arXiv subjects

Yoshiaki Ono

Publications and source records attributed to Yoshiaki Ono.

At least 19 recordsLinked to original sources

arXiv2026

H I Absorbers as Beacons of Hidden Structure at $z \sim 3$: Multi-Component, Metal-Rich Absorption System near a Protocluster

H I gas traces the large-scale structure and provides the primary fuel for star formation. High-$z$ protoclusters are ideal laboratories to study how H I gas is accreted and consumed during the formation of the most massive structures in the Universe. However, much remains unknown about the distribution and physical state of their H I gas. We examine a rare configuration in which a protocluster candidate is located in front of a quasar at $z=3.09$. Our spectroscopic campaign confirms a protocluster at $z=3.079$: however, no corresponding strong H I absorption is found in the background quasar spectrum. Instead, we serendipitously discover a prominent H I absorption feature at $z\sim 3.01$, offset by $\sim 60$ cMpc from the centre of the protocluster. Spanning an exceptionally broad velocity range of $\sim 2000$ km s$^{-1}$ ($\sim 40$ cMpc), this absorption is decoupled from the confirmed member galaxies. Detailed kinematic modelling reveals this absorption comprises five distinct components rather than a single cloud. Moreover, one of these components exhibits a super-solar metallicity ($[\mathrm{O/H}] = +1.19^{+0.91}_{-0.78}$). We propose two physical scenarios for this unique system: (1) an additional, hidden massive protocluster along the line of sight, and/or (2) metal-rich outflows and metal-poor inflows driven by a single massive galaxy. The discovery highlights that while protoclusters are not universally associated with strong H I absorption, targeting the strong H I absorbers may serve as a beacon for uncovering massive, metal-rich protoclusters or complex gas kinematics in the early Universe.

astro-ph.GA↗

arXiv2026

SERENADE III: Insight into the Origin of the High Dust Temperature and High [O III]/[C II] Ratio at $z\gtrsim6$

We present an analysis of ALMA high-frequency observations of nine bright Lyman-break galaxies at $5.8<z_{\rm spec}<8.3$. Our sample consists of five galaxies at $z\sim6$ newly observed in Band-9 and/or 10, allowing us to better constrain the dust temperature ($T_{\rm dust}$) in a statistical sample of $z\gtrsim6$ galaxies. Our measurements of the dust temperature at $z\sim6-9$ suggest most of the star-forming galaxies show $T_{\rm dust}\sim40\,{\rm K}$ on average, whereas three galaxies show significantly higher $T_{\rm dust}$ ($\gtrsim60\,{\rm K}$). We find a potential negative correlation between $T_{\rm dust}$ and gas-phase metallicity with $T_{\rm dust}\propto Z^{-0.50\pm0.19}$, implying decreased dust shielding and efficient dust heating in low-metallicity environments. Given the systematic offset of $T_{\rm dust}$ between $z\sim0$ and $z\sim6-9$ at fixed metallicity, we find $T_{\rm dust}$ is well described by sSFR as well as $Z$ with $\log T_{\rm dust}=-0.25^{+0.03}_{-0.04}\times(\log Z-0.57\times\log {\rm sSFR})+4.88^{+0.47}_{-0.43}$ across $z\sim0$ to $z\sim6-9$. Simultaneously with the dust continuum, these observations cover the [OI]63$μ$m emission line for five galaxies, which traces dense neutral gas. We find a lower [CII]/[OI] ratio in $z\gtrsim6$ galaxies than in local samples, suggesting that [CII] becomes fainter due to collisional de-excitation at high gas density. Combining the [OI], [OIII], and [CII] lines and cloudy modeling, our results imply $\log U_{\rm ion}\sim-2$ and $\log n_{\rm H}\,[{\rm cm}^{-3}]\sim2.5$ in $z\gtrsim6$ galaxies, which is $\sim3-10\times$ higher $U_{\rm ion}$ and $\sim2-3\times$ higher $n_{\rm H}$ than the local samples. The combination of these enhanced $U_{\rm ion}$ and $n_{\rm H}$ naturally explains the high [OIII]/[CII] ratio at $z\gtrsim6$.

