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1. Distance, magnetic field, and kinematics of the filamentary cloud LDN 1157

   https://doi.org/10.1051/0004-6361/202037438  

   Sharma, Ekta ; Gopinathan, Maheswar ; Soam, Archana ; Lee, Chang Won ; Kim, Shinyoung ; Ghosh, Tuhin ; Tej, Anandmayee ; Kim, Gwanjeong ; Sharma, Neha ; Saha, Piyali ( July 2020 , Astronomy & Astrophysics)

   Context. LDN 1157 is one of several clouds that are situated in the cloud complex LDN 1147/1158. The cloud presents a coma-shaped morphology with a well-collimated bipolar outflow emanating from a Class 0 protostar, LDN 1157-mm, that resides deep inside the cloud. Aims. The main goals of this work are (a) mapping the intercloud magnetic field (ICMF) geometry of the region surrounding LDN 1157 to investigate its relationship with the cloud morphology, outflow direction, and core magnetic field (CMF) geometry inferred from the millimeter- and submillimeter polarization results from the literature, and (b) to investigate the kinematic structure of the cloud. Methods. We carried out optical ( R -band) polarization observations of the stars projected on the cloud to map the parsec-scale magnetic field geometry. We made spectroscopic observations of the entire cloud in the 12 CO, C 18 O, and N 2 H + ( J = 1–0) lines to investigate its kinematic structure. Results. We obtained a distance of 340 ± 3 pc to the LDN 1147/1158, complex based on the Gaia DR2 parallaxes and proper motion values of the three young stellar objects (YSOs) associated with the complex. A single filament of ~1.2 pc in length (tracedmore »by the Filfinder algorithm) and ~0.09 pc in width (estimated using the Radfil algorithm) is found to run throughout the coma-shaped cloud. Based on the relationships between the ICMF, CMF, filament orientations, outflow direction, and the hourglass morphology of the magnetic field, it is likely that the magnetic field played an important role in the star formation process in LDN 1157. LDN 1157-mm is embedded in one of the two high-density peaks detected using the Clumpfind algorithm. The two detected clumps lie on the filament and show a blue-red asymmetry in the 12 CO line. The C 18 O emission is well correlated with the filament and presents a coherent structure in velocity space. Combining the proper motions of the YSOs and the radial velocity of LDN 1147/1158 and an another complex, LDN 1172/1174, that is situated ~2° east of it, we found that the two complexes are moving collectively toward the Galactic plane. The filamentary morphology of the east-west segment of LDN 1157 may have formed as a result of mass lost by ablation through interaction of the moving cloud with the ambient interstellar medium.« less
2. The role of magnetic fields in the stability and fragmentation of filamentary molecular clouds: two case studies at OMC-3 and OMC-4

   https://doi.org/10.1093/mnras/stac1527  

   Li, Pak Shing ; Lopez-Rodriguez, Enrique ; Soam, Archana ; Klein, Richard I. ( June 2022 , Monthly Notices of the Royal Astronomical Society)

   We present the stability analysis of two regions, OMC-3 and OMC-4, in the massive and long molecular cloud complex of Orion A. We obtained 214 $\mu$m HAWC + /SOFIA polarization data, and we make use of archival data for the column density and C18O (1–0) emission line. We find clear depolarization in both observed regions and that the polarization fraction is anticorrelated with the column density and the polarization-angle dispersion function. We find that the filamentary cloud and dense clumps in OMC-3 are magnetically supercritical and strongly subvirial. This region should be in the gravitational collapse phase and is consistent with many young stellar objects (YSOs) forming in the region. Our histogram of relative orientation (HRO) analysis shows that the magnetic field is dynamically sub-dominant in the dense gas structures of OMC-3. We present the first polarization map of OMC-4. We find that the observed region is generally magnetically subcritical except for an elongated dense core, which could be a result of projection effect of a filamentary structure aligned close to the line of sight. The relative large velocity dispersion and the unusual positive shape parameters at high column densities in the HROs analysis suggest that our viewing angle may be closemore »to axes of filamentary substructures in OMC-4. The dominating strong magnetic field in OMC-4 is unfavourable for star formation and is consistent with much fewer YSOs than in OMC-3.

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3. G−0.02−0.07, the compact H ii region complex nearest to the galactic center with ALMA

   https://doi.org/10.1093/pasj/psz116  

   Tsuboi, Masato ; Kitamura, Yoshimi ; Uehara, Kenta ; Miyazaki, Atsushi ; Miyawaki, Ryosuke ; Tsutsumi, Takahiro ; Miyoshi, Makoto ( November 2019 , Publications of the Astronomical Society of Japan)

   We have observed the compact H ii region complex nearest to the dynamical center of the Galaxy, G−0.02−0.07, using ALMA in the H42α recombination line, CS J = 2–1, H13CO+J = 1–0, and SiO v = 0, J = 2–1 emission lines, and the 86 GHz continuum emission. The H ii regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright half and a dark half in the recombination line and continuum emission. The analysis of the absorption features in the molecular emission lines show that H ii-A, B, and C are located on the near side of the “Galactic center 50 km s−1 molecular cloud” (50MC), but HII-D is located on the far side of it. The electron temperatures and densities ranges are Te = 5150–5920 K and ne = 950–2340 cm−3, respectively. The electron temperatures in the bright half are slightly lower than those in the dark half, while the electron densities in the bright half are slightly higher than those in the dark half. The H ii regions are embedded in the ambient molecular gas. There are some molecular gas components compressed by a C-type shock wave around the H ii regions. From the line width of the H42αmore »recombination line, the expansion velocities of HII-A, HII-B, HII-C, and HII-D are estimated to be Vexp = 16.7, 11.6, 11.1, and 12.1 km s−1, respectively. The expansion timescales of HII-A, HII-B, HII-C, and HII-D are estimated to be tage ≃ 1.4 × 104, 1.7 × 104, 2.0 × 104, and 0.7 × 104 yr, respectively. The spectral types of the central stars from HII-A to HII-D are estimated to be O8V, O9.5V, O9V, and B0V, respectively. These derived spectral types are roughly consistent with the previous radio estimation. The positional relation among the H ii regions, the SiO molecule enhancement area, and Class-I maser spots suggest that a shock wave caused by a cloud–cloud collision propagated along the line from HII-C to HII-A in the 50MC. The shock wave would have triggered the massive star formation.

