by JWST/NIRCam (R_eff = 209 (+33/-24) pc), with a significant fraction of approximately 70% of the flux arising from a circumgalactic halo. No dust continuum is detected at rest-frame ~160 micron, setting an upper limit on the infrared luminosity of L_IR < 1.4 x 10^11 Lsun, overall consistent with expectations from rest-frame UV to near-infrared SED modeling under energy balance. Converting the galaxy-scale [CII] emission into cold gas mass, we find log(M_mol/Msun) = 9.53 (+0.32/-0.31) and log(M_HI/Msun) = 9.46-10.34, depending on the assumed calibration and metallicity. Despite being approximately 10x more gas-poor than typical star-forming galaxies at fixed redshift, stellar mass, and [CII] to gas mass conversion, RUBIES-UDS-QG-z7 retains a substantial cold gas reservoir with fractions f_gas >~ 20% and long depletion timescales across most assumptions. The extended [CII] halo carries approximately twice as much gas as the galaxy alone and shows a blueshifted velocity offset consistent with the tentative gas outflow detected in MgII absorption in previous work, suggesting a past episode of AGN-driven gas expulsion possibly linked to the suppression of star formation. The presence of a large gas reservoir in and around a massive quiescent galaxy just 700 Myr after the Big Bang implies that whatever mechanism is suppressing star formation must be remarkably effective at maintaining a low star formation efficiency on ~100 Myr timescales, even in the presence of abundant fuel.

astro-ph.GA↗

arXiv2026

Morphology, sizes, and scatter in a large sample of distant quiescent galaxies

After quenching galaxies keep growing in size across time, as established in the literature up to cosmic noon. In this work, we assemble one of the largest and most comprehensive multi-wavelength photometric sample of massive quenched galaxies at z>3, counting 137 quiescent candidates within 825 sq. arcmin and redshift 3 3, albeit with a large scatter. This suggests that the commonly used parameters of a Sersic distribution cannot explain the large intrinsic scatter around the stellar mass-size relation, suggesting that other physical quantities need to be taken into account to break the degeneracy between evolution paths across the galaxy population.

astro-ph.GA↗

arXiv2026

High-ionization coronal lines trace quasar-like activity in recently quenched galaxies at high redshift

We report the detection of the high-ionization line [NeV]$\lambda$3427 in the JWST/NIRSpec archival spectra of 6 massive quenched galaxies at $z \sim 1.5-4.5$, identified from a parent sample of 87 systems. With an ionization potential of approximately 97 eV, [NeV] can only be produced by strong nuclear activity in these massive systems, providing a clean and unambiguous tracer of highly accreting supermassive black holes uncontaminated by residual star formation. For 4 of the 6 [NeV]-detected systems, we detect broad H$\alpha$ emission ($\mathrm{FWHM} \gtrsim 4000$ km s$^{-1}$), yielding black hole masses of $M_{\rm BH} = 10^{8.5-9.5}\,M_\odot$, consistent with local scaling relations with stellar mass and velocity dispersion. The [NeV] luminosities imply quasar-like bolometric outputs ($L_{\rm bol} = 10^{45-46}$ erg s$^{-1}$) and Eddington ratios of $\lambda_{\rm Edd} \approx 10$-$50$%, with black hole accretion rates of a few $M_\odot$ yr$^{-1}$ that match or exceed the residual star formation rates in the most extreme cases. The strongest [NeV] emitters are preferentially found in the youngest post-starburst systems ($D_n4000 \lesssim 1.3$), while old quenched galaxies are systematically devoid of such activity, a trend independently reproduced by theoretical models. These results reveal that intense, radiatively efficient SMBH growth can persist several hundred Myr after the main quenching epoch, with duty cycles of approximately 100-200 Myr. They also underscore the importance of very high accretion episodes and rates in the theoretical models that seek to reproduce the earliest quenched galaxies in the universe.

astro-ph.GA↗

arXiv2026

Dynamical properties and star formation history of a low-mass quenched galaxy at Cosmic Noon

