arXiv subjects

Yoichi Tamura

Publications and source records attributed to Yoichi Tamura.

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$\alpha$-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.

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arXiv2026

RIOJA. Environmental Effects on Stellar Populations and Ionized Gas in a Protocluster at $z=7.88$

Protoclusters in the epoch of reionization provide key laboratories for investigating how environment shapes early galaxy formation and evolution, and may also have contributed to cosmic reionization. We analyze 23 member galaxies of A2744-z7p9OD, a protocluster at $z=7.88$, using JWST/NIRCam and NIRSpec to investigate their stellar population properties, rest-frame UV sizes, and ionized-gas properties. We also quantify the internal structure of A2744-z7p9OD using the projected distance to the most massive galaxy ($D_{\rm YD4}$), and to the nearest neighbor ($D_{\rm nei}$), as global and local environmental indicators, respectively. Stellar mass, SFR on a 100 Myr timescale, dust attenuation, and galaxy size show significant correlations ($p<0.05$) with $D_{\rm YD4}$, but not with $D_{\rm nei}$, suggesting that these properties are primarily linked to the global protocluster structure. The member galaxies also show a large galaxy-to-galaxy variation in R23 ($=\log{(([\mathrm{O}\text{\textsc{iii}}]\lambda\lambda4960,5008\rm{\AA}+[\mathrm{O}\text{\textsc{ii}}]\lambda\lambda3727,3730\rm{\AA})/\rm{H}\beta)}$), implying inhomogeneous chemical enrichment in the protocluster environment. O32 ($=\log{([\mathrm{O}\text{\textsc{iii}}]\lambda5008\rm{\AA}/[\mathrm{O}\text{\textsc{ii}}]\lambda\lambda3727,3730\rm{\AA})}$) correlates with $D_{\rm YD4}$, indicating that the core region is characterized by low-ionization gas. Together with the non-detection of Ly$\alpha$ emission, the possible neutral-gas reservoir traced by ALMA [C{\sc ii}]~$158\mu$m emission, and evidence for high-column-density neutral hydrogen in the core, this suggests a neutral-gas-rich protocluster core where the current escape of ionizing photons may be suppressed, even in a overdense environment during the EoR.

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arXiv2026

Millimeter-wave adaptive optics: Demonstrating closed-loop correction for lowest Zernike modes

We report on a five-element prototype wavefront sensor for millimeter-wave adaptive optics (MAO), enabling closed-loop correction of tip-tilt and defocus via secondary mirror (M2) displacement. MAO is essential for large ground-based millimeter/submillimeter telescopes to maintain surface accuracy under wind and thermal distortions. Our sensor, based on radio interferometry, measures excess path lengths from the primary mirror to a focal-plane receiver. A previous two-element prototype achieved < 10 um accuracy at the Nobeyama 45 m telescope. The new five-element system, operating at 20 GHz, was installed on the same telescope. A ``Moon-edge'' experiment confirmed detection of wavefront gradients through strong correlation with continuum flux. Implementing a PI controller closed the sensor-M2 loop, stably suppressing the lowest Zernike modes. This approach establishes a foundation for metrology in future large-aperture submillimeter facilities such as AtLAST/LST.

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arXiv2026

Anti-windup PI controller for millimeter-wave adaptive optics: a Nobeyama 45 m radio telescope simulation

This work addresses the control problem for Millimeter-wave Adaptive Optics (MAO), which we define as compensating for the distance variation between the primary reflector (M1) and the receiver. We utilize a measurement system developed by Tamura et al. to track these variations. The challenge is formalized as an asymptotic constant disturbance suppression problem. We demonstrate that an anti-windup proportional-integral (AWPI) controller effectively solves this problem while respecting the physical movement constraints of the optical driving system. Simulation results, based on the Nobeyama 45-m Telescope with a two-axis translating sub-reflector (M2), validate the performance of the proposed AWPI approach.

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arXiv2026

ALMA observations of pre-JWST z ~ 10 galaxy candidates: A CO(J = 9-8) line from a ULIRG at z = 2.54 and revisit of the photometric redshifts with JWST photometry