astro-ph.GA↗

arXiv2026

ATLAS. I. A Scaling Relation of LRDs between Broad H$α$ and Bolometric Luminosities: Enhanced Broad H$α$ Emission Relative to Low-$z$ Type 1 AGN

We investigate the demography of little red dots (LRDs) using 37 objects at $z\sim3$-$7$ with JWST/NIRSpec PRISM and grating spectra compiled from various JWST programs. We focus on spectroscopic quantities of the broad H$α$ luminosity $L_\mathrm{Hα,broad}$ (and the broad H$β$ luminosity $L_\mathrm{Hβ,broad}$ where available) and the bolometric luminosity $L_\mathrm{bol}$ represented by modified blackbody emission, avoiding quantities contaminated by host-galaxy emission (e.g., total H$α$ luminosity). We identifiy a tight scaling relation between $L_\mathrm{Hα,broad}$ and $L_\mathrm{bol}$, supporting the interpretation that these emissions are primarily powered by the central engine. Interestingly, the $L_\mathrm{Hα,broad}$-$L_\mathrm{bol}$ scaling relation of LRDs is enhanced by a factor of $\sim40$ in $L_\mathrm{Hα,broad}$ relative to that of low-$z$ Type 1 AGN. A similar trend is found in the $L_\mathrm{Hβ,broad}$-$L_\mathrm{bol}$ relation, although the enhancement in $L_\mathrm{Hβ,broad}$ is smaller, only by a factor of $\sim10$. We explore the physical origin of these enhancements and find that \textsc{Cloudy} photoionization modeling within the classic locally optimally-emitting cloud (LOC) framework can explain them through an increase in the covering factor from $\sim20$\% (Type 1 AGN) to $\sim100$\% (LRDs), together with an increase in the hydrogen column density from $N_\mathrm{H}\sim10^{23}\,\mathrm{cm}^{-2}$ to $\gtrsim10^{24}\,\mathrm{cm}^{-2}$, with a preferred gas density of $\sim10^{10}\,\mathrm{cm}^{-3}$, successfully reproducing the modified blackbody emission. Such a nearly unity covering factor without requiring a gas density increase may result from a significant increase in the BLR filling factor or size, corresponding to a ``stuffed BLR" or ``giant BLR," respectively.

astro-ph.GA↗

arXiv2026

ATLAS. IV. A JWST+MUSE Demographic Study of Ly$α$ Profiles in Little Red Dots

We present an initial demographic study of Ly$α$ profiles in little red dots (LRDs) at $z=3$--9 using $R\sim1000$--4000 spectroscopy. Our sample consists of 8 LRDs observed in the VLT/MUSE Deep and Wide surveys and 23 LRDs observed with JWST/NIRSpec grating spectroscopy from JADES, CANUCS, and GO programs including SPURS. We identify Ly$α$ emission in 5 MUSE LRDs and 9 JWST LRDs. Only two of them exhibit broad Ly$α$ emission (FWHM $>1000\ \mathrm{km\ s^{-1}}$), both reported previously. The other Ly$α$-emitting LRDs show narrow Ly$α$ emission (FWHM $<1000\ \mathrm{km\ s^{-1}}$), with FWHMs mostly in the range 300--600 $\mathrm{km\ s^{-1}}$, comparable to or slightly larger than those of high-redshift star-forming galaxies (100--500 $\mathrm{km\ s^{-1}}$). We measure the fraction of broad Ly$α$ emitters above a broad Ly$α$ luminosity threshold of $L_{\mathrm{Ly}α,\mathrm{broad}}=10^{42}\ \mathrm{erg\ s^{-1}}$, obtaining $0.10^{+0.12}_{-0.07}$ for LRDs, about five times higher than the $2σ$ upper limit of $<0.02$ for high-redshift star-forming galaxies. Although we reproduce the broad Ly$α$ component reported in a previous stacking analysis of eight LRDs, albeit with a large uncertainty, we find no evidence for broad Ly$α$ emission in either the larger JWST stack, after excluding the two individually detected broad Ly$α$ emitters, or the higher-resolution MUSE stack. These results suggest that broad Ly$α$ emission is not ubiquitous among LRDs. Instead, LRDs with broad Ly$α$ emission appear to represent a rare population that may correspond to a particular evolutionary stage, potentially associated with unusually strong outflows or other distinctive physical conditions.

