arXiv subjects

Yoichi Tamura

Publications and source records attributed to Yoichi Tamura.

At least 55 records · Page 3Linked to original sources

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.

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arXiv2024

A 10.24-GHz-wide digital spectrometer array system for LMT-FINER: system design and laboratory performance verification

For efficient spectroscopic redshift identification of early galaxies in the northern hemisphere, we aim to combine the Large Millimeter Telescope (LMT) with a wide-band heterodyne receiver, FINER, which will cover radio frequencies of 120--360 GHz and offer a 3--21 GHz intermediate frequency (IF) per sideband and polarization. To take full advantage of such wide IFs, we present a novel 10.24-GHz-wide digital spectrometer, DRS4 (Elecs Industry Co., Ltd.). It incorporates 20.48 Gsps samplers with an FPGA-based digital signal processing module. To mitigate the noise contamination from the image sideband, it is equipped with a digital sideband separation function to improve the sideband rejection up to 25 dB. Laboratory performance evaluations show that it exhibits an Allan time of at least ~100 s and a total power dynamic range of at least 7 dB. These results demonstrate its capability of instantaneously wide-band spectroscopy toward high-redshift galaxies with position-switching observations.

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arXiv2024

Development Status of Wideband Millimeter-Wave Receivers for LMT-FINER

Spectroscopic observations of the far-infrared [O III] and [C II] lines present a pathway to explore the mechanisms of the emergence of massive galaxies in the epoch of reionization and beyond, which is one of the most fundamental questions in astronomy. To address this question, the Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating heterodyne receivers at 120--210 GHz and 210--360 GHz for the Large Millimeter Telescope (LMT) in Mexico. Compared with Atacama Large Millimeter/submillimeter Array (ALMA), LMT provides 40% of ALMA's light-collecting area and a similar atmospheric transmittance, but FINER plans to have an instantaneous intermediate frequency (IF) of 3--21 GHz per sideband per polarization which is five times wider than current ALMA's bandwidth. Therefore, FINER is going to offer cutting-edge spectral scanning capability in the next several years. The project is currently in an active development phase. In this proceeding, the latest development status for FINER, including the optics, wideband waveguide components as well as low-noise superconductor-insulator-superconductor (SIS) mixers is reported.

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arXiv2024

JWST and ALMA Multiple-Line Study in and around a Galaxy at $z=8.496$: Optical to FIR Line Ratios and the Onset of an Outflow Promoting Ionizing Photon Escape

We present ALMA deep spectroscopy for a lensed galaxy at $z_{\rm spec}=8.496$ with $\log(M_{\rm star}/M_{\odot})\sim7.8$ whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in SMACS0723. Our ALMA spectrum shows [OIII]88$μ$m and [CII]158$μ$m line detections at $4.0σ$ and $4.5σ$, respectively. The redshift and position of the [OIII] line coincide with those of the JWST source, while the [CII] line is blue-shifted by 90 km s$^{-1}$ with a spatial offset of $0.''5$ ($\approx0.5$ kpc in source plane) from the JWST source. The NIRCam F444W image, including [OIII]$λ$5007 and H$β$ line emission, spatially extends beyond the stellar components by a factor of $>8$. This indicates that the $z=8.5$ galaxy has already experienced strong outflows whose oxygen and carbon produce the extended [OIII]$λ$5007 and the offset [CII] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and removals of emission spatially outside the galaxy, we evaluate the [OIII]88$μ$m/$λ$5007 line ratio, and derive the electron density $n_{\rm e}$ by photoionization modeling to be $220^{+170}_{-100}$ cm$^{-3}$, which is comparable with those of $z\sim2-3$ galaxies. We estimate an [OIII]88$μ$m/[CII]158$μ$m line ratio in the galaxy of $>4$, as high as those of known $z\sim6-9$ galaxies. This high [OIII]88$μ$m/[CII]158$μ$m line ratio is generally explained by the high $n_{\rm e}$ as well as the low metallicity ($Z_{\rm gas}/Z_{\odot}=0.04^{+0.02}_{-0.02}$), high ionization parameter ($\log U > -2.27$), and low carbon-to-oxygen abundance ratio ($\log$(C/O) $=[-0.52:-0.24]$) obtained from the JWST/NIRSpec data; further [CII] follow-up observations will constrain the covering fraction of photodissociation regions.

