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ABSTRACT We present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $$B_{||}$$, by combining a 3D electron density ($$n_{\mathrm{ e}}$$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $$n_{\mathrm{ e}}$$ map and compares to the Galactic Faraday rotation sky. We infer $$B_{||}$$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $$|b| \gt 5^{\circ }$$) map of $$B_{||}$$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $$B_{||}$$ of $$1.63\pm 0.16\,\rm \mu G$$. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $$B_{||}$$ field is seen to exhibit a 3D power spectrum with an average slope of $$-2.73 \pm 0.19$$. We validate our $$B_{||}$$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $$n_{e}B_{||}$$ to each pulsar’s distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $$n_{e}$$ map also correlate with measured DMs, albeit with significant scatter. 

ABSTRACT We combine parallax distances to nearby O stars with parsec-scale resolution three-dimensional dust maps of the local region of the Milky Way (within 1.25 kpc of the Sun) to simulate the transfer of Lyman continuum photons through the interstellar medium (ISM). Assuming a fixed gas-to-dust ratio, we determine the density of ionized gas, electron temperature, and H$$\alpha$$ emissivity throughout the local Milky Way. There is good morphological agreement between the predicted and observed H$$\alpha$$ all-sky map of the Wisconsin H$$\alpha$$ Mapper. We find that our simulation underproduces the observed H$$\alpha$$ emission while overestimating the sizes of H ii regions, and we discuss ways in which agreement between simulations and observations may be improved. Of the total ionizing luminosity of $$5.84 \times 10^{50}~{\rm photons \, s^{-1}}$$, 15 per cent is absorbed by dust, 64 per cent ionizes ‘classical’ H ii regions, 11 per cent ionizes the diffuse warm ionized medium, and 10 per cent escapes the simulation volume. We find that 18 per cent of the high-altitude ($$|b| > 30{}^{\circ }$$) H$$\alpha$$ arises from dust scattered rather than direct emission. These initial results provide an impressive validation of the three-dimensional dust maps and O-star parallaxes, opening a new frontier for studying the ionized ISM’s structure and energetics in three dimensions. 

Abstract We present a deep, high-angular-resolution 3D dust map of the southern Galactic plane over 239° < l < 6° and ∣b∣ < 10° built on photometry from the DECaPS2 survey, in combination with photometry from VISTA Variables in the Via Lactea, the Two Micron All Sky Survey, and “Unofficial” Wide-field Infrared Survey Explorer and parallaxes from Gaia Data Release 3 where available. To construct the map, we first infer the distance, extinction, and stellar types of over 700 million stars using thebrutusstellar inference framework with a set of theoretical MESA Isochrone and Stellar Tracks (MIST) stellar models. Our resultant 3D dust map has an angular resolution of $1\prime$, roughly an order of magnitude finer than existing 3D dust maps and comparable to the angular resolution of the Herschel 2D dust emission maps. We detect complexes at the range of distances associated with the Sagittarius-Carina and Scutum-Centaurus arms in the fourth quadrant, as well as more distant structures out to a maximum reliable distance ofd ≈ 10 kpc from the Sun. The map is sensitive up to a maximum extinction of roughlyA_V ≈ 12 mag. We publicly release both the stellar catalog and the 3D dust map, the latter of which can easily be queried via the Python packagedustmaps. When combined with the existingBayestar193D dust map of the northern sky, the DECaPS 3D dust map fills in the missing piece of the Galactic plane, enabling extinction corrections over the entire disk ∣b∣ < 10°. Our map serves as a pathfinder for the future of 3D dust mapping in the era of LSST and Roman, targeting regimes accessible with deep optical and near-infrared photometry but often inaccessible with Gaia. 

Abstract We report the first direct detection of molecular hydrogen associated with the Galactic nuclear wind. The Far-Ultraviolet Spectroscopic Explorer spectrum of LS 4825, a B1 Ib–II star at l , b = 1.67°,−6.63° lying d = 9.9 − 0.8 + 1.4 kpc from the Sun, ∼1 kpc below the Galactic plane near the Galactic center, shows two high-velocity H 2 components at v LSR = −79 and −108 km s −1 . In contrast, the FUSE spectrum of the nearby (∼0.6° away) foreground star HD 167402 at d = 4.9 − 0.7 + 0.8 kpc reveals no H 2 absorption at these velocities. Over 60 lines of H 2 from rotational levels J = 0 to 5 are identified in the high-velocity clouds. For the v LSR = −79 km s −1 cloud we measure total log N (H 2 ) ≥ 16.75 cm −2 , molecular fraction f H 2 ≥ 0.8%, and T 01 ≥ 97 and T 25 ≤ 439 K for the ground- and excited-state rotational excitation temperatures. At v LSR = −108 km s −1 , we measure log N (H 2 ) = 16.13 ± 0.10 cm −2 , f H 2 ≥ 0.5%, and T 01 = 77 − 18 + 34 and T 25 = 1092 − 117 + 149 K, for which the excited-state ortho- to para-H 2 is 1.0 − 0.1 + 0.3 , much less than the equilibrium value of 3 expected for gas at this temperature. This nonequilibrium ratio suggests that the −108 km s −1 cloud has been recently excited and has not yet had time to equilibrate. As the LS 4825 sight line passes close by a tilted section of the Galactic disk, we propose that we are probing a boundary region where the nuclear wind is removing gas from the disk.