We present the spectroscopic confirmation and in-depth analysis of AURORA-LQG1, a low-mass quiescent galaxy at $z_{\rm spec}=2.0834$ with $\log(M_\star/M_\odot)=9.6$ observed with medium-resolution JWST/NIRSpec spectroscopy. The deep medium-resolution spectrum enables the measurement of its stellar velocity dispersion ($\sigma_\star = 95_{-33}^{+38}\,{\rm km\,s^{-1}}$), the smallest value recorded among spectroscopically confirmed quiescent galaxies at $z\sim2$. Coupled with a compact size ($0.41\pm0.03\, {\rm kpc}$), it yields a dynamical mass estimate of $\log(M_{\rm dyn}/M_\odot)=9.75_{-0.38}^{+0.29}$. Its star formation history suggests that half of the stellar mass was in place $\sim1\,{\rm Gyr}$ before the observed epoch, with quenching occurring $\sim0.2\,{\rm Gyr}$ prior to $z=2.08$. These results confirm that AURORA-LQG1 is genuinely quenched, rather than in a temporary phase of suppressed star formation rate. AURORA-LQG1 is consistent with the mass fundamental plane at $z\sim2$, previously constrained only by massive quiescent systems. Compared with more massive counterparts at the same epoch observed with NIRSpec grating spectroscopy, the time since quenching for AURORA-LQG1 is among the shortest observed. The galaxy resides in a possible dense group-scale ($\sim50$ kpc) environment containing one companion with tentative spectroscopic redshift and five companion candidates, and it is embedded in a known protocluster on Mpc scales. A potential environmental influence on its evolution could explain the outside-in quenching suggested by the positive gradient of size with wavelength. This study demonstrates that deep JWST/NIRSpec spectroscopy enables low-mass quiescent galaxies at Cosmic Noon to be characterized with a level of detail long reserved for massive systems, offering valuable new insights into how quenching operates in these underexplored low-mass systems. [Abridged]

astro-ph.GA↗

arXiv2025

Spontaneous Lattice Distortion in the Spin-Triplet Superconductor Cu$_{x}$Bi$_2$Se$_3$

The doped topological insulator Cu$_x$Bi$_2$Se$_3$ has attracted considerable attention as a new platform for studying novel properties of spin-triplet and topological superconductivity. In this work, we performed synchrotron x-ray diffraction measurements on Cu$_x$Bi$_2$Se$_3$ (0.24$\leq x\leq$ 0.46) to investigate the coupling between the superconducting order parameter and crystal lattice. In the crystals in which the vector order parameter (${\boldsymbol d}$ vector) is tilted from the crystal high-symmetry directions as evidenced by nematic diamagnetic susceptibility, we find a sizable lattice distortion ($\sim$100 ppm) associated with the onset of superconductivity. In contrast, in crystals with the ${\boldsymbol d}$ vector aligned along the high-symmetry directions, we find no appreciable change in lattice constant. Together with a pronounced vestigial behavior of the distortion, the results are clear evidence for an odd-parity $E_u$ order parameter that couples with trigonal lattice. Furthermore, in the crystal with $x$ = 0.46 where diamagnetic susceptibility is isotropic in the plane, no lattice distortion accompanying the superconducting transition is found, which is in line with a chiral superconducting state in the highly doped region. Our work shows that lattice distortion can be a powerful diagnosing quantity for nematic superconductivity with two-component order parameter.

cond-mat.supr-con↗

arXiv2025

DeepDive: A deep dive into the physics of the first massive quiescent galaxies in the Universe

We present the DeepDive program, in which we obtained deep JWST/NIRSpec G235M/F170LP spectra for ten primary massive ($\log{(M_\star/M_\odot)}=10.8-11.5$) quiescent galaxies at $z\sim3-4$. A novel reduction procedure was used to extend the nominal wavelength coverage of G235M beyond H$\alpha$ and [NII] at $z\sim 4$, revealing weak, narrow H$\alpha$ lines indicative of low star formation rates. Two out of ten primary targets have broad H$\alpha$ lines, indicating the presence of active galactic nuclei. We also conducted an archival search of quiescent galaxies observed with NIRSpec gratings in the DAWN JWST Archive, providing a statistical context for interpreting the DeepDive targets. This archival search provided a spectroscopic sample of 126 quiescent galaxies spanning $1<z<5$, selected by high Dn4000, UVJ color, or low specific star formation rate, and covering more than an order of magnitude in stellar mass. This sample allowed us to revisit the sample from the different selections, finding $\sim90\%$ overlap between these criteria. The total sample of 136 quiescent galaxies from this study shows that those at $z\sim3-5$, including the DeepDive targets, typically exhibit weaker breaks and bluer colors than their lower-redshift counterparts, indicating generally younger stellar populations. Stacked spectra of sources grouped by the Dn4000 index reveal faint iron and magnesium absorption line features in the stellar continuum even for the low Dn4000 subsample at high redshift ($z\sim3$). In addition, higher Dn4000 subsamples show fainter nebular emission lines. These results demonstrate that medium-resolution NIRSpec spectroscopy is essential for robustly characterizing the diversity and evolution of early quiescent galaxies. The large sample constructed in this paper will allow a statistical census of the properties of quiescent galaxies at high redshift to be obtained.