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arXiv2024

Large-Scale Mapping Observations of DCN and DCO$^+$ toward Orion KL

We present emission maps (1.5'$\times$1.5' scale, corresponding to 0.18 pc) of the DCN ($J=2-1$) and DCO$^+$ ($J=2-1$) lines in the 2 mm band toward the Orion KL region obtained with the 2 mm receiver system named B4R installed on the Large Millimeter Telescope (LMT). The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO$^+$ emission has been detected there. The DCO$^+$ emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO$^+$ at three representative positions where both species have been detected. The gas components with $V_{\rm {LSR}} \approx 7.5-8.7$ km/s are associated with low abundance ratios of $\sim4-6$, whereas much higher abundance ratios ($\sim22-30$) are derived for the gas components with $V_{\rm {LSR}} \approx 9.2-11.6$ km/s. We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO$^+$ abundance ratios are explained by different densities.

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arXiv2023

J0107a: A Barred Spiral Dusty Star-forming Galaxy at $z=2.467$

Dusty Star-Forming Galaxies (DSFGs) are amongst the most massive and active star-forming galaxies during the cosmic noon. Theoretical studies have proposed various formation mechanisms of DSFGs, including major merger-driven starbursts and secular star-forming disks. Here, we report J0107a, a bright ($\sim8$ mJy at observed-frame 888 $μ$m) DSFG at $z=2.467$ that appears to be a gas-rich massive disk and might be an extreme case of the secular disk scenario. J0107a has a stellar mass $M_\star\sim5\times10^{11}M_\odot$, molecular gas mass $M_\mathrm{mol}\sim(1\textendash6)\times10^{11}M_\odot$, and a star formation rate (SFR) of $\sim500M_\odot$ yr$^{-1}$. J0107a does not have a gas-rich companion. The rest-frame 1.28 $μ$m JWST NIRCam image of J0107a shows a grand-design spiral with a prominent stellar bar extending $\sim15$ kpc. ALMA band 7 continuum map reveals that the dust emission originates from both the central starburst and the stellar bar. 3D disk modeling of the CO(4-3) emission line indicates a dynamically cold disk with rotation-to-dispersion ratio $V_\mathrm{max}/σ\sim8$. The results suggest a bright DSFG may have a non-merger origin, and its vigorous star formation may be triggered by bar and/or rapid gas inflow.

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arXiv2023

Molecular outflow in the reionization-epoch quasar J2054-0005 revealed by OH 119 $μ$m observations

Molecular outflows are expected to play a key role in galaxy evolution at high redshift. To study the impact of outflows on star formation at the epoch of reionization, we performed sensitive ALMA observations of OH 119 $μ$m toward J2054-0005, a luminous quasar at $z=6.04$. The OH line is detected and exhibits a P-Cygni profile that can be fitted with a broad blue-shifted absorption component, providing unambiguous evidence of an outflow, and an emission component at near-systemic velocity. The mean and terminal outflow velocities are estimated to be $v_\mathrm{out}\approx670~\mathrm{km~s}^{-1}$ and $1500~\mathrm{km~s}^{-1}$, respectively, making the molecular outflow in this quasar one of the fastest at the epoch of reionization. The OH line is marginally spatially resolved for the first time in a quasar at $z>6$, revealing that the outflow extends over the central 2 kpc region. The mass outflow rate is comparable to the star formation rate ($\dot{M}_\mathrm{out}/\mathrm{SFR}\sim2$), indicating rapid ($\sim10^7~\mathrm{yr}$) quenching of star formation. The mass outflow rate in a sample star-forming galaxies and quasars at $4<z<6.4$ exhibits a positive correlation with the total infrared luminosity, although the scatter is large. Owing to the high outflow velocity, a large fraction (up to $\sim50\%$) of the outflowing molecular gas may be able to escape from the host galaxy into the intergalactic medium.

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arXiv2023

Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The core of the highest redshift galaxy overdensity at $z = 7.88$ confirmed by NIRSpec/JWST

The protoclusters in the epoch of reionization, traced by galaxies overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at $z = 7.88$, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as 4 galaxies detected in [OIII] 4960 Å and 5008 Å in a small area of $\sim 3\arcsec \times 3\arcsec$, corresponding to $\sim$ 11 kpc $\times$ 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, $β\sim -1.3$. The member galaxies have stellar masses in the range of log($M_{*}/M_{\rm \odot}$) $\sim 7.6-9.2$ and star formation rates of $\sim 3-50$ $M_{\rm \odot}$ yr$^{-1}$, showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [OIII] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens Myr to become a large galaxy with $M_{\rm *}\sim 6\times10^{9} M_{\rm \odot}$. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.

