Kimihiko Nakajima
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View article: Fe Abundances of Early Galaxies at <i>z</i> = 9–12 Derived with Deep JWST Spectra
Fe Abundances of Early Galaxies at <i>z</i> = 9–12 Derived with Deep JWST Spectra Open
We derive Fe abundance ratios of seven galaxies at z = 9–12 with −22 < M UV < −19 whose JWST/NIRSpec spectra achieve very high signal-to-noise ratios, S/N = 60–320, at rest-frame UV wavelength. We fit stellar population synthesis model spe…
View article: JWST and ALMA Joint Analysis with [O <scp>II</scp> ] <i>λλ</i> 3726, 3729, [O <scp>III</scp> ] <i>λ</i> 4363, [O <scp>III</scp> ] 88 <i>μ</i> m, and [O <scp>III</scp> ] 52 <i>μ</i> m: Multizone Evolution of Electron Densities at <i>z</i> ∼ 0–14 and its Impact on Metallicity Measurements
JWST and ALMA Joint Analysis with [O <span>II</span> ] <i>λλ</i> 3726, 3729, [O <span>III</span> ] <i>λ</i> 4363, [O <span>III</span> ] 88 <i>μ</i> m, and [O <span>III</span> ] 52 <i>μ</i> m: Multizone Evolution of Electron Densities at <i>z</i> ∼ 0–14 and its Impact on Metallicity Measurements Open
We present a JWST and Atacama Large Millimeter/submillimeter Array (ALMA) detailed study of the interstellar medium properties of high-redshift galaxies. Our JWST/NIRSpec integral field unit spectroscopy targeting three galaxies at z = 6–7…
View article: New methods of identifying AGN in the early Universe using spectroscopy and photometry in the <i>JWST</i> era
New methods of identifying AGN in the early Universe using spectroscopy and photometry in the <i>JWST</i> era Open
We explore spectroscopic and photometric methods for identifying high-redshift galaxies containing an active galactic nucleus (AGN) with James Webb Space Telescope (JWST) observations. After demonstrating the limitations of standard optica…
View article: Morphological Demographics of Galaxies at <i>z</i> ∼ 10–16: Log-normal Size Distribution and Exponential Profiles Consistent with the Disk Formation Scenario
Morphological Demographics of Galaxies at <i>z</i> ∼ 10–16: Log-normal Size Distribution and Exponential Profiles Consistent with the Disk Formation Scenario Open
We homogeneously investigate the morphological properties of 169 galaxies at z ∼ 10–16 with deep JWST NIRCam images employing our established techniques of GALFIT modeling and uncertainty evaluation (systematics+statistics). We obtain effe…
View article: A Galaxy with an Extremely Blue Ultraviolet Slope <i>β</i> = −3 at <i>z</i> = 9.25 Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape?
A Galaxy with an Extremely Blue Ultraviolet Slope <i>β</i> = −3 at <i>z</i> = 9.25 Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape? Open
We investigate UV continuum slopes β of 863 galaxies at 4 < z < 14 using archival JWST/NIRSpec PRISM spectra obtained from major JWST Guaranteed Time Observations (GTO), Early Release Science (ERS), and General Observers (GO) programs, inc…
View article: EMPRESS. XV. A New Determination of the Primordial Helium Abundance Suggesting a Moderately Low $Y_\mathrm{P}$ Value
EMPRESS. XV. A New Determination of the Primordial Helium Abundance Suggesting a Moderately Low $Y_\mathrm{P}$ Value Open
We present a new constraint on the primordial helium abundance, $Y_\mathrm{P}$, based on Subaru observations. A major source of uncertainty in previous $Y_\mathrm{P}$ determinations is the lack of extremely metal-poor galaxies (EMPGs; $0.0…
View article: An Ultra-Faint, Chemically Primitive Galaxy Forming at the Epoch of Reionization
An Ultra-Faint, Chemically Primitive Galaxy Forming at the Epoch of Reionization Open
The formation of the first stars and galaxies marked the onset of cosmic structure and chemical enrichment, yet direct observations of such primordial systems remain elusive. Here we present James Webb Space Telescope spectroscopic observa…