astro-ph.GA↗

arXiv2026

ATLAS. III. Dust Around Little Red Dots: Hydrogen Line Ratios beyond Dust-free Non-Case B Models

We investigate broad hydrogen line ratios in little red dots (LRDs) using five high-redshift ($z>2$) sources from JWST/NIRSpec medium/high-resolution spectra in the DAWN JWST Archive and fifteen low-redshift sources ($z=0.1$--$0.9$) from the literature, all with broad H$β$ detected at $>5σ$. After carefully measuring the broad-line fluxes while accounting for absorption features and neighboring emission lines, we find that the broad H$α$/H$β$ ratios are very high, ranging from 6 to 30, well above the Case B recombination value. Using plane-parallel \textsc{Cloudy} photoionization models with the total line emission from both sides of the slab, we investigate the physical origin of the broad hydrogen line ratios beyond Case B, jointly modeling the Balmer and Paschen line ratios for the subset of one high-$z$ and two low-$z$ LRDs with detected broad Paschen lines. We find that one low-$z$ LRD is reproduced by a high gas number density ($\log (n_{\mathrm H}/{\rm cm^{-3}})\sim10$--11) on the broad-line H$α$/H$β$--Pa$β$/Pa$γ$ plane, whereas the remaining two LRDs additionally require substantial dust extinction of $E(B-V)\gtrsim0.2$--$1.0$, even after accounting for non-Case B effects. Since the narrow H$α$/H$β$ ratios do not indicate such large dust extinction, these results demonstrate that the obscuring dust is spatially associated with the broad-line region. Even without Paschen-line measurements, two and eight LRDs in the high- and low-redshift samples, respectively, exhibit H$α$/H$β>13$, which cannot be reproduced by the non-Case B models, suggesting that dust obscuration might be common among LRDs, occurring in at least about half of the population. Such dust may represent a lower-column-density counterpart of the dusty torus in AGNs, reconciling the weak hot-dust emission.

astro-ph.GA↗

arXiv2026

EMPRESS. XV. A New Determination of the Primordial Helium Abundance Suggesting a Moderately Low $Y_\mathrm{P}$ Value

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; $0.01-0.1\,Z_\odot$), which have metallicities a few to ten times lower than the metal-poor galaxies (MPGs; $0.1-0.4\,Z_\odot$) predominantly used in earlier studies, requiring substantial extrapolation to zero metallicity. Here, we perform Subaru near-infrared spectroscopy of 29 galaxies, including 14 EMPGs. By incorporating existing optical spectra, we derive He/H for each galaxy using photoionization modeling of helium and hydrogen emission lines, including the He \textsc{i} 10830Å\, line to break the density--temperature degeneracy. After carefully selecting galaxies with robust He/H determinations, and adding 58 galaxies from previous studies, we obtain $Y_\mathrm{P} = 0.2402^{+0.0040}_{-0.0040}$. This $Y_\mathrm{P}$ value is $\sim1σ$ lower than most of the previous estimates, but agrees with recent determinations using EMPGs and the CMB constraint from the Atacama Cosmology Telescope (ACT) experiment. Our result indicates $N_\mathrm{eff} = 2.54^{+0.20}_{-0.25}$, showing a mild ($\sim2σ$) tension with the Standard Model and Planck results. These tensions may suggest a nonzero lepton asymmetry $(ξ_\mathrm{e}\neq0)$, which would alleviate the tension with $ξ_\mathrm{e} = 0.05^{+0.02}_{-0.03}$. More observations of EMPGs and further assessments of systematic uncertainties are essential to test the potential tension more rigorously.

astro-ph.GA↗

arXiv2026

ATLAS. II. Extremely High Incidence of Balmer Line Absorption with Predominant Blueshifts in LRDs: Statistical Insights through Comparison with Type 1 AGNs

