# The ISM in the $z = 6.9$ Interacting Galaxies of SPT0311-58

Katrina C. Litke, Daniel P. Marrone, Manuel Aravena, Melanie Archipley, Matthieu Béthermin, James Burgoyne, Jared Cathey, Scott C. Chapman, Anthony H. Gonzalez, Thomas R. Greve, et al.

► To cite this version:

Katrina C. Litke, Daniel P. Marrone, Manuel Aravena, Melanie Archipley, Matthieu Béthermin, et al. The ISM in the $z = 6.9$ Interacting Galaxies of SPT0311-58. The Astrophysical Journal, 2023, 949, 10.3847/1538-4357/acc93a. insu-04479083

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# The ISM in the $z=6.9$ Interacting Galaxies of SPT0311-58

Katrina C. Litke<sup>1,2</sup> <sup>¶</sup>, Daniel P. Marrone<sup>1</sup> <sup>¶</sup>, Manuel Aravena<sup>3</sup> <sup>¶</sup>, Melanie Archipley<sup>4</sup> <sup>¶</sup>, Matthieu Béthermin<sup>5</sup> <sup>¶</sup>,

James Burgoyne<sup>6</sup> <sup>¶</sup>, Jared Cathey<sup>7</sup>, Scott C. Chapman<sup>8,9</sup>, Anthony H. Gonzalez<sup>7</sup> <sup>¶</sup>, Thomas R. Greve<sup>10,11</sup> <sup>¶</sup>,

Gayathri Gururajan<sup>15,13,14</sup>, Christopher C. Hayward<sup>15</sup> <sup>¶</sup>, Matthew A. Malkan<sup>16</sup> <sup>¶</sup>, Kedar A. Phadke<sup>4,17</sup> <sup>¶</sup>, Cassie A. Reuter<sup>18</sup> <sup>¶</sup>,

Kaja M. Rotermund<sup>9</sup>, Justin S. Spilker<sup>19</sup> <sup>¶</sup>, Antony A. Stark<sup>20</sup> <sup>¶</sup>, Nikolaus Sulzenauer<sup>21</sup> <sup>¶</sup>, Joaquin D. Vieira<sup>4,22</sup> <sup>¶</sup>,

David Vizgan<sup>4,10</sup> <sup>¶</sup>, and Axel Weiß<sup>21</sup> <sup>¶</sup>

<sup>1</sup>Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA; kclitke@email.arizona.edu, dmarrone@arizona.edu

<sup>2</sup>School of Physics and Astronomy, University of Minnesota, 116 Church St SE, Minneapolis, MN 55455, USA

<sup>3</sup>Núcleo de Astronomia de la Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile

<sup>4</sup>Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA

<sup>5</sup>Aix Marseille Univ., Centre National de la Recherche Scientifique, Laboratoire d'Astrophysique de Marseille, Marseille, France

<sup>6</sup>Department of Physics and Astronomy, University of British Columbia, 6225, Agricultural Road, Vancouver, V6T 1Z1, Canada

<sup>7</sup>Department of Astronomy, University of Florida, Gainesville, FL 32611, USA

<sup>8</sup>Eureka Scientific, Inc. 2452 Delmer Street Suite 100, Oakland, CA 94602-3017, USA

<sup>9</sup>Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 4R2, Canada

<sup>10</sup>Cosmic Dawn Center, DTU Space, Technical University of Denmark, Elektrovej 327, Kgs. Lyngby, DK-2800, Denmark

<sup>11</sup>Department of Physics and Astronomy, University College London, Gower Street, London WC1E6BT, UK

<sup>12</sup>Aix-Marseille University, CNRS, CNES, LAM, Marseille, France

<sup>13</sup>Department of Physics and Astronomy "Augusto Righi" (DIFA), University of Bologna, Via Gobetti 93/2, I-40129, Bologna, Italy

<sup>14</sup>Osservatorio di Astrofisica e Scienza dello Spazio, INAF, Via Gobetti 93/3, I-40129, Bologna, Italy

<sup>15</sup>Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

<sup>16</sup>Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA

<sup>17</sup>Center for AstroPhysical Surveys, National Center for Supercomputing Applications, 1205 West Clark Street, Urbana, IL 61801, USA

<sup>18</sup>Department of Astronomy and Department of Physics, University of Illinois, 1002 West Green St., Urbana, IL 61801, USA

<sup>19</sup>Department of Physics and Astronomy and George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, 4242 TAMU, College Station, TX 77843-4242, USA

<sup>20</sup>Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA

<sup>21</sup>Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

<sup>22</sup>Center for AstroPhysical Surveys, National Center for Supercomputing Applications, Urbana, IL 61801, USA

Received 2022 December 8; revised 2023 March 20; accepted 2023 March 29; published 2023 June 1

## Abstract

SPT0311-58, a system of two interacting galaxies in the Epoch of Reionization, exists in one of the rarest, most massive dark matter halos theoretically possible in that era. Studying the interstellar medium (ISM) in these galaxies can illuminate the process of galaxy formation in the early Universe. In this work, we explore the multiphase ISM in this system, using ALMA observations of the [C II] 158, [O I] 146, [N II] 122, and [O III] 88 fine-structure lines and dust continuum. We find wide variations in line ratios between the eastern and western galaxies, as well as across the western galaxy. Continuum colors indicate that SPT0311-58 E has a higher ionization parameter (log $U$ ≈ −2.8) than SPT0311-58 W (log $U$ ≈ −3.1). The ratio of [O III] 88–[N II] 122 and the ionization parameter constraints combine to demonstrate near-solar metallicity in these objects just 800 Myr after the Big Bang.

*Unified Astronomy Thesaurus concepts: Interstellar medium (847); High-redshift galaxies (734)*

## 1. Introduction

During the Epoch of Reionization (EoR; 6 ≲ $z$ ≲ 15), the formation of the first galaxies contributed to the ionization of the intergalactic medium (Fan et al. 2006; Bouwens et al. 2011; Finkelstein et al. 2012; Carilli & Walter 2013). During this time, the cosmic star formation rate density rose (Behroozi et al. 2013; Madau & Dickinson 2014) and stellar nucleosynthesis enriched the interstellar medium (ISM) with heavier elements. The accumulation of metals (elements heavier than hydrogen and helium) in the ISM during the EoR is only beginning to be understood using telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA; Miralda-Escudé et al. 2000; Dayal & Ferrara 2018). The

presence of dust in early galaxies is an unambiguous signature of metal enrichment. However, the high dust masses observed in some EoR galaxies can be difficult to explain in the context of known mechanisms for forming (and destroying) dust (Michałowski 2015; Leśniewska & Michałowski 2019).