View article: A black hole in a near-pristine galaxy 700 million years after the Big Bang
A black hole in a near-pristine galaxy 700 million years after the Big Bang Open
The recent discovery of a large number of massive black holes within the first two billion years after the Big Bang, as well as their peculiar properties, have been largely unexpected based on the extrapolation of the properties of luminou…
View article: Census of Ly<i>α</i> Emission from ∼600 Galaxies at <i>z</i> = 5–14: Evolution of the Ly<i>α</i> Luminosity Function and a Late Sharp Cosmic Reionization
Census of Ly<i>α</i> Emission from ∼600 Galaxies at <i>z</i> = 5–14: Evolution of the Ly<i>α</i> Luminosity Function and a Late Sharp Cosmic Reionization Open
We present the statistical properties of Ly α emission in 586 galaxies at z = 4.5–14.2, observed by multiple JWST/NIRSpec spectroscopy projects, including the JADES, GLASS, CEERS, and GO/DDT programs. We obtain Ly α equivalent width (EW), …
View article: JWST & ALMA Joint Analysis with [OII]$λλ$3726,3729, [OIII]$λ$4363, [OIII]88$μ$m, and [OIII]52$μ$m: Multi-Zone Evolution of Electron Densities at $\mathbf{z\sim0-14}$ and Its Impact on Metallicity Measurements
JWST & ALMA Joint Analysis with [OII]$λλ$3726,3729, [OIII]$λ$4363, [OIII]88$μ$m, and [OIII]52$μ$m: Multi-Zone Evolution of Electron Densities at $\mathbf{z\sim0-14}$ and Its Impact on Metallicity Measurements Open
We present a JWST and ALMA detailed study of the ISM properties of high-redshift galaxies. Our JWST/NIRSpec IFU spectroscopy targeting three galaxies at $z=6-7$ detects key rest-frame optical emission lines, allowing us to derive [OII]$λλ$…
View article: Stellar- and AGN-driven Outflows in JWST Galaxies at <i>z</i> = 3–9: More Frequent, Wider Opening Angles, and Mostly Bounded
Stellar- and AGN-driven Outflows in JWST Galaxies at <i>z</i> = 3–9: More Frequent, Wider Opening Angles, and Mostly Bounded Open
We study outflows in 130 galaxies with −22 < M UV < −16 at z = 3–9 identified in JWST NIRSpec and NIRCam WFSS data taken by the ERO, CEERS, FRESCO, GLASS, and JADES programs. We identify 30 out of the 130 galaxies with broad components of …
View article: ChemicalUniverseMachine. I. Uncovering the Cosmic Evolution of Metals in the Galaxy–Interstellar Medium–Circumgalactic Medium Ecosystem
ChemicalUniverseMachine. I. Uncovering the Cosmic Evolution of Metals in the Galaxy–Interstellar Medium–Circumgalactic Medium Ecosystem Open
We present an empirical chemical evolution model that explains the distribution of metals in the interstellar medium (ISM) and the circumgalactic medium (CGM) of galaxies based on the U niverse M achine and N eutral U niverse M achine mode…
View article: Probing the Cosmic Reionization History with JWST: Gunn-Peterson and Ly$α$ Damping Wing Absorption at $4.5 < z < 13$
Probing the Cosmic Reionization History with JWST: Gunn-Peterson and Ly$α$ Damping Wing Absorption at $4.5 < z < 13$ Open
We present a statistical analysis of Ly$α$ absorption using 581 galaxies at $z=4.5$--13 observed with multiple JWST/NIRSpec spectroscopy programs, including JADES, UNCOVER, CEERS, and GO/DDT. We carefully construct composite spectra binned…
View article: Comprehensive JWST+ALMA Study on the Extended Ly$α$ Emitters, Himiko and CR7 at $z\sim 7$: Blue Major Merger Systems in Stark Contrast to Submillimeter Galaxies
Comprehensive JWST+ALMA Study on the Extended Ly$α$ Emitters, Himiko and CR7 at $z\sim 7$: Blue Major Merger Systems in Stark Contrast to Submillimeter Galaxies Open
We present various properties of two bright extended Ly$α$ objects, Himiko and CR7, at $z=6.6$ thoroughly investigated with JWST/NIRCam photometry, NIRSpec-IFU spectroscopy, and ALMA data, uncovering their physical origins. Himiko (CR7) sh…