We present the statistical properties of H$α$ and H$β$ line absorption in little red dots (LRDs) at $z\simeq2.5$--7.2 using archival JWST/NIRSpec spectra from the DAWN JWST Archive and complementary NIRSpec/IFU observations. Among 40 LRDs with broad H$α$ and [O~{\sc iii}] obtained with medium- or high-resolution gratings, 14 objects exhibit H$α$ absorption. We find that the incidence of Balmer line absorption is $\sim35$\% ($=14/40$), significantly higher than that in SDSS low-$z$ type 1 AGNs ($\sim0.04$\%), demonstrating that Balmer line absorption occurs approximately 850 times more frequently in LRDs than in type 1 AGNs. We combine our 14 detections with 32 additional LRD Balmer absorbers from the literature, yielding a census of 46 absorbers. Their velocities span $Δv_\mathrm{abs}(\mathrm{Hα})\sim-430$ to $+140\ {\rm km\,s^{-1}}$, markedly narrower than the $-800$ to $+1600\ {\rm km\,s^{-1}}$ range of Balmer absorption in SDSS type~1 AGNs, for which our simulations confirm that the velocity difference is too large to be explained by detection incompleteness. The lower absolute absorber velocities in LRDs may partly reflect the shallower gravitational potential at their characteristic BLR radii. We also find that 38 of the 46 absorbers (83\%) are blueshifted, with only eight redshifted, indicating that most of Balmer absorbers are moving outward. An analytic model with radiation pressure suggests that most absorbers with $N_{\rm H}\gtrsim10^{24}\ {\rm cm^{-2}}$ remains gravitationally bound. The smaller number of redshifted (i.e., infalling) absorbers may indicate that outbound absorbers lose density: some return to the BLR, whereas others undergo stronger radiative acceleration and escape.

astro-ph.GA↗

arXiv2026

VENUS: A Strongly Lensed Clumpy Galaxy at $z\sim11-12$ behind the Galaxy Cluster MACS J0257.1-2325

We present the discovery of a strongly lensed galaxy at $z\sim11-12$, dubbed the ``Misty Moons'', identified in the JWST Treasury Survey, Vast Exploration for Nascent, Unexplored Sources (VENUS). The Misty Moons is gravitationally lensed by the galaxy cluster MACS J0257.1-2325 at $z=0.505$, and has five multiple images suggested by two independent lensing models. Two of the five images, ID1 and ID2 ($μ\sim 20-30$), are very bright (F200W$\sim26$ AB mag) and exhibit blue SEDs with prominent Ly$α$ breaks. In the source plane, the Misty Moons is a sub-$L^*$ galaxy ($M_{\rm UV}\sim-18.0$ mag) resolved into multiple stellar clumps, each of which has an effective radius of $r_\mathrm{eff}\sim 10-70$ pc and a stellar mass of $\sim10^7\ M_\odot$. These clumps dominate the stellar mass budget of the Misty Moons ($\gtrsim80\%$), similar to other high-$z$ clumps, which suggests a highly clustered mode of star formation in the early Universe, unlike seen in local dwarf galaxies. We convolve the source-plane image with the JWST/NIRCam point-spread function to produce a mock NIRCam image of the Misty Moons without lensing magnification, and find that the intrinsic galaxy has a radial surface-brightness profile comparable to those of $z\gtrsim10$ faint galaxies, such as JADES-GS-z13-0 and JADES-GS-z14-1, indicating that the Misty Moons represents a typical $z\gtrsim10$ faint galaxy. The Misty Moons, a lensed galaxy with resolved internal structures, provides an ideal laboratory for exploring the early stages of galaxy formation at $z\gtrsim10$.

astro-ph.GA↗

arXiv2026

Chemical Abundance Ratios of Nitrogen Rich Galaxies Identified at $z\sim 6-12$: Observational Demographics and Models

