#  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

Seiji Fujimoto Hubble Fellow  Department of Astronomy, The University of Texas
at Austin, Austin, TX 78712, USA  Cosmic Dawn Center (DAWN), Denmark  Niels
Bohr Institute, University of Copenhagen, Lyngbyvej 2, DK2100 Copenhagen Ø,
Denmark  Masami Ouchi National Astronomical Observatory of Japan, 2-21-1
Osawa, Mitaka, Tokyo 181-8588, Japan  Institute for Cosmic Ray Research, The
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan  Kavli
Institute for the Physics and Mathematics of the Universe (WPI), University of
Tokyo, Kashiwa, Chiba 277-8583, Japan  Kimihiko Nakajima National Astronomical
Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan  Yuichi
Harikane Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, Chiba 277-8582, Japan  Yuki Isobe Institute for Cosmic
Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba
277-8582, Japan  Department of Physics, Graduate School of Science, The
University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan  Gabriel
Brammer Cosmic Dawn Center (DAWN), Denmark  Niels Bohr Institute, University
of Copenhagen, Lyngbyvej 2, DK2100 Copenhagen Ø, Denmark  Masamune Oguri
Center for Frontier Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba
263-8522, Japan  Department of Physics, Graduate School of Science, Chiba
University, 1-33 Yayoi-Cho, Inage-Ku, Chiba 263-8522, Japan  Clara Giménez-
Arteaga Cosmic Dawn Center (DAWN), Denmark  Niels Bohr Institute, University
of Copenhagen, Blegdamsvej 17, DK2100 Copenhagen Ø, Denmark  Kasper E. Heintz
Cosmic Dawn Center (DAWN), Denmark  Niels Bohr Institute, University of
Copenhagen, Jagtvej 128, DK-2200 Copenhagen N, Denmark  Vasily Kokorev Cosmic
Dawn Center (DAWN), Denmark  Niels Bohr Institute, University of Copenhagen,
Blegdamsvej 17, DK2100 Copenhagen Ø, Denmark  Franz E. Bauer Instituto de
Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile,
Campus San Joaquín, Av. Vicuña Mackenna 4860, Macul Santiago, Chile, 7820436
Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica
de Chile, Campus San Joaquín, Av. Vicuña Mackenna 4860, Macul Santiago, Chile,
7820436  Millennium Institute of Astrophysics, Nuncio Monseñor Sótero Sanz
100, Of 104, Providencia, Santiago, Chile  Andrea Ferrara Scuola Normale
Superiore, Piazza dei Cavalieri 7, 50126 Pisa, Italy  Takashi Kojima Institute
for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8582, Japan  Claudia del P. Lagos International Centre for Radio
Astronomy Research (ICRAR), M468, University of Western Australia, 35 Stirling
Hwy, Crawley,
WA 6009, Australia.  ARC Centre of Excellence for All Sky Astrophysics in 3
Dimensions (ASTRO 3D).  Cosmic Dawn Center (DAWN), Denmark  Sommovigo Laura
Scuola Normale Superiore, Piazza dei Cavalieri 7, 50126 Pisa, Italy  Daniel
Schaerer Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290
Versoix, Switzerland  CNRS, IRAP, 14 Avenue E. Belin, 31400 Toulouse, France
Kazuhiro Shimasaku Department of Astronomy, School of Science, The University
of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan  Research Center for
the Early Universe, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-0033, Japan  Bunyo Hatsukade Institute of Astronomy, Graduate School of
Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
Kotaro Kohno Institute of Astronomy, Graduate School of Science, The
University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan  Research
Center for the Early Universe, School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan  Fengwu Sun Steward Observatory,
University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721, USA  Francesco
Valentino Cosmic Dawn Center (DAWN), Denmark  Niels Bohr Institute, University
of Copenhagen, Jagtvej 128, DK-2200 Copenhagen N, Denmark  European Southern
Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Munchen, Germany
Darach Watson Cosmic Dawn Center (DAWN), Denmark  Niels Bohr Institute,
University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen N, Denmark
Yoshinobu Fudamoto Waseda Research Institute for Science and Engineering,
Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku,
Tokyo 169-8555, Japan  National Astronomical Observatory of Japan, 2-21-1,
Osawa, Mitaka, Tokyo, Japan  Akio K. Inoue Waseda Research Institute for
Science and Engineering, Faculty of Science and Engineering, Waseda
University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan  Department of
Physics, School of Advanced Science Engineering, Faculty of Science and
Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
Jorge González-López Núcleo de Astronomía de la Facultad de Ingeniería y
Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago,
Chile  Las Campanas Observatory, Carnegie Institution of Washington, Casilla
601, La Serena, Chile  Anton M. Koekemoer Space Telescope Science Institute,
3700 San Martin Dr., Baltimore, MD 21218, USA  Kirsten Knudsen Department of
Space, Earth and Environment, Chalmers University of Technology, Onsala Space
Observatory, SE-43992 Onsala, Sweden  Minju M. Lee Cosmic Dawn Center (DAWN),
Denmark  DTU-Space, Technical University of Denmark, Elektrovej 327, DK2800
Kgs. Lyngby, Denmark  Georgios E. Magdis Cosmic Dawn Center (DAWN), Jagtvej
128, DK2200 Copenhagen N, Denmark  DTU-Space, Technical University of Denmark,
Elektrovej 327, 2800, Kgs. Lyngby, Denmark  Niels Bohr Institute, University
of Copenhagen, Jagtvej 128, 2200, Copenhagen N, Denmark  Johan Richard Univ
Lyon, Univ Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon
UMR5574, F-69230, Saint-Genis-Laval,France  Victoria B. Strait Cosmic Dawn
Center (DAWN), Denmark  Niels Bohr Institute, University of Copenhagen,
Jagtvej 128, DK-2200 Copenhagen N, Denmark  Yuma Sugahara Waseda Research
Institute for Science and Engineering, Faculty of Science and Engineering,
Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan  National
Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo, Japan  Yoichi
Tamura Division of Particle and Astrophysical Science, Graduate School of
Science, Nagoya University, Nagoya 464-8602, Japan  Sune Toft Cosmic Dawn
Center (DAWN), Denmark  Niels Bohr Institute, University of Copenhagen,
Jagtvej 128, DK-2200 Copenhagen N, Denmark  Hideki Umehata Institute for
Advanced Research, Nagoya University, Furocho, Chikusa, Nagoya 464-8602, Japan
Department of physics, Graduate School of Science, Nagoya University, Nagoya,
Aichi 464-8602, Japan  Gregory Walth IPAC, California Institute of Technology,
Mail Code 314-6, 1200 E. California Blvd., Pasadena, CA 91125

###### Abstract

We present ALMA deep spectroscopy for a lensed galaxy at $z_{\rm spec}=8.496$
with $\log(M_{\rm star}/M_{\odot})\sim 7.8$ whose optical nebular lines and
stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release
Observations in SMACS0723. Our ALMA spectrum shows [O iii]88 $\mu$m and [C
ii]158 $\mu$m line detections at $4.0\sigma$ and $4.5\sigma$, respectively.
The redshift and position of the [O iii] line coincide with those of the JWST
source, while the [C ii] line is blue-shifted by 90 km s-1 with a spatial
offset of $0\farcs 5$ ($\approx 0.5$ kpc in source plane) from the centroid of
the JWST source. The NIRCam F444W image, including [O iii]$\lambda$5007 and
H$\beta$ 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 [O
iii]$\lambda$5007 and the offset [C ii] emission, which would promote ionizing
photon escape and facilitate reionization. With careful slit-loss corrections
and removals of emission spatially outside the galaxy, we evaluate the [O
iii]88$\mu$m/$\lambda$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 $z\sim 2$–3 galaxies. We estimate an [O
iii]88$\mu$m/[C ii]158$\mu$m line ratio in the galaxy of $>4$, as high as
those of known $z\sim$6–9 galaxies. This high [O iii]88 $\mu$m/[C ii]158
$\mu$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 [C ii] follow-up observations will constrain the covering fraction of
photodissociation regions.

galaxies: formation — galaxies: evolution — galaxies: high-redshift

††journal: ApJ††software: casa (v6.4.1; THE CASA TEAM et al. 2022), grizli
(Brammer et al. 2022), EAZY, (Brammer et al. 2008), PyNeb (Shaw et al. 1998)
CLOUDY, (Ferland et al. 2017), Interferopy, (Boogaard et al. 2021b), and
CIGALE (Boquien et al. 2019)

##  1 Introduction

Studying early systems in the Epoch of Reionization (EoR; $z\gtrsim 6$) is key
to understanding fundamental cosmological questions such as the development of
large-scale structure, the processes of cosmic reionization, and the first
galaxy formation in the universe. In the last decades, deep Hubble Space
Telescope (HST) surveys provided thousands of EoR galaxies and initial
characterization of their stellar component, in terms of un-obscured star
formation and sizes in the rest-frame ultra-violet (UV) wavelengths (e.g.,
Ellis et al. 2013; Bouwens et al. 2015; Finkelstein et al. 2015; Oesch et al.
2016).

The Atacama Large Millimeter/submillimeter Array (ALMA) offers a unique rest-
frame far-infrared (FIR) window on EoR galaxies to characterize the dust and
gas properties of their interstellar media (ISMs), where the major cooling
lines (e.g., [C ii] 158$\mu$m, [O iii] 88$\mu$m) and underlying dust continuum
are probes of key mechanisms in the ISM such as disk rotation (e.g., Smit et
al. 2018; Rizzo et al. 2020), gravitational instability (e.g., Tadaki et al.
2018), formation of the bulge, disk, and spiral arms (e.g., Tsukui & Iguchi
2021; Lelli et al. 2021), galaxy mergers (e.g., Le Fèvre et al. 2020),
outflows (e.g., Spilker et al. 2018), and dust-obscured star-forming
activities (e.g., Bowler et al. 2022; Inami et al. 2022), which strongly
complements rest-UV studies with HST. Since elements produced in stars are
returned to the ISM, the metal gas properties traced by the fine-structure
lines, with their different ionization potentials and critical densities,
provide powerful probes on the star-formation history and related physical
conditions of the ISM, such as the temperature, density, ionization, and metal
enrichment (e.g., Maiolino & Mannucci 2019).

Previous ALMA observations have also raised questions about what causes large
diversity in EoR galaxies and the difference from local galaxies. Early deep
ALMA [C ii] spectroscopy of some EoR galaxies has shown low $L_{\rm[CII]}$/SFR
values (e.g., Ota et al. 2014; Knudsen et al. 2016), suggesting that they have
characteristic ISM conditions such as high ionization parameter, low
metallicity, or low gas density (e.g., Ferrara et al. 2019). However, recent
ALMA observations detected dust continuum (e.g., Watson et al. 2015; Inami et
al. 2022) and bright [C ii] lines (e.g., Bouwens et al. 2022), pointing to a
$L_{\rm[CII]}$/SFR relation similar to that of local main-sequence galaxies
(e.g., Schaerer et al. 2020) and even low-mass sub-$L^{\star}$ galaxies at
$z\gtrsim 6$ (e.g., Fujimoto et al. 2021; Molyneux et al. 2022). Moreover,
while ALMA observations of EoR galaxies have also shown high
$L_{\rm[OIII]}$/$L_{\rm[CII]}$ ratios (e.g., Inoue et al. 2016; Harikane et
al. 2020; Carniani et al. 2020; Witstok et al. 2022) that are comparable or
even higher than local dwarf galaxies (e.g., Cormier et al. 2015), the main
driver for the high ratios is still under debate (e.g., Harikane et al. 2020;
Vallini et al. 2021; Katz et al. 2022; Witstok et al. 2022). While promising,
past HST and ALMA results have yet to provide a clear picture of the ISM
physics in EoR galaxies.

To understand ISM physics, one of the key quantities is the gas-phase
metallicity ($Z_{\rm gas}$), which is a direct probe of chemical enrichment
and, thus, the evolutionary stage of galaxies. The flux of each metal line is
determined by the abundance of that element and its emissivity (Aller 1984).
Therefore, we can accurately estimate the abundance once we measure the
emissivity based on the electron temperature $T_{\rm e}$, i.e., the so-called
direct method (e.g., Pilyugin & Thuan 2005; Andrews & Martini 2013). However,
since the direct method requires the detection of very faint auroral lines
(e.g., [O iii]$\lambda$4363), this has until recently only been possible for a
handful of sources up to $z\sim 3$ (e.g., Christensen et al. 2012; Kojima et
al. 2017; Sanders et al. 2020).

Our observational landscape has been revolutionized by the advent of JWST. As
part of the Early Release observation (ERO) programs of JWST, deep NIRSpec
multi shutter array (MSA) observations have been performed towards the massive
lensing cluster SMACSJ0723, successfully detecting multiple nebular emission
lines in the rest-frame UV to optical wavelengths and determining
spectroscopic redshifts for distant lensed galaxies out to $z=8.496$ (e.g.,
Carnall et al. 2022; Schaerer et al. 2022; Trump et al. 2022; Curti et al.
2022). Remarkably, the deep NIRSpec spectra also show the detection of the
auroral line [O iii]$\lambda$4363, enabling the first direct temperature
$T_{\rm e}$ method estimates at such high redshifts (e.g., Schaerer et al.
2022; Trump et al. 2022; Curti et al. 2022). With the powerful JWST and ALMA
combination, we are finally in a position to fully reveal how the elements of
galaxies – gas, stellar, and dust – interplay with each other and what governs
the growth of galaxies in the infant Universe.

In this paper, we present ALMA deep follow-up of two major coolant lines, [C
ii] 158$\mu$m and [O iii] 88$\mu$m, and underlying continuum for the lensed
galaxy at $z=8.496$, whose warm ISM properties are best characterized by the
latest deep JWST observations, including the [O iii]$\lambda$4363 line. This
is the first FIR characterization of an EoR galaxy with a robust metallicity
measurement via the direct method, setting the benchmark to understand and
interpret previous results from ALMA EoR galaxy studies over the last decade
and providing a timely, unique reference for future follow-up of EoR galaxies
in the coming decade.