We present Atacama Large Millimetre/submillimetre Array (ALMA) observations targeting the [OIII]$88\,\mu$m line for six $z\sim10$ galaxy candidates selected with the Hubble Space Telescope and the Spitzer Space Telescope. We detect a line ($4.5\sigma$) and dust continuum emission ($30\sigma$) in UDS_18697, while detecting neither robust line nor continuum emission in the remaining five objects. The detected line in UDS_18697 is identified as CO($J=9-8$), because follow-up James Webb Space Telescope (JWST) NIRSpec observations have confirmed the redshift as $z=2.54$. UDS_18697 is classified as an ultra luminous infrared galaxy (ULIRG) with far-infrared (FIR) luminosity of $L_\mathrm{FIR}\approx1.1\times10^{12}\,L_\odot$, assuming a dust temperature of $T_\mathrm{d}\approx42\,$K, estimated using a physically-motivated method. We find that UDS_18697 follows the $L_\mathrm{FIR}-L'_\mathrm{CO}$ relation for local and $z>2$ galaxies, albeit being slightly brighter in CO($J=9-8$). Also, based on the follow-up NIRSpec observations and spectral energy distribution fitting using JWST/NIRCam photometry, we found that most of our targets are suggested to be low-$z$ interlopers. Motivated by these redshift misclassifications, we investigate colour--colour selection criteria for high-$z$ galaxies using JWST spectroscopic survey catalogues. We find that elevating a colour threshold tracing the Lyman break is crucial for constructing a robust high-$z$ sample, particularly for wide field surveys such as Euclid Deep Fields and Roman High-Latitude Wide-Area Survey.

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arXiv2026

The Atacama Large Aperture Submillimeter Telescope (AtLAST): enabling large-scale sub-mm science beyond 2030

AtLAST is designed to be the largest (sub-)mm single-dish astronomical observatory and the first climate-neutral modern research infrastructure. It offers a unique combination of large aperture (50 m), large field of view (>1 deg), fast scanning speed (up to 3 deg/s), and high surface accuracy (20micron nighttime half wavefront error) that allows >=50% Ruze efficiency up to 1 THz. The design features a rocking chair mount with an active main reflector surface, a high precision closed-loop metrology system, and the space to house six major instruments. Instruments will be periodically updated as spectroscopic focal plane array, detector, coherent amplifier, and semiconductor technologies used in readout and backend electronics will advance over the next decades. AtLAST will be a multi-purpose facility that will produce transformational results in nearly all fields of Astrophysics, such as Astrochemistry, Galactic and Extragalactic Astronomy, Cosmology, Planetary science, Stellar and Solar Physics, High energy astrophysics, and Time domain astronomy. Its unrivalled throughput of 6170 m^2 deg^2 will enable wide-field unbiased surveys. These will overcome extragalactic confusion noise and enable the detection of normal galaxy populations out to z=7. AtLAST will reveal and characterise the missing baryons in the Universe, by mapping the elusive, low surface brightness gas within and around galaxies across cosmic time. AtLAST will be the first green off-grid observatory, powered by a bespoke renewable energy system and reusing its braking energy thanks to a cutting-edge energy recovery system. By sharing surplus power and technological know-how with local communities, AtLAST will contribute to energy justice in Chile. AtLAST's new bold vision of a sustainable pursuit of breakthrough astronomy is an exceptional opportunity to shape the future of scientific research infrastructures. [abridged]

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arXiv2026

FINER: development of the wideband millimeter-wave receiver system and preparations for first light on the Large Millimeter Telescope

The recent discovery of an excess of luminous galaxies in the early Universe necessitates sensitive and wideband millimeter spectroscopy to understand their rapid growth. To address this, we present the development of the Far-Infrared Nebular Emission Receiver (FINER) for the Large Millimeter Telescope (LMT). The FINER frontend comprises two receivers covering 120-350 GHz (corresponding to ALMA Bands 4+5 and 6+7). The warm optics are designed to enable simultaneous two-band observations. Combined with the 10.24-GHz-wide digital spectrometer array, the system aims to deliver an instantaneous bandwidth approximately five times wider than current ALMA capabilities. We report that the 210-350 GHz receiver has already achieved commissioning-level performance, with sideband rejection further enhanced by the digital sideband separation technique. With installation expected in 2026, we discuss parallel preparations, including integrated testing and commissioning plans for first-look targets.

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arXiv2026

A Wideband Millimeter-wave Receiver at 210-350 GHz for LMT-FINER

The Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating receivers covering 120-210 GHz and 210-350 GHz to efficiently identify high-redshift galaxy candidates in the early universe. Based on high-critical-current-density superconductor-insulator-superconductor mixer technology originally developed for the ALMA wideband sensitivity upgrade, the FINER receivers are designed to provide an intermediate-frequency bandwidth of 3-21 GHz per sideband and per polarization, approximately five times wider than the current ALMA specifications. After installation on the Large Millimeter Telescope, these receivers are expected to offer highly efficient spectral-scanning capability among (sub)millimeterwave facilities in the northern-hemisphere. This paper reports the initial laboratory characterization of the 210-350 GHz receiver. The measured single sideband receiver noise temperature is approximately 100 K over most of the radio-frequency band. Digital sideband separation was also demonstrated using a wideband spectrometer array (DRS4), achieving an image rejection ratio of around 20 dB in the initial tests. These results represent an important step toward the realization of a wideband spectral-scanning receiver system for FINER.

