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A. K. Inoue

Publications and source records attributed to A. K. Inoue.

At least 19 recordsLinked to original sources
arXiv2026

Stardust Galaxies at z>9: A Dust-Origin Transition Behind the Excess of UV-Bright Galaxies

Recent JWST observations suggest that galaxies at z > 9 may be dominated by low-opacity SNe-produced dust before efficient ISM grain growth is established. This transition in dust origin and opacity could explain both the prevalence of galaxies with extremely low dust attenuation and the excess of UV-bright galaxies relative to most pre-JWST predictions. We investigate whether this transition, combined with evolving star-formation efficiency, can reproduce these observed properties. We develop a physically motivated attenuation framework combining (i) extinction laws for reverse-shock-processed SNe dust, (ii) metallicity- and dust-to-metal-dependent opacity scalings, and (iii) porous radiative-transfer geometries allowing partial UV-photon leakage. Unlike outflow-driven scenarios requiring large-scale gas evacuation, our approach preserves gas reservoirs while reducing effective UV opacity through dust composition and geometry. We introduce extinction-based, gas-based, and hybrid attenuation prescriptions linking SNe-dominated and ISM grain-growth dust regimes. We find that the observed A_FUV-M_star relation at z > 9 is best reproduced for an intrinsic FUV dust opacity kappa_UV(dust)=10^3 - 10^4 cm2/g, characteristic of low-opacity SNe dust, naturally producing very low attenuation even in gas-rich galaxies. This regime reproduces galaxies with extremely low dust attenuation (GELDAs), which dominate observed samples at z > 9. Applied to intrinsic UV luminosity function models, our SNe-dominated and hybrid prescriptions mainly suppress the brightest galaxies, bringing predictions into agreement with JWST measurements without requiring extreme star-formation efficiencies or dust-free interstellar media. Our results suggest that the UV-bright galaxy excess at z > 9 reflects a transition in dust origin and opacity during the earliest phases of galaxy evolution.

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arXiv2026

PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction

We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($\mu\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization.

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arXiv2026

PRISMS. UNCOVER-26185, a metal-poor SFG at z=10.05 with no evidence for a X-ray-luminous AGN

This work presents the first results of the PRImordial galaxy Survey with MIRI Spectroscopy (PRISMS), a JWST cycle 4 program (PID 8051) aimed at the characterization of a relatively large sample of ten galaxies about 500 Myr after the Big Bang. Here, we present deep (13.9 hours) spectroscopy with the MIRI LRS of the lensed galaxy UNCOVER-26185 at a redshift of z=10.054. It is a faint UV galaxy (UV absolut magnitude of -18.83 mag) previously identified as a X-ray luminous AGN. MIRI LRS detects the H$\beta$+[OIII]4960,5008 complex and H$\alpha$ emission line with a significance of 10$\sigma$ and 8$\sigma$, respectively, as well as the optical continuum emission at rest-frame 0.45 $\mu$m and 0.57 $\mu$m with a signal-to-noise ratio of 6-7. The UV-to-optical spectral energy distribution, combining continuum and emission lines, is compatible with: (i) a low stellar (A$_V$= 0.2) and nebular (A$_V$=0.0) extinction, (ii) a SFH composed by a young (7 Myr) starburst and an intermediate-age (65 Myr) stellar population, and (iii) a total stellar mass of 1.7$\times$10$^{8}$ M$_{\odot}$. The H$\alpha$-derived star-formation rate is 1.3 M$_{\odot}$ yr$^{-1}$. The low optical emission line ratios locate UNCOVER-26185 as the most metal-poor (Z = 0.04 Z$_{\odot}$), and as outlier with the lowest ionization (logU=-2.5) galaxy identified so far at redshifts above 9. With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10, with ISM and ionization properties very different than those of the already studied UV-bright galaxies at redshifts beyond 10. PRISMS is starting to explore the population of intermediate-UV luminosity galaxies at z=10, covering UV absolute magnitudes in the range of -17.9 to -20.5, fainter than those of UV-bright galaxies studied so far.