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arXiv2023

The 300 pc resolution imaging of a z = 8.31 galaxy: Turbulent ionized gas and potential stellar feedback 600 million years after the Big Bang

We present the results of 300 pc resolution ALMA imaging of the [OIII] 88 $μ$m line and dust continuum emission from a $z = 8.312$ Lyman break galaxy MACS0416_Y1. The velocity-integrated [OIII] emission has three peaks which are likely associated with three young stellar clumps of MACS0416_Y1, while the channel map shows a complicated velocity structure with little indication of a global velocity gradient unlike what was found in [CII] 158 $μ$m at a larger scale, suggesting random bulk motion of ionized gas clouds inside the galaxy. In contrast, dust emission appears as two individual clumps apparently separating or bridging the [OIII]/stellar clumps. The cross correlation coefficient between dust and ultraviolet-related emission (i.e., [OIII] and ultraviolet continuum) is unity on a galactic scale, while it drops at < 1 kpc, suggesting well mixed geometry of multi-phase interstellar media on sub-kpc scales. If the cutoff scale characterizes different stages of star formation, the cutoff scale can be explained by gravitational instability of turbulent gas. We also report on a kpc-scale off-center cavity embedded in the dust continuum image. This could be a superbubble producing galactic-scale outflows, since the energy injection from the 4 Myr starburst suggested by a spectral energy distribution analysis is large enough to push the surrounding media creating a kpc-scale cavity.

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arXiv2023

Molecular Abundance of the Circumnuclear Region Surrounding an Active Galactic Nucleus in NGC 1068 based on Imaging Line Survey in the 3-mm Band with ALMA

We present an imaging molecular line survey in the 3-mm band (85-114 GHz) focused on one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068, based on observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA). Distributions of 23 molecular transitions are obtained in the central ~3 kpc region, including both the circumnuclear disk (CND) and starburst ring (SBR) with 60 and 350 pc resolution. The column densities and relative abundances of all the detected molecules are estimated under the assumption of local thermodynamic equilibrium in the CND and SBR. Then, we discuss the physical and chemical effects of the AGN on molecular abundance corresponding to the observation scale. We found that H13CN, SiO, HCN, and H13CO+ are abundant in the CND relative to the SBR. In contrast, 13CO is more abundant in the SBR. Based on the calculated column density ratios of N(HCN)/N(HCO+), N(HCN)/N(CN), and other molecular distributions, we conclude that the enhancement of HCN in the CND may be due to high-temperature environments resulting from strong shocks, which are traced by the SiO emission. Moreover, the abundance of CN in the CND is significantly lower than the expected value of the model calculations in the region affected by strong radiation. The expected strong X-ray irradiation from the AGN has a relatively lower impact on the molecular abundance in the CND than mechanical feedback.

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arXiv2023

Characterizing CO Emitters in the SSA22-AzTEC26 Field

We report the physical characterization of four CO emitters detected near the bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from Atacama Large Millimeter/submillileter Array band 3, 4, and 7 observations of the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line emitters with a signal-to-noise ratio $>5.2$ in the cube smoothed with 300 km s$^{-1}$ FWHM Gaussian filter. All four sources have NIR counterparts within 1$\arcsec$. We perform UV-to-FIR spectral energy distribution modeling to derive the photometric redshifts and physical properties. Based on the photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of 1.113 and 1.146 and one is CO(3-2) at $z=2.124$. The three sources are massive galaxies with a stellar mass $\gtrsim10^{10.5}M_\odot$, but have different levels of star formation. Two lie within the scatter of the main sequence (MS) of star-forming galaxies at $z\sim1-2$, and the most massive galaxy lies significantly below the MS. However, all three sources have a gas fraction within the scatter of the MS scaling relation. This shows that a blind CO line search can detect massive galaxies with low specific star formation rates that still host large gas reservoirs and that it also complements targeted surveys, suggesting later gas acquisition and the need for other mechanisms in addition to gas consumption to suppress star formation.

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arXiv2023

Big Three Dragons: Molecular Gas in a Bright Lyman-Break Galaxy at $z=7.15$

We report ALMA Band 3 observations of CO(6-5), CO(7-6), and [CI](2-1) in B14-65666 (``Big Three Dragons''), one of the brightest Lyman-Break Galaxies at $z>7$ in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of [OIII] 88 $μ$m and [CII] 158 $μ$m. CO(6-5), CO(7-6), and [CI](2-1), whose $3σ$ upper limits on the luminosities are approximately 40 times fainter than the [CII] luminosity, are all not detected. The $L_{\rm [CII]}$/$L_{\rm CO(6-5)}$ and $L_{\rm [CII]}$/$L_{\rm CO(7-6)}$ ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) [CII] luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass ($M_{\rm{mol}}$) is $(0.05-11)\times10^{10}$ $M_{\rm \odot}$. This value is consistent with the upper limit inferred from the nondetection of mid-$J$ CO and [CI](2-1). Despite the large uncertauinty in $M_{\rm mol}$, we estimate a molecular gas-to-stellar mass ratio ($μ_{\rm{gas}}$) of $0.65-140$ and a gas depletion time ($τ_{\rm dep}$) of $2.5-550$ Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at $z\gtrsim4$ if no gas is fueled from outside the galaxy.

