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This is the fourth paper exploring the infrared properties of giant H ii regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant H ii regions identified by Conti & Crowther, and in this paper we present the 20 and 37 ÎĽ m imaging data we obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multiwavelength data, we derive and discuss the detailed physical properties of the individual compact sources and subregions as well as the large-scale properties of Sgr D and W42. However, improved measurements have revealed much closer distances to both regions than previously believed, and consequently, both sources are not powerful enough to be considered giant H ii regions any longer. Motivated by this, we revisit the census of giant H ii regions, performing a search of the last two decades of literature to update each source with the most recent and/or most accurate distance measurements. Based on these new distance estimates, we determine that 14 sources in total (25%) are at sufficiently reliable and closer distances that they are not powerful enough to be considered giant H ii regions. We briefly discuss the observational and physical characteristics specific to Sgr D and W42 and show that they have properties distinct from the giant H ii regions previously studied as a part of this survey. [ABSTRACT FROM AUTHOR]

We describe the data processing of the Survey on extragALactic magnetiSm with SOFIA (SALSA Legacy Program). This first data release presents 33% (51.34 hr out of 155.7 hr, including overheads) of the total awarded time from 2020 January to 2021 December. Our observations were performed using the newly implemented on-the-fly mapping (OTFMAP) technique in the polarimetric mode. We present the pipeline steps to obtain homogeneously reduced high-level data products of polarimetric maps of galaxies for use in scientific analysis. Our approach has a general design and can be applied to sources smaller than the field of view of the HAWC+ array in any given band. We estimate that the OTFMAP polarimetric mode offers a reduction of observing overheads by a factor 2.34 and an improvement in sensitivity by a factor 1.80 when compared to the same on-source time polarimetric observations using the chopping and nodding mode. The OTFMAP is a significant optimization of the polarimetric mode of HAWC+, as it ultimately reduces the cost of operations of HAWC+/SOFIA by increasing the science collected per hour of observation up to an overall factor of 2.49. The OTFMAP polarimetric mode is the standard observing strategy of SALSA. The results and quantitative analysis of this first data release are presented in Papers IV and V of the series. [ABSTRACT FROM AUTHOR]

M82 is an archetypal starburst galaxy in the local Universe. The central burst of star formation, thought to be triggered by M82's interaction with other members in the M81 group, is driving a multiphase galaxy-scale wind away from the plane of the disk that has been studied across the electromagnetic spectrum. Here, we present new velocity-resolved observations of the [C ii ] 158 μ m line in the central disk and the southern outflow of M82 using the upGREAT instrument on board SOFIA. We also report the first detections of velocity-resolved (Δ V = 10 km s−1) [C ii ] emission in the outflow of M82 at projected distances of ≈1–2 kpc south of the galaxy center. We compare the [C ii ] line profiles to observations of CO and H i and find that likely the majority (>55%) of the [C ii ] emission in the outflow is associated with the neutral atomic medium. We find that the fraction of [C ii ] actually outflowing from M82 is small compared to the bulk gas outside the midplane (which may be in a halo or tidal streamers), which has important implications for observations of [C ii ] outflows at higher redshift. Finally, by comparing the observed ratio of the [C ii ] and CO intensities to models of photodissociation regions, we estimate that the far-ultraviolet (FUV) radiation field in the disk is ∼103.5 G 0, in agreement with previous estimates. In the outflow, however, the FUV radiation field is 2–3 orders of magnitudes lower, which may explain the high fraction of [C ii ] arising from the neutral medium in the wind. [ABSTRACT FROM AUTHOR]

WR 137 (HD 192641) is a binary system consisting of a carbon-rich Wolf–Rayet (W-R) star and an Oe companion star in a 13 yr orbit. Near periastron, the winds of the two stars collide and form carbonaceous dust. We obtained three mid-infrared grism spectra of the system with SOFIA and FORCAST during the last year of SOFIA's operations in 2021 July, 2021 February, and 2022 May (Cycle 9). Within these spectra, we have identified several wind lines from He i, He ii, C iii, and C iv that are emitted from the W-R wind as well as a weak emission feature around 6.3–6.4 μ m that may have shifted its peak flux from 6.29 to 6.41 μ m through this time period. The weak feature grew as the continuum dust emission grew while the W-R emission appeared to decline due to lower contrast with the continuum. Furthermore, we observe that the peak of the feature shifts to redder wavelengths during the observations. We compare this feature to the unidentified infrared feature and other emission lines identified in dusty carbon-rich W-R (WC) binaries. For WR 137, we speculate that mixing of the winds in the system with the Oe star's disk is important for starting the dust formation and that it is less important as dust formation continues. Previous infrared photometry shows "minieruptions" of dust production, which could then be explained with variations of the Oe star disk. [ABSTRACT FROM AUTHOR]