The structure of this paper is as follows. In Section 2, we describe the
observations and the data processing of both JWST and ALMA. Section 3 outlines
the analyses related to the mass model for the lensing cluster, measurements
of flux, size, and morphology, and the optical–mm SED fitting. In Section 4,
we present the results from the multiple-line studies and discuss the physical
origins of these results. A summary of this study is presented in Section 5.
Throughout this paper, we assume a flat universe with $\Omega_{\rm m}=$ 0.3,
$\Omega_{\Lambda}=$ 0.7, $H_{0}=$ 70 km s-1 Mpc-1, and the Chabrier initial
mass function (IMF; Chabrier 2003). We adopt an angular scale of
$1^{\prime\prime}=4.63$ kpc for the target redshift at $z=8.496$. We take the
cosmic microwave background (CMB) effect into account and correct the flux
measurements at submm and mm bands, following the recipe presented by da Cunha
et al. (2013) (see also e.g., Pallottini et al. 2015; Zhang et al. 2016;
Lagache et al. 2018).

##  2 Observations & Data Processing

Table 1: ALMA DDT Observation & Data Properties for ID4590 at $z=8.496$ in SM0723 Target line | Band | $\lambda_{\rm cent}$ | Obs Date | Baseline | $N_{\rm ant}$ | $T_{\rm int}$ | PWV | beam | $\sigma_{\rm line}$ | $\sigma_{\rm cont}$
---|---|---|---|---|---|---|---|---|---|---
|  | ($\mu$m) | (YYYY-MM-DD) | (m) |  | (min) | (mm) | (${}^{\prime\prime}\times^{\prime\prime}$) | ($\mu$Jy/beam) | ($\mu$Jy/beam)
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) | (11)
[C ii] 158 $\mu$m | 5 | 1540 | 2022-10-17 | 15.1–629.3 (C3) | 44 | 85.7 | 0.5 | $1.35\times 1.25$ | 225 | 11.6
[O iii] 88 $\mu$m | 7 | 854 | 2022-10-14 | 15.1–629.3 (C3) | 44 | 99.8 | 0.4 | $0.71\times 0.58$ | 420 | 20.9
Figure 1:  Summary of ALMA DDT observation results. Top: The ALMA dust
continuum and velocity-integrated line maps for the [O iii]88$\mu$m
($4^{\prime\prime}\times 4^{\prime\prime}$) and [C ii]158$\mu$m lines
($6^{\prime\prime}\times 6^{\prime\prime}$). The solid (dashed) contours are
the 2$\sigma$, 3$\sigma$, and 4$\sigma$ (-3$\sigma$ and -2$\sigma$) levels.
The white bars indicate the target position at the center of the maps, and the
ellipse denotes the synthesized ALMA beam. Bottom: ALMA line spectra, where
the middle panel compares their line profiles in the velocity frame, where the
zero velocity is based on $z=8.496$ determined by NIRSpec. The spectra are
extracted from the mean pixel count within optimized apertures smaller than
the beam size at the source position. The dashed curve shows the best-fit
Gaussian. The black bar shows the best-fit frequency center of the line with
the 1$\sigma$ error, and the corresponding redshift and the line width are
described in the label. The red dashed vertical line denotes the expected line
frequency based on the redshift of $z=8.496$ determined by NIRSpec.

###  2.1 SMACS J0723.3-7327

The target field, SMACS J0723.3-7327 (hereafter SM0723), is a massive galaxy
cluster at $z=0.390$ ($07^{h}23^{m}13.3^{s}$, $-73^{d}27^{m}25^{s}$),
initially discovered via the Sunyaev-Zel’dovich effect in the Planck survey
(Planck Collaboration et al. 2011). The galaxy cluster mass is estimated to be
$M_{200}=8.4\times 10^{14}M_{\odot}$. SM0723 was observed as part of the HST
Reionization Lensing Cluster Survey (RELICS, #GO-14096, PI: D. Coe, Coe et al.
2019) treasury program and the subsequent Spitzer S-RELICS program (#12005,
PI: M. Bradac).

###  2.2 ALMA

ALMA Band 5 and Band 7 follow-up observations of [C ii] and [O iii]
spectroscopy were carried out on October 17th and 14th 2022, respectively, as
a Cycle 8 DDT program (#2022.A.00022.S, PI: S. Fujimoto). The target was a
strongly lensed star-forming galaxy, ID4590, spectroscopically confirmed at
$z=8.496$ with the robust detection of rest-frame optical emission lines
including the [O iii]$\lambda$4363 line (e.g., Carnall et al. 2022; Schaerer
et al. 2022; Trump et al. 2022; Curti et al. 2022). Both observations used the
Frequency Division Mode, and baseline ranges 15–457 m in the C-3
configuration. The mean precipitable water vapour (PWV) was 0.5 mm and 0.4 mm,
and the on-source integration times were 85.7 mins and 99.8 mins in Band 5 and
Band 7, respectively. J0519-4546 was observed as a flux and bandpass
calibrator in both observations, while the phase calibration was performed
with J0601-7036 and J0635-7516 in Band 5 and Band 7 observations,
respectively.

The ALMA data were reduced and calibrated with the Common Astronomy Software
Applications package version 6.4.1.12 (CASA; THE CASA TEAM et al. 2022) with
the pipeline script in the standard manner. We imaged the calibrated
visibilities using natural weighting, a pixel scale of $0\farcs 05$, and a
primary beam limit down to 0.2 by running the CASA task tclean. For cubes, we
adopted spectral channel bins of 20, 30, and 40 km s-1 and performed the CLEAN
algorithm. For continuum maps, the tclean routines were executed down to the
1$\sigma$ level with a maximum iteration number of 100,000 in the automask
mode (Kepley et al. 2020). We mask the central $\pm 120$ km s-1 channels to
avoid contamination from the [C ii] and [O iii] lines in the continuum map.
The natural weighted images, which maximize the S/N, resulted in the full-
width-half-maximum (FWHM) size of the synthesized beam of $1\farcs 35\times
1\farcs 25$ and $0\farcs 71\times 0\farcs 58$ with $1\sigma$ sensitivities for
the continuum (line in a 20 km s-1 channel) of 11.6 (225) $\mu$Jy beam-1 and
20.9 (420) $\mu$Jy beam-1 in Band 5 and Band 7, respectively. Figure 1 shows
the reduced continuum maps and the line cubes for both ALMA Band 5 and Band 7.
We summarize the data properties of the continuum maps and the line cubes in
Table 1.

###  2.3 JWST

As part of the JWST ERO (#ERO-2736; Pontoppidan et al. 2022), SM0723 was
observed with JWST/NIRCam, NIRSpec, MIRI, and NIRISS in June 2022. In the
NIRCam and MIRI observations, six (F090W, F150W, F200W, F277W, F356W, F444W)
and four (F770W, F1000W, F1500W, F1800W) different filters were used with
$\sim$7540 sec and $\sim$5600 sec exposure per filter, reaching 5$\sigma$
limiting magnitudes of $\sim$29.4–30.0 AB and $\sim$23–26.3 AB, respectively
(Pontoppidan et al. 2022).

For NIRCam and MIRI, we use publicly available reduced and calibrated imaging
products via the grizli pipeline.111
https://s3.amazonaws.com/grizli-v2/JwstMosaics/v4/index.html The detailed
calibration and reduction procedures will be presented in Brammer et al. (in
prep.) (see also, e.g., Bradley et al. 2022; Fujimoto et al. 2022b). Briefly,
the JWST pipeline calibrated level-2 NIRCam imaging products were retrieved
and processed with the grizli pipeline (Brammer & Matharu 2021; Brammer et al.
2022), where the photometric zero-point correction was applied, including
other corrections for “snowballs”222 https://jwst-docs.stsci.edu/data-
artifacts-and-features/snowballs-artifact, “wisps”333 https://jwst-
docs.stsci.edu/jwst-near-infrared-camera/nircam-features-and-caveats/nircam-
claws-and-wisps, and detector variations.444
https://github.com/gbrammer/grizli/pull/107 The derived photometric zeropoints
are consistent with those derived by other teams for JWST ERS programs (Boyer
et al. 2022; Nardiello et al. 2022), while we include a systematic error of
10% on the observed flux values in the following analyses as a conservative
measure. The fully-calibrated images in each filter were aligned with the GAIA
DR3 catalog (Gaia Collaboration et al. 2021), co-added, and drizzled at a 20
mas and 40 mas pixel scale for the short-wavelength (SW: F090W, F150W, F200W)
and long-wavelength (LW: F277W, F356W, F444W) NIRCam band images,
respectively. For the produced maps, we also additionally correct the proper
motion effects of the GAIA sources. In the Appendix, we show the residual
astrometric offsets of the GAIA sources. We confirm the residual astrometric
offset with respect to the GAIA DR3 frame is close to zero with the
uncertainty of $\sim$10–20 mas. All the MIRI images (F770W, F1000W, F1500W,
F1800W) are aligned, co-added, and drizzled at 40 mas pixel scale in the same
manner. Existing multi-wavelength WFC3 archival imaging from HST was also
processed with grizli, being aligned, co-added, and drizzled at 40 mas pixel
scale in the same manner (see also Kokorev et al. 2022). We include all MIRI
and HST/F105W, F125W, F140W, and F160W data in our analysis. Given the
existence of nearby objects (Section 3.4), we adopt $0\farcs 36$-diameter
aperture photometry which is corrected to the total flux measurement by
MAG_AUTO. We also correct for the Galactic dust reddening in the target
direction. The JWST and HST photometry used in this paper are summarized in
the Appendix.

For NIRSpec, there are several studies applying the latest reduction and
calibration (Heintz et al. submitted; Nakajima et al. in prep.), compared to
previous studies (e.g., Schaerer et al. 2022; Curti et al. 2022; Trump et al.
2022; Brinchmann 2022; Arellano-Córdova et al. 2022). In our paper, we use
results from Nakajima et al. (in prep.) due to requirements of specific
parameter sets for the photoionization model analysis in Section 4.5 that are
self-consistently derived in Nakajima et al. (in prep.). We confirm that the
measurements and the derived physical parameters are generally consistent with
the previous studies within the errors (e.g., Schaerer et al. 2022; Curti et
al. 2022; Trump et al. 2022; Brinchmann 2022; Arellano-Córdova et al. 2022) as
well as the similarly latest calibration and reduction efforts presented in
Heintz et al. (submitted). Briefly, the NIRSpec 1D spectra are re-created by
using four of the six exposures after removing one with no signal and another
with a noisy 2D spectrum around H$\gamma$+[O iii]$\lambda 4363$. Some
improvements are also implemented, including the background residual
subtractions, hot pixel removals, optimal 1D extractions, as well as flux
calibrations by referring to the standard star observations taken during
commissioning. Using the improved NIRSpec spectrum, Nakajima et al. confirm
the rest-frame UV and optical emission line detection at $z=8.496$ from
ID4590, including [O iii]$\lambda 5007$, [O iii]$\lambda 4363$, H$\beta$,
H$\gamma$, H$\delta$, and C iii]$\lambda\lambda 1907,1909$, and evaluate their
relative line fluxes after applying a slit-loss correction555 The slit-loss is
corrected by convolving and integrating the 1D spectrum with the filter
response of F444W to match it with the total magnitude of the NIRCam
photometry, which is derived with a $0\farcs 3$-diameter circular aperture and
the corresponding aperture correction. . On the other hand, Nakajima et al.
find that the [O ii]3727 doublet is not clearly detected in every nod and
visit, and they place a conservative 3$\sigma$ upper limit, which provides a
lower limit for the ionization parameter $\log$(U)$>-2.27$ based on Kewley &
Dopita (2002). The electron temperature and the gas-phase oxygen abundance are
estimated to be $T_{\rm[OIII]}=(2.08\pm 0.34)\times 10^{4}$ K and
12+$\log$(O/H) = $7.26\pm 0.18$ (equal to $0.04\pm 0.02\,Z_{\odot}$ by
assuming the solar metallicity of 12+$\log$(O/H)=8.69) via the direct $T_{\rm
e}$ method (e.g., Pilyugin et al. 2012) by assuming a negligible contribution
from O+/H+ ($<0.05$ dex at $3\sigma$; Nakajima et al. in prep.). The lower and
upper boundaries of the C/O abundance are also estimated to be $\log$(C/O) =
$[-0.52:-0.24]$ (Isobe et al. in prep.). These physical parameters are derived
including the dust correction based on the best-fit $E(B-V)$ value in this
paper (Section 3.6).

Table 2: FIR properties of ID4590 with ALMA

Target line | [O iii]88$\mu$m | [C ii]158$\mu$m
---|---|---
R.A. | 07:23:26.242 | 07:23:26.243
Dec. |  $-73$:26:56.824 |  $-73$:26:56.514
S/Nline | 4.0 | 4.5
Frequency center [GHz] | $357.305\pm 0.034$ | $200.203\pm 0.010$
$z_{\rm line}$ | $8.4963\pm 0.0009$ | $8.4931\pm 0.0005$
Line width [km s-1] | $136\pm 67$ | 118 $\pm$ 36
Line intensity [Jy km s-1] | $0.113\pm 0.028$ | $0.094\pm 0.027^{\dagger}$
Line luminosity [$\times 10^{8}\,L_{\odot}$] | $3.12\pm 0.76$ | $1.45\pm 0.32^{\dagger}$
Continuum [$\mu$Jy] |  $\,\,<41.8$ (0.85 mm) |  $<23.2$ (1.54 mm)

$\dagger$ Given the spatial and velocity offsets of the [C ii] line, we place
a 3$\sigma$ upper limit of $L_{\rm[CII]}<6.0\times 10^{7}\,L_{\odot}$ at the
galaxy position from the residual map of imfit.