We present chemical abundance ratios of 8 nitrogen-rich ([N/O]$>0.3$) galaxies at $z\sim 6-12$ identified by the first 4 years of the JWST observations, and compare these ratios with chemical evolution models. We reanalyze the JWST/NIRSpec data of these galaxies in the self-consistent manner for line fluxes and upper limits including those previously unconstrained. We derive the abundance ratios and constraints of [N/O], [C/O], [Ne/O], [Ne/C], [Ar/O], [S/O] and [Fe/O], characterizing the nebulae in the galaxies with the electron temperatures and densities measured with {\sc[Oiii]}$\lambda4363$ and {\sc[Oii]}$λ\lambda3727, 3729$ lines, respectively. We develop the chemical evolution models for the three major scenarios, Wolf-Rayet stars, supermassive stars, and tidal disruption events (TDEs) with the AGB star contribution, integrating the ejecta of the stars and core-collapse supernovae (CCSNe) over the age with yields calculated by numerical simulations. We compare the models with the [N/O] measurements and stellar ages, and find that all of the scenarios reproduce [N/O] as high as those of our galaxies. However, the time-scales of the high [N/O] ratios are too short to explain our galaxies in any of the scenarios, suggestive of very frequent failed supernovae that do not increase oxygen against nitrogen. We find that the three scenarios are distinguished in the plane of [Ne/C] vs. [N/O] due to Ne production outside CNO cycle, and that the observed abundance ratios are explained by the Wolf-Rayet models better than supermassive-star and TDE models. We argue that abundance ratios of various elements and time scales are clues for understanding nitrogen-rich galaxies.

astro-ph.GA↗

arXiv2026

Strong Correlation Effect and In-gap State in the Doped Electron-Hole Two-Band Hubbard Model Based on the Dynamical Mean-Field Theory

We investigate the strong correlation effect in the spinless electron-hole two-band Hubbard model using the dynamical mean-field theory. At half filling, both the renormalization factor $Z$ and the number of conduction electrons (valence holes) $n_c$ decrease with increasing the interband Coulomb interaction $U$ down to $Z\sim 0.15$ and $n_c\sim 0.1$ for $U_c \sim \mbox{bandwidth}$ at which the first-order Lifshitz transition occurs from a correlated semimetal with a large effective mass $m^*/m=Z^{-1}$ to a band insulator with a finite gap due to the Hartree shift. A slight hole doping $x$ in the band insulator with a large $U>U_c$ yields a remarkable correlated semimetal with $Z\sim 0.1$ at $x\sim 0.01$, where in-gap states emerge above the valence band top and those weights increase with increasing $x$ together with the increase in $Z$ similar to the in-gap states observed in doped Mott insulators.

cond-mat.str-el↗

arXiv2026

Assessing the Impact of Source Confusion for GREX-PLUS based on Deep JWST NIRCam Imaging

We investigate the effects of source confusion expected in observations with GREX-PLUS, a JAXA L-class space infrared telescope mission candidate with a wide-field infrared camera covering 2-8 um with a field of view of 0.50 deg$^2$. For the deep imaging band near 4 um, we calculate the GREX-PLUS PSF and ghost based on the latest optical design, and consider two representative imaging performance cases with PSF FWHM values of 0.9 and 1.2 arcsec. We construct simulated GREX-PLUS images at different depths by convolving JWST NIRCam imaging data from JADES, GLASS, CEERS, and COSMOS-Web with the PSF+ghost kernel. Comparing the limiting magnitudes estimated from random aperture photometry using the same aperture sizes, we find that the simulated GREX-PLUS images are shallower than the original JWST images, with larger deviations for deeper original JWST images. This likely reflects unresolved faint sources and extended PSF+ghost wings from bright sources, which elevate background fluctuations in blank regions. Nevertheless, the limiting magnitudes continue to improve with increasing integration time down to ~27 mag, without a clear plateau at depths comparable to the planned GREX-PLUS deep survey, although the improvement becomes progressively less efficient toward longer integrations. Based on Monte Carlo simulations, we estimate detection completeness and correct the number counts for magnitude bias and incompleteness, finding that confusion-induced blending can reduce the completeness even at magnitudes well above the nominal 5-sigma depth. The completeness-corrected number counts agree well with the JWST-based number counts down to around the detection limit. Overall, our results suggest that statistical studies of faint galaxies remain feasible for GREX-PLUS; however, survey planning should account for less efficient depth improvement toward longer integrations due to source confusion.