Far-infrared fine-structure lines are powerful tools for studying the ISM in dusty galaxies, in particular for EoR galaxies where they redshift into submillimeter atmospheric windows. The fine-structure line of singly ionized carbon at 158 µm, [C II] 158, is one of the brightest cooling lines of the neutral ISM, emitting up to 1% of the total galactic IR luminosity (Hollenbach & Tielens 1997, 1999). In more highly ionized or lower-metallicity environments, [O III] 88 can be even brighter than [C II] 158 (Spinoglio & Malkan 1992; Carilli & Walter 2013; Cormier et al. 2015). This has led to several detections of [C II] 158 and [O III] 88 at $z$ > 6 in recent years (e.g., Marrone et al. 2018; Hashimoto et al. 2019b; Novak et al. 2019; Carniani et al. 2020; Harikane et al. 2020; Decarli et al. 2022). Combinations

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of these lines and other, weaker, lines can be used to infer conditions in the ISM. For example, line ratios such as [O III] 88/[N II] 122 have shown promise as indicators of the metallicity in high-z galaxies (Pereira-Santaella et al. 2017; Rigopoulou et al. 2018; De Breuck et al. 2019; Novak et al. 2019). Other ratios such as [C II] 158/[O I] 146 have been used to study the dense neutral gas in photodissociation regions (PDRs; Meijerink & Spaans 2005; De Breuck et al. 2019; Novak et al. 2019; Litke et al. 2022). Information from several lines and adjacent continuum bands can even be used to constrain complex ISM models with many free parameters (e.g., De Breuck et al. 2019; Novak et al. 2019; Decarli et al. 2022; Litke et al. 2022; Meyer et al. 2022).

At $z = 6.9$, less than 800 Myr after the Big Bang, SPT0311-58 is the most distant object discovered in the South Pole Telescope (SPT)-SZ survey (Carlstrom et al. 2011; Vieira et al. 2013; Strandet et al. 2017). Using spatially resolved ALMA observations of [C II] 158, [O III] 88, and the underlying dust continuum, combined with optical and IR observations from Hubble, Gemini, Spitzer, and Herschel, Marrone et al. (2018) resolved SPT0311-58 into two sources, separated by less than 8 kpc in projected distance and 700 km s⁻¹ in velocity. Both galaxies are massive, though SPT0311-58 E was found to have an order of magnitude less dust and gas than SPT0311-58 W. Unlike other $z > 6$ dusty galaxies, UV emission is detectable in SPT0311-58 E, though most of the star formation is obscured by dust (Marrone et al. 2018). SPT0311-58 is gravitationally lensed by a nearly edge-on spiral galaxy at $z = 1.4$. Gravitational lens modeling by Marrone et al. (2018) found magnifications of $\mu = 2.2$ and $\mu = 1.3$, in SPT0311-58 W and E, respectively, and $\mu = 2.0$ in the total system. Marrone et al. (2018) also found that SPT0311-58 resides in one of the rarest, most massive dark matter halos that should exist at this epoch, possibly embedded in a protocluster (Wang et al. 2021), representing a peak in the cosmic density field at $z = 6.9$.

Jarugula et al. (2021) followed up on the molecular interstellar medium of SPT0311-58 using high-resolution ALMA observations of CO, [C I], and H₂O. They used nonlocal thermodynamical equilibrium radiative transfer models to estimate the gas masses, dust masses, and other parameters in SPT0311-58 E and W. They also found the CO spectral line energy distributions in both components were similar to other high-z dusty star-forming galaxies (DSFGs). Recently, Spilker et al. (2022) observed [C II] 158 and the underlying dust continuum at 70 mas resolution with ALMA and found at least 12 clumps with sizes ~1 kpc between the two components. They observe chaotic and clumpy structures in this massive dark matter halo, similar to what is observed in simulations of high-z galaxies (Spilker et al. 2022).

In this paper, we expand on previous observations by Marrone et al. (2018) to explore the multiphase ISM in SPT0311-58 with ALMA observations of [C II] 158, [O I] 146, [N II] 122, [O III] 88, and the underlying dust continuum. We begin by describing the ALMA observations and data reduction in Section 2. We then explore the distribution of various ISM properties across the two galaxies in Section 3. Finally, we discuss the heterogeneous conditions observed in this EoR system in Section 4. We adopt the cosmology of Planck Collaboration et al. (2016) ($\Omega_m = 0.309$, $\Omega_\Lambda = 0.691$, and $H_0 = 67.7$ km s⁻¹). At $z = 6.9$, $1'' = 5.4$ kpc.

## 2. ALMA Observations

SPT0311-58 was observed in ALMA Bands 6, 7, and 8 (Project IDs 2016.1.01293.S, 2017.1.01423.S, 2018.1.00575.S, 2018.1.01778.S; PI: Marrone). Table 1 lists the observing dates, frequencies, number of antennas, flux and phase calibrators, maximum baselines, on-source integration times, mean precipitable water vapor, resolution, continuum noise level, and project IDs for the observations of [C II] 158, [O I] 146, [N II] 122, and [O III] 88. The data were processed using the Common Astronomy Software Applications package (CASA; McMullin et al. 2007; Petry & CASA Development Team 2012).

Figure 1 shows the continuum emission (top row) and moment 0 (velocity-integrated) maps of the line emission (bottom row) from SPT0311-58. Images were created using the CASA task TCLEAN with Briggs weighting (robust = 0.5) and the auto-multithresh mask option (noisethreshold = 3). The 158 µm observations have the highest resolution, $0.07' \times 0.08''$, while the 122 µm observations have the lowest resolution at $0.63' \times 0.53''$. [O III] 88 has a native resolution of $0.2' \times 0.3''$, but it was tapered to $0.5''$ to increase the signal-to-noise ratio. For the imaging (Figure 1) and spectra (Figure 2), [C II] 158 was divided into 50 km s⁻¹ channels, [O I] 146 and [N II] 122 were divided into 100 km s⁻¹ channels, and [O III] 88 was divided into 200 km s⁻¹ channels.

