Kohei Ichikawa
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View article: UNIONS: The Ultraviolet Near-infrared Optical Northern Survey
UNIONS: The Ultraviolet Near-infrared Optical Northern Survey Open
The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a “collaboration of collaborations” that is using the Canada–France–Hawai’i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain ugriz images of a core…
View article: Discovery of an X-ray Luminous Radio-Loud Quasar at $z=3.4$: A Possible Transitional Super-Eddington Phase
Discovery of an X-ray Luminous Radio-Loud Quasar at $z=3.4$: A Possible Transitional Super-Eddington Phase Open
We report the multiwavelength properties of eFEDS J084222.9+001000 (hereafter ID830), a quasar at $z=3.4351$, identified as the most X-ray luminous radio-loud quasar in the eROSITA Final Equatorial Depth Survey (eFEDS) field. ID830 shows a…
View article: UNIONS Optical Identifications for VLASS Radio Sources in the Euclid Sky (UNVEIL). I. A Catalog of ∼146,000 Radio Galaxies up to <i>z</i> ∼ 5
UNIONS Optical Identifications for VLASS Radio Sources in the Euclid Sky (UNVEIL). I. A Catalog of ∼146,000 Radio Galaxies up to <i>z</i> ∼ 5 Open
We present the results of optical identifications for Very Large Array Sky Survey (VLASS) radio sources employing the Ultraviolet Near Infrared Optical Northern Survey (UNIONS). A crossmatch between UNIONS and VLASS Epoch 2 catalogs yields…
View article: A $z\simeq0.4$ Little Red Dot analog: An Extended Starburst with an Overmassive Black hole
A $z\simeq0.4$ Little Red Dot analog: An Extended Starburst with an Overmassive Black hole Open
One of the most remarkable discoveries of JWST is a population of compact, red sources at z > 4, commonly referred to as Little Red Dots (LRDs). Spectroscopic identifications reported that most LRDs are active galactic nuclei (AGNs), which…
View article: The X-ray statistical properties of dust-obscured galaxies detected by eROSITA
The X-ray statistical properties of dust-obscured galaxies detected by eROSITA Open
Context. The tight correlation between supermassive black hole (SMBH) and host galaxy masses suggests their coevolution. Dust-obscured galaxies (DOGs) are thought to represent this coevolution phase, with active galactic nuclei (AGNs) buri…
View article: VAR-PZ: Constraining the Photometric Redshifts of Quasars using Variability
VAR-PZ: Constraining the Photometric Redshifts of Quasars using Variability Open
The Vera C. Rubin Observatory LSST is expected to discover tens of millions of new Active Galactic Nuclei (AGNs). The survey's exceptional cadence and sensitivity will enable UV/optical/NIR monitoring of a significant fraction of these obj…
View article: BASS. XLIX. Characterization of Highly Luminous and Obscured AGNs: Local X-Ray and [Ne <scp>V</scp>]<i>λ</i>3426 Emission in Comparison with the High-redshift Universe
BASS. XLIX. Characterization of Highly Luminous and Obscured AGNs: Local X-Ray and [Ne <span>V</span>]<i>λ</i>3426 Emission in Comparison with the High-redshift Universe Open
We present a detailed analysis of the most luminous and obscured active galactic nuclei (AGNs) detected in the ultra-hard X-ray band (14–195 kev) by the Swift/Burst Alert Telescope. Our sample comprises 21 X-ray luminous ( …
View article: BASS. XLVIII. [Ne <scp>V</scp>] <i>λ</i>3427 Emission in Powerful Nearby Active Galactic Nuclei
BASS. XLVIII. [Ne <span>V</span>] <i>λ</i>3427 Emission in Powerful Nearby Active Galactic Nuclei Open
We investigate the high-ionization, narrow [Ne V ] λ 3427 line emission in a sample of over 340 ultrahard X-ray (14–195 keV) selected active galactic nuclei (AGN) drawn from the BAT AGN Spectroscopic Survey project. The analysis includes m…
View article: Dust-obscured Galaxies with Broken Power-law Spectral Energy Distributions Discovered by UNIONS
Dust-obscured Galaxies with Broken Power-law Spectral Energy Distributions Discovered by UNIONS Open
We report on the spectral energy distributions (SEDs) of infrared (IR)-bright dust-obscured galaxies (DOGs) with ( i − [22]) AB ≥ 7.0. Using photometry from the deep and wide Ultraviolet Near-Infrared Optical Northern Survey, combined with…
View article: Synthesis of 2‐Fluoroindoles Via the Base‐Free Nucleophilic 5‐ <i>Endo</i> ‐ <i>Trig</i> Cyclization of <i>o</i> ‐Amido‐β,β‐Difluoro‐α‐Silylstyrenes
Synthesis of 2‐Fluoroindoles Via the Base‐Free Nucleophilic 5‐ <i>Endo</i> ‐ <i>Trig</i> Cyclization of <i>o</i> ‐Amido‐β,β‐Difluoro‐α‐Silylstyrenes Open