astro-ph.GA↗

arXiv2026

DREAMS. JWST Spectroscopy of a $z=8.3$ Galaxy with an ALMA Dust Continuum Detection: Early Dust, Very High $T_{\rm dust}$, and a Multi-wavelength [OIII] Ratio Discrepancy

We present a deep DREAMS JWST/NIRSpec MSA medium-grating spectrum of MACS0416-Y1, a galaxy at $z=8.312$ with the highest-redshift ALMA dust continuum detection to date, in order to characterize its properties together with archival IFU and ALMA data. The deep NIRSpec spectrum reveals a broad H$β$ line with a width of $\sim1100$ km s$^{-1}$. We interpret it as a broad-line AGN whose line diagnostics are consistent with AGN activity across its clumpy structure, given the absence of little red dot signatures. MACS0416-Y1 clearly shows [OIII]4363 emission, suggesting a moderately low metallicity of $12+\log(\mathrm{O/H})=7.86^{+0.09}_{-0.08}$ ($0.15~Z_\odot$). The combination of [CII]158$μ$m and dust continuum emission indicates low dust mass ratios of $\log (M_{\rm dust}/M_{\rm gas})=-3.60^{+0.29}_{-0.22}$ and $\log (M_{\rm dust}/M_{\rm metal})=-0.95^{+0.29}_{-0.20}$. Because the metallicity of MACS0416-Y1 is around the critical metallicity of $0.1\textrm{-}0.2~Z_\odot$, the system is expected to undergo dust growth, explaining these low dust mass ratios as well as its small dust mass, $M_{\rm dust}\sim10^6~M_\odot$. The intense UV radiation from the AGN may contribute to a high dust temperature of $T_{\rm dust}\simeq 91^{+62}_{-35}$ K, boosting the dust-continuum emission above the ALMA detection limit despite the small $M_{\rm dust}$ at $z>8$. We find a very high total flux ratio of [OIII]88$μ$m/[OIII]5007 = $0.26 \pm 0.06$ in MACS0416-Y1, above predictions from single ionized nebular models at any electron density. This discrepancy suggests that the [OIII]88$μ$m and [OIII]5007 trace largely distinct regions, with the optical line suppressed in dusty nebulae, and thus requires careful interpretation when combining optical and infrared emission lines in JWST+ALMA studies.

astro-ph.GA↗

arXiv2026

An Ultra-Faint, Chemically Primitive Galaxy Forming in the Reionization Era

The formation of the first stars and galaxies marked the onset of chemical enrichment, yet direct observations of such primordial systems remain elusive. Here we present James Webb Space Telescope spectroscopic observations of LAP1-B, an ultra-faint galaxy at redshift z_{spec}=6.625 +/-0.001, corresponding to a cosmic age of 800 million years after the Big Bang, strongly magnified by gravitational lensing. LAP1-B exhibits a gas-phase oxygen abundance of (4.2 +/- 1.8) x 10^{-3} times the solar value, making it the most chemically primitive star-forming galaxy discovered to date. The galaxy displays an exceptionally hard ionizing radiation field, which is inconsistent with chemically enriched stellar populations or accreting black holes but matches theoretical predictions for an exceptionally metal-deficient stellar population. It also shows an elevated carbon-to-oxygen abundance ratio for its metallicity in the interstellar medium, consistent with nucleosynthetic yields from a stellar population formed in the absence of initial metals. The lack of detectable stellar continuum constrains the stellar mass to <3,300 Msun, while the dynamical mass, derived from emission-line kinematics, exceeds the combined stellar and gas mass and indicates a dominant dark matter halo. Our findings establish LAP1-B as a "fossil in the making", a direct high-redshift progenitor of the ancient ultra-faint dwarf galaxies observed in the local Universe, offering a rare window into the earliest stages of galaxy formation.

