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1. The Rest-frame Submillimeter Spectrum of High-redshift, Dusty, Star-forming Galaxies from the SPT-SZ Survey

   https://doi.org/10.3847/1538-4357/acaf51  

   Reuter, C. ; Spilker, J. S. ; Vieira, J. D. ; Marrone, D. P. ; Weiss, A. ; Aravena, M. ; Archipley, M. A. ; Chapman, S. C. ; Gonzalez, A. ; Greve, T. R. ; et al ( May 2023 , The Astrophysical Journal)

   We present the average rest-frame spectrum of the final catalog of dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope's SPT-SZ survey and measured with Band 3 of the Atacama Large Millimeter/submillimeter Array. This work builds on the previous average rest-frame spectrum, given in Spilker et al. (2014) for the first 22 sources, and is comprised of a total of 78 sources, normalized by their respective apparent dust masses. The spectrum spans 1.9 <z< 6.9 and covers rest-frame frequencies of 240–800 GHz. Combining this data with low-JCO observations from the Australia Telescope Compact Array, we detect multiple bright line features from¹²CO, [Ci], and H₂O, as well as fainter molecular transitions from¹³CO, HCN, HCO⁺, HNC, CN, H₂O⁺, and CH. We use these detections, along with limits from other molecules, to characterize the typical properties of the interstellar medium (ISM) for these high-redshift DSFGs. We are able to divide the large sample into subsets in order to explore how the average spectrum changes with various galaxy properties, such as effective dust temperature. We find that systems with hotter dust temperatures exhibit differences in the bright¹²CO emission lines, and contain either warmer and more excited dense gas tracers or larger densemore »gas reservoirs. These observations will serve as a reference point to studies of the ISM in distant luminous DSFGs (L_IR> 10¹²L_⊙), and will inform studies of chemical evolution before the peak epoch of star formation atz= 2–3.

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2. ALMA multiline survey of the ISM in two quasar host–companion galaxy pairs at z > 6

   https://doi.org/10.1051/0004-6361/202039696  

   Pensabene, A. ; Decarli, R. ; Bañados, E. ; Venemans, B. ; Walter, F. ; Bertoldi, F. ; Fan, X. ; Farina, E. P. ; Li, J. ; Mazzucchelli, C. ; et al ( August 2021 , Astronomy & Astrophysics)

   We present a multiline survey of the interstellar medium (ISM) in two z  > 6 quasar host galaxies, PJ231−20 ( z  = 6.59) and PJ308−21 ( z  = 6.23), and their two companion galaxies. Observations were carried out using the Atacama Large (sub-)Millimeter Array (ALMA). We targeted 11 transitions including atomic fine-structure lines (FSLs) and molecular lines: [NII] 205 μm , [CI] 369 μm , CO ( J up  = 7, 10, 15, 16), H 2 O 3 12  − 2 21 , 3 21  − 3 12 , 3 03  − 2 12 , and the OH 163 μm doublet. The underlying far-infrared (FIR) continuum samples the Rayleigh-Jeans tail of the respective dust emission. By combining this information with our earlier ALMA [CII] 158 μm observations, we explored the effects of star formation and black hole feedback on the ISM of the galaxies using the CLOUDY radiative transfer models. We estimated dust masses, spectral indexes, IR luminosities, and star-formation rates from the FIR continuum. The analysis of the FSLs indicates that the [CII] 158 μm and [CI] 369 μm emission arises predominantly from the neutral medium in photodissociation regions (PDRs). We find that line deficits agree with those of local luminous IR galaxies. The CO spectral line energy distributions (SLEDs) reveal significant high- J COmore »excitation in both quasar hosts. Our CO SLED modeling of the quasar PJ231−20 shows that PDRs dominate the molecular mass and CO luminosities for J up  ≤ 7, while the J up  ≥ 10 CO emission is likely driven by X-ray dissociation regions produced by the active galactic nucleus (AGN) at the very center of the quasar host. The J up  > 10 lines are undetected in the other galaxies in our study. The H 2 O 3 21  − 3 12 line detection in the same quasar places this object on the L H 2 O  −  L TIR relation found for low- z sources, thus suggesting that this water vapor transition is predominantly excited by IR pumping. Models of the H 2 O SLED and of the H 2 O-to-OH 163 μm ratio point to PDR contributions with high volume and column density ( n H  ∼ 0.8 × 10 5 cm −3 , N H  = 10 24 cm −2 ) in an intense radiation field. Our analysis suggests a less highly excited medium in the companion galaxies. However, the current data do not allow us to definitively rule out an AGN in these sources, as suggested by previous studies of the same objects. This work demonstrates the power of multiline studies of FIR diagnostics in order to dissect the physical conditions in the first massive galaxies emerging from cosmic dawn.« less
3. The Role of Neutral Hydrogen in Setting the Abundances of Molecular Species in the Milky Way’s Diffuse Interstellar Medium. I. Observational Constraints from ALMA and NOEMA

   https://doi.org/10.3847/1538-4357/ac5035  

   Rybarczyk, Daniel R. ; Stanimirović, Snežana ; Gong, Munan ; Babler, Brian ; Murray, Claire E. ; Gerin, Maryvonne ; Winters, Jan Martin ; Luo, Gan ; Dame, T. M. ; Steffes, Lucille ( March 2022 , The Astrophysical Journal)

