arXiv subjects

Tadayuki Kodama

Publications and source records attributed to Tadayuki Kodama.

At least 37 records · Page 2Linked to original sources

arXiv2025

Nature of High Equivalent Width Emitters in the Epoch of Reionization Revealed by JWST Medium-band Imaging

Extreme emission line galaxies (EELGs) at high redshifts are considered key contributors to cosmic reionization at $z>6$ due to their higher ionization efficiencies. We have identified 119 H$β$ + [OIII] emitters at $z\sim7$ selected by a flux excess in the medium-band filter F410M in the public James Webb Space Telescope Cycle-1 fields. Our emitters exhibit a wide range in rest-frame H$β$ + [OIII] equivalent width (EWs), 420 $<$ EW$_{0}$/Å $<$ 6850 (with the median value of $\sim1700$ Å). Among them, 19 are EW$_{0}$ $>$ 3000 Å, which represent extreme populations even in the context of recent findings with JWST. They are characterized by (i) low stellar mass ($\sim 3\times10^{7}$ $\mathrm{M_{\odot}}$), (ii) blue colors ($β_{\rm UV}\sim -2.2$), and (iii) low dust attenuation ($A_{\mathrm{V}}\sim 0.1$ mag). We discuss the physical mechanisms responsible for the observed high rest-frame H$β$ + [OIII] EWs, including (1) photoionization by AGN, (2) stellar photoionization in the vicinity of HII regions, and (3) radiative shocks powered by outflows either from AGN or massive stars. Notably, we find 13 emitters with spatially offset H$β$ + [OIII] emission compared to the UV and stellar components. Given the absence of obvious signatures of actively accreting black holes, these emitters are likely under strong feedback-driven winds from massive stars. Lastly, we report a unique overdensity of EELGs in one of the observed fields. The discovery of such a "star-bursting" overdensity supports the idea that large ionizing bubbles formed around some EEGLs in the early Universe.

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arXiv2025

Enhanced gas-phase metallicities and suppressed outflows for galaxies in a rich cluster core at cosmic noon

We present the result of near-infrared spectroscopy using Keck/MOSFIRE for 23 member galaxies in an X-ray cluster XCS2215 ($z=1.46$) to investigate the environmental dependence of gaseous flows and metallicities. We find that the metallicities derived from H$α$ and [N II] emission lines of the cluster galaxies are enhanced by 0.08-0.15 dex with $\sim$2 $σ$ significance compared to field counterparts for the same stellar mass. It suggests that inefficient gas accretion in the shock-heated intracluster medium (ICM) in the cluster core results in the lack of metallicity dilution. We also estimate the mass-loading factor by comparing the observed galaxies with the chemical evolution model that takes into account the outflow processes on the metallicity versus gas mass fraction diagram constructed together with the ALMA data. We find that the outflows from galaxies in the cluster core region tend to be weaker than those of galaxies in the general field. It is likely due to the confinement of gas by the high pressure of the surrounding ICM in the cluster core, which leads to the recycling of the outflowing gas that comes back to the system and is used for further star formation, resulting in the progression of chemical evolution. Compared with higher redshift protocluster galaxies at $z>2$, which tend to show lower metallicity than the field galaxies due probably to dilution of metals by pristine gas inflow, we are seeing the transition of gas accretion mode from efficient cold stream mode to the inefficient hot mode.

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arXiv2025

Green Flash: Residual Emissions Enshrouded in Low-mass Balmer-break Galaxies at $z\sim5$

Recent James-Webb Space Telescope (JWST) observations have discovered galaxies that are already passively evolving at $z>4$, $\sim1.5$\,Gyr after the Big Bang. Remarkably, some of these galaxies exhibit strong emission lines such as \ha\ and \oiii\ while showing a strong continuum break at $\sim3650$\,Å i.e., Balmer break, giving us a unique insight into the physical mechanisms responsible for early galaxy quenching. In this study, we investigate the nature of four such galaxies at $z=5.10$--$5.78$ identified in the Abell~2744 field, using JWST/NIRCam and NIRSpec data. Our spectral energy distribution (SED) fitting analysis reveals that these galaxies have been mostly quiescent since $\sim100$\,Myr prior to the observed time. We find a higher dust attenuation in the nebular component than in the continuum in all cases. This suggests the presence of dusty star-forming regions or obscured AGN, which could be a {\it residual} signature of past quenching. For one of the galaxies with sufficient medium-band coverage, we derive the \hb+\oiii\ emission line map, finding that the line-emitting region is located in the center and is more compact ($R_e=0.7$\,kpc) than the stellar component ($R_e=0.9$\,kpc). For this specific galaxy, we discuss a scenario where quenching proceeds in the manner of ``outside-in", a stark contrast to the inside-out quenching commonly seen in massive galaxies at later cosmic times.