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arXiv2026

Nitrogen abundances in star-forming galaxies 2.2 Gyr after the Big Bang are not elevated

Using deep medium-resolution JWST rest-optical spectra of a sample of typical star-forming galaxies (Lyman break galaxies and Lyman-$\alpha$ emitters) from the LyC22 survey at $z \sim 3$, we determined the nebular abundances of N, O, and Ne relative to H for a subsample of 25 objects with the direct method, based on auroral [OIII]4363 line detections. Our measurements increases the number of accurate N/O determinations at $z \sim 2-4$ using a homogeneous approach. We found a mean value of $\log({\rm N/O})=-1.29^{+0.25}_{-0.21} $ over a metallicity range 12+log(O/H)=7.5 to 8.44. The observed N/O ratio and scatter are indistinguishable from that observed in low-z galaxies and HII regions over the same metallicity range, showing thus no redshift evolution of N/O for typical galaxies over a significant fraction of cosmic time. We also show that typical $z \sim 3$ galaxies show a similar offset in the BPT diagram as galaxies from the low-z Lyman Continuum Survey (LzLCS), when compared to the average of SDSS galaxies, and show that this offset is not due to enhanced nitrogen abundances. Our results establish a basis for future studies of the evolution of N and O at higher redshifts.

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arXiv2025

RIOJA. Dusty outflows and density-complex ISM in the N-enhanced lensed galaxy RXCJ2248-ID at z=6.1

We present an analysis on the kinematics and physical properties of the ionized gas in the lensed galaxy RXCJ2248-ID at z=6.1 based on high-resolution JWST NIRSpec/IFU data in combination with ALMA observations. Our analysis reveals a high electron temperature ($T_e$$\sim$30000K) in the ionized gas, independent of the ionization level. We measure a wide range in the electron densities derived from [OIII]$\lambda$5008/[OIII]88$\mu$m and [ArIV]$\lambda$4713/[ArIV]$\lambda$4742 ratios (log($n_e$[cm$^{-3}$])$\sim$2.7-3.8), and previous values (log($n_e$[cm$^{-3}$])>4.8) based on high-ionization rest-UV emission lines. The ionized gas appears to be clumpy with a low filling factor ranging from about 10% to 0.2% for the low- and high-density clouds. In addition, we observe a very complex ISM kinematic structure, with the presence of two distinct broad and a very-broad components (FWHM$\sim$210 and $\sim$1000 kms$^{-1}$) in addition to the systemic one (FWHM$\sim$60 kms$^{-1}$) in [OIII]$\lambda$5008 and H$\alpha$. These broad components are heavily extinct (A$_V$$\sim$1.5 and 2.5, respectively), based on their Balmer decrements, while the gas associated to the narrow component is consistent with no extinction. The maximal velocities of these outflows ($\sim$115-500kms$^{-1}$) are such that a fraction of the total outflowing gas (0.16-2.1$\times$10$^7$M$_\odot$) could escape into the IGM. The rest of the gas will fall back to the central regions, being available for additional star formation episodes. The presence of dusty outflows and clumpy (i.e., low filling factor) ISM give support to the Attenuation-Free scenario proposed to explain the high-z UV-bright compact galaxies such as RXCJ2248-ID. On the other hand, the high densities in the ISM, together with the high SFR surface brightness, and the amount of returning outflowing mass give support to the Feedback-Free Starburst scenario.