   We have complemented existing observations of Hiabsorption with new observations of HCO⁺, C₂H, HCN, and HNC absorption from the Atacama Large Millimeter/submillimeter Array and the Northern Extended Millimeter Array in the directions of 20 background radio continuum sources with 4° ≤ ∣b∣ ≤ 81° to constrain the atomic gas conditions that are suitable for the formation of diffuse molecular gas. We find that these molecular species form along sightlines whereA_V≳ 0.25, consistent with the threshold for the Hi-to-H₂transition at solar metallicity. Moreover, we find that molecular gas is associated only with structures that have an Hioptical depth >0.1, a spin temperature <80 K, and a turbulent Mach number ≳ 2. We also identify a broad, faint component to the HCO⁺absorption in a majority of sightlines. Compared to the velocities where strong, narrow HCO⁺absorption is observed, the Hiat these velocities has a lower cold neutral medium fraction and negligible CO emission. The relative column densities and linewidths of the different molecular species observed here are similar to those observed in previous experiments over a range of Galactic latitudes, suggesting that gas in the solar neighborhood and gas in the Galactic plane are chemically similar. For a select sample of previouslymore »observed sightlines, we show that the absorption line profiles of HCO⁺, HCN, HNC, and C₂H are stable over periods of ∼3 yr and ∼25 yr, likely indicating that molecular gas structures in these directions are at least ≳100 au in size.

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4. PHANGS–JWST First Results: Tracing the Diffuse Interstellar Medium with JWST Imaging of Polycyclic Aromatic Hydrocarbon Emission in Nearby Galaxies

   https://doi.org/10.3847/2041-8213/aca972  

   Sandstrom, Karin M. ; Koch, Eric W. ; Leroy, Adam K. ; Rosolowsky, Erik ; Emsellem, Eric ; Smith, Rowan J. ; Egorov, Oleg V. ; Williams, Thomas G. ; Larson, Kirsten L. ; Lee, Janice C. ; et al ( February 2023 , The Astrophysical Journal Letters)

   JWST observations of polycyclic aromatic hydrocarbon (PAH) emission provide some of the deepest and highest resolution views of the cold interstellar medium (ISM) in nearby galaxies. If PAHs are well mixed with the atomic and molecular gas and illuminated by the average diffuse interstellar radiation field, PAH emission may provide an approximately linear, high-resolution, high-sensitivity tracer of diffuse gas surface density. We present a pilot study that explores using PAH emission in this way based on Mid-Infrared Instrument observations of IC 5332, NGC 628, NGC 1365, and NGC 7496 from the Physics at High Angular resolution in Nearby GalaxieS-JWST Treasury. Using scaling relationships calibrated in Leroy et al., scaled F1130W provides 10–40 pc resolution and 3σsensitivity of Σ_gas∼ 2M_⊙pc⁻². We characterize the surface densities of structures seen at <7M_⊙pc⁻²in our targets, where we expect the gas to be Hi-dominated. We highlight the existence of filaments, interarm emission, and holes in the diffuse ISM at these low surface densities. Below ∼10M_⊙pc⁻²for NGC 628, NGC 1365, and NGC 7496 the gas distribution shows a “Swiss cheese”-like topology due to holes and bubbles pervading the relatively smooth distribution of the diffuse ISM. Comparing to recent galaxy simulations, we observe similar topology formore »the low-surface-density gas, though with notable variations between simulations with different setups and resolution. Such a comparison of high-resolution, low-surface-density gas with simulations is not possible with existing atomic and molecular gas maps, highlighting the unique power of JWST maps of PAH emission.

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5. A Massive, Dusty, Hi Absorption–Selected Galaxy at z ≈ 2.46 Identified in a CO Emission Survey

   https://doi.org/10.3847/1538-4357/ac7b2c  

   Kaur, B. ; Kanekar, N. ; Revalski, M. ; Rafelski, M. ; Neeleman, M. ; Prochaska, J. X. ; Walter, F. ( July 2022 , The Astrophysical Journal)

   We report a NOrthern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter/submillimeter Array search for redshifted CO emission from the galaxies associated with seven high-metallicity ([M/H] ≥ −1.03) damped Lyαabsorbers (DLAs) atz≈ 1.64–2.51. Our observations yielded one new detection of CO(3–2) emission from a galaxy atz= 2.4604 using NOEMA, associated with thez= 2.4628 DLA toward QSO B0201+365. Including previous searches, our search results in detection rates of CO emission of$\approx {56}_{-24}^{+38}$% and$\approx {11}_{-9}^{+26}$%, respectively, in the fields of DLAs with [M/H] > −0.3 and [M/H] < −0.3. Further, the Hi–selected galaxies associated with five DLAs with [M/H] > −0.3 all have high molecular gas masses, ≳5 × 10¹⁰M_⊙. This indicates that the highest-metallicity DLAs atz≈ 2 are associated with the most massive galaxies. The newly identifiedz≈ 2.4604 Hi–selected galaxy, DLA0201+365g, has an impact parameter of ≈7 kpc to the QSO sightline, and an implied molecular gas mass of (5.04 ± 0.78) × 10¹⁰× (α_CO/4.36) × (r₃₁/0.55)M_⊙. Archival Hubble Space Telescope Wide Field and Planetary Camera 2 imaging covering the rest-frame near-ultraviolet (NUV) and far-ultraviolet (FUV) emission from this galaxy yield nondetections of rest-frame NUV and FUV emission, and a 5σupper limit of 2.3M_⊙yr⁻¹on the unobscuredmore »star formation rate (SFR). The low NUV-based SFR estimate, despite the very high molecular gas mass, indicates that DLA0201+365g either is a very dusty galaxy, or has a molecular gas depletion time that is around 2 orders of magnitude larger than that of star-forming galaxies at similar redshifts.

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