arXiv subjects

Hideki Umehata

Publications and source records attributed to Hideki Umehata.

At least 37 records · Page 2Linked to original sources

arXiv2025

ELPIS: Accelerated metal and dust enrichment in a proto-cluster core at $z\approx8$

We present a study of the metal, dust, and molecular gas content in galaxies within the A2744-z7p9OD proto-cluster at z ~ 7.88. We focus on two galaxy groups, the Quintet and the Chain, which are covered by the ELPIS survey (The Emission-Line Protocluster Imaging Survey of the furthest overdensity beyond Pandora's Cluster Abell 2744). [C II] 158 um emission is detected in five galaxies, revealing molecular gas reservoirs with log(M_gas/Msun) ~ 9.0-9.6, while dust continuum at the observed frame of 1.26 mm is detected in three galaxies, yielding dust masses of log(M_dust/Msun) ~ 6.0-6.4, assuming a dust temperature of T_dust = 45 (+15, -15) K. The derived properties, including stellar-to-dust mass ratios of log(M_dust/M_star) ~ -3 to -2 at log(M_star/Msun) ~ 9, and dust-to-gas mass ratios of log(M_dust/M_gas) ~ -4 to -3 at 12+log(O/H) ~ 8, place these galaxies in an intermediate regime: higher than the very low ratios expected from supernova-driven dust production, but still below the levels attained once efficient grain growth dominates. These values indicate a transition phase of dust mass assembly, likely reflecting the onset of grain growth via metal accretion under accelerated evolution in the proto-cluster core.

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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

The first direct imaging of the silhouette of a damped Lyman $α$ system along the line-of-sight to a background galaxy

The H~{\sc i} gas distribution in damped Lyman $α$ absorbers (DLAs) has remained elusive due to the point-source nature of background quasar emission. Observing DLAs against spatially extended background galaxies provides a new method for constraining their size and structure. Using the Keck Cosmic Web Imager, we present the first ``silhouette'' image of a DLA at $z=3.34$, identified in the spectrum of a background galaxy at $z=3.61$. Although the silhouette remains unresolved due to limited spatial resolution, this represents a successful proof-of-concept for studying DLA morphology using extended background sources. Possible residual emission in the DLA trough suggests an optical depth contrast exceeding $10^7$ in the internal structure, implying a sharp edge or patchy structure. A Lyman $α$ emitter (LAE) at $z_{\rm LAE}=3.3433\pm0.0005$, consistent with the DLA redshift, is detected at an angular separation of $1.''73\pm0.''28$ ($12.9\pm2.1$ kpc). The DLA is surrounded by three galaxies within 140 kpc in projected distance and 500 km s$^{-1}$ in line-of-sight velocity, indicating that it resides in the circumgalactic medium of the LAE or within a galaxy group/protocluster environment. An O~{\sc i} $\lambda1302$ absorption at $z_{\rm OI}=3.3288\pm0.0004$ is also detected along the line of sight. This absorber may trace metal-enriched outflow from the LAE or a gas-rich galaxy exhibiting the highest star formation activity among the surrounding galaxies. Future large spectroscopic surveys of galaxies will expand such a DLA sample, and three-dimensional spectroscopy for it will shed new light on the role of intergalactic dense gas in galaxy formation and evolution.

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arXiv2025

A Post-Starburst Pathway for the Formation of Massive Galaxies and Black Holes at z>6