Figure 2:  NIRCam image cutouts around ID4590. Left: PSF-matched RGB image
($6^{\prime\prime}\times 6^{\prime\prime}$) whose color assignment is shown in
the label. The light green and magenta contours indicate the [C ii]158$\mu$m
and [O iii]88$\mu$m line intensities at 2$\sigma$, 3$\sigma$, and 4$\sigma$
levels, respectively. The yellow curve denotes the critical curve at $z=8.5$
of SMACS0723 taken from the latest Glafic model (Section 3.1). The light green
and magenta ellipses at the bottom left are the ALMA synthesized beams in Band
5 (for [C ii]) and Band 7 (for [O iii]). The white rectangle shows the
NIRSpec/MSA slit. Middle: Zoom-in ($1\farcs 5\times 1\farcs 5$) NIRCam/F150W
image. The green and black crosses indicate the [C ii]158$\mu$m and F444W
emission peak positions, where the bar scales correspond to their positional
accuracy. The yellow arrows indicate the radial ($\mu_{\rm rad.}$) and
tangential ($\mu_{\rm tang.}$) magnification factors, which combine for a
total magnification of 8.69. There are two nearby ($\sim 0\farcs 4$–$0\farcs
8$) objects towards the East. The SED fitting with EAZY suggests that the
closer one could be a companion of ID4590 with $z_{\rm phot}\sim 8.4$, while
the other is estimated to lie at $z_{\rm phot}\sim 0.5$. The grey arrow
indicates the dust attenuation gradient measured by a pixel-based SED analysis
(Giménez-Arteaga et al. in prep.), implying that the offset of the [C ii]
emission is not caused by a dust-obscured star-forming region. Right: Zoom-in
($1\farcs 5\times 1\farcs 5$) PSF-matched RGB image whose color assignment is
shown in the label. The white contours indicate the flux distribution in the
F444W filter at $\pm$2$\sigma$, $\pm$3$\sigma$, $\pm$4$\sigma$,
$\pm$5$\sigma$, and $\pm$10$\sigma$ levels. For comparison, the cyan contour
represents the PSF-matched F150W flux distribution whose intensity relative to
the peak is equal to that of the 2$\sigma$-level contour in the F444W filter.
The F444W filter includes the rest-frame optical continuum and [O iii]5007 and
H$\beta$ emission line from ID4590, showing an extended structure more than
other NIRCam filters. The NIRCam filters are PSF-matched to the F444W filter
in the left and right panels.

##  3 Data analysis

###  3.1 Mass Model

Several mass models are publicly available in SM0723, including those
developed by using Lenstool (Jullo et al. 2007) and Glafic (Oguri 2010) with
the HST data from the RELICS team (Coe et al. 2019)666
https://archive.stsci.edu/prepds/relics/ . More models have been constructed
for SM0723 with the JWST ERO data, using Lenstool (Mahler et al. 2022; Caminha
et al. 2022), the light-traces-mass approach (LTM; Broadhurst et al. 2005;
Zitrin et al. 2009, 2015) presented in Pascale et al. (2022), and an updated
version of Glafic (Oguri 2021) presented in Harikane et al. (2022).

In this paper, we use the latest Glafic model. The magnification factor for
ID4590 is estimated to be $\mu=8.69$, which is consistent with the latest
Lenstool model prediction ($\mu\sim 9$) based on the JWST ERO and the latest
MUSE data (Caminha et al. 2022). We define the systematic uncertainty due to
the choice of the mass model by

$\displaystyle\Delta\mu\equiv\frac{|\mu_{\rm glafic}-\mu_{\rm
other}|}{\mu_{\rm glafic}},$ (1)

where $\mu_{\rm glafic}$ and $\mu_{\rm other}$ indicate the magnification
factor evaluated by the updated version of Glafic and other models,
respectively. Among the mass models constructed with the JWST ERO data, the
$\Delta\mu$ value is estimated to be $\sim$15–30% for ID4590. In the following
analyses when we correct for the gravitationally lensing effect on ID4590, we
use $\mu=8.69$ and add a systematic uncertainty from the mass models of 30%.
When correcting physical values for lensing, we do not account for
differential magnification in the following analysis, as we confirm it to be
much less than the above systematic uncertainty across the positions in the
galaxy. However, when we discuss the intrinsic morphology and size (Section
3.3 and 3.4), we do consider the difference between the radial ($\mu_{\rm
rad.}$) and tangential ($\mu_{\rm tang.}$) magnifications that are estimated
to be $\mu_{\rm rad.}=1.37$ and $\mu_{\rm tang.}=6.35$ with position angle
(PA) in East of North of $-39.5$ deg.

###  3.2 Continuum & Line Measurements

In the top panels of Figure 1, we show the $6^{\prime\prime}\times
6^{\prime\prime}$ continuum maps of ALMA Band 7 (left) and Band 5 (right). In
both bands, we find that the relevant pixels show negative counts. We assume
that the emission is unresolved in the continuum maps with the current ALMA
beam ($\sim 0\farcs 7$–$1\farcs 3$) and place 2$\sigma$ upper limits of 41.8
$\mu$Jy beam-1 and 23.2 $\mu$Jy beam-1 in Band 7 and Band 5, respectively,
based on the standard deviation of the maps.

In the bottom panels of Figure 1, we also present the line spectra for the [O
iii]88$\mu$m (left) and [C ii]158$\mu$m lines (right). In the spectra, we
identify positive signals in several consecutive channels at around 357.3 GHz
and 200.2 GHz in Band 7 and Band 5, respectively, that are both consistent
with the expected frequencies of the [O iii]88$\mu$m and [C ii]158$\mu$m lines
based on the source redshift spectroscopically determined by NIRSpec. In the
top panels, we show the velocity-integrated (moment 0) maps by using these
line-detected channels. In the moment 0 maps, we find that the S/N in the peak
pixel shows 4.0 and 4.1 for the [O iii] and [C ii] lines, respectively. The
latter is spatially resolved, especially in the Northwest to Southeast
direction, where the S/N increases to 4.5 with a $2\farcs 0$-diameter
aperture. On the other hand, [O iii] line is compact and not spatially
resolved with the current beam size and data depth.

From a single Gaussian fit in the spectra, we estimate the frequency center
and the line redshifts as $z_{\rm[OIII]88}=8.4963\pm 0.0009$ and
$z_{\rm[CII]}=8.4931\pm 0.0005$ with the line width of
FWHM${}_{\rm[OIII]88}=137\pm 67$ km s-1 and FWHM${}_{\rm[CII]}=$ $118\pm 36$
km s-1. The redshift of [O iii]88$\mu$m is in excellent agreement with the
source redshift determined by NIRSpec, while the [C ii] line appears blue-
shifted by $\sim 90$ km s-1 beyond the errors. The line widths are consistent
with each other within the errors.

Given a possibility that the chance projection of the noise fluctuation (e.g.,
Kaasinen et al. 2022) causes the [C ii] velocity offset, we quantify its
probability in our [C ii] line identification by running a blind line search
algorithm of Findclump implemented in a Python library of Interferopy
(Boogaard et al. 2021a) for observational radio–mm interferometry data
analysis777 https://interferopy.readthedocs.io/en/latest/index.html . We use a
20-km -1 channel width cube of Band 5 and adopt the spatial tolerance of
$1\farcs 2$ (= beam size) and the frequency tolerance of 100 MHz ($\sim$150 km
s-1) to match the detection in the cube. We find that $\sim 180$ line features
are identified with similar or higher S/N in the entire data cube within a
20′′-radius circular area and 274 channels, which is equal to 259793
independent beams in the cube. Given that the 200.2 GHz line is identified
within the spatial and frequency tolerances from the expectations of the
target, we estimate the chance projection of the random noise is 0.07% (= 180
/ 259793 $\times$ 1), indicating that the purity of the line detection is
$>99.9\%$. Therefore, we conclude that [C ii] line identification is unlikely
explained by the noise fluctuation, and its velocity and spatial offsets are
real. The reason for the blue-shifted [C ii] would be differential
distributions of the multi-phase gases and their associated kinematics (e.g.,
Pallottini et al. 2019; Arata et al. 2020; Kohandel et al. 2020; Katz et al.
2022; Akins et al. 2022; Valentino et al. 2022); the rest-frame optical
emission lines observed with NIRSpec and the [O iii]88$\mu$m line originate
from the ionized gas, while the [C ii]158$\mu$m line mostly arises in the
photodissociation regions (PDRs). The [C ii] peak position shows a spatial
offset from the JWST source position by $\sim 0\farcs 5$ beyond the
uncertainty of its positional accuracy (Section 3.4), which also supports the
differential distributions of these multi-phase gases.

With a 2′′-diameter aperture in the moment 0 maps, we measure the line
intensities and convert them to the [C ii] line luminosity of
$L_{\rm[CII]}=1.45\pm 0.32\times 10^{8}\,L_{\odot}$ in the observed frame.
Given its spatial and velocity offsets, we also place a $3\sigma$ upper limit
at the galaxy position of $<6.0\times 10^{7}\,L_{\odot}$ by taking the line
width from [O iii] line. From its compact morphology of [O iii] 88$\mu$m, we
assume that [O iii] is spatially unresolved and infer the [O iii] line
luminosity of $L_{\rm[OIII]}=3.12\pm 0.76\times 10^{8}\,L_{\odot}$ from the
peak pixel count. We summarize these continuum and line properties in Table 2.

###  3.3 Sizes

We also measure the spatial sizes of [C ii]158$\mu$m and [O iii]88$\mu$m lines
with ALMA as well as the rest-frame UV and optical continuum with JWST/NIRCam.
In both data, we measure the sizes in the image plane.

First, for the [C ii] and [O iii] lines, we perform CASA imfit task to apply
the 2D elliptical Gaussian fitting. We do not fix any parameters in the
fitting. We obtain the best-fit FWHM of $1\farcs 90\pm 0\farcs 82$ and
$0\farcs 99\pm 0\farcs 57$ in the major and minor axis, respectively, for the
[C ii] line. Although we cannot exclude the possibility that these best-fit
sizes are affected by the noise fluctuation with the current S/N, we confirm
that no significant positive/negative signals remain in the residual map. On
the other hand, the imfit output suggests that [O iii] is not spatially
resolved. We subtract the ALMA synthesized beam profile re-scaled to the [O
iii] peak count from the observed [O iii] map and confirm that no significant
positive/negative signals remain in the residual map. We thus place a
$2\sigma$ upper limit of FWHM $<0\farcs 31$ based on the limit of the reliable
size measurement with interferometric data according to the data sensitivity
and the beam size (Martí-Vidal et al. 2012). The trend of the larger [C ii]
line size than that of the [O iii] line is consistent with recent ALMA
observation results for galaxies at similar redshifts (Carniani et al. 2020;
Akins et al. 2022; Witstok et al. 2022). We list the circularized effective
radii 888 The effective radius is almost FWHM / 2.0 in Gaussian.  of the [C
ii] and [O iii] lines in Table 3. The observed, best-fit model and residual
maps are summarized in the Appendix.

Second, for the rest-frame UV and optical continuum, we use the NIRCam/F150W
and F356W maps, respectively, that are not affected by strong emission line
contributions. We conduct a 2D Sérsic profile fitting with galfit (Peng et al.
2010). The pixel of the F356W map is rebinned to a pixel scale of $0\farcs
02$, which is the same pixel scale as the F150W map. We use NIRCam PSFs for
the ERO data of SM0723 publicly available999
https://github.com/gbrammer/grizli-psf-library , which are generated from the
WebbPSF model and drizzled to a grid of $0\farcs 02$ in the same manner as the
mosaic maps in the grizli pipeline. Note that these PSFs are generated with
the latest version of WebbPSF, including the correction of the optical path
difference101010
https://webbpsf.readthedocs.io/en/latest/jwst_measured_opds.html , where it
mitigates the potential difference from the empirical PSFs (e.g., Ono et al.
2022). In the F150W fit for the rest-frame UV continuum, we do not fix any
parameters, while we adopt the initial parameter set based on the lensing
distortion with the axis ratio of $\mu_{\rm rad.}/\mu_{\rm tang.}=0.22$ and
the PA of $-39.5$ deg. We obtain the best-fit effective radius of $r_{\rm
e}=3.6\pm 0.5$ pixel ($=0.33\pm 0.05$ kpc) in the major axis with the axis
ratio of $0.57\pm 0.09$. The best-fit axis ratio exceeds the prediction from
the lensing distortion ($=0.22$), indicating that ID4590 is well resolved in
the radial magnification axis. We also obtain the PA of $-38\pm 10$ deg, which
is consistent with the lensing distortion ($=-39.5$). This supports the strong
magnification factor in ID4590 of $8.69$ ($=\mu_{\rm rad.}\times\mu_{\rm
tang.}$) and suggests that the observed rest-frame UV morphology is mostly
dominated by the lensing distortion. In the F356W fit for the rest-frame
optical continuum, we fix the best-fit axis ratio, PA, and Seŕsic index from
the F150W results, given the worse spatial resolution than that of F150W. We
obtain the best-fit $r_{\rm e}$ of $3.9\pm 0.2$ pixel ($=0.36\pm 0.02$ kpc) in
the major axis. Given the best-fit axis ratio of $0.57\pm 0.09$, we list the
circularized $r_{\rm e}$ values for these stellar continua also in Table 3.
The observed, best-fit model, and residual maps for these NIRCam results are
also summarized in the Appendix.