astro-ph.GA↗

arXiv2026

A UV-Luminous Galaxy at z=11 with Surprisingly Weak Star Formation Activity

One of the major discoveries by the James Webb Space Telescope (JWST) is the identification of a large population of luminous galaxies at $z>10$, challenging theoretical models for early galaxy formation. The unexpectedly high number density of these systems has triggered intense debate about potential differences in the physical properties of galaxies at such extreme redshifts and those at lower redshift. However, progress has been limited by the lack of rest-frame optical diagnostics, which are critical for constraining the key properties. Here we present deep JWST/MIRI observations of a UV-luminous galaxy at $z=11.04$, CEERS2-588, only 400 Myr after the Big Bang. CEERS2-588 is detected in the MIRI F560W and F770W bands, while deep MIRI/MRS spectroscopy yields no detection of H$α$ or [OIII]$\lambda5007$ line, revealing a prominent Balmer break detected for the first time at $z>10$. Spectral energy distribution (SED) fitting indicates an extended star formation history possibly reaching $z>15$, followed by rapid quenching within the recent $\sim10$ Myr, in stark contrast to other $z>10$ galaxies. The MIRI detections also significantly improve our stellar mass estimate to $\mathrm{log}(M_*/M_\odot)=9.1^{+0.1}_{-0.1}$, making CEERS2-588 the most massive galaxy securely confirmed at $z>10$. Remarkably, the inferred gas-phase metallicity is near solar, exceeding predictions from current theoretical models. These results suggest that efficient starbursts play a key role in producing the abundant luminous galaxy population in the early universe.

astro-ph.GA↗

arXiv2026

VENUS: Two Faint Little Red Dots Separated by $\sim70\,\mathrm{pc}$ Hidden in a Single Lensed Galaxy at $z\sim7$

We report the identification of a pair of faint little red dots (LRDs), dubbed Red Eyes, in a strongly-lensed galaxy at $z\sim7$ behind the PLCKG004.5-10.5 cluster, identified from the JWST Treasury program VENUS. Red Eyes are spatially resolved on the image plane with distinct colors, while the critical curve lies far north of Red Eyes, clearly requiring two different LRDs rather than a single LRD. Red Eyes is an extremely close pair of LRDs separated by $\sim70\,\mathrm{pc}$ in the source plane with a magnification of $μ\sim20$, which consistently explains another counter-image detected to the north-west. Red Eyes is hosted in a typical star-forming galaxy with $M_{\mathrm{UV,int}}\sim -19$, but its own UV emission is very faint ($M_{\mathrm{UV,int}} \gtrsim -16$). Moreover, Red Eyes does not reside at the galaxy center but lies at an offset position of approximately one effective radius $R_{\mathrm{e}}$ away from the galaxy center. If observed without lensing, Red Eyes would appear as a typical star-forming galaxy at $z\sim 7$ with $M_{\mathrm{UV}}\sim -19$, showing no apparent LRD signatures in either morphology or SED. These results suggest that multiple off-center LRDs, similar to Red Eyes, may be commonly hidden in a typical high-$z$ star-forming galaxy. In this case, various plausible scenarios may emerge, one of which is that intermediate-mass black holes (IMBHs) with $M_\mathrm{BH}\sim10^{4\text{--}6}\,M_\odot$ may form in star clusters on a stellar disk and contribute to the growth of the central supermassive black hole via mergers, with some IMBHs detectable as luminous LRDs in a sufficiently active and massive phase.

astro-ph.GA↗

arXiv2025

Near-infrared Variability Detected in the Young Star-Forming Dwarf Galaxy SBS 0335-052E