View article: ChemicalUniverseMachine I: Uncovering the Cosmic Evolution of Metals in the Galaxy-ISM-CGM Ecosystem
ChemicalUniverseMachine I: Uncovering the Cosmic Evolution of Metals in the Galaxy-ISM-CGM Ecosystem Open
We present an empirical chemical evolution model that explains the distribution of metals in the interstellar medium (ISM) and the circumgalactic medium (CGM) of galaxies based on the UniverseMachine and NeutralUniverseMachine models in th…
View article: Fe Abundances of Early Galaxies at $z=9-12$ Derived with Deep JWST Spectra
Fe Abundances of Early Galaxies at $z=9-12$ Derived with Deep JWST Spectra Open
We derive Fe-abundance ratios of 7 galaxies at $z=9-12$ with $-22
View article: The Physical Origin of Extreme Emission Line Galaxies at High Redshifts: Strong [O <scp>iii</scp>] Emission Lines Produced by Obscured Active Galactic Nuclei
The Physical Origin of Extreme Emission Line Galaxies at High Redshifts: Strong [O <span>iii</span>] Emission Lines Produced by Obscured Active Galactic Nuclei Open
We present deep Subaru/FOCAS spectra for two extreme emission line galaxies (EELGs) at z ∼ 1 with strong [ O iii ] λ 5007 emission lines, exhibiting equivalent widths (EWs) of Å and Å, comparable to those of EELGs at …
View article: Morphological Demographics of Galaxies at $z\sim 10-16$: Log-Normal Size Distribution and Exponential Profiles Consistent with the Disk Formation Scenario
Morphological Demographics of Galaxies at $z\sim 10-16$: Log-Normal Size Distribution and Exponential Profiles Consistent with the Disk Formation Scenario Open
We homogeneously investigate the morphological properties of $169$ galaxies at $z\sim10-16$ with deep JWST NIRCam images employing our established techniques of GALFIT modeling and uncertainty evaluation (systematics+statistics). We obtain…
View article: JWST, ALMA, and Keck Spectroscopic Constraints on the UV Luminosity Functions at <i>z</i> ∼ 7–14: Clumpiness and Compactness of the Brightest Galaxies in the Early Universe
JWST, ALMA, and Keck Spectroscopic Constraints on the UV Luminosity Functions at <i>z</i> ∼ 7–14: Clumpiness and Compactness of the Brightest Galaxies in the Early Universe Open
We present the number densities and physical properties of the bright galaxies spectroscopically confirmed at z ∼ 7–14. Our sample is composed of 60 galaxies at z spec ∼ 7–14, including recently confirmed galaxies at z spec = 12.34–14.18 w…
View article: New Methods of Identifying AGN in the Early Universe using Spectroscopy and Photometry in the JWST Era
New Methods of Identifying AGN in the Early Universe using Spectroscopy and Photometry in the JWST Era Open
We explore spectroscopic and photometric methods for identifying high-redshift galaxies containing an Active Galactic Nucleus (AGN) with JWST observations. After demonstrating the limitations of standard optical methods, which appear ineff…
View article: Census of Ly$α$ Emission from $\sim 600$ Galaxies at $z=5-14$: Evolution of the Ly$α$ Luminosity Function and a Late Sharp Cosmic Reionization
Census of Ly$α$ Emission from $\sim 600$ Galaxies at $z=5-14$: Evolution of the Ly$α$ Luminosity Function and a Late Sharp Cosmic Reionization Open
We present the statistical properties of Ly$α$ emission in 586 galaxies at $z=4.5-14.2$, observed by multiple JWST/NIRSpec spectroscopy projects, including JADES, GLASS, CEERS, and GO/DDT programs. We obtain Ly$α$ equivalent width (EW), Ly…
View article: EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall
EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall Open
Using the Subaru/FOCAS IFU capability, we examine the spatially resolved relationships between gas-phase metallicity, stellar mass, and star-formation rate surface densities (Sigma_* and Sigma_SFR, respectively) in extremely metal-poor gal…
View article: A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape?