All four lines and the dust continuum show different morphologies in both the images in Figure 1 and the spectra in Figure 2. The two galaxies of SPT0311-58 show up most clearly in the [C II] 158 and [O I] 146 lines, with the [O I] 146 emission showing clumpiness like that observed by Spilker et al. (2022) in 158 µm continuum and [C II] 158. Differences can be seen in other tracers, however. Continuum emission and [N II] 122 are faint in SPT0311-58 E (blue dotted lines in Figure 2), and [N II] 122 is particularly bright in the north of W (solid magenta lines) and fainter in the south (dashed purple lines). The morphology of [O III] 88 is nearly reversed from that of [N II] 122—it is bright in SPT0311-58 E (dotted blue lines) and the southern part of SPT0311-58 W (dashed purple lines), but faint in the northern part of SPT0311-58 W (solid magenta lines).

These morphological differences result in varying spectra, shown in Figure 2. The spectra are also shown on a common vertical scale in Figure 3. The [C II] 158, [O I] 146, and [N II] 122 spectra were obtained using images tapered to 400kλ, while [O III] 88 was tapered to 200kλ. The flux in each channel was summed within the ellipses shown in Figure 1 in tapered images. While [C II] 158 and [O I] 146 span approximately –600 km s⁻¹ to +1200 km s⁻¹ in velocity (red and orange spectra, respectively), covering both SPT0311-58 W and SPT0311-58 E, the brightest [N II] 122 emission is within ±600 km s⁻¹ of the systemic velocity ($z = 6.900$) (green spectra), the velocity range covered by SPT0311-58 W, and the [O III] 88 emission is mostly at velocities $>0$ km s⁻¹ (blue spectra). [C II] 158 and [O III] 88 are comparably bright in SPT0311-58 E (top center panel of Figure 3). [O I] 146 and [N II] 122 are comparably bright in the redshifted (southern) portion of SPT0311-58 W (bottom right of Figure 3), but [O I] 146 is brighter than [N II] 122 in SPT0311-58 E.

Previous studies (e.g., Marrone et al. 2018; Jarugula et al. 2021) have analyzed the emission from the two galaxies in the SPT0311-58 (E and W) system separately. Because of the clearly varying line ratios across SPT0311-58 W, we further
<figure><img src="image_4.png" /><figcaption>**Figure 1.** Observed emission from SPT0311-58. Top: Continuum images in mJy. Bottom: Moment 0 maps of line images in mJy km s⁻¹. From left to right: 158 µm, 146 µm, 122 µm, and 88 µm. All images show the beam as an ellipse in the lower left corner. The 158 µm continuum emission is shown as red 10σ contours on each panel. The white ellipses in the 158 µm continuum image show the apertures used to find the flux in each component. The fluxes in SPT0311-58 E and SW are summed within their respective ellipses, while SPT0311-58 NW is summed over the region within the large ellipse and excluding the region of SPT0311-58 SW. The [O III] 88 µm observations have intrinsic resolution 0.′′3 × 0.′′2, but they were tapered to 0.′′5 resolution to increase the signal-to-noise ratio. All four lines show different morphologies across SPT0311-58, as detailed in Section 2.</figcaption></figure>

<table><caption>**Table 1**
ALMA Observations of SPT0311-58</caption><thead><tr><th>Date</th><th>Freq.<sup>a</sup><br>(GHz)</th><th>#<br>Ant.</th><th>Flux<br>Calibrator</th><th>Phase<br>Calibrator</th><th>Baseline<sup>b</sup><br>(m)</th><th>t<sub>int</sub><sup>c</sup><br>(min)</th><th>PWV<sup>d</sup><br>(mm)</th><th>Resolution<br>(arcsec)</th><th>Noise<sup>e</sup><br>(µJy beam<sup>-1</sup>)</th><th>Project ID</th></tr></thead><tbody><tr><td colspan="11"><strong>Band 6</strong></td></tr><tr><td colspan="11"><strong>[C II] 158</strong></td></tr><tr><td>03-Nov-2016</td><td>233.651</td><td>44</td><td>J0334-4008</td><td>J0303-6211</td><td>1124</td><td>32</td><td>0.5</td><td>0.08 × 0.07</td><td>10</td><td></td></tr><tr><td>23-Nov-2017</td><td>233.43</td><td>48</td><td>J0519-4546</td><td>J0309-6058</td><td>8547</td><td>31</td><td>0.5</td><td>0.31 × 0.26</td><td>26</td><td>2016.1.01293.S<sup>f</sup></td></tr><tr><td>25-Nov-2017</td><td>233.43</td><td>49</td><td>J0635-7516</td><td>J0309-6058</td><td>8547</td><td>31</td><td>0.6</td><td>0.06 × 0.05</td><td>19</td><td>2017.1.01423.S</td></tr><tr><td>22-Oct-2018</td><td>233.433</td><td>49</td><td>J2357-5311</td><td>J0309-6058</td><td>1397</td><td>39</td><td>0.8</td><td>0.34 × 0.26</td><td>18</td><td></td></tr><tr><td colspan="11"><strong>[O I] 146</strong></td></tr><tr><td>29-Nov-2018</td><td>252.658</td><td>46</td><td>J2357-5311</td><td>J0309-6058</td><td>1240</td><td>39</td><td>1.8</td><td>0.46 × 0.25</td><td>21</td><td>2018.1.00575.S</td></tr><tr><td>29-Nov-2018</td><td>252.658</td><td>46</td><td>J0519-4546</td><td>J0309-6058</td><td>1240</td><td>39</td><td>1.6</td><td>0.45 × 0.25</td><td>34</td><td></td></tr><tr><td>29-Nov-2018</td><td>252.658</td><td>44</td><td>J0519-4546</td><td>J0309-6058</td><td>951</td><td>39</td><td>0.9</td><td>0.46 × 0.37</td><td>36</td><td>29</td></tr><tr><td colspan="11"><strong>Band 7</strong></td></tr><tr><td colspan="11"><strong>[N II] 122</strong></td></tr><tr><td>25-Dec-2018</td><td>305.126</td><td>45</td><td>J0519-4546</td><td>J0309-6058</td><td>500</td><td>50</td><td>0.5</td><td>0.63 × 0.53</td><td>29</td><td>2018.1.00575.S</td></tr><tr><td>07-Nov-2019</td><td>305.13</td><td>46</td><td>J0334-4008</td><td>J0309-6058</td><td>500</td><td>50</td><td>1.2</td><td>0.70 × 0.53</td><td>37</td><td></td></tr><tr><td colspan="11"><strong>Band 8</strong></td></tr><tr><td colspan="11"><strong>[O III] 88</strong></td></tr><tr><td>15-Nov-2016</td><td>423.631</td><td>41</td><td>J0538-4405</td><td>J0253-5441</td><td>918</td><td>11</td><td>0.8</td><td>0.29 × 0.21</td><td>51</td><td></td></tr><tr><td>16-Nov-2016</td><td>423.63</td><td>42</td><td>J0538-4405</td><td>J0253-5441</td><td>918</td><td>34</td><td>0.4</td><td>0.29 × 0.22</td><td>189</td><td>2016.1.01293.S<sup>f</sup></td></tr><tr><td>16-Nov-2016</td><td>423.63</td><td>42</td><td>J0538-4405</td><td>J0253-5441</td><td>918</td><td>34</td><td>0.3</td><td>0.31 × 0.21</td><td>117</td><td></td></tr><tr><td>17-Nov-2016</td><td>423.63</td><td>43</td><td>J0538-4405</td><td>J0303-6211</td><td>918</td><td>34</td><td>0.5</td><td>0.37 × 0.20</td><td>108</td><td></td></tr><tr><td>01-May-2019</td><td>423.651</td><td>41</td><td>J0522-3627</td><td>J0309-6058</td><td>740</td><td>49</td><td>0.9</td><td>0.30 × 0.23</td><td>120</td><td>2018.1.01778.S</td></tr></tbody></table>