###  3.4 Morphology

In Figure 2, we compare the spatial distribution of each emission from ID4590.
The left panel shows the [C ii]158$\mu$m and [O iii]88$\mu$m line contours
overlaid on the $6^{\prime\prime}\times 6^{\prime\prime}$ RGB color image with
NIRCam filters. The middle and right panels display zoom-in ($1\farcs 5\times
1\farcs 5$ ) F150W image (middle) and RGB color image (right) with NIRCam
filters of F150W, F356W, and F444W, where the first two filters trace the
rest-frame UV and optical continuum, while the last filter includes the [O
iii]5007 and H$\beta$ lines in addition to the underlying rest-frame optical
continuum. For the RGB images, the maps are PSF-matched to the F444W filter,
and the white and cyan contours in the right panel represent the flux
distribution in the F444W and F150W filters, respectively. The green and black
crosses indicate the peak position of the [C ii]158$\mu$m line and the F444W
emission, where the bar sizes of the cross are equal to the uncertainty of the
positional accuracy based on its beam size and S/N111111 The positional
accuracy of ALMA (posacc) can be approximated by the relationship of
$\theta_{\rm beam}$ / SNR / 0.9, where SNR is the signal-to-noise ratio of the
image target peak (https://help.almascience.org/kb/articles/what-is-the-
absolute-astrometric-accuracy-of-alma). . The yellow arrows in the middle
panel denote the radial ($\mu_{\rm rad.}$) and tangential magnifications
($\mu_{\rm tang.}$) to understand the distortion of ID4590 due to the lensing
effect. To investigate faint tails of the emission, we additionally subtract
the local background in all NIRCam filters by evaluating the median pixel
count in a black field near from ID4590.

We find that the peak position of the [O iii]88$\mu$m is consistent with the
JWST source position of ID4590, while the [C ii]158$\mu$m has an offset of
$\sim 0\farcs 5$ beyond the uncertainty of the positional accuracy. In the
source-plane reconstruction of the JWST and [C ii] source positions, we find
that the intrinsic offset decreases down to $\sim 0\farcs 1$, which is equal
to $\sim 0.5$ kpc. Because of the significantly low probability of the chance
projection of the noise (Section 3.2), the spatial offset in [C ii] indicates
that physical origins of the emission is associated with ID4590, while it
arises outside the galaxy (e.g., Maiolino et al. 2015; Carniani et al. 2017).
We further discuss the physical origins of the [C ii] offset in Section 4.4.

We also find that the emission in the F444W filter is extended more than the
rest-frame UV and optical continuum observed in F150W and F356W filters. We
interpret this extended emission attributed to strong emission lines of [O
iii]5007 and H$\beta$ from ID4590, implying that a powerful mechanism of
forming the extended ionized gas structure is taking place. Note that there
are two nearby objects towards the East with offsets of $\simeq 0\farcs 4$ and
$\simeq 0\farcs 8$. We run the SED fitting code EAZY (Brammer et al. 2008) for
these two nearby objects with the available JWST/NIRCam, MIRI, and HST
photometry in the public grizli catalog (Section 2.3) by using the default
template set of tweak_fsps_QSF_12_v3. The results suggest the photometric
redshifts of $z_{\rm phot}=8.45^{+0.29}_{-0.28}$ and $z_{\rm
phot}=0.37^{+0.11}_{-0.10}$ each from the nearest. Therefore, the nearest
object might be a companion galaxy associated with ID4590. However, if the
presence of nearby objects is the cause of the extended structure, the same
structure should also be observed in the other NIRCam filters, which is not
the case. Besides, the structure is also extended towards South $\sim$
Southeast, where no rest-frame UV continuum is identified. Furthermore, the
PSF size of the NIRCam/F444W filter is $\sim 0\farcs 15$, where the emission
should be individually resolved if the extended ionized gas is caused by
individual further faint satellites. We thus conclude that this diffuse,
extended structure in the F444W filter is hardly explained either by these two
nearby objects or further faint satellites. The structure extends to $\sim
0\farcs 5$ towards the Southeast most. Given the circularized rest-frame
optical effective radius of $0\farcs 059\pm 0\farcs 010$ (Section 3.3), the
structure extends out to $\sim 8$ times more than the stellar distribution of
the galaxy. If we take the differential magnification effects into account,
the structure is aligned to the radial magnification axis ($\mu_{\rm
rad.}=1.37$), indicating that the intrinsic physical distance after the lens
correction is $\sim 1.7$ kpc. For the same direction, the rest-frame optical
effective radius after the lens correction is estimated to be $0.11\pm 0.03$
kpc. These results suggest that the ionized gas distribution over the
effective radius of the stellar distribution even increases to a factor of
$\sim$15\. The relative ratio of $>8$ is well beyond the diffused ionized gas
(DIG) structure observed among local galaxies ($\sim$10% of the galaxy size;
see e.g., Rossa & Dettmar 2003). We further discuss the physical origins of
the extended ionized gas in Section 4.4.

By comparing the total flux correction factors in F356W and F444W filters
(Section 2.3), we find that the extended component in F444W contributes to the
total flux measurement by $\sim 8$%. In the following analyses for the same
emitting regions (e.g., Section 3.6 and Section 4.1), we remove this 8%
contribution of the extended ionized gas to the total flux measurement in the
F444W filter. With the same motivation for analyses that assume the emission
originated from the same regions, we also use the 3$\sigma$ upper limit for
the [C ii] luminosity at the galaxy position imfit (Section 3.2).

###  3.5 FIR SED

Figure 3:  Constrain of the FIR SED of ID4590. The red arrows indicate the
2$\sigma$ upper limits obtained in ALMA Band 5 and Band 7. The dotted, solid,
and dashed curves show the single modified black body (MBB) scaled to the Band
7 upper limit, with the dust temperature of $T_{\rm d}=$ 30 K, 60 K, and 90 K,
respectively. In each case, the induced IR luminosity $L_{\rm IR}$ by
integrating MBB over 8–1000 $\mu$m and the dust mass $M_{\rm dust}$ are shown
in the label. We fix the dust spectral index $\beta_{\rm d}=1.8$ (e.g., Chapin
et al. 2009; Planck Collaboration et al. 2011).

From the upper limits of the dust continuum both in Band 5 and Band 7, we
attempt to constrain the FIR SED of ID4590. Recent FIR SED studies for
high-$z$ dusty star-forming galaxies at $z\sim 1$–4, including Herschel and
ALMA photometry, suggest the typical dust temperature of $T_{\rm d}\sim 30$ K
(e.g., Swinbank et al. 2014; Sun et al. 2022). For UV-selected galaxy
populations such as Lyman-break galaxies (LBGs) at $z\sim 4$–7, ALMA multiple
band observations show a higher dust temperature distribution typically
ranging from $\sim$40 K even out to $\sim$80 K (e.g., Faisst et al. 2020; Bakx
et al. 2020; Akins et al. 2022; Witstok et al. 2022), where several analytical
models have been developed and well reproduced the observation results,
including the potential redshift evolution of $T_{\rm d}$ (e.g., Inoue et al.
2020; Fudamoto et al. 2022a; Sommovigo et al. 2022b).

Because of the limited constraints due to lack of the detection in both ALMA
Bands, we assume the single modified black body (MBB) for the FIR SED of
ID4590. We adopt a fiducial $T_{\rm d}$ estimate of 60 K based on the
extrapolation of the best-fit redshift evolution model of $T_{\rm d}$
following the decrease of the gas depletion time scale ($t_{\rm depl}$)
derived in Sommovigo et al. (2022b), while we include the uncertainty of
$T_{\rm d}$ by 30 K given the $T_{\rm d}$ distribution so far observed in
high-$z$ LBGs with ALMA. We fix dust spectral index $\beta_{\rm d}$ at a
typical value of 1.8 (Chapin et al. 2009; Planck Collaboration et al. 2011)
and take the CMB temperature effect (e.g., da Cunha et al. 2013) into account
in the MBB model.

In Figure 3, we show three MBB models with $T_{\rm d}=30$ K, 60 K, and 90 K
normalized to the upper limit of Band 7. The inset labels show the derived IR
luminosity $L_{\rm IR}$, integrated over 8–1000 $\mu$m, and the dust mass
$M_{\rm dust}$, with the dust opacity coefficient of
$\kappa_{\nu}=5.1(\nu/\nu_{250\mu{\rm m}})^{\beta_{\rm d}}$. In the observed
frame (i.e. no lens correction), we obtain the upper limits of $\log(L_{\rm
IR}/L_{\odot})<11.2$ and $\log(M_{\rm dust}/M_{\odot})<6.0$ with the fiducial
$T_{\rm d}$ value of 60 K. This indicates that ID4590 has the observed-frame
dust-obscured SFR of SFR${}_{\rm IR}<16\,M_{\odot}$ yr-1. The FIR SED
properties are summarized in Table 3.

Figure 4:  Full SED shape of ID4590 from optical to mm wavelengths in the
observed frame. Top: $2^{\prime\prime}\times 2^{\prime\prime}$ image cutouts
of JWST/NIRCam, JWST/MIRI, and ALMA from left to right. The red bars indicate
the source postion of ID4590, and the corresponding filter/Band in each panel
is shown in the label. The most-left panel shows the segmentation map from the
grizli pipeline. Bottom: Blue curve indicates the best-fit SED obtained with
CIGALE. The red squares are the observed photometry of ID4590, and the blue
circles present the predicted photometry from the best-fit SED. The inset
panel zooms in the SED at 1–9 $\mu$m, clearly showing the flux boosting in the
F444W filter by strong [O iii]$\lambda$5007 and H$\beta$ emission lines,
instead of the stellar continuum, where the MIRI photometry helps to
disentangle their contributions to the F444W filter. The inset panels also
presents the red UV continuum slope ($\beta_{\rm UV}=-1.7\pm 0.07$) of ID4590,
while the dust continuum is not detected likely because of the high dust
temperature (Section 4.3). The brown curve highlights the FIR SED using the
Casey (2012) model in CIGALE.

###  3.6 Full SED analysis and physical properties

Table 3: Physical properties of ID4590 in the image plane

Name |  ID4590
---|---
R.A. |  07:23:26.255
Dec. |  $-73$:26:57.041
$z_{\rm spec}$ |  8.496
$\mu^{\dagger}$ |  8.69
SFR $\times\mu$ [$M_{\odot}$ yr-1] |  26${}^{+9}_{-4}$
$M_{\rm star}\times\mu$ [$10^{8}\,M_{\odot}$] |  5.3${}^{+5.6}_{-2.6}$
$L_{\rm UV}\times\mu$ [1010 $L_{\odot}$] |  $2.8\pm 0.3$
$\beta_{\rm UV}$ |  $-1.70\pm 0.07$
$E(B-V)$ |  $0.16\pm 0.03$
$L_{\rm IR}^{\dagger\dagger}\times\mu$ [$10^{11}\,L_{\odot}$] |  $<1.6$
$M_{\rm dust}^{\dagger\dagger}\times\mu$ [$10^{6}\,M_{\odot}$] |  $<1.0$
$M_{\rm gas}\times\mu$ [$10^{9}\,M_{\odot}$] |  $7\pm 3^{a}$
$r_{\rm e,UV}^{\natural}\times\sqrt{\mu}$ [arcsec] |  $0.056\pm 0.012$
$r_{\rm e,opt}^{\natural}\times\sqrt{\mu}$ [arcsec] |  $0.059\pm 0.010$
$r_{\rm e,[CII]158}^{\natural}\times\sqrt{\mu}$ [arcsec] |  $0.69\pm 0.42$
$r_{\rm e,[OIII]88}^{\natural}\times\sqrt{\mu}$ [arcsec] |  $<0.16$
$n_{\rm e}$ [cm-3] |  220${}^{+170}_{-100}$
$T_{\rm e}$ [104 K] |  $2.08\pm 0.34^{b}$
12 + $\log$(O/H) |  $7.26\pm 0.18^{b}$
$\log(U)$ |  $>-2.27^{b}$
$\log$(C/O) |  $[-0.52:-0.24]^{c}$

$\dagger$ From the mass model with Glafic (Oguri 2010, 2021) using the JWST
ERO data presented in Harikane et al. (2022). For the lens corrected values,
we add a systematic uncertainty of 30% throughout the paper (Section 3.1).
${\dagger\dagger}$ Based on the single MBB with $T_{\rm d}=60$ K and
$\beta_{\rm d}=1.8$ without the energy balance, where a $T_{\rm d}$ difference
by $\pm 30$ K changes the estimates by $\sim\pm$0.5–1.0 dex (see also Figure
3).
$\natural$ Circularized effective radius. The best-fit axis ratio is $0.57\pm
0.09$.
$a$ Heintz et al. (submitted.)
$b$ Nakajima et al. (in prep.)
$c$ Isobe et al. (in prep.)

Figure 4 shows the JWST and ALMA image cutouts, including the segmentation map
(top), and the optical–mm photometry in the observed frame (i.e. no lens
correction) measured with HST, JWST, and ALMA for ID4590 (bottom). A
significant flux enhancement is observed in the F444W filter (rest-frame
$\sim$4000–5000${\rm\AA}$). Some remarkably massive early galaxies have been
reported at $z\sim 7$–11 whose SED shape shows a secondary peak, most likely
because of the strong Balmer break in the NIRCam LW filters (Labbe et al.
2022). In contrast, the MIRI photometry of ID4590 suggests the flux
enhancement only occurs in the F444W filter, which is explained by the strong
[O iii]+H$\beta$ emission lines, rather than a large stellar mass. Such strong
contributions of the [O iii]+H$\beta$ lines also agree with the extended
morphology observed in the F444W filter, which is interpreted as the presence
of the extended ionized gas emission (Section 3.4).

To perform a panchromatic characterization of ID4590, we perform SED fitting
to the optical–mm photometry using cigale (Burgarella et al. 2005; Noll et al.
2009; Boquien et al. 2019). While we examine the FIR SED in Section 3.5, the
SED modelling with cigale allows us to take the energy balance between the
dust absorption and re-emission into account, which is complementary with the
independent FIR SED analysis. The fitting was performed similarly as in
Fujimoto et al. (2022b), and we summarize the details of the fitting and
parameter ranges used in the fitting in the Appendix.