Understanding the rapid formation of supermassive black holes (SMBHs) in the early universe requires insight into stellar mass growth in host galaxies. Here, we present NIRSpec rest-frame optical spectra and NIRCam imaging from JWST of two galaxies at z>6, both hosting moderate-luminosity quasars. These galaxies exhibit Balmer absorption lines, similar to low-redshift post-starburst galaxies. Our analyses of the medium-resolution spectra and multiband photometry show bulk of the stellar mass (log (M_* / M_sun) > 10.6) formed in starburst episodes at redshift 9 and 7. One of the galaxies shows a clear Balmer break and lacks spatially resolved H alpha emission. It falls well below the star formation main sequence at z = 6, indicating quiescence. The other is transitioning to quiescence; together, these massive galaxies are among the most distant post-starburst systems known. The blueshifted wings of the quasar [O III] emission lines suggest quasar-driven outflow possibly influencing star formation. Direct stellar velocity dispersion measurements reveal one galaxy follows the local black hole mass-sigma_* relation while the other is overmassive. The existence of massive post-starburst galaxies hosting billion-solar-mass BHs in short-lived quasar phases suggests SMBHs and host galaxies played a major role in each other's rapid early formation.

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arXiv2025

Compact Ionized Gas Region Surrounded by Porous Neutral Gas in a Dusty Lyman Break Galaxy at Redshift $z=8.312$

Porous interstellar medium (ISM) structure in galaxies at the epoch of reionization (EoR) gives us a hint to understand what types of galaxies contribute to reionization. Although recent studies have pointed out the positive correlation between high ionizing photon escape fractions and high [O III] $88~μ\mathrm{m}$-to-[C II] $158~μ\mathrm{m}$ ratios found in UV-luminous star-forming galaxies at $z > 6$ with ALMA, previous studies have paid little attention to the neutral gas porosity that allows ionizing photons to escape. Here, we present a detailed analysis of a $z=8.312$ Lyman break galaxy, MACS0416_Y1 with a high $L_\mathrm{[OIII]88}/L_\mathrm{[CII]158}$ ratio ($\approx9$) and dust continuum detection. We construct a multi-phase ISM model incorporating the neutral gas covering fraction ($cov_\mathrm{PDR}$). The best-fit model reveals a $cov_\mathrm{PDR}\approx25 \%$, indicating that $\approx75 \%$ of the ionized gas region is exposed to intercloud space. We confirm that our conclusions hold even when varying star-formation history, stellar age, gas/stellar metallicity, and carbon-to-oxygen abundance ratio. This finding meets one of the necessary conditions for galaxies to have a non-zero escape fraction of ionizing photons and supports recent studies that galaxies with a high [O III] $88~μ\mathrm{m}/$[C II] $158~μ\mathrm{m}$ ratio, such as MACS0416_Y1, could contribute to cosmic reionization. Furthermore, the modeled H II region with the best-fitting parameters has a typical size ($D=0.90~\mathrm{pc}$) and gas density ($\log n_\mathrm{H,c}/\mathrm{cm^{-3}}=2.7$) that are comparable to local compact H II regions. This suggests that the H II regions in MACS0416_Y1 are in an early evolutionary stage.

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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

Medium-band Astrophysics with the Grism of NIRCam In Frontier fields (MAGNIF): Spectroscopic Census of H$α$ Luminosity Functions and Cosmic Star Formation at $z\sim 4.5$ and 6.3