**Notes.**

a First local oscillator frequency.

b Maximum baseline.

c On-source integration time.

d Precipitable water vapor at zenith.

e Root-mean-square noise level in continuum image.

f Previously published by Marrone et al. (2018).
<figure><img src="image_5.png" /><figcaption>**Figure 2.** Observed spectra from SPT0311-58 for each of the targeted fine-structure lines. The colored region is the total line emission, while the solid pink, dashed purple, and dotted light blue outline the spectra of SPT0311-58 NW, SW, and E, respectively. Top row: [C II] 158 and [O I] 146. Bottom row: [N II] 122 and [O III] 88. Spectra are obtained by summing the tapered images within the ellipses plotted in Figure 1.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>**Figure 3.** Comparing the observed spectra from SPT0311-58 in each component on the same vertical scale. Top: total emission, SPT0311-58 E, SPT0311-58 W. Bottom: SPT0311-58 NW and SPT0311-58 SW. [C II] 158 is shown in solid red, [O I] 146 in dashed orange, [N II] 122 in dotted green, and [O III] 88 in dashed-dotted blue.</figcaption></figure>

divide SPT0311-58 W into two components: SPT0311-58 NW and SPT0311-58 SW. The moment 0 maps in Figure 1 were created by summing the emission from −600 km s⁻¹ to +1200 km s⁻¹. To separate the components, elliptical apertures were then drawn over the moment 0 maps of SPT0311-58 E and SPT0311-58 SW (shown as white ellipses in Figure 1). Emission within these ellipses was assigned to SPT0311-58 E and SPT0311-58 SW. A third ellipse is shown encompassing all of SPT0311-58 W. Emission within the SPT0311-58 W ellipse but

outside the SPT0311-58 SW ellipse was summed to find the total emission in SPT0311-58 NW. Spilker et al. (2022) used the [C II] 158 and continuum emission to identify kpc-scale clumps in the galaxies; SPT0311-58 NW is associated with their clumps W1–W4, SPT0311-58 SW with clumps W5–W8, and SPT0311-58 E with clumps E1–E4. The lensing configuration of this system results in a counterimage (visible at the center of each panel of Figure 1) of clumps W1–W4. These clumps and their counterimage are all included within the region defining the NW
<table><caption>**Table 2**
SPT0311-58 Flux Densities and Luminosities<sup>a</sup></caption><thead><tr><th>Wavelength/Line</th><th>NW</th><th>SW</th><th>E</th></tr></thead><tbody><tr><td>Continuum Flux Density (mJy)<sup>b</sup></td><td></td><td></td><td></td></tr><tr><td>158 µm</td><td>15.7 ± 1.6</td><td>10.4 ± 1.1</td><td>2.8 ± 0.3</td></tr><tr><td>146 µm</td><td>12.1 ± 1.2</td><td>8.2 ± 0.8</td><td>1.8 ± 0.2</td></tr><tr><td>122 µm</td><td>19.4 ± 2.0</td><td>10.0 ± 1.0</td><td>2.7 ± 0.3</td></tr><tr><td>88 µm</td><td>24.0 ± 2.5</td><td>16.8 ± 1.7</td><td>5.0 ± 0.5</td></tr><tr><td>FIR Luminosity (10<sup>12</sup> L<sub>☉</sub>)</td><td></td><td></td><td></td></tr><tr><td>L<sub>FIR</sub><sup>c</sup></td><td>25.2 ± 6.5</td><td>17.6 ± 4.5</td><td>3.5 ± 0.9</td></tr><tr><td>Line Luminosity (10<sup>8</sup> L<sub>☉</sub>)</td><td></td><td></td><td></td></tr><tr><td>[C II] 158 µm</td><td>317.9 ± 34.1</td><td>188.4 ± 20.4</td><td>126.3 ± 14.0</td></tr><tr><td>[O I] 146 µm</td><td>42.9 ± 4.9</td><td>21.6 ± 2.6</td><td>20.1 ± 2.4</td></tr><tr><td>[N II] 122 µm</td><td>37.2 ± 5.7</td><td>20.5 ± 3.4</td><td>10.5 ± 2.2</td></tr><tr><td>[O III] 88 µm</td><td>35.0 ± 7.2</td><td>109.5 ± 13.5</td><td>103.7 ± 12.6</td></tr></tbody></table>

**Notes.**

<sup>a</sup> Observed values (not corrected for lensing). E has magnification $\mu = 1.3$, W has $\mu = 2.2$, and the total system has $\mu = 2.0$ (Marrone et al. 2018).

<sup>b</sup> The aperture used to obtain the continuum fluxes in SPT0311-58 E is slightly larger than the aperture used for the line luminosities to fully encompass the 122 µm emission.