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arXiv2023

Detections of [C II] 158 $μ$m and [O III] 88 $μ$m in a Local Lyman Continuum Emitter, Mrk 54, and its Implications to High-redshift ALMA Studies

We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman Continuum Emitter (LCE), obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C II] 158 $μ$m and [O III] 88 $μ$m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C II] emission that accounts for $\sim1$% of the total FIR luminosity, whereas it has only moderate [O III] emission, resulting in the low [O III]/[C II] luminosity ratio of $0.22\pm0.06$. In order to investigate whether [O III]/[C II] is a useful tracer of $f_{\rm esc}$ (LyC escape fraction), we examine the correlations of [O III]/[C II] and (i) the optical line ratio of $\rm O_{32} \equiv$ [O III] 5007 Å/[O II] 3727 Å, (ii) specific star formation rate, (iii) [O III] 88 $μ$m/[O I] 63 $μ$m ratio, (iv) gas phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O III]/[C II] luminosity ratios could be the result of high ionization (traced by $\rm O_{32}$), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O III] 88 $μ$m/[O I] 63 $μ$m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O III]/[C II] ratio and $f_{\rm esc}$ based on the combination of the [O III]/[C II] and $\rm O_{32}$ correlation, and the known relation between $\rm O_{32}$ and $f_{\rm esc}$. The relation implies that high-redshift galaxies with high [O III]/[C II] ratios revealed by ALMA may have $f_{\rm esc}\gtrsim0.1$, significantly contributing to the cosmic reionization.

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arXiv2023

The Extended [CII] under Construction? Observation of the brightest high-z lensed star-forming galaxy at z = 6.2

We present results of [CII]$\,158\,\rm{μm}$ emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed ($μ\sim20$) star-forming galaxy, MACS0308-zD1 at $z=6.2078\pm0.0002$. The [CII] emission line is detected with a signal-to-noise ratio $>6$ within the rest-frame UV bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [CII] has a velocity full-width-half-maximum (FWHM) of $110\pm20\,\rm{km/s}$, while broader [CII] is seen with an FWHM of $230\pm20\,\rm{km/s}$. The broader [CII] component is blueshifted ($-80\pm20\,\rm{km/s}$) with respect to the narrow [CII] component, and has a morphology which extends beyond the UV-bright clump. We find that while the narrow [CII] emission is most likely associated with zD1.1, the broader component is possibly associated with outflowing gas. Based on the non-detection of $λ_{\rm 158\,μm}$ dust continuum, we find that MACS0308-zD1's star-formation activity occurs in a dust-free environment with the stringent upper limit of infrared luminosity $\lesssim9\times10^{8}\,{\rm L_{\odot}}$. Targeting this strongly lensed faint galaxy for follow-up ALMA and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

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arXiv2023

The SSA22 HI Tomography Survey (SSA22-HIT). I. Data Set and Compiled Redshift Catalog

We conducted a deep spectroscopic survey, named SSA22-HIT, in the SSA22 field with the DEep Imaging MultiObject Spectrograph (DEIMOS) on the Keck telescope, designed to tomographically map high-z HI gas through analysis of Lya absorption in background galaxies' spectra. In total, 198 galaxies were spectroscopically confirmed at 2.5 < z < 6 with a few low-z exceptions in the 26 x 15 arcmin^2 area, of which 148 were newly determined in this study. Our redshift measurements were merged with previously confirmed redshifts available in the 34 x 27 arcmin^2 area of the SSA22 field. This compiled catalog containing 730 galaxies of various types at z > 2 is useful for various applications, and it is made publicly available. Our SSA22-HIT survey has increased by approximately twice the number of spectroscopic redshifts of sources at z > 3.2 in the observed field. From a comparison with publicly available redshift catalogs, we show that our compiled redshift catalog in the SSA22 field is comparable to those among major extragalactic survey fields in terms of a combination of wide area and high surface number density of objects at z > 2. About 40 % of the spectroscopically confirmed objects in SSA22-HIT show reasonable quality of spectra in the wavelengths shorter than Lya when a sufficient amount of smoothing is adopted. Our data set enables us to make the HI tomographic map at z > 3, which we present in a parallel study.

