arXiv subjects

Kouichiro Nakanishi

Publications and source records attributed to Kouichiro Nakanishi.

At least 19 recordsLinked to original sources

arXiv2026

ADF22-WEB: Massive galaxy formation shaped by cosmic web filaments in the z = 3.1 proto-cluster core

We present a census of dust, molecular gas, and galaxy structure in 18 dusty star-forming galaxies (DSFGs) at $z=3.09$ embedded in Ly$α$-traced cosmic web filaments in the core of the SSA22 proto-cluster, using multi-band ALMA, JWST imaging, and JVLA CO(1--0). Using up to six ALMA bands and Herschel/SPIRE data, we construct rest-frame far-infrared spectral energy distributions. The DSFGs span two orders of magnitude in far-infrared luminosity ($L_{\rm FIR}\sim10^{11}$--$10^{13}L_\odot$), with median values of $\log(L_{\rm FIR}/L_\odot)=11.56^{+0.32}_{-0.37}$ and $T_{\rm dust}=25^{+6}_{-3}{\rm K}$. For eight DSFGs with high-resolution ($\sim1$ kpc) JWST and ALMA imaging, we measure stellar and dust surface densities and find a positive correlation, suggesting that structural compaction of the stellar component proceeds together with that of the interstellar medium. We report 12 detections of CO(1--0), 18 of CO(3--2), four each of CO(8--7) and CO(9--8), and one of CO(12--11). The median brightness temperature ratio between CO(3--2) and CO(1--0) is $r_{31}=0.66^{+0.05}_{-0.04}$, consistent with field galaxies at similar redshifts. The high-$J$ CO lines show relatively low excitation, and the CO(8--7)/CO(3--2) ratio correlates with star-formation rate surface density, suggesting that molecular gas excitation is primarily regulated by star formation. Lower-mass galaxies show excess molecular gas fractions and depletion times relative to field scaling relations. By combining quiescent galaxy samples in the same field, we identify a sequence from gas-rich systems with low stellar surface density to gas-poor, compact systems with high stellar surface density. These results suggest that massive galaxy evolution in dense environments is governed by a baryon cycle linking gas supply, star formation, and structural transformation within the cosmic web environment.

astro-ph.GA↗

arXiv2026

Formation of Substructure in Luminous Submillimeter Galaxies (FOSSILS): Evidence of Multiple Pathways to Trigger Starbursts in Luminous Submillimeter Galaxies

We present an analysis of rest-frame optical and far-infrared continuum emission in three luminous submillimeter galaxies (SMGs) at $3.0\lesssim z\lesssim4.5$. The SMGs are spatially resolved down to 400-500 pc (0.05'') resolution by James Webb Space telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations. Despite similarities in their observed far-infrared properties (flux density, infrared luminosity, and effective radius), the three SMGs exhibit heterogeneous morphologies both across wavelengths and among the sources themselves. While two of them (AzTEC-4 and AzTEC-8) show a disk-like structure in optical continuum, AzTEC-1 is dominated by highly concentrated component with the Sersic index of $n=5.4$, where its far-infrared continuum emission is clumpy and less concentrated. AzTEC-4, which is confirmed to be at $z=4.198$, shows a two-arm spiral of dust, but not in the stellar distribution. These three SMGs exemplify that multiple physical mechanisms exist in triggering starbursts in luminous SMGs at high redshift: secular instability in gas disks (AzTEC-4) in addition to possible minor mergers (AzTEC-8), and a combination of the efficient gas supply to the central core induced by a gas-rich major merger and the reformation of cold gas disk (AzTEC-1).