<sup>c</sup> $L_{FIR}$ for the three components of SPT0311-58. $L_{FIR}$ for SPT0311-58 E is taken from Marrone et al. (2018). For SPT0311-58 NW and SW, we take $L_{FIR}$ for SPT0311-58 W from Marrone et al. (2018) and scale it based on the fraction of 88 µm emission from SPT0311-58 NW and SW compared to the total 88 µm emission in SPT0311-58 W.

subcomponent. In addition to the total spectra, Figure 2 outlines the individual spectra of the three components for each line, while Figure 3 shows all four lines overlaid on the same vertical scale for each component.

Table 2 lists the observed continuum flux densities and line luminosities for the three components of SPT0311-58. The far-infrared luminosity ($L_{FIR}$) is also listed for each component. For SPT0311-58 E, $L_{FIR}$ was determined by Marrone et al. (2018) using SED fitting that included resolved ALMA and unresolved Herschel photometry. Marrone et al. (2018) used the ALMA continuum observations to divide the total flux density from Herschel into SPT0311-58 E and W, and we adopt those values here. For SPT0311-58 NW and SW, we take the observed $L_{FIR}$ for SPT0311-58 W from Marrone et al. (2018) and scale it based on the 88 µm continuum emission: $L_{FIR,NW} = L_{FIR,W} \times f_{88,NW}/f_{88,W}$ and $L_{FIR,SW} = L_{FIR,W} \times f_{88,SW}/f_{88,W}$. None of these values have been corrected for magnification due to gravitational lensing. Throughout this paper, we work with ratios of lines and/or continuum, so effects from magnification due to gravitational lensing within each component should cancel.

## 3. ISM Properties

In this section, we explore the properties of the multiphase ISM throughout SPT0311-58 using line and continuum ratios. In Section 3.1, we explore the metallicity and ionization state of the ISM using [O III] 88 line ratios and continuum color. In Section 3.2, we look at the density of neutral gas using the [C II] 158/[O I] 145 line ratios.

The line ratios observed across these galaxies can be usefully contextualized by considering other galaxies for which there are measurements of (subsets of) the same lines. Because Marrone et al. (2018) discussed the possibility that the high

[O III] 88/[C II] 158 luminosity ratio in SPT0311-58 E could result from lower-metallicity gas in the ISM, we include the Dwarf Galaxy Survey (DGS; Madden et al. 2013; Cormier et al. 2015; Rémy-Ruyer et al. 2015), which includes nearby galaxies with a range of metallicities down to $Z = 0.02Z_{☉}$ as one comparison sample, even though these nearby galaxies are less massive than our objects. SPT0311-58 W is dusty and luminous in the FIR, so we also compare to (Ultra-)Luminous Infrared Galaxies (ULIRGs) from the Great Observatories All-sky LIRG Survey (GOALS; Israel et al. 2015; Lutz et al. 2016; Lu et al. 2017a; Díaz-Santos et al. 2017). A third relevant sample is the Survey with Herschel of the Interstellar medium in Nearby Infrared Galaxies (SHINING; Herrera-Camus et al. 2018), which includes normal star-forming galaxies, active galactic nucleus (AGN) host galaxies, and LIRGs. Finally, we compare to a selection of $z > 4$ sources in the literature (Table 3) with continuum detections and at least two of the lines explored in this work. The galaxies in this high-$z$ reference sample are comprised of massive, dusty, infrared-luminous galaxies, with $L_{FIR} > 10^{12} L_{☉}$ (Wagg et al. 2012; Novak et al. 2019; Shao et al. 2019; Reuter et al. 2020; Dye et al. 2022; Litke et al. 2022; Meyer et al. 2022). Table 3 also lists which galaxies are dusty star-forming galaxies (DSFGs) and which host quasars (QSOs).

### 3.1. Ionization Parameter and Metallicity

A critical question for understanding galaxy formation in the EoR is how and when the ISM becomes enriched by metals. One method for estimating the metallicity of the gas at high $z$ is to use the [O III] 88/[N II] 122 ratio. Pereira-Santaella et al. (2017) found, using photoionization models, that this ratio varies significantly with metallicity, but it is highly dependent on the ionization parameter, $U$. This strong dependence results from the significant difference in the ionization energies needed to create [O III] and [N II] (35.1 eV and 14.5 eV, respectively), making the [O III] abundance much more sensitive to the ionization parameter. Accordingly, other authors (e.g., Fernández-Ontiveros et al. 2016) have suggested using the same [O III] 88/[N II] 122 ratio as a measure of ionization instead.

To use the [O III] 88/[N II] 122 ratio to constrain the average metallicity in a galaxy, we require independent information about the average ionization parameter. One method is to use the IR color to constrain the ionization state. Abel et al. (2009) found, using the photoionization code CLOUDY, that $C(60/100)$ (the $f_i(60\mu m)/f_i(100\mu m)$ continuum flux density ratio) is correlated with the ionization parameter, where warmer IR colors (higher ratios) indicate higher ionizations. Rigopoulou et al. (2018) found similar trends using $C(88/122)$. This connection is understood to result from the additional heating of the surrounding gas and dust when the radiation field is larger—this heating increases the dust temperature and changes the IR color toward increased short-wavelength emission (Rigopoulou et al. 2018).

We choose to use the 88 and 158 µm continuum measurements to calculate the IR color because these are our deepest, highest-resolution measurements. To be able to compare against other literature sources (for example, Rémy-Ruyer et al. 2015 report 70 and 100 µm fluxes for the DGS sample), we convert $C(88/158)$ to $C(70/100)$ by creating a set of modified blackbodies with dust temperatures ranging from 20 to 80 K, the range observed in the SPT survey (Reuter et al. 2020). Following Reuter et al. (2020), we fix the slope of the
<table><caption>**Table 3**
High-z Reference Sample</caption><thead><tr><th>Source</th><th>Redshift</th><th>Lines</th><th>Type</th><th>References</th></tr></thead><tbody><tr><td>SPT0418-47</td><td>4.22</td><td>[C II] 158</td><td>[N II] 122</td><td>DSFG</td><td>1, 2</td></tr><tr><td>ID141</td><td>4.24</td><td>[C II] 158</td><td></td><td>DSFG</td><td>3, 4</td></tr><tr><td>BR1202-0725</td><td>4.70</td><td>[C II] 158</td><td>[N II] 122</td><td>QSO</td><td>5, 6, 7</td></tr><tr><td>BR1202-0725</td><td>4.70</td><td>[C II] 158</td><td>[N II] 122</td><td>DSFG</td><td>5, 6, 7</td></tr><tr><td>SPT0346-52</td><td>5.66</td><td>[C II] 158</td><td>[O I] 146</td><td>DSFG</td><td>1, 8</td></tr><tr><td>J2310+1855</td><td>6.00</td><td>[C II] 158</td><td>[O I] 146</td><td>QSO</td><td>9, 10, 11</td></tr><tr><td>J1148+5251</td><td>6.42</td><td>[C II] 158</td><td>[O I] 146</td><td>QSO</td><td>12, 13, 14</td></tr><tr><td>J1342+0928</td><td>7.54</td><td>[C II] 158</td><td>[O I] 146</td><td>QSO</td><td>15, 16</td></tr></tbody></table>