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arXiv2023

Updated measurements of [O III] 88 $μ$m, [C II] 158 $μ$m, and Dust Continuum Emission from a z=7.2 Galaxy

We present updated measurements of the [O III] 88 $μ$m, [C II] 158 $μ$m, and dust continuum emission from a star-forming galaxy at $z=7.212$, SXDF-NB1006-2, by utilizing Atacama Large Millimeter/submillimeter Array (ALMA) archival data sets analysed in previous studies and data sets that have not been analysed before. The follow-up ALMA observations with higher angular resolution and sensitivity reveal a clumpy structure of the [O III] emission on a scale of $0.32-0.85\,\rm{kpc}$. We also combined all the ALMA [O III] ([C II]) data sets and updated the [O III] ([C II]) detection to $5.9σ$ ($3.6σ-4.5σ$). The non-detection of [C II] with data from the REBELS large program implies the incompleteness of spectral-scan surveys using [C II] to detect galaxies with high star formation rates (SFRs) but marginal [C II] emission at high-$z$. The dust continuum at 90 $μ$m and 160 $μ$m remains undetected, indicating little dust content of $<3.9\times10^{6}\,M_\odot\,(3σ)$, and we obtained a more stringent constraint on the total infrared luminosity. We updated the [O III]/[C II] luminosity ratios to $10.2\pm4.7~(6.1\pm3.5$) and $20\pm12~(9.6\pm6.1$) for $4.5σ$ and $3.6σ$ [C II] detections, respectively, where the ratios in the parentheses are corrected for the surface brightness dimming effect on the extended [C II] emission. We also found a strong [C II] deficit ($0.6-1.3$ dex) between SXDF-NB1006-2 and the mean $L_{\rm{[CII]}}-\rm{SFR}$ relation of galaxies at $0<z<9$.

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arXiv2023

Deep ALMA redshift search of a z~12 GLASS-JWST galaxy candidate

The James Webb Space Telescope (JWST) has discovered a surprising abundance of bright galaxy candidates in the very early Universe ($< 500$ Myrs after the Big Bang), calling into question current galaxy formation models. Spectroscopy is needed to confirm the primeval nature of these candidates, as well as to understand how the first galaxies form stars and grow. Here we present deep spectroscopic and continuum ALMA observations towards GHZ2/GLASS-z12, one of the brightest and most robust candidates at $z > 10$ identified in the GLASS-JWST Early Release Science Program. We detect a $5.8 σ$ line, offset 0.5" from the JWST position of GHZ2/GLASS-z12 that, associating it with the [OIII] 88 micron transition, implies a spectroscopic redshift of $z = 12.117 \pm 0.001$. We verify the detection using extensive statistical tests. The oxygen line luminosity places GHZ2/GLASS-z12 above the [OIII]-SFR relation for metal-poor galaxies, implying an enhancement of [OIII] emission in this system while the JWST-observed emission is likely a lower-metallicity region. The lack of dust emission seen by these observations is consistent with the blue UV slope observed by JWST, which suggest little dust attenuation in galaxies at this early epoch. Further observations will unambiguously confirm the redshift and shed light on the origins of the wide and offset line and physical properties of this early galaxy. This work illustrates the synergy between JWST and ALMA and paves the way for future spectroscopic surveys of $z > 10$ galaxy candidates.

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arXiv2022

ALMA Observations for CO Emission from Luminous Lyman-break Galaxies at $z=6.0293$-$6.2037$

We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6-5) emission from three luminous Lyman break galaxies (LBGs) at $z_{\rm spec} = 6.0293$-$6.2037$ found in the Subaru/Hyper Suprime-Cam survey, whose [OIII]$88μ$m and [CII]$158μ$m emission have been detected with ALMA. We find a marginal detection of the CO(6-5) line from one of our LBGs, J0235-0532, at the $\simeq 4 σ$ significance level and obtain upper limits for the other two LBGs, J1211-0118 and J0217-0208. Our $z=6$ luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveal that J0235-0532 has a relatively high hydrogen nucleus density that is comparable to those of low-$z$ (U)LIRGs, quasars, and Galactic star-forming regions with high $n_{\rm H}$ values, while the other two LBGs have lower $n_{\rm H}$ consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain total gas mass and gas surface density constraints from their CO luminosity measurements. We find that J0235-0532 locates below the Kennicutt-Schmidt (KS) relation, comparable to the previously CO(2-1) detected $z=5.7$ LBG, HZ10. Combined with previous results for dusty starbursts at similar redshifts, the KS relation at $z=5$-$6$ is on average consistent with the local one.

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