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arXiv2025

Deciphering Gas Dynamics and Star Formation in a z=1.1 Main Sequence Spiral Galaxy with ALMA and JWST

We present a joint analysis of high-resolution CO(2-1) and Paschen-$α$ emission lines to trace gas dynamics and spatially resolved star formation in ASPECS-LP.3mm.06, a $z=1.1$ main sequence galaxy. Utilizing data from the ALMA and JWST NIRCam Wide Field Slitless Spectroscopy (WFSS), we explore both ionized gas and molecular gas within this galaxy. With a substantial molecular gas fraction (f$_\mathrm{mol}$ = 0.44 $\pm$ 0.02), ASPECS-LP.3mm.06 remains on the star-forming main sequence and adheres to the Kennicutt-Schmidt (KS) relation, indicating typical gas-to-star conversion efficiency. Our analysis reveals extended structures across multiple wavelengths, suggesting regulated star formation within a stable disk. The spatially resolved star formation efficiency (SFE) and kinematic analysis indicate that ASPECS-LP.3mm.06 features a smooth mass assembly process across bulge and disk. Additionally, the galaxy exhibits modest dust extinction (A$_\mathrm{V}$ = 0.8), potentially linked to self-regulation during bulge formation. These findings position ASPECS-LP.3mm.06 as a prototypical galaxy, offering valuable insights into the mechanisms governing normal disk galaxy growth at z$\sim$1.

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arXiv2024

BEACON: JWST NIRCam Pure-parallel Imaging Survey. I. Survey Design and Initial Results

We introduce the Bias-free Extragalactic Analysis for Cosmic Origins with NIRCam (BEACON) survey, a JWST Cycle2 program allocated up to 600 pure-parallel hours of observations. BEACON explores high-latitude areas of the sky with JWST/NIRCam over $\sim100$ independent sightlines, totaling $\sim0.3$deg$^2$, reaching a median F444W depth of $\approx28.2$AB mag (5$σ$). Based on existing JWST observations in legacy fields, we estimate that BEACON will photometrically identify 25--150 galaxies at $z>10$ and 500--1000 at $z\sim7$--10 uniquely enabled by an efficient multiple filter configuration spanning $0.9$--5.0$μ$m. The expected sample size of $z>10$ galaxies will allow us to obtain robust number density estimates and to discriminate between different models of early star formation. In this paper, we present an overview of the survey design and initial results using the first 19 fields. We present 129 galaxy candidates at $z>7$ identified in those fields, including 11 galaxies at $z>10$ and several UV-luminous ($M_{\rm UV}<-21$mag) galaxies at $z\sim8$. The number densities of $z<13$ galaxies inferred from the initial fields are overall consistent with those in the literature. Despite reaching a considerably large volume ($\sim10^5$Mpc$^3$), however, we find no galaxy candidates at $z>13$, providing us with a complimentary insight into early galaxy evolution with minimal cosmic variance. We publish imaging and catalog data products for these initial fields. Upon survey completion, all BEACON data will be coherently processed and distributed to the community along with catalogs for redshift and other physical quantities.

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arXiv2024

Revealing the quiescent galaxy population in the Spiderweb protocluster at z=2.16 with deep HST/WFC3 slitless spectroscopy

We report the HST WFC3 G141 grism slitless spectroscopy observation of the core region of the Spiderweb protocluster at $z=2.16$. We analyzed the spectra of all objects in a $\sim 2 \times 2 \text{ arcmin}^2$ field of view and identified 40 protocluster members, recovering 19 previously identified H$α$-emitters in addition to revealing 21 new members. The spectra allowed us to identify 11 galaxies with quiescent spectra. Three galaxies with quiescent spectra are possibly still star-forming according to SED fitting, indicating a possible left-over or dust-obscured star formation. We estimate a quiescent fraction of $\sim 50\%$ for $M_\star > 10^{11} M_\odot$. About half of the quiescent galaxies possibly host AGN, hinting at AGN's key role in quenching galaxies in the protocluster environment. These quiescent galaxies have relatively more compact and concentrated light profiles than the star-forming members, but they are not yet as bulge-dominated as local ellipticals. These results are consistent with previous studies that indicate the Spiderweb protocluster is in the maturing stage, with a red sequence that has begun forming.