**References.** (1) Reuter et al. 2020; (2) De Breuck et al. 2019; (3) Dye et al. 2022; (4) Cox et al. 2011; (5) Lee et al. 2021; (6) Lu et al. 2017b; (7) Wagg et al. 2012; (8) Litke et al. 2022; (9) Li et al. 2020; (10) Hashimoto et al. 2019b; (11) Shao et al. 2019; (12) Meyer et al. 2022; (13) Riechers et al. 2009; (14) Robson et al. 2004; (15) Novak et al. 2019; (16) Venemans et al. 2017.

Rayleigh–Jeans tail to $\beta=2$ and use the empirical relation between $\lambda_0$ and $T_{\text{dust}}$ from Spilker et al. (2016), where $\lambda_0$ is the wavelength where the optical depth reaches unity. We calculate $C(70/100)$ and $C(88/158)$, then fit a quadratic line to the output. The fit is given by

$$C(70/100) = 0.44 \times (C(88/158))^2 - 0.70 \times (C(88/158)) + 0.67. \quad (1)$$

The continuum colors obtained from this fit were within 10% of the known continuum colors obtained from the modified blackbody distributions. A quadratic relation was used because it fit the data more closely than a linear relation. Similarly, we convert the $C(88/122)$ colors from the models in Figure 4 of Rigopoulou et al. (2018) to $C(70/100)$. We then use these converted colors and Figure 4 of Rigopoulou et al. (2018) to calculate the ionization parameter, $U$. We find $C(70/100) = 0.81 \pm 0.41$ and $\log U = -2.82 \pm 0.39$ in SPT0311-58 E, $C(70/100) = 0.62 \pm 0.27$ and $\log U = -3.07 \pm 0.35$ in SPT0311-58 NW, and $C(70/100) = 0.69 \pm 0.32$ and $\log U = -2.98 \pm 0.37$ in SPT0311-58 SW. If SPT0311-58 is considered as a single system, the continuum ratio and ionization parameter are $C(70/100) = 0.66 \pm 0.26$ and $\log U = -3.02 \pm 0.32$. The two high-z sources with the highest ionization parameters are both quasar host galaxies (J2310+1855 and J1342+0928; Venemans et al. 2017; Hashimoto et al. 2019b; Novak et al. 2019; Shao et al. 2019; Li et al. 2020). Marrone et al. (2018) argued against the presence of a strong AGN, due to the absence of a region of strongly peaked IR emission, and the lower ionization parameter observed here is consistent with that picture.

Figure 4 shows the metallicity constraints for the components of SPT0311-58. In the upper panel, we show the CLOUDY models for the [O III] 88/[N II] 122 ratio from Table A.1 of Pereira-Santaella et al. (2017), with our observed line ratios overplotted for each component. We use their starburst photoionization models, which assume continuous star formation and a Kroupa initial mass function. They also varied the gas-to-dust mass ratio as a function of metallicity. The five model traces, each of which has a distinct value of $\log U$, demonstrate clearly the importance of the ionization parameter in determining the line ratio. To fold in our constraints on $U$ from the continuum colors, in the lower panel we transform the plot to $\log U$ versus $Z$, with the model now plotted as lines of constant [O III] 88/[N II] 122 ratio, interpolated from the grid

<table><caption>**Table 4**
Derived Parameters</caption><thead><tr><th>Component</th><th>log U</th><th>Z/Z<sub>☉</sub></th></tr></thead><tbody><tr><td>SPT0311-58 NW</td><td>-3.1 ± 0.4</td><td>1.4 ± 1.0</td></tr><tr><td>SPT0311-58 SW</td><td>-3.0 ± 0.4</td><td>0.9 ± 0.4</td></tr><tr><td>SPT0311-58 E</td><td>-2.8 ± 0.4</td><td>0.8 ± 0.4</td></tr><tr><td>SPT0311-58</td><td>-3.0 ± 0.3</td><td>1.0 ± 0.4</td></tr></tbody></table>

of values presented in Pereira-Santaella et al. (2017). Their model also includes gridding in density, but this amounts to a 20% effect on line ratio across three decades of density variation at fixed $Z$, so we average over the densities in the grid. In this plot, our observed line ratios are similarly curved in the log $U$ versus $Z$ plane, and the observed line ratios allow a very wide range of metallicity. When those confidence regions are restricted to the range of log $U$ allowed by the continuum colors, we obtain the metallicity constraints indicated in the dark shaded regions. Despite line ratios that vary by more than a decade, the metallicities inferred this way are very similar in all components. The ionization parameters and metallicities for each component of SPT0311-58 are listed in Table 4. SPT0311-58 E ($Z/Z_{☉} = 0.8 \pm 0.4$) and SPT0311-58 SW ($Z/Z_{☉} = 0.9 \pm 0.4$) may have slightly lower metallicities than SPT0311-58 NW ($Z/Z_{☉} = 1.4 \pm 1.0$), but the uncertainties overlap heavily.