We present the analysis of the magnetic field (B -field) structure of galaxies measured with far-infrared (FIR) and radio (3 and 6 cm) polarimetric observations. We use the first data release of the Survey of extragALactic magnetiSm with SOFIA of 14 nearby ( < 20 Mpc) galaxies with resolved ( 5 ″ – 18 ″ ; 90 pc–1 kpc) imaging polarimetric observations using SOFIA/HAWC+ from 53 to 214 μ m. We compute the magnetic pitch-angle ( Ψ B ) profiles as a function of the galactocentric radius. We introduce a new magnetic alignment parameter (ζ) to estimate the disordered-to-ordered ratio of spiral B -fields. We find FIR and radio wavelengths to not generally trace the same B -field morphology in galaxies. The Ψ B profiles tend to be more ordered across all galactocentric radii in radio ( ζ 6 cm = 0.93 ± 0.03) than in FIR ( ζ 154 μ m = 0.84 ± 0.14). For spiral galaxies, FIR B -fields are 2%–75% more turbulent than the radio B -fields. For starburst galaxies, we find that FIR polarization is a better tracer of the B -fields along the galactic outflows than radio polarization. Our results suggest that the B -fields associated with dense, dusty, turbulent star-forming regions (those traced at FIR) are less ordered than warmer, less dense regions (those traced at radio) of the interstellar medium. The FIR B -fields seem to be more sensitive to the activity of the star-forming regions and molecular clouds within a vertical height of a few hundred parsecs in the disk of spiral galaxies than the radio B -fields. [ABSTRACT FROM AUTHOR]

The heart of the Large Magellanic Cloud, 30 Doradus, is a complex region with a clear core-halo structure. Feedback from the stellar cluster R136 has been shown to be the main source of energy creating multiple parsec-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. We present the morphology and strength of the magnetic fields (B -fields) of 30 Doradus inferred from the far-infrared polarimetric observations by SOFIA/HAWC+ at 89, 154, and 214 μ m. The B -field morphology is complex, showing bending structures around R136. In addition, we use high spectral and angular resolution [C ii ] observations from SOFIA/GREAT and CO(2-1) from APEX. The kinematic structure of the region correlates with the B -field morphology and shows evidence of multiple expanding-shells. Our B -field strength maps, estimated using the Davis–Chandrasekhar–Fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350 μ G at 89, 154, and 214 μ m, respectively. We estimated that the majority of the 30 Doradus clouds are subcritical and sub-Alfvénic. The probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. We show that the B -field is sufficient to hold the cloud structure integrity under feedback from R136. We suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. The velocity gradient technique using [C ii ] and CO(2-1) is likely to confirm these suggestions. [ABSTRACT FROM AUTHOR]

We present the first data release of the Survey on extragALactic magnetiSm with SOFIA (SALSA Legacy Program) with a set of 14 nearby (<20 Mpc) galaxies with resolved imaging polarimetric observations using HAWC+ from 53 to 214 ÎĽ m at a resolution of 5″â€"18″ (90 pcâ€"1 kpc). We introduce the definitions of and background on extragalactic magnetism and present the scientific motivation and sample selection of the program. Here we focus on the general trends in the emissive polarization fraction. Far-infrared polarimetric observations trace the thermal polarized emission of magnetically aligned dust grains across the galaxy disks with polarization fractions of P = 0%â€"15% in the cold, T d = [19, 48] K, and dense, log 10 (N H I + H 2 [ cm âˆ' 2 ]) = [ 19.96 , 22.91 ] , interstellar medium. The spiral galaxies show a median 〈 P 154 ÎĽ m〉 = 3.3% ± 0.9% across the disks. We report the first polarized spectrum of starburst galaxies showing a minimum within 89â€"154 ÎĽ m. The falling 53â€"154 ÎĽ m polarized spectrum may be due to a decrease in the dust grain alignment efficiency produced by variations in dust temperatures along the line of sight in the galactic outflow. We find that the starburst galaxies and the star-forming regions within normal galaxies have the lowest polarization fractions. We find that 50% (seven out of 14) of the galaxies require a broken power law in the P âˆ' N H I + H 2 and P âˆ' T d relations with three different trends. Group 1 has a relative increase of anisotropic random B-fields produced by compression or shear of B-fields in the galactic outflows, starburst rings, and inner bars of galaxies, and groups 2 and 3 have a relative increase of isotropic random B-fields driven by star-forming regions in the spiral arms and/or an increase of dust grain alignment efficiency caused by shock-driven regions or evolutionary stages of a galaxy. [ABSTRACT FROM AUTHOR]