In the bottom panel of Figure 4, the blue curve shows the best-fit SED, where
the brown curve highlights the re-emission of the dust in the rest-frame FIR
wavelength based on the Casey (2012) model. The inset panel shows the zoom-in
spectrum of the best-fit SED at $\sim$1–9 $\mu$m. Our best-fit SED reproduces
the observed photometry, including the flux enhancement in the F444W filter
with the reduced $\chi^{2}$ value of 0.99. We obtain the best-fit values of
SFR = 26${}^{+9}_{-4}\,M_{\odot}$ yr-1, $M_{\rm star}=5.3^{+5.6}_{-2.6}\times
10^{8}\,M_{\odot}$, UV continuum slope $\beta_{\rm UV}=-1.70\pm 0.07$, and
$E(B-V)=0.16\pm 0.03$ in the observed-frame (i.e. no lens correction),
respectively, that are generally consistent with previous NIRcam and/or
NIRspec based measurements (e.g., Carnall et al. 2022; Schaerer et al. 2022;
Tacchella et al. 2022; Heintz 2022), as well as an independent NIRCam and
NIRISS based measurements in the separated paper of Heintz et al. (submitted).
The $\log(L_{\rm IR}/L_{\odot})$ value is estimated to be $10.8$, which is
consistent with the upper limit obtained from the independent FIR SED analysis
(Section 3.5). This indicates that the current non-detection of the dust
continuum with ALMA does not violate the energy balance with the SMC dust
attenuation curve, while the $\beta_{\rm UV}$ and $E(B-V)$ values suggest that
ID4590 is a certainly dust-attenuated system, in contrast to very blue
galaxies observed in recent JWST observations at similar redshifts (e.g.,
Nanayakkara et al. 2022; Furtak et al. 2022; Cullen et al. 2022; Finkelstein
et al. 2022; Atek et al. 2022; Fujimoto et al. 2022b; Robertson et al. 2022).
We further examine the dust and the obscured properties of ID4590 in Section
4.3 and discuss the potential underlying physical mechanisms in Section 4.4.

Because several Balmer emission lines are detected in ID4590 with NIRSpec, we
compare our best-fit $E(B-V)$ with the measurement from the Balmer decrement.
The line flux measurements from the latest NIRSpec reduction and calibration
(Section 2.3) yield $E(B-V)=0.07^{+0.10}_{-0.07}$ and $0.24^{+0.07}_{-0.07}$
from H$\gamma$/H$\beta$ and H$\delta$/H$\beta$, respectively, by assuming the
SMC dust attenuation law. Our SED-based estimate falls between those estimates
from the Balmer decrement approach, suggesting the general consistency between
the photometry- and spectroscopic-based approaches. However, caution remains
in the different $E(B-V)$ suggested between H$\gamma$/H$\beta$ and
H$\delta$/H$\beta$, where the difference can change the H$\beta$-based SFR
estimate (e.g., Kennicutt & Evans 2012) by a factor of $\sim$3 after the dust
correction. We confirm that similarly different $E(B-V)$ values are obtained
by assuming other dust attenuation laws (e.g., LMC, Calzetti et al. 2000), and
thus the difference is unlikely caused by an improper choice of the dust
attenuation law. We speculate that it is caused by the difficulty of the
optimal wavelength-dependent slit-loss correction for each emission, taking
their potential differential distributions. We thus use the SED-based physical
properties in the following analysis.

We note that Giménez-Arteaga et al. (in prep.) discuss the potential
underestimate of $M_{\rm star}$ by $\sim$0.5–1 dex in the spatially-integrated
SED analysis, compared to the sum of the spatially-resolved SED analysis,
especially in strong optical emission line systems 121212 This is because the
young bursty stellar populations, causing the strong optical emission lines,
dominate the emission in the spatially-integrated photometry, hiding the
possible presence of underlying older stellar populations, and yield extremely
young ages ($<10$ Myr) and therefore lower masses in the SED fit. . However,
we confirm that our $M_{\rm star}$ estimate is consistent with the results
from the spatially-resolved SED analysis in Giménez-Arteaga et al. (in prep.),
owing to the additional constraints from the MIRI bands (Bisigello et al.
2019).

Figure 5:  Electron density $n_{\rm e}$ measurement for ID4590 via the [O
iii]88$\mu$m/$\lambda$5007 line ratio enabled by JWST and ALMA. In both
panels, the red circles denote ID4590. Left: Line ratio as a function of
electron temperature $T_{\rm e}$ with different $n_{\rm e}$ assumptions,
calculated with the nebular emission code PyNeb. The green shade presents the
1$\sigma$ range of the $n_{\rm e}$ estimate for ID4590. Right: Redshift
evolution of $n_{\rm e}$. The green square is the measurement for a dusty
star-forming galaxy at $z=7.13$ (Watson et al. 2015; Killi et al. 2022), and
the black symbols are the measurements at $z\sim$0–3 taken from literature
(Steidel et al. 2014; Sanders et al. 2016; Stott et al. 2016; Kaasinen et al.
2017; Davies et al. 2021).

##  4 Results & Discussions

###  4.1 Electron density at $z=8.5$ via [O iii]88$\mu$m/[O iii]$\lambda$5007

Owing to the same species and ionized state with different critical densities,
the line ratio of [O iii]88$\mu$m/[O iii]$\lambda$5007 is regulated by the
electron density $n_{\rm e}$ and temperature $T_{\rm e}$. In the left panel of
Figure 5, we show the line ratio of [O iii]88$\mu$m/[O iii]$\lambda$5007 as a
function of $T_{\rm e}$ with different assumptions for the electron density
$n_{\rm e}$, drawn by using the nebular emission code PyNeb131313
http://research.iac.es/proyecto/PyNeb// . The relations show monotonic
decreasing functions towards the increase of $T_{\rm e}$ or $n_{\rm e}$. This
indicates that we can evaluate $n_{\rm e}$ with a secure $T_{\rm e}$
measurement (or vice versa – evaluate $T_{\rm e}$ with a secure $n_{\rm e}$
measurement).

The NIRSpec observations successfully detect the multiple nebular emission
lines from ID4590 in rest-frame UV to optical wavelength, including [O
iii]$\lambda$5007 and [O iii]$\lambda$4363, which provides us with the robust
measure of $T_{\rm e}$ (e.g., Schaerer et al. 2022; Curti et al. 2022; Trump
et al. 2022; Heintz et al. submitted; Nakajima et al. in prep.). In
conjunction with the secure $T_{\rm e}$ measurement and our ALMA measurements
(Section 3.2), we derive the [O iii]88$\mu$m/$\lambda$5007 line ratio for
ID4590, and the red circle in the left panel of Figure 5 shows the relation.
Based on the 1$\sigma$ uncertainties, we evaluate $n_{\rm
e}=220^{+170}_{-100}$ cm-3.

The $n_{\rm e}$ value has been typically measured by using density-sensitive
line ratios such as [S ii]6716/6731, [O ii]3729/3726, and C iii]1907/1909
(e.g., Kewley et al. 2019). Previous spectroscopic surveys have found the
presence of the redshift evolution of $n_{\rm e}$: the typical $n_{\rm e}$ in
local galaxies has increased from $n_{\rm e}\simeq 30$ cm-3 at $z\sim 0$
(e.g., Herrera-Camus et al. 2016) to $n_{\rm e}\simeq$100–200 cm-3 at $z\sim
1.5$ (e.g., Kaasinen et al. 2017; Kashino et al. 2017), and to $n_{\rm
e}\simeq$ 200–300 cm-3 at $z\sim 2$–3 (Steidel et al. 2014; Sanders et al.
2016; Davies et al. 2021).

Because of the required high spectral resolution and subsequently high
sensitivity to resolve those rest-frame UV and optical doublet lines, the
results have been limited at $z\lesssim 3$, while recent rest-frame FIR
observations have been exploring the $n_{\rm e}$ measurement even out to the
EoR. By using a FIR fine-structure line ratio of [O iii]52$\mu$m and [O
iii]88$\mu$m detected with ALMA, Killi et al. (2022) estimate $n_{\rm e}<260$
cm-3 in a dusty lensed star-forming galaxy at $z=7.13$, A1689-zD1 (Watson et
al. 2015). Our measurement of a high electron density provides a new
determination of $n_{\rm e}$ at EoR and is consistent with the results in
A1689-zD1. For several $z\sim 6$–9 galaxies with the [O iii]88$\mu$m and [C
ii]158$\mu$m line measurements, Vallini et al. (2021) show that their gas
density $n_{\rm gas}$ generally fall within $\simeq 100$–1000 cm-3 by
advancing analytical models for these FIR emission lines (Ferrara et al. 2019;
Vallini et al. 2020). Although systematic uncertainties remain in this
approach due to the C/O abundance and the different emitting regions of the [O
iii] and [C ii] lines that suggest $n_{\rm e}$ and $n_{\rm gas}$ are not
identical, these $n_{\rm gas}$ measurements at similar redshift also in line
with our $n_{\rm e}$ measurement for ID4590.

In the right panel of Figure 5, we summarize the $n_{\rm e}$ measurement as a
function of redshift. The $n_{\rm e}$ value of ID4590 is similar to $z\sim
2$–3 star-forming galaxies. This might suggest that the physical mechanisms
responsible for driving the high $n_{\rm e}$ values observed at $z\sim$2–3
initially took place in the EoR, and there was a little redshift evolution
between $z=8.5$ and $z\sim$2–3. However, this redshift trend strongly depends
on the galaxy types selected, and similarly high $n_{\rm e}$ measurements
($\simeq 400$ cm-3) are also obtained in compact star-forming galaxies at
$z\sim 0.3$–0.4 (Guseva et al. 2020). The upcoming JWST/NIRSpec observations
in the high-resolution spectrograph mode ($R\sim 2700$) will sufficiently
resolve the rest-frame UV and optical doublet lines, statistically evaluate
$n_{\rm e}$ based on a mass complete sample, verify the presence of its
redshift evolution, and determine what key mechanisms regulate $n_{\rm e}$ out
to the EoR.

Figure 6:  Relations between SFR and $L_{\rm[CII]}$ (left) and $L_{\rm[OIII]}$
(right). In both panels, the color of the circles corresponds to the gas-phase
metallicity $Z_{\rm gas}$ denoted in the color bar. The open red squares
remark the measurements of ID4590, where the filled and open circles indicate
the measurements inside and outside the galaxy. The red arrows present the
3$\sigma$ upper limit of [C ii] at the JWST source position given its spatial
and velocity offsets (Section 3.2). We assume that the [C ii]-detected gas
outside the galaxy is illuminated by ionizing photons escaping from the galaxy
and thus use the same SFR value for both results of inside and outside the
galaxy. Other color circles represent the local dwarf galaxies with the
$Z_{\rm gas}$ measurements (De Looze et al. 2014; Cormier et al. 2015), where
the best-fit relation and its 1$\sigma$ dispersion is shown with the dashed
line and the grey-shaded area, respectively. The open black squares show the
results for $z\sim 6$–9 galaxies compiled in Harikane et al. (2020).  Figure
7:  Same as Figure 6, but for $L_{\rm[OIII]}/L_{\rm[CII]}$. ID4590 shows a
high $L_{\rm[OIII]}/L_{\rm[CII]}$ ratio of $>4$ at the galaxy position similar
to those of known $z\sim 6-9$ galaxies.

###  4.2 SFR–$L_{\rm[CII]}$, $L_{\rm[OIII]}$, and $L_{\rm[OIII}/L_{\rm[CII]}$
Relations

In Figure 6 and 7, we present $L_{\rm[CII]}$, $L_{\rm[OIII]}$, and
$L_{\rm[OIII]}/L_{\rm[CII]}$ as a function of SFR for ID4590. We show the
results after the lens correction, where the systematic uncertainty of 30% for
the magnification factor (Section 3.1) is propagated in the error bars. In
SFR–$L_{\rm[CII]}$ (SFR–$L_{\rm[OIII]}/L_{\rm[CII]}$) relation, we also show
the $3\sigma$ upper limit (lower limit) for $L_{\rm[CII]}$
($L_{\rm[OIII]}/L_{\rm[CII]}$) at the JWST source position, given its spatial
offset (Section 3.4), and separate the results inside and outside the galaxy
with filled and open circles, respectively. For comparison, we also present
compilations of recent ALMA results for $z\sim 6$–9 galaxies in literature
(e.g., Harikane et al. 2020; Fujimoto et al. 2021) with black squares, and
local dwarf galaxy results with the gas-phase metallicity ($Z_{\rm gas}$)
measurements (De Looze et al. 2014; Cormier et al. 2015) with color circles.
The color scale is equal to 12+$\log$(O/H) denoted in the color bar, except
for the $z\sim 6$–9 galaxy results whose $Z_{\rm gas}$ values have not been
constrained. The average relation for the local dwarf galaxies is shown in the
dashed black line with the 1$\sigma$ range in the grey shade. In all
relations, ID4590 are generally consistent with the results estimated in other
$z\sim 6$–9 galaxies. In addition, ID4590 explores the faint-end of the
$z\sim$6–9 galaxy results, owing to the aid of the gravitational lensing
effect. Therefore, ID4590 is a faint, thus abundant, and representative early
galaxy with physical properties similar to other galaxies so far observed with
ALMA at similar redshifts. This indicates that ID4590 is a unique laboratory
to study what regulates the FIR major coolant lines of [C ii]158$\mu$m and [O
iii]88$\mu$m in EoR galaxies.