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arXiv2026

Development of TIFUUN: Terahertz Integral Field Units with Universal Nanotechnology

TIFUUN (THz Integral Field Units with Universal Nanotechnology) is an ultra-wideband mm-submm wave imaging spectrometer that capitalizes on the highly scalable integrated superconducting spectrometer technology. TIFUUN has two slots for integral field units (IFUs), which can jointly be optimized as open-hardware for each astronomical observation in terms of spatial and spectral coverage. These IFUs can have observation frequencies in the range of 90--360 GHz, with spectral resolution up to $R\equiv F/\Delta F \le 1,000$, with up to $\sim$18,000 kinetic inductance detectors (shared by the two IFUs with a flexible ratio). The ultra-wide 4:1 (2 octave) bandwidth optics fits in a remarkably compact volume, by means of thin silicon lenses and a high chief ray angle design. The first pair of IFUs are being developed for the SUBLIME (Study of the Universe By Line Intensity Mapping Experiments) experiment that aims to map CII emission at redshift $\sim$6 to trace the cosmic large-scale structure and the buildup of galaxies during reionization, using TIFUUN on the ASTE 10-m telescope. The scalability, flexibility and compactness makes TIFUUN a highly compatible and portable system suited also for upcoming telescope facilities in the vicinity, such as FYST and AtLAST/LST.

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arXiv2026

Control problem in millimeter-wave adaptive optics

Millimeter-wave Adaptive Optics (MAO) is essential for high-precision large-aperture submillimeter telescopes, requiring real-time compensation of wavefront errors by capturing them as spatially-discrete excess path length (EPL) fluctuations. This paper presents a unified control-theoretic framework for the EPL compensation problem. We first model the optical drive system as a plant where input commands relate to measured EPL through a first-order system representing mechanical response delay and a measurement matrix characterizing the actuator-to-sensor coupling. We mathematically formulate the control task as an asymptotic disturbance suppression problem, specifically targeting low-frequency disturbances such as thermal and wind-induced deformations. Second, we propose an Anti-Windup Proportional-Integral (AWPI) control law. By employing a decoupling strategy, the design is reduced to a loop-shaping problem for decoupled scalar sensitivity functions, ensuring both stability margins and asymptotic disturbance suppression of constant-valued disturbances. The anti-windup mechanism is integrated to maintain control continuity during the recovery from saturation, preventing undesirable discontinuities in the drive command. Third, we introduce practical operational tools: a manual focus adjustment scheme that allows observer intervention without interfering with the feedback loop, and the cosine similarity index to quantify the suppressibility of specific Zernike modes. Numerical simulations, incorporating a three-axis secondary reflector drive and five-point EPL measurements, demonstrate direction-dependent disturbance rejection and the suppression of von Karman-modeled wind turbulence, validating the effectiveness of the proposed framework for real-world telescope applications.

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arXiv2026

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

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

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arXiv2026

Resolving the Dust Budget Crisis at $z \sim 8$ with Optically Thick, High-Density Molecular Clumps: MACS0416_Y1

Dust plays a crucial role in galaxy evolution by shaping the spectral energy distribution (SED) and star formation history. However, standard models often underestimate the infrared luminosity of high-redshift galaxies ($z \sim 8$), leading to the so-called dust budget crisis. In this work, we modify the theoretical framework by focusing on compact star-forming clumps in the interstellar medium. Motivated by the observed compactness of high-z galaxies, we treat the cold neutral medium density as a free parameter. Our analysis reveals that the ISM must reach extreme densities ($n_{\text{H,CNM}} \sim 7.5 \times 10^3 \, \mathrm{cm}^{-3}$). This enhances UV photon trapping, accelerates dust processing in dense gas, and reduces dust destruction by supernova shocks. Our model successfully reproduces the observed UV-to-FIR SED of MACS0416_Y1 ($z = 8.312$). A grain-size-resolved treatment further shows that the warm IR emission is dominated by intermediate-size grains ($a = 0.01$ - $0.1\,\mu$m), which contribute about 89% of the luminosity near the SED peak and in the ALMA Band~9 continuum. These grains are nearly in thermal equilibrium at characteristic temperatures of $\sim 70$ K, while the largest grains remain cooler and the smallest grains exhibit a high-temperature tail with low probability. We conclude that extreme ISM densities can alleviate the dust budget crisis by promoting efficient UV photon trapping and rapid dust evolution, thereby increasing dust mass and producing a multi-temperature grain population.