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arXiv2024

Galaxy Morphologies Revealed with Subaru HSC and Super-Resolution Techniques II: Environmental Dependence of Galaxy Mergers at z~2-5

We super-resolve the seeing-limited Subaru Hyper Suprime-Cam (HSC) images for 32,187 galaxies at z~2-5 in three techniques, namely, the classical Richardson-Lucy (RL) point spread function (PSF) deconvolution, sparse modeling, and generative adversarial networks to investigate the environmental dependence of galaxy mergers. These three techniques generate overall similar high spatial resolution images but with some slight differences in galaxy structures, for example, more residual noises are seen in the classical RL PSF deconvolution. To alleviate disadvantages of each technique, we create combined images by averaging over the three types of super-resolution images, which result in galaxy sub-structures resembling those seen in the Hubble Space Telescope images. Using the combined super-resolution images, we measure the relative galaxy major merger fraction corrected for the chance projection effect, f_merg, for galaxies in the ~300 deg^2-area data of the HSC Strategic Survey Program and the CFHT Large Area U-band Survey. Our f_merg measurements at z~3 validate previous findings showing that f_merg is higher in regions with a higher galaxy overdensity delta at z~2-3. Thanks to the large galaxy sample, we identify a nearly linear increase in f_merg with increasing delta at z~4-5, providing the highest-z observational evidence that galaxy mergers are related to delta. In addition to our f_merg measurements, we find that the galaxy merger fractions in the literature also broadly align with the linear f_merg-delta relation across a wide redshift range of z~2-5. This alignment suggests that the linear f_merg-delta relation can serve as a valuable tool for quantitatively estimating the contributions of galaxy mergers to various environmental dependences. This super-resolution analysis can be readily applied to datasets from wide field-of-view space telescopes such as Euclid and Roman.

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arXiv2024

Thirty Meter Telescope International Observatory Detailed Science Case 2024

The Thirty Meter Telescope (TMT) International Observatory (TIO) will be a revolutionary leap forward in astronomical observing capabilities, enabling us to address some of the most profound questions about the universe. From unraveling the mysteries of dark matter and dark energy to exploring the origins of stars and planets, TMT will transform our understanding of the cosmos. The TIO Detailed Science Case (DSC) presents science goals that inform the top-level requirements for the observatory's design and operations, including the telescope, enclosure, instruments, and adaptive optics system.

astro-ph.IM↗

arXiv2024

Spider-Webb: JWST Near Infrared Camera resolved galaxy star formation and nuclear activities in the Spiderweb protocluster at z=2.16

Near-infrared (NIR) emission is less affected by dust than UV and optical emission and is therefore useful for studying the properties of dust-obscured galaxies. Although rest-frame NIR observations of high-redshift galaxies have long been made using space telescopes, their structures were unresolved due to the lack of angular resolution. This letter reports the early results from the analysis of high-resolution Pa$β$ imaging of the Spiderweb protocluster at $z=2.16$ with the JWST Near Infrared Camera. We investigate radial profiles of Pa$β$ lines and rest-frame NIR continua from luminous H$α$-emitting galaxies (HAEs) in the protocluster. Particularly, we compare those of 11 HAEs (N-HAEs) on the star-forming main sequence with those of 8 HAEs (X-HAEs) with X-ray AGNs. Resultant composite Pa$β$ line images of N-HAEs indicate significant star formation in galactic disks. In contrast, X-HAEs are dominated by point source components rather than outer star formation, as inferred from our earlier work based on multi-wavelength SED fitting. Given their higher stellar potentials suggested from their rest-frame NIR images, the different characteristics may be driven by the impact of AGN feedback.

