We present newly obtained three-dimensional gaseous maps of the Milky Way Galaxy: H i, H₂, and total-gas (H i plus H₂) maps, which were derived from the H i and ¹²CO(J = 1–0) survey data and rotation curves based on the kinematic distance. The H i and H₂ face-on maps show that the H i disk is extended to a radius of 15–20 kpc and its outskirts are asymmetric to the Galactic center, while most of the H₂ gas is distributed inside the solar circle. The total gas mass within a radius of 30 kpc amounts to 8.0 × 10⁹ M_⊙, 89% and 11% of which are H i and H₂, respectively. The vertical slices show that the outer H i disk is strongly warped and the inner H i and H₂ disks are corrugated. The total gas map is advantageous for tracing spiral structures from the inner to outer disk. Spiral structures such as the Norma–Cygnus, the Perseus, the Sagittarius–Carina, the Scutum–Crux, and the Orion arms are more clearly traced in the total gas map than ever. All the spiral arms are well explained by logarithmic spiral arms with pitch angles of 11°–15°. The molecular fraction of the total gas is high near the Galactic center and decreases with Galactocentric distance. The molecular fraction is also locally enhanced at the spiral arms compared with the inter-arm regions.

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey’s aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous “integral filament” in the densest regions of that filament. Furthermore, we see an “hourglass” magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

The Leading Arm of the Magellanic System is a tidally formed HI feature extending $\sim 60\arcdeg$ from the Magellanic Clouds ahead of their direction of motion. Using atomic hydrogen (HI) data from the Galactic All Sky-Survey (GASS), supplemented with data from the Australia Telescope Compact Array, we have found evidence for an interaction between a cloud in the Leading Arm and the Galactic disk where the Leading Arm crosses the Galactic plane. The interaction occurs at velocities permitted by Galactic rotation, which allows us to derive a kinematic distance to the cloud of 21 kpc, suggesting that the Leading Arm crosses the Galactic Plane at a Galactic radius of $R\approx 17$ kpc.Comment: 14 pages, 5 figures, accepted to Astrophysical Journal Letters. Full resolution version available at ftp://ftp.atnf.csiro.au/pub/people/nmcclure/papers/LeadingArm_apjl.pd

We conducted astrometric very long baseline interferometry (VLBI) observations of water-vapor maser emission in the massive star-forming region IRAS 21379+5106 in order to measure the annual parallax and proper motion, using VLBI Exploration of Radio Astrometry (VERA). The annual parallax measured 0.262 ± 0.031 mas, corresponding to a distance of $$3.82^{+0.51}_{-0.41}\:$$kpc. The proper motion was (μ_αcos δ, μ_δ) = (−2.74 ± 0.08, −2.87 ± 0.18) mas yr⁻¹. By using this result, the Galactic rotational velocity was estimated to be V_θ = 218 ± 19 km s⁻¹ at the galactocentric distance R = 9.22 ± 0.43 kpc, when we adopted the Galactic constants R₀ = 8.05 ± 0.45 kpc and V₀ = 238 ± 14 km s⁻¹. With the newly determined distance, the bolometric luminosity of the central young stellar object was reestimated to be (2.15 ± 0.54) × 10³ L_⊙, which corresponds to the spectral type of B2–B3. The maser features were found to be distributed along a straight line extending from the southwest to the northeast. In addition, a vector map of the internal motions, constructed from the residual proper motions, implies that the maser features trace a bipolar flow, and that it cannot be explained by simple ballistic motions.

We compared theoretical and observational molecular mass fractions (f_mol: ratio of molecular gas density to total gas density) using observational data of ten nearby spiral galaxies. For determination of f_mol, the three parameters–interstellar pressure P, UV radiation U, and metallicity Z–were obtained from the spectral line data of ¹²CO(J = 1–0), H i, Hα, [O iii], and [O ii]. Interstellar pressure was calculated with the sum of the hydrogen gas densities and the stellar potential based on the K_s-band data. For most data other than metallicity, we used archived NRO CO Atlas, THINGS, SINGS, and 2MASS data. For comparison, we also investigated the dependence of the CO-to-H₂ conversion factor X_CO. It was found that the theoretical f_mol agreed with the observational f_mol only when the interstellar pressure is calculated with both the gas density and stellar disk potential. To fit observations more accurately, either the metallicity or the UV radiation needs to be adjusted. It was also found that, in UV radiation scaling, scaling factor γ has a correlation with the diffuse fraction of the Hα emission line data, f_DIG. As for X_CO, it was shown that the difference between both values of f_mol becomes the least when X_CO is 1.0 × 10²⁰ cm⁻² (K km s⁻¹)⁻¹.

A jet termination region provides us with useful information about how a jet interacts with the interstellar medium. Identifying the strength and orientation of magnetic fields at the terminal is crucially important to understanding the mechanism of cosmic-ray acceleration. In this article, we report results of our Faraday-tomography analysis of the eastern region of the radio nebula W50, where a jet from the microquasar SS433 seems to terminate. We apply QU-fitting, a method of Faraday-tomography, to data from the Australia Telescope Compact Array (ATCA) at 1.3–3.0 GHz. In the analysis, we distinguish multiple polarized sources along the line of sight. We identify Galactic emission candidates at Faraday depths around 0 rad m⁻² and 300 rad m⁻². The Galactic emission around 0 rad m⁻² is possibly located in front of W50. We also find emission from W50 with Faraday depths between φ = −112 to 228 rad m⁻².