In the SFR–$L_{\rm[CII]}$ relation, we find that ID4590 falls below the
typical relation of the local dwarf galaxies in both results obtained inside
and outside the galaxy. Among the local dwarf galaxies, there are two galaxies
of IZw18 and SBS0335-052 whose $Z_{\rm gas}$ measurements are similarly low as
ID4590 (12+$\log$(O/H) $\simeq$ 7.1–7.3). We confirm that the
$\log(L_{\rm[CII]}$/SFR) ratio inside the galaxy shows $<6.3$, which is
consistent with these two very metal-poor local galaxies ($\sim 5.7$). This
might indicate that the low [C ii] line emissivity of ID4590 is explained by
the low $Z_{\rm gas}$ ISM condition (e.g., Vallini et al. 2015), while there
are also other key factors which reduce the [C ii] emissivity such as high
ionization parameter or low gas density (see Section 1). In fact, ID4590 shows
strong [O iii]$\lambda$5007+H$\beta$ emission (Section 3.6), which generally
represents recent young bursty stellar populations (e.g., Witstok et al.
2022), where the high ionization parameter, as a result, might be a more
critical driver. The [C ii] emission outside the galaxy shows
$\log(L_{\rm[CII]}$/SFR)$\sim 6.7$, being higher than these very metal-poor
local galaxies but still lower than the typical relation. This might be
explained by a huge amount of gas around ID4590 which efficiently uses all the
photons to boost the [C ii] emission eventually. With an analytical model,
Ferrara et al. (2019) predict that the surface density of [C ii] luminosity
becomes almost constant around $\Sigma_{\rm[CII]}\approx
10^{6}-10^{7}\,L_{\odot}$ yr-1 kpc-1 at a high SFR surface density regime of
$\Sigma_{\rm SFR}\gtrsim 10\,M_{\odot}$ yr-1 kpc-2 with a linear scale
dependence on the gas density, regardless of $Z_{\rm gas}$ in 0.1–1.0
$Z_{\odot}$ (see eq. 42 in Ferrara et al. 2019). Based on our size and full
SED analyses in Section 3, ID4590 indeed shows $\Sigma_{\rm[CII]}\simeq
2\times 10^{6}\,L_{\odot}$ yr-1 kpc-2 with $\Sigma_{\rm SFR}\simeq
100\,M_{\odot}$ yr-1 kpc-2, which agrees with the prediction from the
analytical model. For more discussions related to the rich gas aspect around
ID4590, we refer the reader to a separate paper by Heintz et al. (submitted).

In the SFR–$L_{\rm[OIII]}$ relation, we find that ID4590 is consistent with
the local relation within the errors but likely falls slightly below it. This
would also be explained by the low [O iii] line emissivity with low $Z_{\rm
gas}$ values (e.g., Popping 2022), which is also shown in the monotonic
decreasing function in the [O iii]88/[O iii]$\lambda$5007–$T_{\rm e}$
relation, regardless of $n_{\rm e}$ (Figure 5). In fact, the slightly low
$\log(L_{\rm[OIII]}$/SFR) ratio of ID4590 is consistent with those of the two
very metal-poor local galaxies of IZw18 and SBS0335-052 ($\sim 6.5$) within
the errors. We also confirm that the SFR-$L_{\rm[OIII]}$ relation of ID4590 is
consistent with the serra zoom-in simulation results (e.g., Pallottini et al.
2022; Kohandel et al. 2022) for galaxies whose $\log(U)$ values are similar to
that of ID4590 ($\log(U)>-2.27$; Section 2.3).

In the SFR–$L_{\rm[OIII]}/L_{\rm[CII]}$ relation, we find that ID4590 shows
higher $L_{\rm[OIII]}/L_{\rm[CII]}$ ratios both inside and outside the
galaxies than the local relation. In particular, the lower limit of $>4$
obtained inside the galaxy is similarly high to other $z\sim 6$–9 galaxies so
far observed (e.g., Harikane et al. 2020; Witstok et al. 2022). We discuss the
physical origins of the high [O iii]/[C ii]line ratio in Section 4.5.

###  4.3 IRX-$\beta$ relation

Figure 8:  IRX–$\beta_{\rm UV}$ relation. The red symbols represent ID4590,
where the square and the circle show the upper limits with the $T_{\rm d}$
assumptions of 30 K and 90 K, respectively. The solid and dashed curves
indicate the relations derived with the dust attenuation of SMC and Calzetti
et al. (2000), respectively. The dotted curve shows the relation derived from
SMC dust attenuation and bluer intrinsic $\beta_{\rm UV}$ (Reddy et al. 2018).
For comparison, we also show other star-forming galaxy results at $z\sim$4–7
taken from ALPINE (green squares; Le Fèvre et al. 2020; Fudamoto et al. 2020)
and REBELS (brown circles; Bouwens et al. 2021; Inami et al. 2022). The black
crosses indicate semi-analytical simulation results of SHARK (Lagos et al.
2020), for galaxies at $z\sim 8$ with $\log(M_{\rm star}/M_{\rm
star})=7.5$–8.5, where the error bars are the 16–84th percentile.

Figure 8 presents the infrared excess ($L_{\rm IR}/L_{\rm UV}\equiv$ IRX) and
the UV continuum slope $\beta_{\rm UV}$ relation of ID4590. Although we adopt
the fiducial value of $T_{\rm d}=60$ K in Section 3.5, here we show two
extreme cases for ID4590, with $T_{\rm d}=$30 K and 90 K, by assuming the
potential uncertainty of $\Delta T_{\rm d}=\pm 30$ K. For comparison, we also
show the relations based on several dust attenuation laws (Reddy et al. 2018;
Calzetti et al. 2000), a semi-analytical model of SHARK141414 The dust
extinction and re-emission are modeled with Charlot & Fall (2000) and the
templates of Dale et al. (2014), respectively, while the final IRX–$\beta_{\rm
UV}$ relation is also regulated by dust surface density, $Z_{\rm gas}$,
$M_{\rm gas}$, and galaxy structure.  for galaxies at $z\sim 8$ (Lagos et al.
2020), and the recent measurements for $z\sim$4–7 star-forming galaxies
observed in the ALPINE (Le Fèvre et al. 2020) and REBELS surveys (Bouwens et
al. 2021) taken from Fudamoto et al. (2021) and Inami et al. (2022),
respectively. While several Balmer emission lines are detected in ID4590, we
note that concluding which dust attenuation law fits the best with ID4590 is
still challenging with their current S/N and the potential difficulty of the
proper aperture correction for each Balmer emission (Section 3.6).

In Figure 8, ID4590 falls in a moderately red UV color regime, where the dust
continuum is detected from the previous ALMA observations for the $z\sim$ 4–7
galaxies. If ID4590 has a relatively low $T_{\rm d}$ ($\sim$30–40 K) and
follows a dust attenuation law similar to Calzetti et al. (2000) or SMC in
Reddy et al. (2018), the upper limit suggests that the dust continuum should
be detected from ID4590 with the current ALMA depth151515 In the energy
balance between the dust attenuation and re-emission, a lower $T_{\rm d}$
makes the FIR SED peak wavelength longer at a given $L_{\rm IR}$, where the
ALMA sensitivity limit may reach the FIR SED peak at some point.. This
indicates that ID4590 has a $T_{\rm d}$ value higher than $\sim$30–40 K or an
SMC-like steep dust attenuation law with the intrinsic UV continuum slope of
$\beta_{\rm UV,0}\simeq-2.3$ (e.g., Meurer et al. 1999; McLure et al. 2018).
Given the low dust content implied from the low metallicity of ID4590 from the
NIRSpec results (Section 2.3) and the high $\Sigma\\_{\rm SFR}$ from the
compact rest-frame UV size (Section 3.3), the dust is efficiently heated at a
given UV field (e.g., Behrens et al. 2018; Sommovigo et al. 2022b, a), and the
former high $T_{\rm d}$ scenario might be plausible. We also find that the
semi-analytical model of SHARK predicts the IRX–$\beta_{\rm UV}$ relation even
lower than the SMC relation for the simulated galaxies with similar redshift
and $M_{\rm star}$ as ID4590, the non-detection of the dust could be simply
because of the difference of the dust attenuation law between local and
high-$z$ galaxies.

Future ALMA high-frequency follow-up observations (e.g., Band 8, 9, and 10)
will confirm or rule out the high $T_{\rm d}$ scenario in ID4590. Furthermore,
the detection of the rest-frame UV–optical continuum and/or multiple high-
significance detection of Balmer and Paschen emission lines in upcoming
JWST/NIRSpec and MIRI observations will help us to directly constrain the dust
attenuation curve in high-redshift galaxies, including ID4590.

###  4.4 Onset of outflow at $z>8.5$, helping reionization

In Figure 2, we find the spatial offset of [C ii] from the JWST source
position (Section 3.4). The spatial offset suggests the presence of the
accreting/satellite gas clump(s) (e.g., Maiolino et al. 2015) or the extended
[C ii] gas beyond the stellar distribution (e.g., Fujimoto et al. 2019, 2020;
Ginolfi et al. 2020; Carniani et al. 2020; Herrera-Camus et al. 2021; Akins et
al. 2022; Lambert et al. 2022), tracing the diffuse neutral hydrogen (Heintz
et al. 2021, 2022). The [C ii] size measurement result, almost $\sim 10$ times
larger than the stellar distribution of ID4590 (Section 3.3), supports the
latter scenario of the presence of the extended [C ii] gas. Although we cannot
rule out the possibility that the noise fluctuation makes the [C ii]
morphology look extended with the current S/N, it is worth mentioning that
similarly extended [C ii] morphology with spatial offsets have also been
observed in other galaxies at $z\sim 7$–9 (Carniani et al. 2020). The other
possibility could be nearby faint, dusty objects (e.g., Fujimoto et al. 2016,
2022a) emitting [C ii] (e.g., Romano et al. 2020; Fudamoto et al. 2022b).
However, no counterparts are identified down to a 3$\sigma$ upper limit in
F150W of $\sim$32.5 mag (with $0\farcs 2$-diameter; Harikane et al. 2022)
after the lens correction, which corresponds to SFR $\approx 0.05\,M_{\odot}$
yr-1 at $z=8.5$ (e.g., Kennicutt & Evans 2012). Similarly, no counterparts in
F444W place a $3\sigma$ upper limit of $M_{\rm star}\lesssim 1\times
10^{6}\,M_{\odot}$ by scaling the best-fit SED of ID4590. A pixel-based SED
analysis in Giménez-Arteaga et al. (in prep.) shows the gradient of the dust
obscuration decreasing towards the [C ii]-emitting region, which also supports
the absence of the counterparts at the [C ii] peak position.

Whichever the [C ii]-emitting gas is compact clump(s) diffuse & extended,
these results suggest that the carbon in the gas is illuminated not by local
star-forming activities, but by i) the ionizing photon escaped from inside the
galaxy, ii) shock heating of the outflowing gas, or iii) a cooling process of
the hot outflowing gas (see also discussions in e.g., Fujimoto et al. 2019,
2020; Pizzati et al. 2020; Akins et al. 2022). In Figure 6, we find that the
$L_{\rm[CII]}$/SFR ratio of this [C ii] emission outside of galaxy is
consistent with other local dwarf galaxies whose $Z_{\rm gas}$ values are
similarly low as ID4590 (IZw18 and SBS0335-052). This suggests that the input
energy from i) is enough to explain the observed $L_{\rm[CII]}$. In fact, the
high ionization parameter of $\log(U)\gtrsim-2$ observed in ID4590 is in line
with the scenario of i).

In Figure 2, we also find the extended ionized gas ([O iii]$\lambda$5007,
H$\beta$) structure in the deep NIRCam/F444W filter (Section 3.4). Similar to
the [C ii] emission, no NIRCam counterparts are identified in the extended
ionized gas regions. In addition, the extended ionized gas regions are also
not matched with the direction of the high dust obscuration gradient, which
denies the possibility that the obscured star-forming regions cause the
extended ionized emission. Based on the size measurement results in the image
plane (Section 3.3) and the different radial and tangential magnifications
(see middle panel of Figure 2), the ionized [O iii]$\lambda$5007+H$\beta$
structure extends out to $\sim 6$ times more than the effective radius of the
stellar distribution of ID4590 (Section 3.4). Same as [C ii], i)–iii) are the
possible physical origins of the extended ionized gas emission. Interestingly,
from the center of ID4590, the regions of the extended ionized gas
distribution ($\sim$Southeastern) and the peak position of the [C ii] emission
($\sim$Northern) are in different directions. This might indicate that the
differential distributions of the nebular parameters, such as $n_{\rm e}$,
$Z_{\rm gas}$, $\log(U)$, and C/O abundance cause these differential
distributions, even if the same physical process is taking place, either of
i)—iii).

Importantly, regardless of the true physical processes to give rise to an
offset-[C ii] and extended [O iii]$\lambda$5007+H$\beta$ gas emission, the
presence of the metal-enriched gas away from the galaxy is strong evidence of
past and/or ongoing outflow activities already taking place in a low-mass
($M_{\rm star}=6\times 10^{7}\,M_{\odot}$), metal-poor ($Z=0.04Z_{\odot}$)
nascent galaxy at $z=8.496$. The presence of the extended carbon gas
structure, so-called [C ii] Halo, has been reported around more massive
($M_{\rm star}>10^{9}$–10${}^{10}\,M_{\odot}$) star-forming galaxies at
$z=4-7$ (e.g., Fujimoto et al. 2019, 2020; Ginolfi et al. 2020; Herrera-Camus
et al. 2021; Akins et al. 2022; Lambert et al. 2022), which is challenging to
the current cosmological galaxy formation models (Fujimoto et al. 2019; see
also e.g., Pizzati et al. 2020; Arata et al. 2020; Katz et al. 2022). Our
results in ID4590 provide new insight that such metal enrichment beyond the
galaxy ISM scale starts to occur even in the very early phase of the galaxy
assembly just $\sim$580 Myr after the Big Bang, which is likely linked to the
origin of the [C ii] halo at a later epoch of the Universe.