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arXiv2026

Insights into Jet-Induced Cloud Disruption in NGC 1316: ALMA Reveals a Spatially Extended Molecular Gas

We present ALMA CO($J=1-0$) observations of a nearby radio galaxy NGC1316 at a 100-pc resolution to investigate the impact of AGN jets on the molecular gas. The molecular gas exhibits complex spatial and kinematic distributions, with broad CO line widths ($>50$ km s$^{-1}$) observed in several regions. The interferometric CO flux is only 34%-38% compared to single-dish data, indicating a large fraction of spatially extended molecular gas, especially in the central regions. We identified 24 Giant Molecular Clouds Associations (GMAs) primarily within the ``NW Shell'' and the ``SE Blob''; these GMAs show velocity dispersions approximately twice as high as those in typical star-forming galaxies for their sizes. Analysis of archival ALMA CO($J=2-1$) and CO($J=3-2$) data reveals elevated line ratios ($R_{21} \sim 1$ and $R_{31} \sim 1$) in gas near the jet, whereas, away from the jet, typical values ($R_{21} \sim 0.7$, $R_{31} \sim 0.3$). A multi-wavelength comparison reveals a $\sim$5 kpc warm ionized gas shell that encompasses the molecular NW Shell. The observed energetics and bubble morphology are consistent with an expanding bubble model driven by the jet assuming a jet power of $1.6\times10^{43}$~erg~s$^{-1}$. We propose that the high extended gas fraction results from the destruction of molecular clouds due to interactions with the jet plasma. NGC1316 may be a good example of jet-induced negative feedback through the ablation, dispersal, and rarification of dense molecular clouds through jet-ISM interactions.

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arXiv2026

Molecular Gas Structure and Star Formation Diversity in Stephan's Quintet Revealed by ACA CO(1-0) Mapping

We present $^{12}$CO(1-0) mapping across the entire system of Stephan's Quintet, a well-known compact galaxy group, observed by Atacama Compact Array (7\,m array + Total Power) of the Atacama Large Millimeter/submillimeter Array. These observations provide the first large-scale ($137\,\mathrm{kpc}\times119\,\mathrm{kpc}$), spatially resolved ($\sim$5.5\,$\mathrm{kpc}$) molecular gas map of a compact group. Our CO map revealed that most of the molecular gas resides in the disk of the member galaxy NGC~7319 and in the intergalactic regions, including components along the shocked filament and the optically identified tidal tail extending from NGC~7319. Along the tidal tail and its surroundings, we found not only an extended molecular gas component but also four discrete CO clumps, with velocity dispersions of $\sim$10-30 $\mathrm{km\,s^{-1}}$ and molecular gas masses of order $10^7$-$10^8\,M_\odot$. Three of these clumps spatially overlap with H\,{\sc i}, whereas the remaining clump shows no associated H\,{\sc i} or counterparts at optical and infrared wavelengths. Using star formation rates derived from H$α$ luminosities of H\,{\sc ii} regions, we found that star formation efficiencies (SFEs) span $\sim$2.2\,dex ($\sim$0.02--4\,Gyr$^{-1}$) and negatively correlate with CO velocity dispersion. While regions with small velocity dispersion exhibit SFEs comparable to those of nearby disk galaxies, those with large velocity dispersion ($\sim$50-150$\,\mathrm{km\,s^{-1}}$) around the shocked filament show strongly suppressed star formation. These results suggest that turbulence plays a significant role in regulating star formation in interacting systems.

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arXiv2026

Compact dusty starbursts at cosmic noon linked to high-energy neutrinos

The origin of high-energy astrophysical neutrinos remains unresolved, and secure electromagnetic counterparts to individual events are rare despite rapid follow-up. Dusty star-forming galaxies (DSFGs) at cosmic noon (z ~ 1-4) are natural cosmic-ray calorimeters, yet observational links between DSFGs and neutrinos have remained elusive. Here we report a compact-core DSFG within an IceCube localization, JCMT0402-0424, a quadruply lensed galaxy at z = 2.988 located inside the 90% containment region of the IceCube event IC 210922A. ALMA imaging and lens modeling resolve a highly magnified, compact starburst with no bright gamma-ray or X-ray counterpart above current sensitivity limits. Considering the positional agreement, the low chance-coincidence probability (less than about 1%) for such an extreme submillimeter source, the absence of equally plausible alternatives in the field, and the compact, gas-rich core revealed by ALMA, JCMT0402-0424 is the most plausible electromagnetic counterpart candidate within the IC 210922A localization. In a population context, compact-core starbursts at cosmic noon can provide a non-negligible population-level contribution to the diffuse high-energy neutrino background, even though the neutrino yield from any single DSFG is modest. This result connects high-energy neutrino production to the peak epoch of cosmic star formation, opening a new avenue to probe galaxy evolution and cosmic-ray acceleration across cosmic time.

astro-ph.HE↗

arXiv2026

An AGN in the Antennae galaxies ?