We measure H$α$ luminosity functions (LFs) at redshifts $z \sim 4.5$ and 6.3 using the JWST MAGNIF (Medium-band Astrophysics with the Grism of NIRCam In Frontier fields) survey. MAGNIF obtained NIRCam grism spectra with the F360M and F480M filters in four Frontier Fields. We identify 248 H$α$ emitters based on the grism spectra and photometric redshifts from combined HST and JWST imaging data. The numbers of the H$α$ emitters show a large field-to-field variation, highlighting the necessity of multiple fields to mitigate cosmic variance. We calculate both observed and dust-corrected H$α$ LFs in the two redshift bins. Thanks to the gravitational lensing, the measured H$α$ LFs span three orders of magnitude in luminosity, and the faint-end luminosity reaches $L_{\mathrm{H}α} \sim 10^{40.3} \mathrm{erg} \mathrm{s}^{-1}$ at $z \sim 4.5$ and $10^{41.5} \mathrm{erg} \mathrm{s}^{-1}$ at $z \sim 6.3$, corresponding to star-formation rates (SFRs) of $\sim$ 0.1 and 1.7 $\mathrm{M}_\odot \mathrm{yr}^{-1}$. We conclude no or weak redshift evolution of the faint-end slope of H$α$ LF across $z\simeq0.4-6.3$, and the comparison with the faint-end slopes of UV LF indicates stochastic star formation history among low-mass H$α$ emitters. The derived cosmic SFR densities are $0.058^{+0.008}_{-0.006}\ \ M_\odot\ \mathrm{yr}^{-1}\ \mathrm{Mpc}^{-3}$ at $z \sim 4.5$ and $0.025^{+0.009}_{-0.007}\ \ M_\odot\ \mathrm{yr}^{-1}\ \mathrm{Mpc}^{-3}$ at $z \sim 6.3$. These are approximately 2.2 times higher than previous estimates based on dust-corrected UV LFs, but consistent with recent measurements from infrared surveys. We discuss uncertainties in the H$α$ LF measurements, including those propagate from the lens models, cosmic variance, and AGN contribution.

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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

ALMA Lensing Cluster Survey: Physical characterization of near-infrared-dark intrinsically faint ALMA sources at z=2-4

We present results from Atacama Large Millimeter/submillimeter Array (ALMA) spectral line-scan observations at 3-mm and 2-mm bands of three near-infrared-dark (NIR-dark) galaxies behind two massive lensing clusters MACS J0417.5-1154 and RXC J0032.1+1808. Each of these three sources is a faint (de-lensed $S_{\text{1.2 mm}}$ $<$ 1 mJy) triply lensed system originally discovered in the ALMA Lensing Cluster Survey. We have successfully detected CO and [C I] emission lines and confirmed that their spectroscopic redshifts are $z=3.652$, 2.391, and 2.985. By utilizing a rich multi-wavelength data set, we find that the NIR-dark galaxies are located on the star formation main sequence in the intrinsic stellar mass range of log ($M_*$/$M_\odot$) = 9.8 - 10.4, which is about one order of magnitude lower than that of typical submillimeter galaxies (SMGs). These NIR-dark galaxies show a variety in gas depletion times and spatial extent of dust emission. One of the three is a normal star-forming galaxy with gas depletion time consistent with a scaling relation, and its infrared surface brightness is an order of magnitude smaller than that of typical SMGs. Since this galaxy has an elongated axis ratio of $\sim 0.17$, we argue that normal star-forming galaxies in an edge-on configuration can be heavily dust-obscured. This implies that existing deep WFC3/F160W surveys may miss a fraction of typical star-forming main-sequence galaxies due to their edge-on orientation.

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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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arXiv2025

ALMA/SCUBA-2 COSMOS Survey: Properties of X-ray- and SED-selected AGNs in Bright Submillimeter Galaxies

We investigate the properties of active galactic nuclei (AGNs) in the brightest submillimeter galaxies (SMGs) in the COSMOS field. We utilize the bright sample of ALMA/SCUBA-2 COSMOS Survey (AS2COSMOS), which consists of 260 SMGs with $S_{\mathrm{870}\, μ\mathrm{m}}=0.7\text{--}19.2\,\mathrm{mJy}$ at $z=0\text{--}6$. We perform optical to millimeter spectral energy distribution (SED) modeling for the whole sample. We identify 24 AGN-host galaxies from the SEDs. Supplemented by 23 X-ray detected AGNs (X-ray AGNs), we construct an overall sample of 40 AGN-host galaxies. The X-ray luminosity upper bounds indicate that the X-ray undetected SED-identified AGNs are likely to be nearly Compton thick or have unusually suppressed X-ray emission. From visual classification, we identify $25^{+6}_{-5}$\% of the SMGs without AGNs as major merger candidates. This fraction is almost consistent with the general galaxy population at $z\sim2$, suggesting that major mergers are not necessarily required for the enhanced star formation in SMGs. We also identify $47^{+16}_{-15}$\% of the AGN hosts as major merger candidates, which is about twice as high as that in the SMGs without AGNs. This suggests that major mergers play a key role in triggering AGN activity in bright SMGs.