Another important fact is that the presence of diffuse extended ionized gas
around ID4590 directly indicates the high filling factor of the ionized gas,
where the ionizing photons escaping from the galaxy may contribute to the
Reionization. After the lens correction, ID4590 is $\sim 5\times$ fainter than
the characteristic UV luminosity of the UV luminosity function (UVLF) at
$z\sim 9$ ($M^{*}_{\rm UV}=-19.6$ mag; e.g., Harikane et al. 2022). Once we
confirm the high escape fraction of the ionizing photons from faint, low-mass
galaxies, probably related to the onset of the outflow from the early stage of
the galaxy assembly, it also provides us with a new insight into the process
of the Reionization, in contrast to the scenario that huge ionized bubbles are
formed around UV-bright galaxies ($M_{\rm UV}\lesssim-22$) at similar
redshifts (e.g., Mason et al. 2018). The significantly low metallicity of
ID4590, falling below the $z\sim 8$ mass–metallicity relations predicted from
current galaxy formation models (e.g., Curti et al. 2022), despite the dust
obscuration in ID4590 ($\beta=-1.7\pm 0.07$), may suggest that dust
obscuration occurs in a part of the galaxy with a very low dust content. This
may also be caused by the past or ongoing outflow activities (Ferrara et al.
2022; Ziparo et al. 2022) that carry the dust away from the galaxy and make it
diffuse, cold, and undetectable in the observations (e.g., Akins et al. 2022),
while the dust in regions that are not invested by the outflow, or that are
shielded by Giant Molecular Clouds, could survive (see also Martínez-González
et al. 2019; Nath et al. 2022). This small amount of surviving dust may be
responsible for a certain amount of dust obscuration. In any case, the low
dust content in the galaxy is also helpful for ionizing photons to escape from
the system.

Note that diffuse ionized gases (DIGs) have been observed in local galaxies,
from inter-arm regions (e.g., Zurita et al. 2000) to areas above the galactic
mid-plane out to 1–2 kpc scales (e.g., Rossa & Dettmar 2000). However, even in
the latter case, the sizes of these DIGs are only about $\sim 10$% relative to
the size of the host galaxy (e.g., Rossa & Dettmar 2003). In contrast, the
extended ionized gas structure around ID4590 is well beyond the central galaxy
size (Section 3.4). Therefore, the physical origins of the extended ionized
gas structure around ID4590 are likely different from those of the DIGs in the
local Universe.

Another note is that we do not find evidence of the ongoing outflow via the
broad-wing feature in the NIRSpec spectrum. However, the slit of the NIRSpec
MSA is aligned perpendicular to the extended ionized gas structure (See the
white rectangle in Figure 2), which might be the reason for the absence of the
broad-wing feature in the current NIRSpec spectrum.

Figure 9:  FIR line diagnostic of $L_{\rm[OIII]}$/SFR and $L_{\rm[CII]}$/SFR,
produced in the same manner as Figure 12 in Harikane et al. (2020). Left: The
relation from the observations. The color and symbols represent the same as
Figure 6. The grey crosses are newly added in this panel, showing the local
LIRGs (Howell et al. 2010; Díaz-Santos et al. 2017) whose SFR values are
comparable to $z\sim 6$–9 galaxies in the panel. The grey curve is the typical
relation for the local LIRGs. Right: Same as the left panel, but comparing
with Cloudy calculations. The magenta-shaded region represents the possible
parameter space for ID4590 calcualted with Cloudy based on its best-fit
nebular parameters of $Z_{\rm gas}=0.04\pm 0.02$, $n_{\rm
e}=220^{+170}_{-100}$ cm-3, $\log(U)>-2.27$, and $\log$(C/O)=$[-0.52:-0.26]$
constrained by our joint JWST and ALMA analysis. For comparison, we also show
the relations with different parameter sets; the orange, dark light blue, and
dark blue lines are the results with $Z_{\rm gas}=0.05,0.1,$ and 1.0
$Z_{\odot}$; the dotted, dashed, and solid lines correspond to densities of
$\log(n_{\rm gas}$/[cm-3]) = 0.5, 2.0, and 3.0; and the larger circles
indicate higher ionization parameters, from $\log U$ = $-4.0$ ion to $-0.5$
with a step size of 0.5. The black arrows in the inset panel show directions
and possible shifts in the $L_{\rm[OIII]}/$SFR–$L_{\rm[CII]}/$SFR plane due to
the physical mechanisms of b), c), and d). To perform a fair comparison, we
use the SFR value based on the dust-corrected H$\alpha$ luminosity in the same
manner as Harikane et al. (2020), instead of the SED based estimate. Using
H$\alpha$ luminosity is also beneficial to count the ionizing photons
contributing to the line emissivities more directly.

###  4.5 Physical origins of the high [OIII]88$\mu$m/[CII]158$\mu$m ratio

Previous ALMA observations reported the detections of the luminous [O
iii]88$\mu$m line from star-forming galaxies at $z\sim$ 6–9, showing their [O
iii]88$\mu$m/[C ii]158$\mu$m line ratio of $\gtrsim 3$–10 that are higher than
local dwarf galaxies and/or local Luminous Infrared Galaxies (LIRGs) with
similar SFRs (Inoue et al. 2016; Harikane et al. 2020; Witstok et al. 2022).
The origin of such high ratios is still unclear. Major solutions that have
been argued include a) observational bias (e.g., Carniani et al. 2020), b) low
C/O abundance ratio (Katz et al. 2022), c) low covering fraction of PDRs161616
This is equal to the high filling factor of the ionized gas relative to dense
PDRs.  $C_{\rm PDR}$ (Cormier et al. 2015; Harikane et al. 2020), and d) the
characteristic ISM parameters in early galaxies such as the high ionization
parameter (Katz et al. 2017; Harikane et al. 2020) probably caused by recent
strong bursts of star-formation (Ferrara et al. 2019; Arata et al. 2020;
Vallini et al. 2021; Witstok et al. 2022; Sugahara et al. 2022) and/or low
stellar-to-gaseous metallicity ratio (Sugahara et al. 2022).

In Section 6, we find that ID4590 also shows a similarly high [O
iii]88$\mu$m/[C ii]158$\mu$m line ratio of $>4$ at the galaxy position. In
addition to the accurate measures of $Z_{\rm gas}$ and $n_{\rm e}$ (Section
4.1), the deep NIRSpec observations also cover the [O ii]3729 and C iii]1909
emission lines from ID4590, which allow us to constrain the ionization
parameter $\log(U)$ (e.g., Schaerer et al. 2022; Curti et al. 2022; Brinchmann
2022; Trump et al. 2022; Heintz et al. submitted; Nakajima et al. in prep.)
and the C/O abundance in ID4590 (e.g., Arellano-Córdova et al. 2022; Isobe et
al. in prep.). This indicates that we can investigate the physical origins of
the high [O iii]88$\mu$m/[C ii]158$\mu$m line ratio, taking the possible
solutions of b) and d) into account via the actual observed measurements for
ID4590. Besides, the spatial offset of the [C ii] line (Section 3.4) allows us
to separate the emission arising inside and outside the galaxy and fairly
compare the line ratio, also managing the observational bias of point a).
Therefore, with this best optical–mm characterization of an early galaxy owing
to the joint JWST and ALMA analysis, we are ready to address the physical
origins of the high [C ii]/[O iii] and verify whether the remaining possible
solution of c) is critical or other solutions can answer already.

In Figure 9, we show the $L_{\rm[OIII]}/$SFR and $L_{\rm[CII]}/$SFR relation
of ID4590. Given the purpose of the analysis, we use the [C ii] results at the
galaxy position. For comparison, we also present the relations from
observations (left panel) and the predictions from the photoionization model
with cloudy (right panel) drawn in the same manner as Harikane et al. (2020)
(see also Sugahara et al. 2022), where the possible shifts on the plane by b),
c), and d) are presented with black arrows (Harikane et al. 2020). We also
show the magenta-shaded region that corresponds to the possible space for
ID4590 calculated by Cloudy with our fiducial estimates of $Z_{\rm
gas}/Z_{\odot}=0.04\pm 0.02$, $n_{\rm e}=220^{+170}_{-100}$ cm-3,
$\log(U)>-2.27$, and $\log$(C/O)=$[-0.52:-0.26]$. Following Harikane et al.
(2020), we use the SFR value based on the dust-corrected H$\alpha$ luminosity
estimated from NIRSpec (Section 2.3), instead of the SED-based value, for this
analysis.

In the left panel, we find that ID4590 shows the $L_{\rm[OIII]}$/SFR ratio
much higher than local LIRGs, falling on the high [O iii]/[C ii] line ratio
regime similar to other $z\sim 6$–9 galaxies. We also find that several metal-
poor galaxies (12+$\log(O/H)\lesssim 8.0$) among the local dwarf galaxies are
located in the similarly high [O iii]/[C ii] line ratio regime to these $z\sim
6$–9 galaxies. This may suggest that the ISM conditions of these $z\sim 6$–9
galaxies are similar to those of the local metal-poor galaxies, while an
important note is that these local metal-poor galaxies have much lower SFRs
than these $z\sim 6$–9 galaxies by $\sim$1–2 orders of magnitudes.

In the right panel, we find that the observed $L_{\rm[OIII]}$/SFR and
$L_{\rm[CII]}$/SFR relation of ID4590 is consistent with the magenta-shaded
region within the errors. This indicates that the [C ii] and [O iii]
emissivities at a given input energy in ID4590 are generally explained by the
combination of high $\log(U)$, high $n_{\rm e}$, low $Z_{\rm gas}$, and low
$\log$(C/O). Therefore, the physical origin of the high [O iii]/[C ii] ratio
observed among $z\sim 6$–9 galaxies may be sufficiently explained by b) and
d).

As discussed in Harikane et al. (2020), another possible origin of c) – the
low $C_{\rm PDR}$ – could also be the additional reason to boost the [O
iii]/[C ii] ratio. As indicated in the black arrow, this effect makes the data
points horizontally to move to the left in Figure 9 (i.e., towards low [C
ii]/SFR). Because the current $\log(U)$ estimate provides the upper limit
alone, the possible parameter space of ID4590 extends to the low
$L_{\rm[CII]}$/SFR regime, where we cannot disentangle the contributions from
$\log(U)$ and $C_{\rm PDR}$. Once the upper boundary of $\log(U)$ is
constrained, the lower limit of the $L_{\rm[CII]}$/SFR ratio in the possible
parameter space will be determined, where the additional $C_{\rm PDR}$
contribution will be evaluated if the observed $L_{\rm[CII]}$/SFR upper limit
is lower than the possible parameter space. With future deep [C ii] follow
providing a much more stringent upper limit or the faint detection of [C ii],
we may be able to investigate further the additional contribution from $C_{\rm
PDR}$.

##  5 Summary

In this paper, we present the ALMA Band 7 and Band 5 deep spectroscopy for the
two major coolant FIR lines of [O iii]88 $\mu$m and [C ii]158 $\mu$m from
ID4590, a metal-poor, low-mass, strongly lensed sub-$L^{*}$ galaxy at
$z=8.496$, whose warm interstellar medium and stellar properties have been the
best characterized with the JWST Early Release Observations (ERO) for the
SMACS0723 field. The JWST ERO observations include the deep imaging with
NIRCam and MIRI at $\sim$1–20 $\mu$m as well as deep spectroscopy with NIRSpec
at $\sim$2–5 $\mu$m which detects multiple rest-frame optical emission lines,
including [O iii]$\lambda$4363 line, and provides us with the robust measure
of the gas-phase metallicity via the direct temperature method for the first
time at $z\gtrsim 3$. Combining these rich JWST data with HST and ALMA, the
high-spatial-resolution, homogeneous data set from optical to mm wavelengths
enables us to perform a panchromatic characterization of an early galaxy in
and out, which sets the benchmark for synergetic studies of ALMA and JWST in
the coming decades. The main findings of this paper are summarized as follows:

  1. 1.

We detect both [C ii]158$\mu$m and [O iii]88$\mu$m lines at 4.0$\sigma$ and
4.5$\sigma$ levels, respectively. The redshift and the spatial position of the
[O iii] line exactly coincide with those of the JWST source. On the other
hand, the [C ii] line is blue-shifted by 90 km -1 and has a spatial offset by
$\sim 0\farcs 5$ ($\approx 0.5$ kpc in source plane) beyond the errors, where
the chance projection of the noise fluctuation is very unlikely ($\sim 0.07$%)
from a blind line search analysis in the same data cube. This indicates that
[C ii] velocity and spatial offsets are real and associated with some physical
mechanisms of ID4590.

  2. 2.

We evaluate the sizes of [C ii], [O iii], rest-frame UV, and rest-frame
optical continuum by using ALMA and JWST/NIRCam images. With the 2D profile
fitting in the image plane, we obtain the best-fit circularized effective
radii of $0\farcs 69\pm 0\farcs 42$, $0\farcs 056\pm 0\farcs 012$, and
$0\farcs 059\pm 0\farcs 010$ for [C ii], rest-frame UV, and rest-frame optical
continuum, respectively. The [O iii] line is not spatially resolved with the
current resolution and sensitivity, and we place its upper limit of $0\farcs
16$. We find that the position angle estimated in the F150W filter shows an
excellent agreement with the lensing distortion predicted from the mass model,
validating the high magnification of $\mu=8.69$ in ID4590. The extended [C ii]
distribution relative to the stellar continuum is reminiscent of the [C ii]
Halo reported in recent ALMA studies, while we cannot exclude the possibility
that the [C ii] size estimate is affected by the noise fluctuation with the
current S/N.

  3. 3.