Time variability is a strong probe of energetic phenomena which occur at small spatial scales, like Active Galactic Nuclei (AGN). We use ALMA observations at 100 GHz executed over a period of 2.5 months to look for time variability in the Antennae galaxies, a prototypical early stage merger galaxy pair, for which there are no previous signatures of an AGN in the optical, infrared or X-ray. Most 100 GHz detections in the Antennae are spatially extended and associated with star forming regions, but two sources in the southern galaxy NGC 4039 are compact. One of these compact sources, S3, is offset by 1 arcsecond in the northeast direction from the stellar peak of NGC 4039, and marginally resolved at 10 parsec resolution. The other source, S4, is co-spatial with the stellar peak of NGC 4039 and unresolved even at a resolution of 4 parsec. We examine the time variability of these two sources using their power spectrum. We find that S4 varies with a characteristic timescale of 13+/-3 days, indicating that the phenomena responsible for the 100 GHz emission is smaller than 0.01 parsecs. By comparing the observed flux of the two sources with various candidate origins, we show that while S3 can be explained either by a young massive stellar cluster or an AGN, S4 is likely to be an AGN that is possibly Compton-thick.

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arXiv2026

Spectrally and spatially resolved (sub)millimeter HCN-to-HCO$^{+}$ flux ratios in nearby ultraluminous infrared galaxies

We present the results of our investigations of spectrally and spatially resolved (sub)millimeter HCN-to-HCO$^{+}$ flux ratios at J=2-1, J=3-2, and/or J=4-3 in 18 nearby ($z <$ 0.15) ultraluminous infrared galaxies (ULIRGs), using ALMA $\lesssim$0.2" ($\lesssim$500 pc) resolution data. The geometry of elevated HCN-to-HCO$^{+}$ flux ratios (with $>$3$σ$ detections for both molecular lines) in position-position-velocity (PPV) space is visually classified into (i) spherical shell (spectrally and spatially distinct), (ii) spectrally distinct and spatially compact, and (iii) filled (spectrally filled and spatially compact). These can naturally be explained by the elevation of the flux ratio due to (i) a spatially resolved outflow, (ii) an AGN and/or a spatially unresolved outflow with blueshifted and redshifted emission components, and (iii) an AGN and/or a spatially confined outflow with not clearly separated blueshifted and redshifted velocity components, respectively. Signatures of elevated HCN-to-HCO$^{+}$ flux ratios originated from (a) spatially resolved outflow and (b) AGN and/or spatially unresolved outflow are seen in seven and nine ULIRGs, respectively. In the former spatially resolved outflow-origin case, modest-velocity components relative to the maximum outflow velocity tend to be probed by spaxels with elevated HCN-to-HCO$^{+}$ flux ratios. The spectrally and spatially resolved HCN-to-HCO$^{+}$ flux ratios can provide additional information on the physical origin of the elevated flux ratios in nearby ULIRG nuclei, compared to previously conducted spatially integrated and/or velocity-integrated analyses.

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arXiv2026

Multiphase Gas Structure in the Circumnuclear Region of NGC 5506 Observed with ALMA

We present a study of the multiphase gas structure and kinematics of the circumnuclear disk (CND) of NGC 5506, a nearby edge-on Seyfert galaxy, at a spatial resolution of $\sim20$ pc. Observations of [C I](1-0), CO(3-2), and HCO$^{+}$(4-3) obtained with the Atacama Large Millimeter/submillimeter Array reveal the CND dominated by rotational motion on scales of several hundred parsecs. No significant differences in geometrical thickness or velocity structure are found between [C I](1-0) and CO(3-2) across the CND, whereas HCO$^{+}$(4-3) emission is more concentrated toward the disk plane. The ratio of velocity dispersion to rotational velocity, a proxy for disk scale height-to-radius ratio, is high ($\gtrsim0.9$) in the central region ($\lesssim30$ pc) for both [C I](1-0) and CO(3-2), indicating geometrically thick structures in both tracers. Regions where the [C I](1-0)/CO(3-2) ratio exceeds the CND average are spatially correlated with the [O III]$λ$5007 bicone observed with the Hubble Space Telescope, suggesting that CO is preferentially dissociated by the AGN-driven biconical ionized outflow. The observed CND scale height and velocity dispersions traced by [C I](1-0) and CO(3-2) are consistent with a model in which supernova-driven turbulence provides the vertical support for the CND.