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arXiv2026

Upper limit on HF(1-0) absorption in a dusty star-forming galaxy at $z = 6$: Constraints on early fluorine enrichment

Wolf-Rayet (WR) stars have recently attracted attention as possible drivers of early chemical enrichment, including the production of fluorine, whose nucleosynthetic origin remains debated. To test the contribution of massive stars to fluorine production in the early Universe, we conducted Atacama Large Millimeter/submillimeter Array Band 5 spectroscopy of the HF(1-0) absorption line toward a dusty star-forming galaxy at $z=6.024$. This galaxy has a known gas-phase metallicity and is too young for low-mass AGB stars to have contributed significantly, providing a clean environment to isolate massive-star yields. We do not detect significant HF absorption ($\sim2\sigma$) and derive a conservative 5$\sigma$ upper limit of $N_\mathrm{HF}/N_\mathrm{H_2} < 2.2\times10^{-9}$. This limit is about an order of magnitude below typical local measurements, indicating inefficient fluorine enrichment $\sim0.9$ Gyr after the Big Bang. Comparison with chemical evolution models shows that our constraint is consistent with scenarios without WR yields at this epoch. Expanding the sample of HF absorption measurements in high-redshift galaxies with well-characterized metallicities will be crucial for tracing the onset of WR enrichment and fluorine production across cosmic time.

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arXiv2025

Probing Infrared eXcess to Investigate Early-Universe Dust (PIXIEDust)

Despite the implied presence of dust through reddened UV emission in high-redshift galaxies, no dust emission has been detected in the (sub)millimetre regime beyond $z > 8.3$. This study combines around two hundred hours of Atacama Large Millimeter/submillimeter Array (ALMA) and Northern Extended Millimeter Array (NOEMA) observations on ten $z > 8$ galaxies, revealing no significant dust emission down to a $1 \sigma$ depth of $2.0$, $2.0$, and $1.5 \,\mu$Jy at rest-frame 158, 88 $\mu$m, and across all the data, respectively. This constrains average dust masses to be below $< 10^{5}$ M$_{\odot}$ at $3 \sigma$ and dust-to-stellar mass ratios to be below $3.7 \times{} 10^{-4}$ (assuming $T_{\rm dust} = 50$ K and $\beta_{\rm dust} = 2.0$). Binning by redshift ($8 < z < 9.5$ and $9.5 < z < 15$), UV-continuum slope ($\beta_{\rm UV} \lessgtr -2$) and stellar mass ($\log_{10} M_{\ast}/{\rm M_{\odot}} \lessgtr 9$) yields similarly stringent constraints. Combined with other studies, these results are consistent with inefficient dust build-up in the $z > 8$ Universe, likely due to inefficient supernova production, limited interstellar grain growth and/or ejection by outflows. We provide data and tools online to facilitate community-wide high-redshift dust searches.

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arXiv2025

The LMT 2 millimeter receiver system (B4R). II. Science demonstration observations toward Orion-KL/OMC-1

We present the results of mapping and single-point spectral scans toward Orion-KL/OMC-1 performed as science demonstrations of a 2 mm SIS receiver, the Band 4 Receiver (B4R), installed on the 50 m Large Millimeter Telescope (LMT). To prove the capabilities of mapping and spectral scans with the B4R on the LMT, commissioning observations were conducted employing the on-the-fly mapping technique toward Orion-KL/OMC-1, which covers a map size of 5$'\times$5$'$. These mapping observations were performed with two frequency settings providing 10 GHz in total (131.4-133.9 GHz and 145.1-147.6 GHz; 136.2-138.7 GHz and 149.9-152.4 GHz) with a frequency resolution of 76.293 kHz. We conducted spectral line identification analysis for the hot core and compact ridge regions in the Orion-KL with a beam size of 11-12$''$. We detected nearly 400 emission lines and identified two recombination lines and 29 molecular species, including isotopologues, deuterated molecules, and vibrational excited states, despite the short integration time. These results are consistent with those of previous studies. The 29 molecular species include nitrogen (N)-bearing complex organic molecules (COMs) and oxygen (O)-bearing COMs. To demonstrate the capability of the B4R in astrochemistry, we conducted detailed analyses of column densities, rotational temperatures, and relative abundances with respect to H$_2$ on two representative COMs, N-bearing C$_2$H$_5$CN and O-bearing CH$_3$OCHO in the central 40$''\times$40$''$ area of the map. The wide bandwidth of 10 GHz enabled the use of 8 and 34 emission lines, respectively. The spatial differences in the physical and chemical properties between these molecules were derived at a spatial resolution of $\sim$12$''$. The B4R on the LMT was successfully demonstrated to be powerful for mapping and spectral scans and to have high potential for the study of interstellar chemistry.

