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1. Turbulence in the Local Interstellar Medium and the IBEX Ribbon

   https://doi.org/10.3847/1538-4357/ab594d  

   Zirnstein, E. J.; Giacalone, J.; Kumar, R.; McComas, D. J.; Dayeh, M. A.; Heerikhuisen, J. (January 2020, The Astrophysical Journal)

   null (Ed.)
2. Unveiling polarized emission from interstellar dust of the Large Magellanic Cloud with Planck

   https://doi.org/10.1093/mnras/stac3164  

   Alina, D.; Bernard, J-Ph; Yuen, K. H.; Lazarian, A.; Hughes, A.; Iskakova, M.; Akimkhan, A.; Mukanova, A. (November 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Polarization of interstellar dust emission is a powerful probe of dust properties and magnetic field structure. Yet studies of external galaxies are hampered by foreground dust contribution. The study aims at separating the polarized signal from the Large Magellanic Cloud (LMC) from that of the Milky Way (MW) to construct a wide-field, spatially complete map of dust polarization using the Planck 353 GHz data. To estimate the foreground polarization direction, we used velocity gradients in H i spectral line data and assessed the performance of the output by comparing to starlight extinction polarization. We estimate the foreground intensity using the dust-to-gas correlation and the average intensity around the LMC and we assume the foreground polarization to be uniform and equal to the average of the MW around the galaxy to derive foreground I, Q, and U parameters. After foreground removal, the geometry of the plane-of-the-sky magnetic field tends to follow the structure of the atomic gas. This is notably the case along the molecular ridges extending south and south-east of the 30 Doradus star-forming complex and along the more diffuse southern arm extending towards the Small Magellanic Cloud. There is also an alignment between the magnetic field and the outer arm in the western part. The median polarization fraction in the LMC is slightly lower than that observed for the MW as well as the anticorrelation between the polarization angle dispersion function and the polarization fraction. Overall, polarization fraction distribution is similar to that observed in the MW. 

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3. Toward the limits of complexity of interstellar chemistry: Rotational spectroscopy and astronomical search for n - and i -butanal

   https://doi.org/10.1051/0004-6361/202142848  

   Sanz-Novo, M.; Belloche, A.; Rivilla, V. M.; Garrod, R. T.; Alonso, J. L.; Redondo, P.; Barrientos, C.; Kolesniková, L.; Valle, J. C.; Rodríguez-Almeida, L.; et al (October 2022, Astronomy & Astrophysics)

   Context.In recent times, large organic molecules of exceptional complexity have been found in diverse regions of the interstellar medium. Aims.In this context, we aim to provide accurate frequencies of the ground vibrational state of two key aliphatic aldehydes,n-butanal and its branched-chain isomer, i-butanal, to enable their eventual detection in the interstellar medium. We also want to test the level of complexity that interstellar chemistry can reach in regions of star formation. Methods.We employ a frequency modulation millimeter-wave absorption spectrometer to measure the rotational features ofn- andi-butanal. We analyze the assigned rotational transitions of each rotamer separately using theA-reduced semirigid-rotor Hamiltonian. We use the spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array to search forn- andi-butanal toward the star-forming region Sgr B2(N). We also search for both aldehydes toward the molecular cloud G+0.693−0.027 with IRAM 30 m and Yebes 40 m observations. The observational results are compared with computational results from a recent gas-grain astrochemical model. Results.Several thousand rotational transitions belonging to the lowest-energy conformers of two distinct linear and branched isomers have been assigned in the laboratory spectra up to 325 GHz. A precise set of the relevant rotational spectroscopic constants has been determined for each structure as a first step toward identifying both molecules in the interstellar medium. We report non-detections ofn-and i-butanal toward both sources, Sgr B2(N1S) and G+0.693-0.027. We find thatn- andi-butanal are at least 2-6 and 6-18 times less abundant than acetaldehyde toward Sgr B2(N1S), respectively, and thatn-butanal is at least 63 times less abundant than acetaldehyde toward G+0.693−0.027. While propanal is not detected toward Sgr B2(N1S) either, with an abundance at least 5–11 lower than that of acetaldehyde, propanal is found to be 7 times less abundant than acetaldehyde in G+0.693−0.027. Comparison with astrochemical models indicates good agreement between observed and simulated abundances (where available). Grain-surface chemistry appears sufficient to reproduce aldehyde ratios in G+0.693−0.027; gas-phase production may play a more active role in Sgr B2(N1S). Model estimates for the larger aldehydes indicate that the observed upper limits may be close to the underlying values. Conclusions.Our astronomical results indicate that the family of interstellar aldehydes in the Galactic center region is characterized by a drop of one order of magnitude in abundance at each incrementation in the level of molecular complexity. 