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arXiv2026

Cloud-Cloud Collisions Induce Filament-Mediated Super Star Cluster Formation in the Antennae Overlap Region: Evidence from ALMA and JWST

The formation of super star clusters (SSCs) in galaxies remains a fundamental yet unresolved problem. Among the proposed mechanisms, cloud-cloud collisions (CCCs) have been suggested as a potential trigger, although observational validation has been limited. Here we present high-resolution ($0.12^{\prime\prime}$, $\sim14\,\mathrm{pc}$) ALMA observations of CO ($J=1\!-\!0$) emission toward a super giant molecular cloud (SGMC) in the overlap region of the Antennae galaxies. The data resolve the SGMC into two distinct velocity components separated by $\sim50\,\mathrm{km\,s^{-1}}$. One component exhibits a ``U-shaped'' structure within a large filament likely shaped by ram pressure, while the other shows hub-filament morphology. Such a morphology is naturally interpreted as a CCC scenario. The 108\,GHz continuum emission detected at the apparent collision interface is dominated by free-free radiation, with an ionizing photon rate consistent with the stellar mass and age of the optically identified SSCs. Supplementary infrared imaging with JWST reveals emission spatially coincident with the inferred collision interface, further supporting the CCC scenario. These results provide compelling, multi-wavelength evidence that CCCs play a key role in triggering SSC formation in merging galaxies.

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arXiv2025

ALMA Sub-parsec Resolution Dense Molecular Line Observations of the NGC 1068 Nucleus

We present the results of our ALMA observations of the dense molecular HCN J=4-3 and HCO$^{+}$ J=4-3 lines at $\lesssim$1 pc ($\lesssim$14 mas) resolution in the nuclear region of the nearby ($\sim$14 Mpc) well-studied AGN NGC 1068. Both emission lines are clearly detected around the AGN along an almost east-west direction, which we ascribe to the dusty molecular torus. The HCN J=4-3 emission is brighter than the HCO$^{+}$ J=4-3 emission in the compact ($\lesssim$3-5 pc) torus region. Apparent counter-rotation between the inner ($\lesssim$2 pc) and outer ($\gtrsim$2 pc) parts of the western torus, previously seen in $\sim$1.5 pc-resolution HCN J=3-2 and HCO$^{+}$ J=3-2 data, is also confirmed in our new $\lesssim$1 pc-resolution HCN J=4-3 and HCO$^{+}$ J=4-3 data. We apply a physically counter-rotating torus model, in which a compact dense gas clump collided with the western side of the existing rotating torus from the opposite direction, and we find that this model largely reproduces the observed properties of the combined new $\lesssim$1 pc-resolution HCN J=4-3 and HCO$^{+}$ J=4-3 data, and the previously obtained $\lesssim$1.5 pc-resolution HCN J=3-2 and HCO$^{+}$ J=3-2 data.