Upon heating in the presence of molecular sieves 4A, β,β‐difluoro‐α‐silylstyrenes bearing an ortho ‐amido group readily underwent nucleophilic 5‐ endo ‐ trig cyclization, affording 2‐fluoro‐3‐silylindoles in high yields. The silicon‐ and f…
View article: J1406+0102: A Dust-obscured Galaxy Hiding a Super-Eddington Accretion System with Bright Radio Emission
J1406+0102: A Dust-obscured Galaxy Hiding a Super-Eddington Accretion System with Bright Radio Emission Open
Recent high- z quasar observations strongly indicate that super-Eddington accretion is a crucial phase to describe the presence of supermassive black holes (SMBHs) with M BH ≳ 10 9 M ⊙ at z ≳ 7. Motivated by theoretical predictions that th…
View article: Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows
Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows Open
The James Webb Space Telescope (JWST) observations have revolutionized extragalactic research, particularly with the discovery of little red dots (LRDs), which have been discovered as a population of dust-reddened broad-line active galacti…
View article: Implication of Galaxy-scale Negative Feedback by One of the Most Powerful Multiphase Outflows in a Hyperluminous Infrared Galaxy at Intermediate Redshift
Implication of Galaxy-scale Negative Feedback by One of the Most Powerful Multiphase Outflows in a Hyperluminous Infrared Galaxy at Intermediate Redshift Open
Powerful galactic outflows driven by active galactic nuclei (AGNs) are commonly considered as one of the main mechanisms to regulate star formation in massive galaxies. Ultra- and hyperluminous IR galaxies (U/HyLIRGs) are thought to repres…
View article: A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). X. The Massive and Passive Nature of Radio Galaxies at z ∼ 4
A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). X. The Massive and Passive Nature of Radio Galaxies at z ∼ 4 Open
High- z radio galaxies (HzRGs) are considered important objects for understanding the formation and evolution of massive galaxies in the early Universe. However, until to date, detailed studies of the stellar population of HzRGs, such as t…
View article: A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). X. The Massive and Passive Nature of Radio Galaxies at $z \sim 4$
A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). X. The Massive and Passive Nature of Radio Galaxies at $z \sim 4$ Open
High-$z$ radio galaxies (HzRGs) are considered important objects for understanding the formation and evolution of massive galaxies in the early universe. However, till date, detailed studies of the stellar population of HzRGs such as the s…
View article: BASS. XLI. The Correlation between Mid-infrared Emission Lines and Active Galactic Nuclei Emission
BASS. XLI. The Correlation between Mid-infrared Emission Lines and Active Galactic Nuclei Emission Open
We analyze Spitzer spectra of 140 active galactic nuclei (AGN) detected in the hard X-rays (14–195 keV) by the Burst Alert Telescope on board Swift. This sample allows us to probe several orders of magnitude in black hole masses (10 6 –10 …
View article: Implication of a galaxy-scale negative feedback by one of the most powerful multi-phase outflows in a hyper-luminous infrared galaxy at the intermediate redshift
Implication of a galaxy-scale negative feedback by one of the most powerful multi-phase outflows in a hyper-luminous infrared galaxy at the intermediate redshift Open
Powerful, galactic outflows driven by Active Galactic Nuclei (AGNs) are commonly considered as a main mechanism to regulate star formation in massive galaxies. Ultra- and hyper-luminous IR galaxies (U/HyLIRGs) are thought to represent a tr…
View article: Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe
Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe Open
The James Webb Space Telescope (JWST) has unveiled numerous massive black holes (BHs) in faint, broad-line active galactic nuclei (AGNs). The discovery highlights the presence of dust-reddened AGN populations, referred to as “little red do…
View article: BASS XLI: the correlation between Mid-infrared emission lines and Active Galactic Nuclei emission
BASS XLI: the correlation between Mid-infrared emission lines and Active Galactic Nuclei emission Open
We analyze the Spitzer spectra of 140 active galactic nuclei (AGN) detected in the hard X-rays (14-195 keV) by the Burst Alert Telescope (BAT) on board Swift. This sample allows us to probe several orders of magnitude in black hole masses …
View article: Ongoing and Fossil Large-scale Outflows Detected in a High-redshift Radio Galaxy: [C ii] Observations of TN J0924-2201 at z = 5.174
Ongoing and Fossil Large-scale Outflows Detected in a High-redshift Radio Galaxy: [C ii] Observations of TN J0924-2201 at z = 5.174 Open