astro-ph.GA↗

arXiv2025

A merging pair of massive quiescent galaxies at $z=3.44$ in the Cosmic Vine

We report the spectroscopic confirmation of a merging pair of massive quiescent galaxies at $z=3.44$. Using JWST observations, we confirm that the two galaxies lie at a projected separation of 4.5 kpc with a velocity offset of $\sim 680\, {\rm km\, s^{-1}}\ (\delta_z \sim 0.01)$. The pair resides in the core of a known rich overdensity of galaxies, dubbed the "Cosmic Vine". For both pair members, modeling of the Spectral Energy Distributions and faint rest-frame optical emission lines indicate high stellar masses ($\log{(M_\star/M_\odot)}\sim10.9$) and suppressed star formation ($\log{\rm (sSFR/yr^{-1})}<-10$), more than an order of magnitude below the level of the star formation main sequence at this redshift. We then explore the Illustris-TNG simulation and the GAEA and SHARK semi-analytical models to examine whether they produce a pair of massive quiescent galaxies akin to that of the Cosmic Vine. While all models produce close pairs of massive quiescent galaxies at $2 90\%$ of simulated pairs in the models that we analyzed merge by $z=0$, our findings suggest that our observed pair will likely coalesce into a single massive galaxy. The merger, occurring in the dense core of a large-scale structure, might represent a critical event in the formation of a brightest cluster galaxy and the morphological transformation of high-redshift disky quiescent galaxies into early-type ellipticals.

astro-ph.GA↗

arXiv2025

Gas outflows in two recently quenched galaxies at z = 4 and 7

Outflows are a key element in the baryon cycle of galaxies, and their properties provide a fundamental test for our models of how star formation quenches in galaxies. Here we report the detection of outflowing gas in two recently quenched, massive ($M_\star\sim10^{10.2}M_\odot$) galaxies at z=4.106 (NS_274) and z=7.276 (RUBIES-UDS-QG-z7) observed with JWST/NIRSpec. The outflows are traced by blue-shifted MgII absorption lines, and in the case of the z=4.1 system, also by FeII and NaI features. The spectra of the two sources are similar to those of local post-starburst galaxies, showing deep Balmer features and minimal star formation on 10 Myr timescales as traced by the lack of bright emission lines, also suggesting the absence of a strong and radiatively efficient AGN. The galaxies' SFHs are consistent with an abrupt quenching of star formation, which continued at rates of $\sim15\,M_\odot$/yr averaged over 100 Myr timescales. Dedicated millimeter observations of NS_274 constrain its dust obscured SFR to $<12\,M_\odot$/yr. Under simple geometrical assumptions, we derive mass loading factors $\lesssim1$ and $>10$ for the z=4.1 and z=7.3 systems, respectively, and similarly different energies carried by the outflows. Supernova feedback can account for the mass and energy of the outflow in NS_274. However, the low mass loading factor and average gas velocity suggest that the observed outflow is likely not the primary factor behind its quenching. SF-related processes seem to be insufficient to explain the extreme mass outflow rate of RUBIES-UDS-QG-z7, which would require an additional ejective mechanism such as an undetected AGN. Finally, the average outflow velocities per unit $M_\star$, SFR, or its surface area are consistent with those of lower-redshift post-starburst galaxies, suggesting that outflows in rapidly quenched galaxies might occur similarly across cosmic time. [Abridged]

astro-ph.GA↗

arXiv2024

Scattering theory for $C^2$ long-range potentials

We develop a complete stationary scattering theory for Schr\"odinger operators on $\mathbb R^d$, $d\ge 2$, with $C^2$ long-range potentials. This extends former results in the literature, in particular [Is1, Is2, II, GY], which all require a higher degree of smoothness. In this sense the spirit of our paper is similar to [H\"o2, Chapter XXX], which also develops a scattering theory under the $C^2$ condition, however being very different from ours. While the Agmon-H\"ormander theory is based on the Fourier transform, our theory is not and may be seen as more related to our previous approach to scattering theory on manifolds [IS1,IS2,IS3]. The $C^2$ regularity is natural in the Agmon-H\"ormander theory as well as in our theory, in fact probably being `optimal' in the Euclidean setting. We prove equivalence of the stationary and time-dependent theories by giving stationary representations of associated time-dependent wave operators. Furthermore we develop a related stationary scattering theory at fixed energy in terms of asymptotics of generalized eigenfunctions of minimal growth. A basic ingredient of our approach is a solution to the eikonal equation constructed from the geometric variational scheme of [CS]. Another key ingredient is strong radiation condition bounds for the limiting resolvents originating in [HS]. They improve formerly known ones [Is1, Sa] and considerably simplify the stationary approach. We obtain the bounds by a new commutator scheme whose elementary form allows a small degree of smoothness.