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arXiv2025

ALMA Deep Field in SSA22: Reconstructed [CII] Luminosity Function at z = 6

The ADF22 line survey reported detections of two high-$z$ line-emitting source candidates above 6-$σ$, both of which were shown to be spurious after follow-up observations. We investigate the detectability of far-infrared emitters in ALMA deep fields using mock observations by injecting artificial line-emitting sources into the visibility planes. We also discuss our investigation, conducted together with the ALMA operations team, of a possible technical problem in the original observations. Finally, we devise a method to estimate the [CII] luminosity function (LF) at $z \sim 6$, including a full analysis of signal contamination and sample completeness. The comparison of pixel distributions between the real and mock datacubes does not show significant differences, confirming that the effect of non-Gaussian noise is negligible for the ADF22 datacube. Using 100 blank mock-mosaic datasets, we show 0.43 $\pm$ 0.67 false detections per datacube with the previous source-finding method. We argue that the underestimation of the contamination rate in the previous work is caused by the smaller number of datacubes, using only 4 real ADF22 datacubes. We compare the results of clump-finding between the time division mode and frequency division mode correlator datacubes and confirm that the velocity widths of the clumps in the TDM case are up to 3 times wider than in the FDM case. The LF estimation using our model shows that a correction for the number count is required, up to one order of magnitude, in the luminosity range of $\geq 5 \times 10^8 L_\odot$. Our reconstruction method for the line LF can be applied to future blind line surveys.

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arXiv2025

Revisiting the supermassive black hole mass of NGC 7052 using high spatial resolution molecular gas observed with ALMA

We present our dynamical mass constraints on the central supermassive black hole (SMBH) in the early-type galaxy NGC 7052 using high spatial-resolution observations of $^{12}$CO(2-1) emission from the Atacama Large Millimeter/submillimeter Array (ALMA). The data were obtained during ALMA Cycle 7 and have a synthesized beam size of 0''.29 $\times$ 0''.22 (97 $\times$ 73 pc$^2$). The dynamical model yielded an SMBH mass of $\approx (2.50 \pm 0.37 \, [{\rm statistical}] \pm 0.8 \, [{\rm systematic}]) \times 10^9$ M$_{\odot}$ and a stellar-$I$ band mass-to-light ratio of $\approx 4.08 \pm 0.23\, [{\rm statistical}] \pm 0.4 \, [{\rm systematic}]$ M$_{\odot}$/L$_{\odot}$ ($3σ$ confidence intervals). Although our new ALMA observation has three times lower spatial resolution than previous ALMA data, it still resolves the SMBH's sphere of influence with a spatial resolution that is 1.5 times smaller than this sphere radius. While our $M_{\rm BH}$ estimate is fully consistent with the previous determination, the $I$-band mass-to-light ratio is lower by 10%. This difference arises from our improved galaxy mass model, which incorporates both the molecular gas distribution and the extended stellar mass in the outer regions of the galaxy, components that were previously neglected.

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arXiv2025

Spatially and Dynamically Extended Molecular Gas in Stephan's Quintet Revealed by ALMA CO(1-0) Total Power Mapping

We present ALMA Total Power CO(1-0) mapping of Stephan's Quintet (SQ), a prototypical compact galaxy group, with a uniform noise level at a spatial scale of ~25 kpc. These observations provide the first complete view of molecular gas across the whole system. Molecular gas is found to spread over a wide area (~120 x 80 kpc), mainly over the two main member galaxies (NGC7318B and 7319), but also in the shocked ridges between these galaxies, the tidal tail, and also in intergalactic regions north of the tail. The total CO(1-0) luminosity is $(2.47\pm0.12)\times10^9~\mathrm{K~km~s^{-1}~pc^2}$, corresponding to a molecular gas mass of $(1.07\pm0.05)\times10^{10}~M_\odot$ assuming the Galactic CO-to-H2 conversion factor. The global star formation efficiency of SQ is estimated at 0.29-0.70 $\mathrm{Gyr^{-1}}$, comparable to or lower than that of nearby star-forming galaxies. Molecular gas spans a velocity range of ~1300 km/s, which can be divided into three components (low, mid, high). The low- and mid-velocity components, linked to NGC7318B and the ridge, show relatively active star formation, whereas the high-velocity component, associated with NGC7319, shows suppressed star formation. Our mapping reveals molecular gas extending ~100 kpc in projection along the inner tail and north of it, containing $(1.64\pm0.08)\times10^9~M_\odot$ (15% of total) with low velocity dispersion (~20 km/s) and ongoing star formation. While previous studies suggested in situ molecular gas formation in the tail, our data suggest an additional contribution from gas stripped from NGC7319.