The high metallicity implied by our observations is perhaps surprising for galaxies at such an early time in cosmic history. However, similar results have been found for other galaxies in our high-z reference sample. The galaxies for which we have metallicity constraints (SPT0418-47, ID141, SPT0346-52, J2310+1855, J1148+5251, and J1342+0928) from the [O III] 88/[N II] 122 ratio, CLOUDY modeling, or gas-to-dust mass ratios, show solar or supersolar metallicities (De Breuck et al. 2019; Novak et al. 2019; Shao et al. 2019; Li et al. 2020; Dye et al. 2022; Litke et al. 2022). Previous studies have argued that there must have been major episodes of galaxy evolution and chemical enrichment within the first 800 Myr after the Big Bang to account for these high metallicities (Kurk et al. 2007; Bouwens et al. 2014; De Rosa et al. 2014). In addition, all of the galaxies in the high-z reference sample show some evidence for interactions with other galaxies, whether through direct detection of a companion or through kinematic analysis (Riechers et al. 2009; Feruglio et al. 2018; Bañados et al. 2019; Litke et al. 2019; Dye et al. 2022; Peng et al. 2023). These observations are consistent with recent simulations by Lower
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Ionization parameter, metallicity, and [O III] 88/[N II] 122. Top: log O III 88/N II 122 vs. Z/Z⊙. The orange and yellow shaded regions represent the CLOUDY models from Pereira-Santaella et al. (2017) for different values of U and $1 \le \log n_{\text{cm}^{-3}} \le 4$. The horizontal shaded regions represent the values and $1\sigma$ errors for the different components of SPT0311. Bottom: log U vs. Z/Z⊙. The contours represent log O III 88/N II 122 ratios as a function of U and Z as modeled by Pereira-Santaella et al. (2017). For each data point, the IR color is used to calculate U (Rigopoulou et al. 2018), which is combined with the observed [O III] 88/[N II] 122 ratio to determine Z (Pereira-Santaella et al. 2017). Pink stars represent SPT0311-58 NW, purple stars SPT0311-58 SW, light blue stars SPT0311-58 E, and turquoise stars represent SPT0311-58 as a whole. The dark shaded regions represent the $1\sigma$ uncertainties in ionization parameter (IR color) and [O III] 88/[N II] 122 ratio. The light shaded regions indicate the metallicities allowed by the observed [O III] 88/[N II] 122 ratios. Gray dots are local dwarf galaxies (Madden et al. 2013; Cormier et al. 2015; Rémy-Ruyer et al. 2015), dark green dots are local star-forming galaxies (Herrera-Camus et al. 2018), and navy blue dots are local (U) LIRGs (Lutz et al. 2016; Lu et al. 2017a; Díaz-Santos et al. 2017). Brown circles are $z > 4$ galaxies from the literature (see Table 3 for references).</figcaption></figure>

et al. (2022), who found that these massive galaxies are built up through many mergers with smaller galaxies, increasing their star formation rates and resulting in chemically evolved galaxies by $z \sim 10$.

Another line ratio found to correlate with metallicity is [O III] 88/[C II] 158 (Cormier et al. 2015; Inoue et al. 2016). Based on its larger values of [O III] 88/[C II] 158 and the [C II] 158 line to continuum ratio, Marrone et al. (2018) discussed the possibility that SPT0311-58 E has a more primordial ISM than SPT0311-58 W. However, we find from the [O III] 88/[N II] 122 line ratio and continuum color that SPT0311-58 E is quite metal-rich, with approximately solar metallicity. Larger values of [O III] 88/[C II] 158 were found in high-z galaxies, as compared to local galaxies, by Harikane et al. (2020) and Hashimoto et al. (2019a). They note that, in addition to metallicity, the significant ionization energy difference between these two lines means that the ionization parameter can strongly affect their luminosity ratio, just as in the case of [O III] 88/[N II] 122. Resolving this ambiguity would be possible with the addition of a higher ionization nitrogen line, [N III] 57. In particular, as a ratio of the same element, [N III] 57/[N II] 122 would constrain the ionization parameter independent of possible variations between nitrogen and other elemental abundances (Nagao et al. 2011; Pereira-Santaella et al. 2017; Herrera-Camus et al. 2018), while [O III] 88/[N III] 57 would constrain the metallicity with minimal dependence on the ionization parameter. However, observations of the [N III] 57 line are only marginally possible for this source, owing to atmospheric opacity.

## 3.2. Density Constraints in Neutral Gas

While [C II] 158 can originate from either ionized or neutral gas, ~85% of the emission is produced in neutral gas, particularly in PDRs (e.g., Pavesi et al. 2018; Zhang et al. 2018; De Breuck et al. 2019; Li et al. 2020; Litke et al. 2022). Because [O I] 146 has a higher critical density than [C II] 158 (~$10^4 \text{ cm}^{-3}$ versus ~50 cm$^{-3}$; Stacey 2011) and a higher excitation temperature needed to populate the upper level (329 K versus 91 K; Stacey 2011), [O I] 146 traces warmer, denser gas than [C II] 158. We can therefore use the [C II] 158/[O I] 146 ratio to examine the relative contribution of warm, dense, neutral gas to the ISM. Figure 5 shows [C II] 158/[O I] 146 as versus [O III] 88/[O I] 146. We also plot [C II] 158/[O I] 146 from the PDR models of Meijerink & Spaans (2005) for $\log G_0 = 3$ ($\log U \approx -3$; Abel et al. 2009; Litke et al. 2022) at $\log n_{\text{H}}/\text{cm}^{-3} = 3$ and $\log n_{\text{H}}/\text{cm}^{-3} = 5.5$. We chose the $\log G_0 = 3$ models because they are more consistent with the ionization parameters discussed in Section 3.1 than $\log G_0 = 10^5$ ($\log U \approx -1$). These models also assume solar abundances. Lower ratios indicate a higher average neutral gas density, which may indicate more gas in dense PDR regions (Meijerink & Spaans 2005; De Breuck et al. 2019).

While SPT0311-58 E has a slightly lower [C II] 158/[O I] 146 ratio than SPT0311-58 NW and SW, all components of SPT0311-58 have [C II] 158/[O I] 146 ratios comparable to other high-z sources with continuum detections. The ratios in SPT0311-58 and other high-z sources are closer to the $\log n_{\text{H}}^{-3}/\text{cm}^{-3} = 5.5$ than the $\log n_{\text{H}}^{-3}/\text{cm}^{-3} = 3$ model ratio, indicating a higher neutral gas density and/or a larger contribution from PDRs. The density constraint is consistent with radiative
<figure><img src="image_8.png" /><figcaption>**Figure 5.** *L*<sub>C 1158</sub>/<i>L</i><sub>O 146</sub> vs. *L*<sub>O 88</sub>/<i>L</i><sub>O 146</sub>. The pink star represents SPT0311-58 NW, purple SPT0311-58 SW, light blue SPT0311-58 E, and turquoise represents SPT0311-58 as a whole. Gray dots are local dwarf galaxies (Madden et al. 2013; Cormier et al. 2015) and dark green dots are local star-forming galaxies (Herrera-Camus et al. 2018). Brown circles are *z* > 4 galaxies from the literature (see Table 3 for references).</figcaption></figure>

transfer modeling of the molecular gas in SPT0311-58 by
Jarugula et al. (2021) and Strandet et al. (2017). This high
density is in contrast to the local dwarf galaxies, which are
consistent with smaller PDR contributions or lower neutral gas
densities (Cormier et al. 2019).