SBS~0335-052E is a young star-forming dwarf galaxy with a total stellar mass of $M_{*} \lesssim 10^{8}~M_{\odot}$ and an extremely low metallicity ($Z \sim 1/40~Z_{\odot}$), which has long been considered to be devoid of an active galactic nucleus (AGN). Here we report the detection of temporal flux variability of SBS~0335-052E in near-infrared (NIR) 3-4\ ${\rm μ}$m bands on timescales of several years, showing dimming and brightening of up to 50\% over 14~years, based on archival data from the Wide-field Infrared Survey Explorer. Our spectral energy distribution (SED) fitting of archival ultraviolet (UV)-NIR photometry, including AGN SED models, indicates that the variable NIR emission arises from an edge-on AGN dust torus. The UV-optical emission from the accretion disk is obscured and does not reach us, leading to the dominance of the host galaxy's young stellar population in the UV-optical wavelengths. This analysis favors the presence of a Compton-thick, heavily obscured AGN in SBS~0335-052E, consistent with its observed X-ray weakness. From the SED fitting, we estimate an AGN bolometric luminosity of $L_{\rm bol} = 1.2\times10^{43}\ {\rm erg\ s^{-1}}$, which implies a black hole mass of $M_{\rm BH} \simeq 10^{5}\ M_\odot$ if the AGN is accreting at the Eddington limit. If confirmed, SBS~0335-052E would be the least massive galaxy known to host an AGN, likely harboring an intermediate-mass black hole.

astro-ph.GA↗

arXiv2025

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

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) shows at least five (four) clumps with small separations of 2.4--7.3 kpc and velocity offsets of $Δv<220~\mathrm{km~s^{-1}}$ in the [OIII]$λ\lambda4959,5007$ line maps, three of which exhibit stellar components with comparable stellar masses ranging in $\log{(M_*/M_\odot)}=8.4$--$9.0$ ($8.3$--$8.8$), indicative of major merger systems that are consistent with our numerical simulations. The [CII]158$μ$m and Ly$α$ lines are found in the middle of two clumps (the brightest clump) in Himiko (CR7), suggesting that the distribution of neutral gas does not always coincide with that of ionized gas or stars in merging processes. We find that some of the clumps have broad [OIII] components (250--400$~\mathrm{km~s^{-1}}$) in Himiko and CR7, likely tracing outflow and tidal features, while the central clump in Himiko presents a broad H$α$ ($\sim1000~\mathrm{km~s^{-1}}$) line explained by an AGN with a low mass black hole of $M_\mathrm{BH}=10^{6.6}~M_\odot$, which contribute to the extended and bright nature of Himiko and CR7. We find low metallicities of $12+\log(\mathrm{O/H})=$7.9--8.1 in Himiko and CR7 based on auroral [OIII]$\lambda4363$ and strong lines that are consistent with no 1-mm continuum detection corresponding to the dust mass limits of $M_\mathrm{dust}\lesssim 9\times 10^6 M_\odot$. Himiko and CR7 are metal- and dust-poor blue merger systems with stellar and dust masses $\gtrsim2$ orders of magnitude smaller than the massive dust-rich merger systems represented by submillimeter galaxies.

astro-ph.GA↗

arXiv2025

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

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$3726,3729-based electron densities of $n_\mathrm{e,optical}\sim1000$ cm$^{-3}$ on average and [OIII]$λ$4363-based metallicities of $\mathrm{12+log(O/H)}=8.0-8.2$ in two galaxies. New ALMA Band 9/10 observations detect the [OIII]52$μ$m line in one galaxy but do not in the others, resulting in FIR-based densities of $n_\mathrm{e,FIR}\lesssim500$ cm$^{-3}$ from the [OIII]52$μ$m/[OIII]88$μ$m ratios, systematically lower than the optical [OII]-based measurements. These low FIR-based densities are comparable to those at both $z\sim0$ and $z>6$ in the literature, including JADES-GS-z14-0 at $z=14.18$, suggesting little evolution up to $z\sim14$, in contrast to the increasing trend of optical-based densities with redshift. By conducting a JWST and ALMA joint analysis using emission lines detected with both telescopes, we find that the observed FIR [OIII]52,88$μ$m luminosities are too high to be explained by the optical-based densities at which they would be significantly collisionally de-excited. Instead, a 2-zone model with distinct high- and low-density regions is required to reproduce all observed lines, indicating that FIR [OIII] emission arises predominantly from low-density gas, while optical [OIII] and [OII] lines trace both regions. We further demonstrate that the direct-$T_\mathrm{e}$ method can sometimes significantly underestimate metallicities up to 0.8 dex due to the presence of the low-density gas not fully traced by optical lines alone, highlighting the importance of combining optical and FIR lines to accurately determine gas-phase metallicities in the early universe.

astro-ph.GA↗