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arXiv2025

ADF22+: a declining faint end in the far-infrared luminosity function in the SSA22 protocluster at z=3.09

Protoclusters represent the densest regions of cosmic large-scale structure in the early universe and are the environment where present-day massive elliptical galaxies are assembled. Millimeter continuum emission offers a powerful probe of obscured star formation at high redshifts across various environments. In this paper, we present a deep ALMA 1.17 mm mosaic of the central 8 arcmin$^2$ ($\approx30$ comoving Mpc$^{2}$) region in the SSA22 protocluster at $z=3.09$ to study the faint dusty star-forming galaxy (DSFG) population. The continuum map achieves an RMS noise level of $\approx25$ $μ$Jy beam$^{-1}$ at $\approx1\arcsec$ spatial resolution, $\approx2\times$ the depth of previous observation of this field. We detected 53 sources with a signal-to-noise ratio above 4.2, doubling the number of detections. Utilizing optical to mid-infrared ancillary data, we search for spectroscopic redshift and identify 18 of 53 as cluster members. For sources with more than two photometric data points in the near-infrared, stellar mass ($M_\star$) and star formation rate (SFR) from spectral energy distribution fitting are presented. The 1.17 mm number count shows $>2\times$ excess at flux density $\gtrsim1$ mJy but are consistent with blank field in fainter flux bins. The monochromatic far-infrared luminosity function of the SSA22 protocluster core region suggests a lack of faint DSFGs. All SSA22 protocluster member galaxies detected at 1.17 mm have SFR within the $M_\star$-SFR relation of general star-forming galaxies. Our results suggest that an early overdense environment like SSA22 protocluster predominantly enhances the formation of massive early-type galaxies in present-day galaxy clusters, but that the star formation in individual member galaxies is likely driven by gas supply along the cosmic web and occurs in a secular way.

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arXiv2025

From Non-Detection to Detection: Atacama Compact Array Mosaic Observations of Faint Extended [C I] Emission in NGC 7679

We report the detection of [C I] $^3P_1$--$^3P_0$ emission in the nearby galaxy NGC 7679 using the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array (ALMA). In Michiyama et al. (2021), [C I] $^3P_1$--$^3P_0$ emission in NGC 7679 was reported as undetected based on ACA observations conducted in 2019 (ALMA Cycle 6). These observations had ~1 minute on-source time and used a single pointing with a field of view (FoV) of ~20 arcsec. In 2023 (Cycle 9), we carried out mosaic observations using seven pointings with an FoV of ~27 arcsec and 4-5 minutes on-source per pointing. The additional data have significantly improved the line sensitivity, uv-sampling, and noise uniformity across the galaxy disk. Our Cycle 9 observations confirm the presence of extended [C I] $^3P_1$--$^3P_0$ emission in NGC 7679, which was completely missed in the Cycle 6 observations due to insufficient sensitivity and uv-sampling. This highlights the basic technical challenges of estimating the total flux by interferometric observations with sparse uv-sampling.

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arXiv2025

No Galaxy-Scale [CII] Fast Outflow in the z=6.72 Red Quasar HSC J1205$-$0000

HSC 120505.09-000027.9 (J1205$-$0000) is one of the highest redshift ($z=6.72$) dust-reddened quasars (red quasars) known to date. We present an improved analysis of Atacama Large Millimeter/submillimeter Array data of the [CII] $158\ \rm{μm}$ line and the underlying rest-frame far-infrared (FIR) continuum emission, previously reported in Izumi et al. (2021a), toward J1205$-$0000. Red quasars are thought to be a transitional phase from an obscured starburst to a luminous blue quasar, in some cases associated with massive outflows driven by the active galactic nucleus (AGN). J1205$-$0000 has a high FIR luminosity, $L_{\mathrm{FIR}}=2.5\times 10^{12}\ L_{\odot}$ and a total IR luminosity of $L_{\mathrm{TIR}}=3.5\times 10^{12}\ L_{\odot}$, corresponding to a star formation rate (SFR) of $\sim 528\ M_{\odot}\ \mathrm{yr}^{-1}$. With the [CII]-based dynamical mass of $\sim 1 \times 10^{11}~M_\odot$, we conclude that J1205$-$0000 is hosted by a starburst galaxy. In contradiction to Izumi et al. (2021a), our improved analysis shows no hint of a broad component in the [CII] line spectrum. Thus there is no evidence for a host galaxy-scale fast [CII] outflow, despite the fact that J1205$-$0000 has fast nuclear ionized outflows seen in the rest-frame UV. We explore several scenarios for this discrepancy (e.g., early phase of AGN feedback, reliability of the [CII] line as a tracer of outflows), and we claim that it is still too early to conclude that there is no significant negative AGN feedback on star formation in this red quasar.