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arXiv2025

JWST spectroscopic confirmation of the Cosmic Gems arc at z=9.625 -- Insights into the small scale structure of a post-burst system

We present JWST/NIRSpec integral field spectroscopy of the Cosmic Gems arc, strongly magnified by the galaxy cluster SPT-CL J0615$-$5746. Six-hour integration using NIRSpec prism spectroscopy (resolution $\rm R\simeq 30-300$), covering the spectral range $0.8-5.3~\mu m$, reveals a pronounced $\rm Ly\alpha$-continuum break at $\lambda \simeq 1.3~\mu m$, as well as weak optical $\rm H\beta$ and $\rm [OIII]\lambda4959$ emission lines at $z=9.625\pm0.002$, located in the reddest part of the spectrum ($\lambda > 5.1~\mu m$). No additional ultraviolet or optical emission lines are reliably detected. A weak Balmer break is measured alongside a very blue ultraviolet slope ($\beta \leq-2.5$, $\rm F_{\lambda} \sim \lambda^{\beta}$). Spectral fitting with $\tt Bagpipes$ suggests that the Cosmic Gems galaxy is in a post-starburst phase, making it the highest-redshift system currently observed in a mini-quenched state. Spatially resolved spectroscopy at tens of parsecs shows relatively uniform features across subcomponents of the arc. These findings align well with the physical properties previously derived from JWST/NIRCam photometry of the stellar clusters, now corroborated by spectroscopic evidence. In particular, five observed star clusters exhibit ages of $\rm 7-30~Myr$. An updated lens model constrains the intrinsic sizes and masses of these clusters, confirming they are extremely compact and denser than typical star clusters in local star-forming galaxies. Additionally, four compact stellar systems consistent with star clusters ($\lesssim10$ pc) are identified along the extended tail of the arc. A sub-parsec line-emitting HII region straddling the critical line, lacking a NIRCam counterpart, is also serendipitously detected.

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arXiv2024

Euclid preparation. The Cosmic Dawn Survey (DAWN) of the Euclid Deep and Auxiliary Fields

Euclid will provide deep NIR imaging to $\sim$26.5 AB magnitude over $\sim$59 deg$^2$ in its deep and auxiliary fields. The Cosmic DAWN survey complements the deep Euclid data with matched depth multiwavelength imaging and spectroscopy in the UV--IR to provide consistently processed Euclid selected photometric catalogs, accurate photometric redshifts, and measurements of galaxy properties to a redshift of $z\sim 10$. In this paper, we present an overview of the survey, including the footprints of the survey fields, the existing and planned observations, and the primary science goals for the combined data set.

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arXiv2024

The impact of nebular Lyman-Continuum on ionising photons budget and escape fractions from galaxies

Several Lyman Continuum (LyC) emitters have been detected so far, but their observed ionising spectra sometimes differ from attenuated stellar spectra predicted by stellar population synthesis modelling. This discrepancy may be due to a significant contribution of LyC nebular emission. We aim to quantify the importance this emission in LyC leakers: its contribution to the ionising photons budget, and to measurements of LyC escape. To estimate the nebular contribution to the LyC spectra of galaxies, we run photoionisation models with Cloudy for a range of BPASS templates, varying the column density of the surrounding gas, from density-bounded (log(NH$_{\rm{stop}}$/cm$^{-2}$)=16) to ionisation-bounded (log(NH$_{\rm{stop}}$/cm$^{-2}$)=19) regimes. In the limits of very optically thin (f$_{\rm{esc}}$ = 1), or thick configurations (f$_{\rm{esc}}$ = 0), there is no nebular contribution to the emergent LyC spectra. This contribution matters only at intermediate LyC opacities ($0 <$ f$_{\rm{esc}}$ $< 1$), where it alters the shape of the LyC spectrum chromatically, so that escape fractions estimates are highly sensitive to the wavelength range over which they are calculated. We propose a formula to estimate integrated escape fractions using f$_{λ700}$/f$_{λ1100}$ flux ratios, since this wavelength range is not affected by nebular emission. Regarding simulations, the boost of hydrogen ionising photons escaping galaxies is inversely proportional to the stellar escape fractions, but since typical simulated escape fractions are low, LyC photons escape is important. Nebular LyC is a non-negligible additional source of ionising photons from galaxies, which contribution has been overlooked so far in observations and in cosmic reionisation simulations.