math-ph↗

arXiv2024

Euclid: ERO -- NISP-only sources and the search for luminous $z=6-8$ galaxies

This paper presents a search for high redshift galaxies from the Euclid Early Release Observations program "Magnifying Lens." The 1.5 deg$^2$ area covered by the twin Abell lensing cluster fields is comparable in size to the few other deep near-infrared surveys such as COSMOS, and so provides an opportunity to significantly increase known samples of rare UV-bright galaxies at $z\approx6-8$ ($M_{\rm UV}\lesssim-22$). Beyond their still uncertain role in reionisation, these UV-bright galaxies are ideal laboratories from which to study galaxy formation and constrain the bright-end of the UV luminosity function. Of the 501994 sources detected from a combined $Y_{\rm E}$, $J_{\rm E}$, and $H_{\rm E}$ NISP detection image, 168 do not have any appreciable VIS/$I_{\rm E}$ flux. These objects span a range in spectral colours, separated into two classes: 139 extremely red sources; and 29 Lyman-break galaxy candidates. Best-fit redshifts and spectral templates suggest the former is composed of both $z\gtrsim5$ dusty star-forming galaxies and $z\approx1-3$ quiescent systems. The latter is composed of more homogeneous Lyman break galaxies at $z\approx6-8$. In both cases, contamination by L- and T-type dwarfs cannot be ruled out with Euclid images alone. Additional contamination from instrumental persistence is investigated using a novel time series analysis. This work lays the foundation for future searches within the Euclid Deep Fields, where thousands more $z\gtrsim6$ Lyman break systems and extremely red sources will be identified.

astro-ph.GA↗

arXiv2023

Laser cooling of positronium

When laser radiation is skilfully applied, atoms and molecules can be cooled allowing precise measurements and control of quantum systems. This is essential in fundamental studies of physics as well as practical applications such as precision spectroscopy, quantum-statistical-property manifesting ultracold gases, and quantum computing. In laser cooling, repeated cycles of laser photon absorption and direction-independent spontaneous emission can slow atoms and molecules to otherwise unattainable velocities. Simple systems can provide a rigorous testing ground for fundamental theories of physics; one such system is the purely leptonic positronium, an exotic atom of an electron and its antiparticle, the positron. However, the cooling of positronium has hitherto remained unrealised. Here, we demonstrate laser cooling of positronium. A novel laser system of a train of broadband pulses with successively increasing central frequencies was used to overcome major challenges presented by the short lifetime of positronium and the significant Doppler broadening and recoil as a consequence of its very light mass. One-dimensional chirp cooling of the dilute positronium gas in a counter-propagating configuration gave a final velocity distribution corresponding to approximately 1 K in a short time of 100 ns. This study on a pure leptonic system is a major step in the field of low-temperature fundamental physics of antimatter, and is complementary to the laser cooling of antihydrogen, a hadron-containing exotic atom. Progress in this field is vital in elucidating the origin of the matter-antimatter asymmetry in the universe. The application of laser cooling to positronium may afford a unique opportunity to rigorously test bound-state quantum electrodynamics. Moreover, laser cooling of positronium is key to the realisation of Bose-Einstein condensation in this matter-antimatter system.

physics.atom-ph↗

arXiv2023

Development of advanced photon calibrator for Kamioka gravitational wave detector (KAGRA)

The Kamioka Gravitational wave detector (KAGRA) cryogenic gravitational-wave observatory has commenced joint observations with the worldwide gravitational wave detector network. Precise calibration of the detector response is essential for accurately estimating parameters of gravitational wave sources. A photon calibrator is a crucial calibration tool used in laser interferometer gravitational-wave observatory, Virgo, and KAGRA, and it was utilized in joint observation 3 with GEO600 in Germany in April 2020. In this paper, KAGRA implemented three key enhancements: a high-power laser, a power stabilization system, and remote beam position control. KAGRA employs a 20 W laser divided into two beams that are injected onto the mirror surface. By utilizing a high-power laser, the response of the detector at kHz frequencies can be calibrated. To independently control the power of each laser beam, an optical follower servo was installed for power stabilization. The optical path of the photon calibrator beam positions was controlled using pico-motors, allowing for the characterization of the detector rotation response. Additionally, a telephoto camera and quadrant photodetectors were installed to monitor beam positions, and beam position control was implemented to optimize the mirror response. In this paper, we discuss the statistical errors associated with the measurement of relative power noise. We also address systematic errors related to the power calibration model of the photon calibrator and the simulation of elastic deformation effects using finite element analysis. Ultimately, we have successfully reduced the total systematic error from the photon calibrator to 2.0 /%.