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arXiv2024

JWST/NIRCam Pa$\mathrmβ$ narrow-band imaging reveals ordinary dust extinction for H$\mathrmα$ emitters within the Spiderweb protocluster at z=2.16

We combine JWST/NIRCam and Subaru/MOIRCS dual Pa$\mathrmβ$ + H$\mathrmα$ narrow-band imaging to trace the dust attenuation and the star-formation activities of a sample of 43 H$\mathrmα$ emitters at the core of one of the most massive and best-studied clusters in formation at the cosmic noon: the Spiderweb protocluster at $\mathrm{z=2.16}$. We find that most H$\mathrmα$ emitters display Pa$\mathrmβ$/H$\mathrmα$ ratios compatible with Case B recombination conditions, which translates into nebular extinction values ranging at $\mathrm{A_V\approx0-3}$ magnitudes, and dust corrected $\mathrm{Paβ}$ star formation rates consistent with coeval main sequence field galaxies at fixed stellar mass ($\mathrm{9.4<\log M_*/M_\odot<11.0}$) during this cosmic epoch. Furthermore, we investigate possible environmental impacts on dust extinction across the protocluster large-scale structure and find no correlation between the dustiness of its members and environmental proxies such as phase-space position, clustercentric radius, or local density. These results support the scenario for which dust production within the main galaxy population of this protocluster is driven by secular star formation activities fueled by smooth gas accretion across its large-scale structure. This downplays the role of gravitational interactions in boosting star formation and dust production within the Spiderweb protocluster, in contrast with observations in higher redshift and less evolved protocluster cores.

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arXiv2024

JWST/NIRCam Narrowband Survey of Pa$β$ Emitters in the Spiderweb Protocluster at z=2.16

We report the initial result of our Pa$β$ narrowband imaging on a protocluster with the JWST Near Infrared Camera (NIRCam). As NIRCam enables deep narrowband imaging of rest-frame NIR lines at $z>1$, we target one of the most studied protoclusters, the Spiderweb protocluster at $z=2.16$, in which previous studies have confirmed more than a hundred member galaxies. The NIRCam F405N narrowband filter covers in Pa$β$ line the protocluster redshift given by known protocluster members, allowing the search for new member candidates. The weight-corrected color-magnitude diagram obtained 57 sources showing narrowband excesses, 41 of which satisfy further color selection criteria for limiting the sample to Pa$β$ emitter candidates at $z\sim2.16$, and 24 of them do not have H$α$ emitter counterparts. The Pa$β$ emitter candidates appear to follow the spatial distribution of known protocluster members; however, follow-up spectroscopic confirmation is required. Only 17 out of 58 known H$α$-emitting cluster members are selected as Pa$β$ emitters in the current data, albeit the rest fall out of the narrowband selection owing to their small Pa$β$ equivalent widths. We derive Pa$β$ luminosity function in the Spiderweb protocluster, showing a normalization density of $\log{ϕ^\ast}=-2.53\pm0.15$ at a characteristic Pa$β$ luminosity of $\log{L^\ast}=42.33\pm0.17$. Furthermore, we examine the possibility of detecting faint line emitters visible only in the narrow-band image, but find no promising candidates.

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arXiv2024

A Systematic Search of Distant Superclusters with the Subaru Hyper Suprime-Cam Survey

Superclusters, encompassing environments across a wide range of overdensities, can be regarded as unique laboratories for studying galaxy evolution. Although numerous supercluster catalogs have been published, none of them goes beyond redshift $z=0.7$. In this work, we adopt a physically motivated supercluster definition, requiring that superclusters should eventually collapse even in the presence of dark energy. Applying a friends-of-friends (FoF) algorithm to the CAMIRA cluster sample constructed using the Subaru Hyper Suprime-Cam survey data, we have conducted the first systematic search for superclusters at $z=0.5-1.0$ and identified 673 supercluster candidates over an area of 1027 deg$^2$. The FoF algorithm is calibrated by evolving $N$-body simulations to the far future to ensure high purity. We found that these high-$z$ superclusters are mainly composed of $2-4$ clusters, suggesting the limit of gravitationally bound structures in the younger Universe. In addition, we studied the properties of the clusters and brightest cluster galaxies (BCGs) residing in different large-scale environments. We found that clusters associated with superclusters are typically richer, but no apparent dependence of the BCG properties on large-scale structures is found. We also compared the abundance of observed superclusters with mock superclusters extracted from halo light cones, finding that photometric redshift uncertainty is a limiting factor in the performance of superclusters detection.