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arXiv2025

Discovery of a Unique Close Quasar-DSFG Pair Linked by a [C II] Bridge at $z=5.63$

We report the discovery of a unique quasar-dusty star-forming galaxy (DSFG) system at $z = 5.63$, consisting of the bright quasar J1133+1603 ($M_{\rm UV} = -27.42$) and its compact, dust-obscured companion, J1133c. ALMA observations reveal a prominent [C II] bridge connecting the quasar and DSFG, indicating ongoing interaction at a projected separation of 1.8 arcsec ($\sim$10 proper kpc). J1133c exhibits unusually bright and broad [C II] emission ($L_{\rm [CII]} > 10^{43}$ erg s$^{-1}$, FWHM $> 500$ km s$^{-1}$), with a [C II] luminosity five times that of the quasar, suggesting intense star formation or potential AGN activity. The inferred star formation rate from [C II] is approximately $10^3$ M$_\odot$ yr$^{-1}$. The remarkable properties of this pair strongly suggest that galaxy interactions may simultaneously trigger both starburst and quasar activity, driving rapid evolution in the early universe.

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arXiv2024

Merging gas-rich galaxies that harbor low-luminosity twin quasars at z = 6.05: a promising progenitor of the most luminous quasars

We present ALMA [CII] 158 $μ$m line and underlying far-infrared (FIR) continuum emission observations ($0''.57 \times 0''.46$ resolution) toward a quasar-quasar pair system recently discovered at $z = 6.05$ (Matsuoka et al. 2024). The quasar nuclei (C1 and C2) are faint ($M_{\rm 1450} \gtrsim -23$ mag), but we detect very bright [CII] emission bridging the 12 kpc between the two objects and extending beyond them (total luminosity $L_{\rm [CII]} \simeq 6 \times 10^9~L_\odot$). The [CII]-based total star formation rate of the system is $\sim 550~M_\odot$ yr$^{-1}$ (IR-based dust-obscured SFR is $\sim 100~M_\odot$ yr$^{-1}$), with a [CII]-based total gas mass of $\sim 10^{11}~M_\odot$. The dynamical masses of the two galaxies are large ($\sim 9 \times 10^{10}~M_\odot$ for C1 and $\sim 5 \times 10^{10}~M_\odot$ for C2). There is a smooth velocity gradient in [CII], indicating that these quasars are a tidally interacting system. We identified a dynamically distinct, fast [CII] component around C1: detailed inspection of the line spectrum there reveals the presence of a broad wing component, which we interpret as the indication of fast outflows with a velocity of $\sim 600$ km s$^{-1}$. The expected mass loading factor of the outflows, after accounting for multiphase gas, is $\gtrsim 2-3$, which is intermediate between AGN-driven and starburst-driven outflows. Hydrodynamic simulations in the literature predicted that this pair will evolve to a luminous ($M_{\rm 1450} \lesssim -26$ mag), starbursting ($\gtrsim 1000~M_\odot$ yr$^{-1}$) quasar after coalescence, one of the most extreme populations in the early universe.