We present Atacama Large Millimeter/submillimeter Array observations of the [C ii ] 158 μ m line and the underlying continuum emission of TN J0924−2201, which is one of the most distant known radio galaxies at z > 5. The [C ii ] line and 1…
View article: Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows
Little Red Dots: Rapidly Growing Black Holes Reddened by Extended Dusty Flows Open
The James Webb Space Telescope (JWST) observations have revolutionized extragalactic research, particularly with the discovery of little red dots (LRD), which we propose are dust-reddened broad-line active galactic nuclei (AGNs). Their uni…
View article: Ongoing and fossil large-scale outflows detected in a high-redshift radio galaxy: [C II] observations of TN J0924$-$2201 at $z=5.174$
Ongoing and fossil large-scale outflows detected in a high-redshift radio galaxy: [C II] observations of TN J0924$-$2201 at $z=5.174$ Open
We present Atacama Large Millimeter/submillimeter Array observations of the [C II] 158 $μ$m line and the underlying continuum emission of TN J0924$-$2201, which is one of the most distant known radio galaxies at $z>5$. The [C II] line and …
View article: Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys
Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys Open
The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4–11. Spectroscopic observations have provided estimates of the nuclear black hole (BH) masses for these sourc…
View article: [O iv]- and [Ne v]-weak Active Galactic Nuclei Hidden by Compton-thick Material in Late Mergers
[O iv]- and [Ne v]-weak Active Galactic Nuclei Hidden by Compton-thick Material in Late Mergers Open
We study “buried” active galactic nuclei (AGNs) almost fully covered by circumnuclear material in ultra/luminous infrared galaxies (U/LIRGs), which show weak ionized lines from narrow-line regions. Employing an indicator of a [O iv ] 25.89…
View article: Observational properties of active galactic nucleus obscuration during the peak of accretion growth
Observational properties of active galactic nucleus obscuration during the peak of accretion growth Open
We investigated the gas obscuration and host galaxy properties of active galactic nuclei (AGNs) during the peak of cosmic accretion growth of supermassive black holes at redshift 0.8–1.8 using X-ray-detected AGNs with mid-infrared and far-…
View article: Observational Properties of AGN Obscuration During the Peak of Accretion Growth
Observational Properties of AGN Obscuration During the Peak of Accretion Growth Open
We investigated the gas obscuration and host galaxy properties of active galactic nuclei (AGN) during the peak of cosmic accretion growth of supermassive black holes (SMBHs) at redshift 0.8-1.8 using X-ray detected AGN with mid-infrared an…
View article: Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe
Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe Open
The James Webb Space Telescope (JWST) has unveiled numerous massive black holes (BHs) in faint, broad-line active galactic nuclei (AGNs). The discovery highlights the presence of dust-reddened AGN populations, referred to as "little red do…
View article: [O IV] and [Ne V]-weak AGNs Hidden by Compton-thick Material in Late Mergers
[O IV] and [Ne V]-weak AGNs Hidden by Compton-thick Material in Late Mergers Open
We study "buried" active galactic nuclei (AGNs) almost fully covered by circumnuclear material in ultra-/luminous infrared galaxies (U/LIRGs), which show weak ionized lines from narrow line regions. Employing an indicator of [O IV] 25.89-u…
View article: Deconvolution of JWST/MIRI Images: Applications to an Active Galactic Nucleus Model and GATOS Observations of NGC 5728
Deconvolution of JWST/MIRI Images: Applications to an Active Galactic Nucleus Model and GATOS Observations of NGC 5728 Open
The superb image quality, stability, and sensitivity of JWST permit deconvolution techniques to be pursued with a fidelity unavailable to ground-based observations. We present an assessment of several deconvolution approaches to improve im…
View article: Black Hole Mass and Eddington-ratio Distributions of Less-luminous Quasars at z ∼ 4 in the Subaru Hyper Suprime-Cam Wide Field
Black Hole Mass and Eddington-ratio Distributions of Less-luminous Quasars at z ∼ 4 in the Subaru Hyper Suprime-Cam Wide Field Open
We investigate the black hole mass function (BHMF) and Eddington-ratio distribution function (ERDF) of broad-line active galactic nuclei (AGNs) at z = 4, based on a sample of 52 quasars with i < 23.2 at 3.50 ≤ z ≤ 4.25 from the Hyper Supri…