The dust continuum is not detected in neither Band 7 or Band 5, and we place
2$\sigma$ upper limits of 41.8 $\mu$Jy and 23.2 $\mu$Jy at 0.85 mm and 1.54
mm, respectively. By assuming a single modified black body with the dust
temperature $T_{\rm d}=60$ K and the dust spectral index of $\beta_{\rm
d}=1.8$, we estimate the upper limits of infrared luminosity over 8–1000
$\mu$m of $L_{\rm IR}<1.8\times 10^{10}\,L_{\odot}$ and the dust mass of
$M_{\rm dust}<1.2\times 10^{5}\,M_{\odot}$ after the lens correction, while a
different $T_{\rm d}$ assumption by $\pm 30$ K changes these constraints by
$\sim\pm$0.5–1.0 dex. The upper limit of infrared excess (IRX$\equiv L_{\rm
IR}/L_{\rm UV}$) in ID4590 suggests that $T_{\rm d}$ is higher than $30$–40 K
or that steep dust attenuation laws similar to SMC are favored.

  4. 4.

The NIRCam/F444W filter, including the contributions from [O iii]$\lambda$5007
and H$\beta$ emission lines, shows an extended structure where the rest-frame
UV and optical continuum are invisible and the 3$\sigma$ upper limit in the
rest-frame UV continuum after the lens correction are placed at 32.5 mag
($\approx 0.05\,M_{\odot}$ yr-1). Given the high-spatial-resolution of the
F444W filter ($\sim 0\farcs 15$), the smooth morphology of the extended
structure is the direct evidence of the presence of the extended, diffuse
ionized gas structure around ID4590. The structure extends towards the radial
magnification axis out to $\sim 0\farcs 5$. After the lens correction, this
corresponds to $\sim 1.7$ kpc and at least eight times larger than the rest-
frame optical effective radius of ID4590.

  5. 5.

We perform the optical–mm SED analysis with HST, JWST/NIRCam+MIRI, and ALMA
photometry. We exclude the emission outside of the galaxy observed in the
F444W filter, and the remaining contribution of the strong emission lines of
[O iii]$\lambda$5007+H$\beta$ and the stellar continuum is well separated by
the rich filter sets of NIRCam and MIRI. After the lens correction, we
estimate the stellar mass of $M_{\rm star}=6\times 10^{7}\,M_{\odot}$, the
total star-formation of SFR $=3\,M_{\odot}$ yr-1, UV continuum slope of
$\beta_{\rm UV}=-1.7$, suggesting that ID4590 is a low-mass, but a little dust
attenuated galaxy, in contrast to very blue galaxies ($\beta_{\rm UV}<-2.0$)
that have been observed in recent JWST observations at similar redshifts.

  6. 6.

Regardless of the ongoing physical mechanisms, past outflow activities are
required to make the surrounding pristine gas of ID4590 metal-enriched and
produce the [C ii] offset and the extended ionized gas structure traced by [O
iii]$\lambda$5007+H$\beta$. This would also help produce high ionizing photon
escape from ID4590 and contribute to reionization at $z>8.5$.

  7. 7.

With careful slit-loss correction and the separation of the emission inside
and outside of the galaxy, we evaluate the electron density of $n_{\rm
e}=220^{+170}_{-100}$ cm-3 via the [O iii]88$\mu$m/[O iii]$\lambda$5007 line
ratio. This is much higher than that of local galaxies ($n_{\rm e}\simeq 30$
cm-3), but consistent with $z\sim 2$–3 galaxies ($n_{\rm e}\simeq 200-300$
cm-3). This is also consistent with the upper limit of $n_{\rm e}<260$ cm-3
obtained in a lensed dusty galaxy at $z=7.13$.

  8. 8.

We examine relations between the line luminosities of [C ii]158$\mu$m, [O
iii]88$\mu$m, and SFR. ID4590 shows $L_{\rm[CII]}$–SFR and $L_{\rm[OIII]}$–SFR
relations generally consistent with other $z\sim 6$–9 galaxies and explores
the faint-end of the relations, owing to the aid of the lensing support. The
$L_{\rm[CII]}$/SFR ratio of ID4590 falls below the typical relation estimated
among the local dwarf galaxies beyond the errors. Still, it is consistent with
similarly metal-poor local galaxies of IZw18 and SBS0335-052. The same result
is obtained in the SFR–$L_{\rm[OIII]}$ relation, while the relation of ID4590
is still consistent with the typical range of the local dwarf galaxies within
the errors. ID4590 shows a $L_{\rm[OIII]}/L_{\rm[CII]}$ ratio of $>4$, which
is also as high as other $z\sim$6–9 galaxies, falling above the typical
relation of the local dwarf galaxies in the SFR–$L_{\rm[OIII]}/L_{\rm[CII]}$
relation.

  9. 9.

We investigate the physical origins of the high $L_{\rm[OIII]}/L_{\rm[CII]}$
ratio with the photoionization model of Cloudy. The
$L_{\rm[OIII]}$/SFR–$L_{\rm[CII]}$/SFR relation of ID4590 is generally
reproduced by the high $n_{\rm e}$, low gas-phase metallicity ($Z_{\rm
gas}/Z_{\odot}=0.04$), 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. While the other potential mechanism of the low covering
fraction of the photodissociation region is not constrained by the current
data, it will be achieved by further deep ALMA [C ii] follow-up.

We thank Catherine Vlahakis and Holly Sheets for their kind support in the
processing of the ALMA data, despite the unusual circumstances due to the
cyberattack. We also thank Pablo Albalo Halo for sharing deep insights into
the NIRSpec data analysis. We are grateful to Caitlin Casey and Steven
Finkelstein for helpful discussions for this paper. This paper makes use of
the ALMA data: ADS/JAO. ALMA #2022.A.00022.S. ALMA is a partnership of the ESO
(representing its member states), NSF (USA) and NINS (Japan), together with
NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in
cooperation with the Republic of Chile. The Joint ALMA Observatory is operated
by the ESO, AUI/NRAO, and NAOJ. This work is based on observations and
archival data made with the Spitzer Space Telescope, which is operated by the
Jet Propulsion Laboratory, California Institute of Technology, under a
contract with NASA, along with archival data from the NASA/ESA Hubble Space
Telescope. This research also made use of the NASA/IPAC Infrared Science
Archive (IRSA), which is operated by the Jet Propulsion Laboratory, California
Institute of Technology, under contract with the National Aeronautics and
Space Administration. The Early Release Observations171717
https://www.stsci.edu/jwst/science-execution/approved-programs/webb-first-
image-observations and associated materials were developed, executed, and
compiled by the ERO production team: Hannah Braun, Claire Blome, Matthew
Brown, Margaret Carruthers, Dan Coe, Joseph DePasquale, Nestor Espinoza,
Macarena Garcia Marin, Karl Gordon, Alaina Henry, Leah Hustak, Andi James, Ann
Jenkins, Anton Koekemoer, Stephanie LaMassa, David Law, Alexandra Lockwood,
Amaya Moro-Martin, Susan Mullally, Alyssa Pagan, Dani Player, Klaus
Pontoppidan, Charles Proffitt, Christine Pulliam, Leah Ramsay, Swara
Ravindranath, Neill Reid, Massimo Robberto, Elena Sabbi, Leonardo Ubeda. The
EROs were also made possible by the foundational efforts and support from the
JWST instruments, STScI planning and scheduling, and Data Management teams.
This project has received funding from the European Union’s Horizon 2020
research and innovation program under the Marie Sklodowska-Curie grant
agreement No. 847523 ‘INTERACTIONS’ and from NASA through the NASA Hubble
Fellowship grant HST-HF2-51505.001-A awarded by the Space Telescope Science
Institute, which is operated by the Association of Universities for Research
in Astronomy, Incorporated, under NASA contract NAS5-26555. F.S. acknowledges
support from the NRAO Student Observing Support (SOS) award SOSPA7-022. The
Cosmic Dawn Center is funded by the Danish National Research Foundation under
grant No. 140.

.

##  Appendix A Accuracy of the astrometry of JWST and HST maps from grizli

In Figure 10, we show the residual spatial offsets of the Right ascension
($\Delta$R.A.) and Declination ($\Delta$Dec.) for the GAIA sources. We
evaluate the residual offsets by running the source extractor (Bertin &
Arnouts 1996) on the JWST and HST maps produced by the grizli pipeline and
being corrected for the proper motion effect of the GAIA sources, and
comparing with those from the GAIA DR3 catalogs. We confirm that the average
offset shows an excellent agreement with zero and the standard deviation in
R.A and Dec. of $0\farcs 01$ and $0\farcs 02$, respectively. We regard these
standard deviations as the positional uncertainty of the JWST sources in
Figure 2.

Figure 10:  Accuracy of astrometry of the JWST and HST maps used in our
analysis. The black circles show the relative offsets of the coordinates from
the GAIA DR3 catalog for the GAIA sources identified in the JWST maps, after
correcting their proper motion effects. The red cross indicates the average
offset, showing excellent agreement with zero. The red cross size corresponds
to the standard deviations of $\Delta$R.A. and $\Delta$Dec., which we assume
as the uncertainty of the positional accuracy for the JWST sources (black bar
in Figure 2).

##  Appendix B CIGALE parameters for the full SED fit

We assume a delayed star-formation history (SFH): SFR($t$) $\propto
t/\tau^{2}$ exp$(-t/\tau)$ with stellar models from Bruzual & Charlot (2003)
and an exponential recent burst implemented in the sfhdeleyed module. We use
the dustatt_modified_starburst module for the dust attenuation, where the
nebular emission (continuum + lines) are attenuated with a screen model and an
SMC extinction curve (Pei 1992). During the SED fitting, the same $E(B-V)$ is
used between stellar and nebular emission. Finally, the dust emission is re-
emitted in the infrared with Casey (2012) models. We fix $\beta_{\rm d}=1.8$
and the mid-infrared power-law slope $\alpha_{\rm d}=2.0$ and adopt the
$T_{\rm d}$ range of 30–90 K. Because no evidence of the presence of AGN has
been reported, we do not include an AGN component in the model. We list the
modules and the parameter ranges used in the fitting in Table 4. In the
fitting, we use the photometry with the $1\sigma$ error also for the
measurements below the $2\sigma$ upper limits. To avoid the lens model
uncertainty, we perform the SED fitting with the optical–mm photometry without
the lens correction.

Parameters |  Symbol |  Range
---|---|---
Delayed SFH and recent burst
e-folding time scale of the delayed SFH |  $\tau_{main}$ [Myr] |  100, 250, 500, 1000
Age of the main population |  Agemain[Myr] |  51 log values in [1: 3.3]
Burst |  fburst |  0.05, 0.10, 0.15, 0.25
SSP
SSP |  |  BC03
Initial mass function |  IMF |  Chabrier
Metallicity |  Z |  0.0004, 0.004, 0.02
Nebular emission
Ionization parameter |  logU |  -2.0
Line width [km/s] |  — |  150
Gas-phase Metallicity |  zgas |  0.0004, 0.004, 0.02
Electron density |  ne |  100
Dust attenuation law
Color excess for both the old and young stellar populations |  E_BV_lines |  21 log values in [$-3$: 1.3]
Reduction factor to apply on E_BV_lines to compute E(B-V)s the stellar continuum attenuation |  E_BV_factor |  1.0
Bump amplitude |  uv_bump_amplitude |  0.0
Power law slope |  power law_slope |  0.0
Extinction law to use for attenuating the emission lines flux |  Ext_law_emission_lines |  SMC
Ratio of total to selective extinction, A_V / E(B-V) |  Rv |  2.93
Dust emission (Casey2012)
Dust temperature |  temperature |  20 log values in [1.5:1.95]
Dust emissivity index |  beta |  1.8
Mid-infrared power law slope |  alpha |  2.0
No AGN emission

Table 4: cigale modules and input parameters used for all the fits. BC03
indicates Bruzual & Charlot (2003), and the Chabrier IMF refers to Chabrier
(2003).

##  Appendix C HST/NIRcam/MIRI photometry of ID4590

We summarize the optical–mm photometry used in this paper in Table 5.

Table 5: NIR–mm photometry of ID4590 used in this paper Filter |  Flux (nJy)
---|---
HST/F105W |  $-4.7\pm 12.3$
HST/F125W |  $44.5\pm 13.8$
HST/F140W |  $60.5\pm 11.9$
HST/F160W |  $61.7\pm 14.7$
NIRCam/F090W |  $-12.0\pm 3.9$
NIRCam/F115W |  $22.7\pm 8.2$
NIRCam/F150W |  $60.7\pm 6.6$
NIRCam/F200W |  $66.9\pm 7.0$
NIRCam/F277W |  $69.0\pm 7.1$
NIRCam/F356W |  $71.3\pm 7.3$
NIRCam/F444W |  $145.2\pm 14.7$
MIRI/F770W |  $92.2\pm 38.0$
MIRI/F1000W |  $111.2\pm 72.0$
MIRI/F1500W |  $314.1\pm 234.4$
MIRI/F1800W |  $263.9\pm 464.6$
ALMA/Band7 |  $<41800\,(2\sigma)$
ALMA/Band5 |  $<23200\,(2\sigma)$

##  Appendix D Size measurements

In Figure 11, we summarize the observed, the best-fit model, and the residual
maps from the best-fit size measurements for the [C ii], [O iii], rest-frame
UV and optical continuum emission using the ALMA and JWST/NIRcam. The methods
are described in Section 3.3. We confirm that significant positive and
negative pixels remain in the residual maps.

Figure 11:  Size measurement results in the image plane. The observed, the
best-fit model, and residual (=obserevd - model) maps are shown from left to
right. For the [C ii] and [O iii] line with ALMA data, we use CASA imfit,
while for the rest-frame UV and optical continuum with NIRCam/F150W and F356W
data, we use galfit (Peng et al. 2010). The ellipse (circle) at bottom right
shows the ALMA synthesized beam (PSF). Note that imfit suggests that [O iii]
is not spatially resolved, and we use the beam rescaled to the peak of the [O
iii] line as the best-fit model.

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