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arXiv2025

The LMT 2 Millimeter Receiver System (B4R). I. Overview and Results of Science Demonstration

We report on the results of the on-sky test and science demonstration conducted with the 2 mm receiver system, B4R, on the 50 m Large Millimeter Telescope (LMT), located at an altitude of 4600 m in Mexico. The B4R receiver was developed based on the dual-polarization sideband-separating mixer technology of the Atacama Large Millimeter/submillimeter Array, and is equipped with a fast Fourier transform digital spectrometer, XFFTS. The primary science objective is the spectroscopic redshift identification of high-redshift dusty star-forming galaxies, complementing the existing 3 mm Redshift Search Receiver by enabling the detection of multiple carbon monoxide lines. Additionally, the B4R receiver broadens the range of science cases possible with the LMT, including astrochemistry, as the 2 mm band encompasses unique molecular lines such as deuterated molecules and shock tracers. During on-site commissioning in 2018 and 2019, we successfully demonstrated on-the-fly mapping and position-switching observations toward the Orion Molecular Cloud 1 and bright high-redshift dusty star-forming galaxies, respectively. We confirmed that the installed B4R system largely met its basic performance specifications. Furthermore, we measured the LMT's aperture efficiencies across the entire B4R frequency range (130-160 GHz), finding them to be roughly consistent with expectations based on a surface accuracy of 100 $\mu$m and the receiver optics design. These results with the B4R will enable the most sensitive single-dish spectroscopic observations at 2 mm using the LMT.

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arXiv2025

Large gas inflow driven by a matured galactic bar in the early Universe

Bar structures are present in about half of local disk galaxies and play pivotal roles in secular galaxy evolution. Bars impose a non-axisymmetric perturbation to the rotating disk and transport gas inward to feed central starburst and, possibly, the activity of the nuclear supermassive black hole. They are believed to be long-lived structures and are now identified at redshift $z>2$. Yet, little is known about the onset and effect of bars in the early cosmic epoch because spectroscopy of distant bars at sufficient resolution is prohibitively expensive. Here, we report a kinematic study of a galactic bar at redshift 2.467, 2.6 billion years after the Big Bang. We observe the carbon monoxide and atomic carbon emission lines of the dusty star-forming galaxy J0107a and find the bar of J0107a has gas distribution and motion in a pattern identical to local bars. At the same time, the bar drives large-scale non-circular motions that dominate over disk rotation, funneling molecular gas into its center at a rate of $\approx600$ solar masses per year. Our results show that bar-driven dynamical processes and secular evolution were already at play 11.1 billion years ago, powering active star formation amid the gas-rich and far-infrared luminous growth phase in a massive disk galaxy.

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arXiv2025

A warm ultra-luminous infrared galaxy just 600 million years after the Big Bang

We present an Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 continuum detection ($3.3 \sigma$) of MACS0416_Y1 that confirms the suspected warm dust (91$^{+62}_{-35}$ K) of this Lyman-Break Galaxy (LBG) at $z = 8.3$ with $\log_{10} M_{\ast}/$M$_{\odot} = 9.0 \pm 0.1$. A modified black-body fit to the ALMA Bands 3 through 9 data of MACS0416_Y1 finds an intrinsic infrared luminosity of 1.0$^{+1.8}_{-0.6} \times{} 10^{12}\ \mathrm{L_{\odot}}$, placing this UV-selected LBG in the regime of Ultra Luminous Infrared Galaxies (ULIRGs). Its luminous but modest dust reservoir (1.4$^{+1.3}_{-0.5} \times{} 10^{6}\ \mathrm{M_{\odot}}$) is co-spatial to regions with a UV-continuum slope $\beta_{\rm UV} \approx -1.5$ as seen by James Webb Space Telescope (JWST) imaging. Although this implies some dust obscuration, the JWST photometry implies less obscured star formation than seen in the complete characterization by ALMA, implying some spatial separation of dust and stars on scales below 200 pc, i.e., smaller than those probed by JWST and ALMA. This source is an extreme example of dust-obscured star formation contributing strongly to the cosmic build-up of stellar mass, which can only be revealed through direct and comprehensive observations in the (sub)mm regime.

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