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arXiv2023

NOEMA observations of GN-z11: Constraining Neutral Interstellar Medium and Dust Formation in the Heart of Cosmic Reionization at $z=10.6$

We present results of dust continuum and [CII]$\,158\,{\rm μm}$ emission line observations of a remarkably UV-luminous ($M_{\rm UV}=-21.6$) galaxy at $z=10.603$: GN-z11. Using the Northern Extended Millimeter Array (NOEMA), observations have been carried out over multiple observing cycles. We achieved a high sensitivity resulting in a $λ_{\rm rest}=160\,{\rm μm}$ continuum $1\,σ$ depth of $13.0\,\rm{μJy/beam}$ and a [CII] emission line $1\,σ$ sensitivity of $31\,\rm{mJy/beam\,km/s}$ using $50\,\rm{km/s}$ binning with a $\sim 2\,{\rm arcsec}$ synthesized beam. Neither dust continuum nor [CII]$\,158\,{\rm μm}$ line emission are detected at the expected frequency of $ν_{\rm [CII]} = 163.791\,\rm{GHz}$ and the sky location of GN-z11. The upper limits show that GN-z11 is neither luminous in $L_{\rm IR}$ nor $L_{\rm [CII]}$, with a dust mass $3\,σ$ limit of ${\rm log}(M_{\rm dust}/{\rm M_{\odot}}) < 6.5-6.9$ and with a [CII] based molecular gas mass $3\,σ$ limit of ${\rm log}(M_{\rm mol,[CII]}/{\rm M_{\odot}}) < 9.3$. Together with radiative transfer calculations, we also investigated the possible cause of the dust poor nature of the GN-z11 showed by the blue color in the UV continuum of GN-z11 ($β_{\rm UV}=-2.4$), and found that $\gtrsim3\times$ deeper observations are crucial to study dust production at very high-redshift. Nevertheless, our observations show the crucial role of deep mm/submm observations of very high redshift galaxies to constrain multiple phases in the interstellar medium.

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arXiv2023

Estimating Dust Temperature and Far-IR Luminosity of High-Redshift Galaxies using ALMA Single-Band Continuum Observations

We present a method that derives the dust temperatures and infrared (IR) luminosities of high-redshift galaxies assuming radiation equilibrium in a simple dust and stellar distribution geometry. Using public data from the Atacama Large Millimeter/submillimeter Array (ALMA) archive, we studied dust temperatures assuming a clumpy interstellar medium (ISM) model for high-redshift galaxies, then tested the consistency of our results with those obtained using other methods. We find that a dust distribution model assuming a clumpiness of ${\rm log}\,ξ_{\rm clp}=-1.02\pm0.41$ may accurately represent the ISM of high-redshift star-forming galaxies. By assuming a value of $ξ_{\rm{clp}}$, our method enables the derivation of dust temperatures and IR luminosities of high-redshift galaxies from dust continuum fluxes and emission sizes obtained from single-band ALMA observations. to demonstrate the method proposed herein, we determined the dust temperature ($T_{\rm d}=95^{+13}_{-17}\,\rm{K}$) of a $z\sim8.3$ star-forming galaxy, MACS0416-Y1. Because the method only requires a single-band dust observation to derive a dust temperature, it is more easily accessible than multi-band observations or high-redshift emission line searches and can be applied to large samples of galaxies in future studies using high resolution interferometers such as ALMA.

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arXiv2022

The ALMA REBELS Survey: Average [CII] $158\,\rm{μm}$ sizes of Star-Forming Galaxies from $z\sim 7$ to $z\sim 4$