astro-ph.CO↗

arXiv2024

Star formation activity of low-mass galaxies at the peak epoch of galaxy formation probed by deep narrow-band imaging

Low-mass galaxies at high redshifts are the building blocks of more massive galaxies at later times and are thus key populations for understanding galaxy formation and evolution. We have made deep narrow-band observations for two protoclusters and the general field in COSMOS at $z$ $\sim$ 2. In a clumpy young protocluster, USS1558$-$003, at $z$ = 2.53, we find many star-forming galaxies well above the star-forming main sequence of field galaxies at the low-mass end ($M_{\star}/\mathrm{M_{\odot}}<10^{8.9}$). This suggests that some environmental effects may be at work in low-mass galaxies in high-density regions to enhance their star formation activities. In the core of this protocluster, we also find that enhanced star formation activity of middle-mass galaxies ($10^{8.9} < M_{\star}/\mathrm{M_{\odot}} < 10^{10.2}$) while such trends are not observed in a more mature protocluster, PKS1138$-$262 at $z$ = 2.16. We expect these activities to be mainly due to galaxy mergers/interactions and differences in the amount of cold gas accretion. As one piece of evidence, we show that the star formation activity within individual galaxies in the protoclusters is more centrally concentrated than those in the field. This is probably due to the enhanced interactions between galaxies in the protocluster, which can reduce the angular momentum of the gas, drive the gas towards the galaxy center, and lead to a central starburst.

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arXiv2024

SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). V. Confusion-limited Submillimeter Galaxy Number Counts at 450 $μ$m and Data Release for the COSMOS Field

We present confusion-limited SCUBA-2 450-$μ$m observations in the COSMOS-CANDELS region as part of the JCMT Large Program, SCUBA-2 Ultra Deep Imaging EAO Survey (STUDIES). Our maps at 450 and 850 $μ$m cover an area of 450 arcmin$^2$. We achieved instrumental noise levels of $σ_{\mathrm{450}}=$ 0.59 mJy beam$^{-1}$ and $σ_{\mathrm{850}}=$ 0.09 mJy beam$^{-1}$ in the deepest area of each map. The corresponding confusion noise levels are estimated to be 0.65 and 0.36 mJy beam$^{-1}$. Above the 4 (3.5) $σ$ threshold, we detected 360 (479) sources at 450 $μ$m and 237 (314) sources at 850 $μ$m. We derive the deepest blank-field number counts at 450 $μ$m, covering the flux-density range of 2 to 43 mJy. These are in agreement with other SCUBA-2 blank-field and lensing-cluster observations, but are lower than various model counts. We compare the counts with those in other fields and find that the field-to-field variance observed at 450 $μ$m at the $R=6^\prime$ scale is consistent with Poisson noise, so there is no evidence of strong 2-D clustering at this scale. Additionally, we derive the integrated surface brightness at 450 $μ$m down to 2.1 mJy to be $57.3^{+1.0}_{-6.2}$~Jy deg$^{-2}$, contributing to (41$\pm$4)\% of the 450-$μ$m extragalactic background light (EBL) measured by COBE and Planck. Our results suggest that the 450-$μ$m EBL may be fully resolved at $0.08^{+0.09}_{-0.08}$~mJy, which extremely deep lensing-cluster observations and next-generation submillimeter instruments with large aperture sizes may be able to achieve.

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arXiv2024

JWST's first glimpse of a z > 2 forming cluster reveals a top-heavy stellar mass function

Clusters and their progenitors (protoclusters) at z = 2-4, the peak epoch of star formation, are ideal laboratories to study the formation process of both the clusters themselves and their member galaxies. However, a complete census of their member galaxies has been challenging due to observational difficulties. Here we present new JWST/NIRCam observations targeting the distant cluster CLJ1001 at z = 2.51 from the COSMOS-Web program, which, in combination with previous narrowband imaging targeting H-alpha emitters and deep millimeter surveys of CO emitters, provide a complete view of massive galaxy assembly in CLJ1001. In particular, JWST reveals a population of massive, extremely red cluster members in the long-wavelength bands that were invisible in previous Hubble Space Telescope (HST)/F160W imaging (HST-dark members). Based on this highly complete spectroscopic sample of member galaxies, we show that the spatial distribution of galaxies in CLJ1001 exhibits a strong central concentration, with the central galaxy density already resembling that of low-z clusters. Moreover, we reveal a "top-heavy" stellar mass function for the star-forming galaxies (SFGs), with an overabundance of massive SFGs piled up in the cluster core. These features strongly suggest that CLJ1001 is caught in a rapid transition, with many of its massive SFGs likely soon becoming quiescent. In the context of cluster formation, these findings suggest that the earliest clusters form from the inside out and top to bottom, with the massive galaxies in the core assembling first, followed by the less massive ones in the outskirts.