A Galaxy with an Extremely Blue UV Slope $β=-3$ at $z=9.25$ Identified by JWST Spectroscopy: Evidence for a Weak Nebular Continuum and Efficient Ionizing Photon Escape? Open
We investigate UV continuum slopes $β$ of 863 galaxies at $z=4-14$ using archival JWST/NIRSpec PRISM spectra obtained from major JWST GTO, ERS, and GO programs, including JADES, CEERS, and UNCOVER. Among these galaxies, we identify a remar…
View article: Dynamics of a Galaxy at z > 10 Explored by JWST Integral Field Spectroscopy: Hints of Rotating Disk Suggesting Weak Feedback
Dynamics of a Galaxy at z > 10 Explored by JWST Integral Field Spectroscopy: Hints of Rotating Disk Suggesting Weak Feedback Open
We investigate the dynamics of GN-z11, a luminous galaxy at z = 10.60, carefully analyzing the public deep integral field spectroscopy (IFS) data taken with the JWST NIRSpec integral field unit. While the observations of the IFS data origi…
View article: Low [O/Fe] Ratio in a Luminous Galaxy at the Early Cosmic Epoch (z > 10): Signature of Short Delay Time or Bright Hypernovae/Pair-instability Supernovae?
Low [O/Fe] Ratio in a Luminous Galaxy at the Early Cosmic Epoch (z > 10): Signature of Short Delay Time or Bright Hypernovae/Pair-instability Supernovae? Open
We present an [O/Fe] ratio of a luminous galaxy GN-z11 at z = 10.60 derived with the deep public JWST/NIRSpec data. We fit the medium-resolution grating (G140M, G235M, and G395M) data with the model spectra consisting of BPASS-stellar and …
View article: A luminous and young galaxy at z = 12.33 revealed by a JWST/MIRI detection of Hα and [O iii]
A luminous and young galaxy at z = 12.33 revealed by a JWST/MIRI detection of Hα and [O iii] Open
The James Webb Space Telescope has discovered a surprising population of bright galaxies in the very early Universe (≲500 Myr after the Big Bang) that is hard to explain with conventional galaxy-formation models and whose physical properti…
View article: The Physical Origin of Extreme Emission Line Galaxies at High redshifts: Strong {\sc [Oiii]} Emission Lines Produced by Obscured AGNs
The Physical Origin of Extreme Emission Line Galaxies at High redshifts: Strong {\sc [Oiii]} Emission Lines Produced by Obscured AGNs Open
We present deep Subaru/FOCAS spectra for two extreme emission line galaxies (EELGs) at $z\sim 1$ with strong {\sc[Oiii]}$λ$5007 emission lines, exhibiting equivalent widths (EWs) of $2905^{+946}_{-578}$ Å and $2000^{+188}_{-159}$ Å, compar…
View article: Strong He i Emission Lines in High N/O Galaxies at z ∼ 6 Identified in JWST Spectra: High He/H Abundance Ratios or High Electron Densities?
Strong He i Emission Lines in High N/O Galaxies at z ∼ 6 Identified in JWST Spectra: High He/H Abundance Ratios or High Electron Densities? Open
We present He i /H β flux and He/H abundance ratios in three James Webb Space Telescope galaxies with significant constraints on N/O abundance ratios, GS-NDG-9422, RXCJ2248-ID, and GLASS150008 at z ∼ 6 mostly with the spectroscopic coverag…
View article: Balmer Decrement Anomalies in Galaxies at z ∼ 6 Found by JWST Observations: Density-bounded Nebulae or Excited H i Clouds?
Balmer Decrement Anomalies in Galaxies at z ∼ 6 Found by JWST Observations: Density-bounded Nebulae or Excited H i Clouds? Open
We investigate the physical origins of the Balmer decrement anomalies in GS-NDG-9422 and RXCJ2248-ID galaxies at z ∼ 6 whose H α /H β values are significantly smaller than 2.7, the latter of which also shows anomalous H γ /H β and H δ /H β…
View article: New AGN diagnostic diagrams based on the [OIII]<i>λ</i>4363 auroral line
New AGN diagnostic diagrams based on the [OIII]<i>λ</i>4363 auroral line Open
The James Webb Space Telescope (JWST) is revolutionizing our understanding of black hole formation and growth in the early Universe. However, JWST has also revealed that some of the classical diagnostics, such as the Baldwin, Phillips & Te…