Lee et al. (2021) found an inverse relation between $L_{\text{FIR}}$ and
$[\text{C II}]~158/[\text{O I}]~146$, indicating that higher-density gas is
associated with the high star formation rates observed in high-$z$
dusty galaxies. Both galaxies in SPT0311-58 have high star
formation rates, forming stars at $2900 \pm 1800~M_{\odot}~\text{yr}^{-1}$ in
SPT0311-58 W and $540 \pm 175~M_{\odot}~\text{yr}^{-1}$ in SPT0311-58 E,
similarly to other high-$z$ dusty galaxies (Cooray et al. 2014; Decarli
et al. 2017; Marrone et al. 2018). Dense neutral gas has also been
associated with higher densities in the ionized gas phase (De
Breuck et al. 2019; Lee et al. 2021). Lee et al. (2021) argue that
this may be expected because H II regions (ionized gas) are
physically connected to PDRs (neutral gas). The low $[\text{C II}]~158/
[\text{O I}]~146$ ratios are consistent with the high star formation rates and
indicate high gas densities in regions of active star formation.

As seen in Figure 5, SPT0311-58 and the other high-z
sources with [O III] 88 and continuum detections all have lower
[C II] 158/[O I] 146 and [O III] 88/[O I] 146 ratios than nearby
dwarf galaxies (Madden et al. 2013; Cormier et al. 2015;
Venemans et al. 2017; Hashimoto et al. 2019b; De Breuck et al.
2019; Novak et al. 2019; Shao et al. 2019; Li et al. 2020;
Reuter et al. 2020). Cormier et al. (2019) and De Breuck et al.
(2019) argued that lower [O III] 88/[O I] 146 ratios indicated a
decreased volume filling factor of ionized gas. This could
indicate that more of the gas in these dusty galaxies and quasar-
host galaxies is in neutral regions like PDRs than in the ionized
phase, resulting in higher inferred average densities.

4. Summary and Conclusions

We have explored the ISM in SPT0311-58 using ALMA
observations of [C II] 158, [O I] 146, [N II] 122, [O III] 88, and
the underlying dust continuum. Across SPT0311-58, we found
widely varying line ratios and divided the galaxies into three
components to consider the conditions giving rise to these
variations. We then determined the metallicities using [O III] 88/
[N II] 122 and the models of Pereira-Santaella et al. (2017).
Despite the significant line ratio changes, we see near-solar
metallicity across all components, with no strong evidence for
metal-poor gas even though this system of galaxies exists just
800 Myr after the Big Bang. From the observed [C II] 158/[O I]
146 ratio and PDR models from Meijerink & Spaans (2005), we
found high average neutral gas densities throughout SPT0311-
58, as expected from the high star formation rates in this system.

The formation of early galaxies is a chaotic process, as
suggested by the heterogeneity of the line and continuum
emission in these galaxies. While the line ratios available to us in
the current data do not translate to clear differences in physical
conditions, further spatially resolved studies of FIR line emission
in very early galaxies can provide an important path to
reconstructing the assembly processes for galaxies in the EoR.

The SPT is supported by the U.S. National Science
Foundation (NSF) through grant OPP-1852617. K.C.L., D.P.
M. J.D.V., K.P., and S.J. acknowledge support from the US
NSF under grants AST-1715213 and AST-1716127. K.C.L and
S.J. acknowledge support from the US NSF NRAO under
grants SOSPA4-007 and SOSPA5-001, respectively. J.D.V.
acknowledges support from an A. P. Sloan Foundation
Fellowship. D.N. acknowledges support from the US NSF
under grant 1715206 and Space Telescope Science Institute
under grant AR-15043.0001. M.A. acknowledges partial
support from FONDECYT grant 1211951, ANID+PCI
+INSTITUTO MAX PLANCK DE ASTRONOMIA MPG
190030, ANID+PCI+REDES 190194 and ANID BASAL
project FB210003. K.A.P. is supported by the Center for
AstroPhysical Surveys at the National Center for Super-
computing Applications as an Illinois Survey Science Graduate
Fellow. The National Radio Astronomy Observatory is a
facility of the National Science Foundation operated under
cooperative agreement by Associated Universities, Inc. This
paper makes use of the following ALMA data: ADS/JAO.
ALMA #2016.1.01293.S, #2017.1.01423.S, #2018.1.00575.
S, and #2018.1.01778.S. ALMA is a partnership of 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 ESO, AUI/NRAO and NAOJ. This research has
made use of NASA's Astrophysics Data System. This research
also uses the Cosmology Calculator by Wright (2006).

*Software:* CASA (v5.4.0; McMullin et al. 2007; Petry & CASA Development Team 2012), Astropy (Astropy Collaboration et al. 2013, 2018), matplotlib (Hunter 2007).

ORCID iDs

Katrina C. Litke https://orcid.org/0000-0002-4208-3532
Daniel P. Marrone https://orcid.org/0000-0002-2367-1080
Manuel Aravena https://orcid.org/0000-0002-6290-3198
Melanie Archipley https://orcid.org/0000-0002-0517-9842
Matthieu Béthermin https://orcid.org/0000-0002-3915-2015

James Burgoyne https://orcid.org/0000-0001-8706-1268

Anthony H. Gonzalez https://orcid.org/0000-0002-0933-8601

Thomas R. Greve https://orcid.org/0000-0002-2554-1837

Christopher C. Hayward https://orcid.org/0000-0003-4073-3236

Matthew A. Malkan https://orcid.org/0000-0001-6919-1237

Kedar A. Phadke https://orcid.org/0000-0001-7946-557X

Cassie A. Reuter https://orcid.org/0000-0001-7477-1586

Justin S. Spilker https://orcid.org/0000-0003-3256-5615

Antony A. Stark https://orcid.org/0000-0002-2718-9996

Nikolaus Sulzenauer https://orcid.org/0000-0002-3187-1648

Joaquin D. Vieira https://orcid.org/0000-0001-7192-3871

David Vizgan https://orcid.org/0000-0001-7610-5544

Axel Weiß https://orcid.org/0000-0003-4678-3939

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