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4. Nobeyama 45 m Local Spur CO survey. I. Giant molecular filaments and cluster formation in the Vulpecula OB association

   https://doi.org/10.1093/pasj/psab107  

   Kohno, Mikito ; Nishimura, Atsushi ; Fujita, Shinji ; Tachihara, Kengo ; Onishi, Toshikazu ; Tokuda, Kazuki ; Fukui, Yasuo ; Miyamoto, Yusuke ; Ueda, Shota ; Kiridoshi, Ryosuke ; et al ( December 2021 , Publications of the Astronomical Society of Japan)

   We have performed new large-scale 12CO, 13CO, and C18O J = 1–0 observations toward the Vulpecula OB association (l ∼ 60°) as part of the Nobeyama 45 m Local Spur CO survey project. Molecular clouds are distributed over ∼100 pc, with local peaks at the Sh 2-86, Sh 2-87, and Sh 2-88 high-mass star-forming regions in the Vulpecula complex. The molecular gas is associated with the Local Spur, which corresponds to the nearest inter-arm region located between the Local Arm and the Sagittarius Arm. We discovered new giant molecular filaments (GMFs) in Sh 2-86, with a length of ∼30 pc, width of ∼5 pc, and molecular mass of $\sim\!\! 4 \times 10^4\, M_{\odot }$. We also found that Sh 2-86 contains the three velocity components at 22, 27, and 33 km s−1. These clouds and GMFs are likely to be physically associated with Sh 2-86 because they have high 12CO J = 2–1 to J = 1–0 intensity ratios and coincide with the infrared dust emission. The open cluster NGC 6823 exists at the common intersection of these clouds. We argue that the multiple cloud interaction scenario, including GMFs, can explain cluster formation in the Vulpecula OB association.
5. Excitation mechanisms in the intracluster filaments surrounding brightest cluster galaxies

   https://doi.org/10.1051/0004-6361/202039730  

   Polles, F. L. ; Salomé, P. ; Guillard, P. ; Godard, B. ; Pineau des Forêts, G. ; Olivares, V. ; Beckmann, R. S. ; Canning, R. E. ; Combes, F. ; Dubois, Y. ; et al ( July 2021 , Astronomy & Astrophysics)

   Context. The excitation of the filamentary gas structures surrounding giant elliptical galaxies at the center of cool-core clusters, also known as brightest cluster galaxies (BCGs), is key to our understanding of active galactic nucleus (AGN) feedback, and of the impact of environmental and local effects on star formation. Aims. We investigate the contribution of thermal radiation from the cooling flow surrounding BCGs to the excitation of the filaments. We explore the effects of small levels of extra heating (turbulence), and of metallicity, on the optical and infrared lines. Methods. Using the C LOUDY code, we modeled the photoionization and photodissociation of a slab of gas of optical depth A V  ≤ 30 mag at constant pressure in order to calculate self-consistently all of the gas phases, from ionized gas to molecular gas. The ionizing source is the extreme ultraviolet (EUV) and soft X-ray radiation emitted by the cooling gas. We tested these models comparing their predictions to the rich multi-wavelength observations from optical to submillimeter, now achieved in cool core clusters. Results. Such models of self-irradiated clouds, when reaching sufficiently large A V , lead to a cloud structure with ionized, atomic, and molecular gas phases. These models reproduce most ofmore »the multi-wavelength spectra observed in the nebulae surrounding the BCGs, not only the low-ionization nuclear emission region like optical diagnostics, [O  III ] λ 5007 Å/H β , [N  II ] λ 6583 Å/H α , and ([S  II ] λ 6716 Å+[S  II ] λ 6731 Å)/H α , but also the infrared emission lines from the atomic gas. [O  I ] λ 6300 Å/H α , instead, is overestimated across the full parameter space, except for very low A V . The modeled ro-vibrational H 2 lines also match observations, which indicates that near- and mid-infrared H 2 lines are mostly excited by collisions between H 2 molecules and secondary electrons produced naturally inside the cloud by the interaction between the X-rays and the cold gas in the filament. However, there is still some tension between ionized and molecular line tracers (i.e., CO), which requires optimization of the cloud structure and the density of the molecular zone. The limited range of parameters over which predictions match observations allows us to constrain, in spite of degeneracies in the parameter space, the intensity of X-ray radiation bathing filaments, as well as some of their physical properties like A V or the level of turbulent heating rate. Conclusions. The reprocessing of the EUV and X-ray radiation from the plasma cooling is an important powering source of line emission from filaments surrounding BCGs. C LOUDY self-irradiated X-ray excitation models coupled with a small level of turbulent heating manage to simultaneously reproduce a large number of optical-to-infrared line ratios when all the gas phases (from ionized to molecular) are modeled self-consistently. Releasing some of the simplifications of our model, like the constant pressure, or adding the radiation fields from the AGN and stars, as well as a combination of matter- and radiation-bounded cloud distribution, should improve the predictions of line emission from the different gas phases.« less