We present the average [CII] $158\,\rm{μm}$ emission line sizes of UV-bright star-forming galaxies at $z\sim7$. Our results are derived from a stacking analysis of [CII] $158\,\rm{μm}$ emission lines and dust continua observed by ALMA, taking advantage of the large program Reionization Era Bright Emission Line Survey (REBELS). We find that the average [CII] emission at $z\sim7$ has an effective radius $r_e$ of $2.2\pm0.2\,\rm{kpc}$. It is $\gtrsim2\times$ larger than the dust continuum and the rest-frame UV emission, in agreement with recently reported measurements for $z\lesssim6$ galaxies. Additionally, we compared the average [CII] size with $4<z<6$ galaxies observed by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE). By analysing [CII] sizes of $4<z<6$ galaxies in two redshift bins, we find an average [CII] size of $r_{\rm e}=2.2\pm0.2\,\rm{kpc}$ and $r_{\rm e}=2.5\pm0.2\,\rm{kpc}$ for $z\sim5.5$ and $z\sim4.5$ galaxies, respectively. These measurements show that star-forming galaxies, on average, show no evolution in the size of the [CII] $158\,{\rm μm}$ emitting regions at redshift between $z\sim7$ and $z\sim4$. This finding suggest that the star-forming galaxies could be morphologically dominated by gas over a wide redshift range.

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arXiv2021

Large format imaging spectrograph for the Large Submillimeter Telescope (LST)

We present a conceptual study of a large format imaging spectrograph for the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Recent observations of high-redshift galaxies indicate the onset of earliest star formation just a few 100 million years after the Big Bang (i.e., z = 12--15), and LST/AtLAST will provide a unique pathway to uncover spectroscopically-identified first forming galaxies in the pre-reionization era, once it will be equipped with a large format imaging spectrograph. We propose a 3-band (200, 255, and 350 GHz), medium resolution (R = 2,000) imaging spectrograph with 1.5 M detectors in total based on the KATANA concept (Karatsu et al. 2019), which exploits technologies of the integrated superconducting spectrometer (ISS) and a large-format imaging array. A 1-deg2 drilling survey (3,500 hr) will capture a large number of [O III] 88 um (and [C II] 158 um) emitters at z = 8--9, and constrain [O III] luminosity functions at z > 12.

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arXiv2020

A puzzling non-detection of [O III] and [C II] from a $z \approx 7.7$ galaxy observed with ALMA

Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, the number of observations at the very highest redshifts are to date, few. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-$α$ emitting galaxy z7\_GSD\_3811 at $z=7.664$ with band 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). We target the far-infrared [O III] 88 $μm$, [C II] 158 $μm$ emission lines and dust continuum in the star-forming galaxy z7\_GSD\_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object, and compare results to those of earlier studies observing [O III] and [C II] emission in high-redshift galaxies. The [O III] 88 $μm$ and [C II] 158 $μm$ emission lines are undetected at the position of z7\_GSD\_3811, with $3σ$ upper limits of $1.6 \ \times \ 10^{8} \ L_{\odot}$ and $4.0 \ \times \ 10^{7} \ L_{\odot}$, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continuum is 26 and 9.9 $μJy \ beam^{-1}$, respectively. Similar to several other high-redshift galaxies, z7\_GSD\_3811 exhibits low [C II] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O III] line luminosity is lower than all the previously observed [O III] lines in high-redshift galaxies with similar ultraviolet luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7\_GSD\_3811 likely has a low dust content, and our non-detections of the [O III] and [C II] lines could indicate that z7\_GSD\_3811 has a low metallicity ($Z \lesssim 0.1 \ Z_{\odot}$).

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arXiv2020

Outside the Lyman-break box: detecting Lyman continuum emitters at $3.5<z<5.1$ with CLAUDS

Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS $u$-band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at $z\geq3.5$ and outside the standard Lyman-break galaxy colour selection expectations. Complementary to the CLAUDS data, we use Subaru multi-filter photometry, \textit {Hubble Space Telescope} ($HST$) multi-filter imaging, and the spectroscopic surveys D10K, VUDS and 3D-HST. We present a sample of Lyman continuum galaxy (LCG) candidates in the redshift range $3.5\lesssim z\lesssim5.1$. Here, we introduce 5 LCG candidates, where two are flagged quality 1 and three quality 2. The estimated $f_{\rm esc}^{\rm abs}$ for quality 1 candidates are in the range $\sim5\% - 73\%$ and $\sim30\% - 93\%$. These estimates are based on our derived parameters from individual galaxies as inputs to a range of BPASS models as well as mean intergalactic medium (IGM) and maximal intergalactic and circumgalactic media (IGM+CGM) transmission. We conclude that our search for LCGs is most likely biased to lines of sight with low HI densities or free from Lyman limit systems. Our two best LCG candidates have EW (Ly$α)\leq50$Å and we find no correlation or anti-correlation between EW (Ly$α$), $f_{\rm esc}^{\rm abs}$, and $R_{\rm obs}$, the ratio of ionizing to non-ionizing observed flux in the measured passbands. Stacking candidates without solid LyC detections ($S/N<3$) results in an estimated $f_{\rm esc}^{\rm abs}$ from galaxies not greater than $1\%$.

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arXiv2020

Observational and theoretical constraints on the formation and early evolution of the first dust grains in galaxies at 5 < z < 10

The first generation of stars were born a few hundred million years after the big bang. These stars synthesized elements heavier than H and He, that are later expelled into the interstellar medium, initiating the rise of metals. Within this enriched medium, the first dust grains formed. This event is cosmological crucial for molecule formation as dust plays a major role by cooling low-metallicity star-forming clouds which can fragment to create lower mass stars. Collecting information on these first dust grains is difficult because of the negative alliance of large distances and low dust masses. We combine the observational information from galaxies at redshifts 5 < z < 10 to constrain their dust emission and theoretically understand the first evolutionary phases of the dust cycle. Spectral energy distributions (SEDs) are fitted with CIGALE and the physical parameters and their evolution are modelled. From this SED fitting, we build a dust emission template for this population of galaxies in the epoch of reionization. Our new models explain why some early galaxies are observed and others are not. We follow in time the formation of the first grains by supernovae later destroyed by other supernova blasts and expelled in the circumgalactic and intergalactic media. We have found evidence for the first dust grains formed in the universe. But, above all, this letter underlines the need to collect more data and to develop new facilities to further constrain the dust cycle in galaxies in the epoch of reionization.

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arXiv2019

Balmer breaks in simulated galaxies at z>6

Photometric observations of the spectroscopically confirmed $z\approx 9.1$ galaxy MACS1149-JD1 have indicated the presence of a prominent Balmer break in its spectral energy distribution, which may be interpreted as due to very large fluctuations in its past star formation activity. In this paper, we investigate to what extent contemporary simulations of high-redshift galaxies produce star formation rate variations sufficiently large to reproduce the observed Balmer break of MACS1149-JD1. We find that several independent galaxy simulations are unable to account for Balmer breaks of the inferred size, suggesting that MACS1149-JD1 either must be a very rare type of object or that our simulations are missing some key ingredient. We present predictions of spectroscopic Balmer break strength distributions for $z\approx 7-9$ galaxies that may be tested through observations with the upcoming James Webb Space Telescope and also discuss the impact that various assumptions on dust reddening, Lyman continuum leakage and deviations from a standard stellar initial mass function would have on the results.

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arXiv2019

The Absence of [CII] 158$μ$m Emission in Spectroscopically-Confirmed Galaxies at $z>8$

The scatter in the relationship between the strength of [CII] 158$μ$m emission and the star formation rate at high-redshift has been the source of much recent interest. Although the relationship is well-established locally, several intensely star-forming galaxies have been found whose [CII] 158$μ$m emission is either weak, absent or spatially offset from the young stars. Here we present new ALMA data for the two most distant, gravitationally-lensed and spectroscopically-confirmed galaxies, A2744\_YD4 at $z=$8.38 and MACS1149\_JD1 at $z=$9.11, both of which reveal intense [OIII] 88$μ$m emission. In both cases we provide stringent upper limits on the presence of [CII] 158$μ$m with respect to [OIII] 88$μ$m. We review possible explanations for this apparent redshift-dependent [CII] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies.

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