astro-ph.IM↗

arXiv2022

Input optics systems of the KAGRA detector during O3GK

KAGRA, the underground and cryogenic gravitational-wave detector, was operated for its solo observation from February 25th to March 10th, 2020, and its first joint observation with the GEO 600 detector from April 7th -- 21st, 2020 (O3GK). This study presents an overview of the input optics systems of the KAGRA detector, which consist of various optical systems, such as a laser source, its intensity and frequency stabilization systems, modulators, a Faraday isolator, mode-matching telescopes, and a high-power beam dump. These optics were successfully delivered to the KAGRA interferometer and operated stably during the observations. The laser frequency noise was observed to limit the detector sensitivity above a few kHz, whereas the laser intensity did not significantly limit the detector sensitivity.

gr-qc↗

arXiv2022

Noise subtraction from KAGRA O3GK data using Independent Component Analysis

In April 2020, KAGRA conducted its first science observation in combination with the GEO~600 detector (O3GK) for two weeks. According to the noise budget estimation, suspension control noise in the low frequency band and acoustic noise in the middle frequency band are identified as the dominant contribution. In this study, we show that such noise can be reduced in offline data analysis by utilizing a method called Independent Component Analysis (ICA). Here the ICA model is extended from the one studied in iKAGRA data analysis by incorporating frequency dependence while linearity and stationarity of the couplings are still assumed. By using optimal witness sensors, those two dominant contributions are mitigated in the real observational data. We also analyze the stability of the transfer functions for whole two weeks data in order to investigate how the current subtraction method can be practically used in gravitational wave search.

astro-ph.IM↗

arXiv2022

Strong radiation condition bounds

We construct solutions to the eikonal equation for a class of long-range potentials, derive strong radiation condition bounds for the corresponding Schr\"odinger operator and apply them to construct the generalized Fourier transform, diagonalizing the continuous part the operator.

math-ph↗

arXiv2022

Performance of the KAGRA detector during the first joint observation with GEO 600 (O3GK)

KAGRA, the kilometer-scale underground gravitational-wave detector, is located at Kamioka, Japan. In April 2020, an astrophysics observation was performed at the KAGRA detector in combination with the GEO 600 detector; this observation operation is called O3GK. The optical configuration in O3GK is based on a power recycled Fabry-P\'{e}rot Michelson interferometer; all the mirrors were set at room temperature. The duty factor of the operation was approximately 53%, and the strain sensitivity was $3\times10^{-22}~/\sqrt{\rm{Hz}}$ at 250 Hz. In addition, the binary-neutron-star (BNS) inspiral range was approximately 0.6 Mpc. The contributions of various noise sources to the sensitivity of O3GK were investigated to understand how the observation range could be improved; this study is called a "noise budget". According to our noise budget, the measured sensitivity could be approximated by adding up the effect of each noise. The sensitivity was dominated by noise from the sensors used for local controls of the vibration isolation systems, acoustic noise, shot noise, and laser frequency noise. Further, other noise sources that did not limit the sensitivity were investigated. This paper provides a detailed account of the KAGRA detector in O3GK including interferometer configuration, status, and noise budget. In addition, strategies for future sensitivity improvements such as hardware upgrades, are discussed.

astro-ph.IM↗

arXiv2021

Stationary scattering theory for one-body Stark operators, I

We study the stationary scattering theory for a perturbed 1-body Stark operator. We prove existence and completeness of the stationary wave operators, construct the associated generalized Fourier transforms, and characterize asymptotics of the generalized eigenfunctions of minimal growths in terms of the stationary scattering matrix.

math-ph↗

arXiv2021

Overview of KAGRA: Calibration, detector characterization, physical environmental monitors, and the geophysics interferometer

KAGRA is a newly built gravitational wave observatory, a laser interferometer with a 3 km arm length, located in Kamioka, Gifu, Japan. In this series of articles, we present an overview of the baseline KAGRA, for which we finished installing the designed configuration in 2019. This article describes the method of calibration (CAL) used for reconstructing gravitational wave signals from the detector outputs, as well as the characterization of the detector (DET). We also review the physical environmental monitors (PEM) system and the geophysics interferometer (GIF). Both are used for characterizing and evaluating the data quality of the gravitational wave channel. They play important roles in utilizing the detector output for gravitational wave searches. These characterization investigations will be even more important in the near future, once gravitational wave detection has been achieved, and in using KAGRA in the gravitational wave astronomy era.

gr-qc↗