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arXiv2024

Ongoing and fossil large-scale outflows detected in a high-redshift radio galaxy: [C II] observations of TN J0924$-$2201 at $z=5.174$

We present Atacama Large Millimeter/submillimeter Array observations of the [C II] 158 $μ$m line and the underlying continuum emission of TN J0924$-$2201, which is one of the most distant known radio galaxies at $z>5$. The [C II] line and 1-mm continuum emission are detected at the host galaxy. The systemic redshift derived from the [C II] line is $z_{\rm [C II]}=5.1736\pm0.0002$, indicating that the Ly$α$ line is redshifted by a velocity of $1035\pm10$ km s$^{-1}$, marking the largest velocity offset between the [C II] and Ly$α$ lines recorded at $z>5$ to date. In the central region of the host galaxy, we identified a redshifted substructure of [C II] with a velocity of $702\pm17$ km s$^{-1}$, which is close to the CIV line with a velocity of $500\pm10$ km s$^{-1}$. The position and the velocity offsets align with a model of an outflowing shell structure, consistent with the large velocity offset of Ly$α$. The non-detection of [C II] and dust emission from the three CO(1--0)-detected companions indicates their different nature compared to dwarf galaxies based on the photodissociation region model. Given their large velocity of $\sim1500$ km s$^{-1}$, outflowing molecular clouds induced by the AGN is the most plausible interpretation, and they may exceed the escape velocity of a $10^{13}\,M_{\odot}$ halo. These results suggest that TN J0924$-$2201, with the ongoing and fossil large-scale outflows, is in a distinctive phase of removing molecular gas from a central massive galaxy in an overdense region in the early universe. A dusty HI absorber at the host galaxy is an alternative interpretation.

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arXiv2024

ALMA Lensing Cluster Survey: Deep 1.2 mm Number Counts and Infrared Luminosity Functions at $z\simeq1-8$

We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $μ$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects.

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arXiv2024

FINER: Far-Infrared Nebular Emission Receiver for the Large Millimeter Telescope

Unveiling the emergence and prevalence of massive/bright galaxies during the epoch of reionization and beyond, within the first 600 million years of the Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has been made by JWST in identifying an immense population of bright galaxies, which hints at exceptionally efficient galaxy assembly processes. However, the underlying physical mechanisms propelling their rapid growth remain unclear. With this in mind, millimeter and submillimeter-wave spectroscopic observations of redshifted far-infrared spectral lines, particularly the [O III] 88 micron and [C II] 158 micron lines, offers a crucial pathway to address this fundamental query. To this end, we develop a dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements from ALMA's wideband sensitivity upgrade (WSU) technology, FINER covers radio frequencies spanning 120-360 GHz, delivering an instantaneous intermediate frequency (IF) of 3-21 GHz per sideband per polarization, which is followed by a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA's light-collecting area, the LMT's similar atmospheric transmittance and FINER's 5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral scanning capability in the northern hemisphere, paving the way for finer spectral-resolution detection of distant galaxies.

astro-ph.IM↗

arXiv2024

ALMA Lensing Cluster Survey: Full SED Analysis of z~0.5-6 Lensed Galaxies Detected with Millimeter Observations

Sub/millimeter galaxies are a key population for the study of galaxy evolution because the majority of star formation at high redshifts occurred in galaxies deeply embedded in dust. To search for this population, we have performed an extensive survey with ALMA, called the ALMA Lensing Cluster Survey (ALCS). This survey covers 133 arcmin^2 area and securely detects 180 sources at z~0.5-6 with a flux limit of ~0.2 mJy at 1.2 mm (Fujimoto et al. 2023). Here we report the results of multi-wavelength spectral energy distribution (SED) analysis of the whole ALCS sample, utilizing the observed-frame UV to millimeter photometry. We find that the majority of the ALCS sources lie on the star-forming main sequence, with a smaller fraction showing intense starburst activities. The ALCS sample contains high infrared-excess sources IRX=log(Ldust/LUV)>1), including two extremely dust-obscured galaxies (IRX>5). We also confirm that the ALCS sample probes a broader range in lower dust mass than conventional SMG samples in the same redshift range. We identify six heavily obscured AGN candidates that are not detected in the archival Chandra data in addition to the three X-ray AGNs reported by Uematsu et al. (2023). The inferred AGN luminosity density shows a possible excess at z=2-3 compared with that determined from X-ray surveys below 10 keV.

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