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arXiv2025

ADF22-WEB: Detection of a molecular gas reservoir in a massive quiescent galaxy located in a $z\approx3$ proto-cluster core

We present a study of the molecular gas reservoirs and dust contents in three quiescent galaxies (QGs) located in the core of the $z=3.09$ SSA22 proto-cluster. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we detect CO(3--2) emission in one galaxy, ADF22-QG1, marking the first direct detection of molecular gas in a quiescent galaxy from the early universe. The detected galaxy, ADF22-QG1, has a molecular gas mass of log$M_{\rm H_2}$/M$_\odot = 10.26 \pm 0.07$ assuming a CO-to-H$2$ conversion factor $α_{\rm CO} = 4.4$ (log$M_{\rm H_2}$/M$_\odot = 9.52 \pm 0.07$ for $α_{\rm CO} = 0.8$), corresponding to a gas mass fraction of $f_{\rm gas} \approx 14\%$ (2.5\%). The gas-to-dust ratio $δ_{\rm gdr}\gtrsim170$ ($δ_{\rm gdr}\gtrsim30$) for $α_{\rm CO} = 4.4$ ($α_{\rm CO} =0.8$) is also derived for the first time for a QG at the epoch. For the other two galaxies, ADF22-QG2 and ADF22-QG3, non detections of CO(3--2) emission provide upper limits, $f_{\rm gas} \approx 17\%$ (3.1\%) and $f_{\rm gas} \approx 13\%$ (2.4\%), respectively. The inferred gas-consumption history of ADF22-QG1, based on its star-formation history, suggests that (i) dusty star-forming galaxies (DSFGs) at $z = 4$--$6$ are plausible progenitors, and (ii) the cessation of gas accretion from cosmic web filaments plays an important role in their evolution to quenched systems. Furthermore, the presence of a detectable molecular gas reservoir in ADF22-QG1 indicates that additional mechanisms, such as morphological quenching, may be required to fully explain its quiescent nature.

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arXiv2025

ADF22-WEB: ALMA and JWST (sub)kpc-scale views of dusty star-forming galaxies in a $z\approx$3 proto-cluster

We present a morphological analysis of ALMA and JWST NIRCam images of nine dusty star-forming galaxies (DSFGs) at zspec=3.09, all embedded within the cosmic web filaments at the SSA22 proto-cluster core. The ALMA 870um and 1.1mm images are obtained at spatial resolutions ranging from 0.5" to 0.05" (350 pc at z=3.09). The high-resolution images enable us to resolve inner structures traced by dust continuum, identifying compact dusty cores, clumps, and offset ridges within bars. Sersic profile fit was performed for both ALMA 870um and NIRCam F444W images at comparable resolutions (0.15"). The Sersic index measured for 870um, masking bright regions, indicates values close to unity, suggesting that dust emission arises from disks with superimposed compact core components. For the JWST F444W images (restframe 1um), the Sersic indices range between nF444W = 1-3, pointing to the coexistence of bulges and stellar disks in these DSFGs. A comparison of dust mass surface density, nF444W, and F200W-F444W color (restframe 0.5-1um) reveals diversity among the DSFGs, likely reflecting different evolutionary stages including some DSFGs with red cores, indicating ongoing rapid bulge growth phases heavily obscured by dust. The predominantly disk-like morphologies observed in most DSFGs in the proto-cluster core contrast sharply with early-type morphologies that dominate the highest density environment in the local universe. This suggests that we are witnessing the early formation of the morphology-density relation, as massive galaxies undergo rapid growth as late-type galaxies fueled by cosmic web gas filaments.

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