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arXiv2024

Insights into Galaxy Morphology and Star Formation: Unveiling Filamentary Structures around an Extreme Overdensity at $z \sim 1.5$ Traced by [OII] Emitters

We explore the morphological features and star formation activities of [OII] emitters in the COSMOS UltraDeep field at $z \sim 1.5$ using JWST NIRCam data from the COSMOS-Web survey and Subaru Hyper Suprime-Cam. We also report the discovery of large filamentary structures traced by [OII] emitters, surrounding an extremely overdense core with a galaxy number density $\sim11\times$ higher than the field average. These structures span over 50 cMpc, underscoring their large scale in the cosmic web at this epoch. After matching the stellar mass distributions, the core galaxies show a higher frequency of disturbances (50$\%$ $ \pm$ 9$\%$) than those in outskirts (41$\%$ $ \pm$ 9$\%$) and the field (21$\%$ $ \pm$ 5$\%$), indicative of more frequent mergers and interactions in the innermost $\lesssim1.5 $ arcmin region. Additionally, we observe that specific star formation rates are elevated in denser environments. A Kolmogorov-Smirnov (KS) test comparing the distribution of specific star formation rates of core and field galaxies yields a $\textit{p}$-value of 0.02, suggesting an enhancement of star-formation activity driven by the dense environment. Our findings underscore the environmental impact on galaxy evolution during a pivotal cosmic epoch and set the stage for further investigation with the increasing larger data from upcoming surveys.

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arXiv2024

Multiple emission lines of H$α$ emitters at $z \sim 2.3$ from the broad and medium-band photometry in the ZFOURGE Survey

We present a multiple emission lines study of $\sim$1300 H$α$ emitters (HAEs) at $z \sim 2.3$ in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE-$K_s$ broad-band data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [OIII]$λ\lambda4959,5007$, [OII]$λ\lambda3726,3729$. Our measurements exhibit good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate (SFR), specific SFR (sSFR), ionization states (O32). We have identified a discrepancy between between HAEs at $z\sim2.3$ and typical local star-forming galaxy observed in the SDSS, suggesting the evolution of lower gas-phase metallicity ($Z$) and higher ionization parameters ($U$) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high $EW_{\mathrm{[OIII]}}$. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters (O3Es) and Ly$α$ emitters (LAEs) at $z\simeq2-3$. Considering that these characteristics may indicate potential strong Lyman continuum (LyC) leakage, higher redshift anaglogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations on this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization.

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arXiv2024

New insights into the role of AGNs in forming the cluster red sequence

As a considerable investment of time from various telescope facilities were dedicated toward studying the Spiderweb protocluster at $z=2.2$, it so far remains one of the most extensively studied protocluster. We report here the latest results in this field, adding a new dimension to previous research on cluster formation at high redshift. Previous studies have reported a significant overdensity ($δ\sim10$) of massive H$α$ (+ [Nii]) -emitting galaxies in 3700 comoving Mpc$^3$. Many of these were previously considered to be dusty, actively star-forming galaxies, given their rest-frame optical and infrared features. However, this study argues that a third of them are more likely to be "passively-evolving" galaxies with low-luminosity active galactic nuclei (AGNs) rather than star-forming galaxies, given the multi-wavelength spectral energy distribution (SED) fitting including an AGN component. For their SED-based star formation rates to be valid, bulk of their H$α$ + [Nii] emission should come from the central AGNs. This difference in interpretation between this work and past studies, including ours, is particularly supported by the recent deep Chandra X-ray observation. Furthermore, we have spectroscopically confirmed a quiescent nature for one of these AGNs, with its multiple stellar absorption lines but also low ionisation emission lines. This important update provides new insights into the role of AGNs in forming the cluster red sequence observed in the present-day universe.

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