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4. The Interstellar Interlopers

   https://doi.org/10.1146/annurev-astro-071221-054221  

   Jewitt, David; Seligman, Darryl Z. (August 2023, Annual Review of Astronomy and Astrophysics)

   Interstellar interlopers are bodies formed outside of the Solar System but observed passing through it. The first two identified interlopers, 1I/‘Oumuamua and 2I/Borisov, exhibited unexpectedly different physical properties. 1I/‘Oumuamua appeared unresolved and asteroid-like, whereas 2I/Borisov was a more comet-like source of both gas and dust. Both objects moved under the action of nongravitational acceleration. These interlopers and their divergent properties provide our only window so far onto an enormous and previously unknown galactic population. The number density of such objects is ∼0.1 AU⁻³which, if uniform across the galactic disk, would imply 10²⁵to 10²⁶similar objects in the Milky Way. The interlopers likely formed in, and were ejected from, the protoplanetary disks of young stars. However, we currently possess too little data to firmly reject other explanations. ▪ 1I/‘Oumuamua and 2I/Borisov are both gravitationally unbound, subkilometer bodies showing nongravitational acceleration. ▪ The acceleration of 1I/‘Oumuamua in the absence of measurable mass loss requires either a strained explanation in terms of recoil from sublimating supervolatiles or the action of radiation pressure on a nucleus with an ultralow mass column density, ∼1 kg m⁻². ▪ 2I/Borisov is a strong source of CO and H₂O, which together account for its activity and nongravitational acceleration. ▪ The interlopers are most likely planetesimals from the protoplanetary disks of other stars, ejected by gravitational scattering from planets. 1I/‘Oumuamua and 2I/Borisov have dynamical ages ∼10⁸and ∼10⁹years, respectively. ▪ Forthcoming observatories should detect interstellar interlopers every year, which will provide a rapid boost to our knowledge of the population. 

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5. A comprehensive view of the interstellar medium in a quasar host galaxy at z  ≈ 6.4

   https://doi.org/10.1051/0004-6361/202245674  

   Decarli, Roberto; Pensabene, Antonio; Diaz-Santos, Tanio; Ferkinhoff, Carl; Strauss, Michael A.; Venemans, Bram P.; Walter, Fabian; Bañados, Eduardo; Bertoldi, Frank; Fan, Xiaohui; et al (May 2023, Astronomy & Astrophysics)

   Characterizing the physical conditions (density, temperature, ionization state, metallicity, etc) of the interstellar medium is critical to improving our understanding of the formation and evolution of galaxies. In this work, we present a multi-line study of the interstellar medium in the host galaxy of a quasar atz ≈ 6.4, that is, when the universe was 840 Myr old. This galaxy is one of the most active and massive objects emerging from the dark ages and therefore represents a benchmark for models of the early formation of massive galaxies. We used the Atacama Large Millimeter Array to target an ensemble of tracers of ionized, neutral, and molecular gas, namely the following fine-structure lines: [O III] 88 μm, [N II] 122 μm, [C II] 158 μm, and [C I] 370 μm – as well as the rotational transitions of CO(7–6), CO(15–14), CO(16–15), and CO(19–18); OH 163.1 μm and 163.4 μm; along with H₂O 3(0,3)–2(1,2), 3(3,1)–4(0,4), 3(3,1)–3(2,2), 4(0,4)–3(1,3), and 4(3,2)–4(2,3). All the targeted fine-structure lines were detected, along with half of the targeted molecular transitions. By combining the associated line luminosities with the constraints on the dust temperature from the underlying continuum emission and predictions from photoionization models of the interstellar medium, we find that the ionized phase accounts for about one-third of the total gaseous mass budget and is responsible for half of the total [C II] emission. This phase is characterized by a high density (n ∼ 180 cm⁻³) that typical of HII regions. The spectral energy distribution of the photoionizing radiation is comparable to that emitted by B-type stars. Star formation also appears to be driving the excitation of the molecular medium. We find marginal evidence for outflow-related shocks in the dense molecular phase, but not in other gas phases. This study showcases the power of multi-line investigations in unveiling the properties of the star-forming medium in galaxies at cosmic dawn. 

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