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1. Magnetogram-matching Biot–Savart Law and Decomposition of Vector Magnetograms

   https://doi.org/10.3847/1538-4357/add895  

   Titov, Viacheslav S; Downs, Cooper; Török, Tibor; Linker, Jon A; Prazak, Michael; Qiu, Jiong A (July 2025, The Astrophysical Journal)

   Abstract We generalize a magnetogram-matching Biot–Savart law (BSl) from planar to spherical geometry. For a given coronal current densityJ, this law determines the magnetic field $\tilde{\mathit{B}}$whose radial component vanishes at the surface. The superposition of $\tilde{\mathit{B}}$with a potential field defined by a given surface radial field,B_r, provides the entire configuration whereB_rremains unchanged by the currents. Using this approach, we (1) upgrade our regularized BSls for constructing coronal magnetic flux ropes (MFRs) and (2) propose a new method for decomposing a measured photospheric magnetic field as $\mathit{B}={\mathit{B}}_{\mathrm{pot}}+{\mathit{B}}_T+{\mathit{B}}_{\tilde{S}}$, where the potential,B_pot, toroidal,B_T, and poloidal, ${\mathit{B}}_{\tilde{S}}$, fields are determined byB_r,J_r, and the surface divergence ofB–B_pot, respectively, all derived from magnetic data. OurB_Tis identical to the one in the alternative Gaussian decomposition by P. W. Schuck et al., whileB_potand ${\mathit{B}}_{\tilde{S}}$are different from their poloidal fields ${\mathit{B}}_{\mathrm{P}}^{<}$and ${\mathit{B}}_{\mathrm{P}}^{>}$, which arepotentialin the infinitesimal proximity to the upper and lower side of the surface, respectively. In contrast, our ${\mathit{B}}_{\tilde{S}}$has no such constraints and, asB_potandB_T, refers to thesameupper side of the surface. In spite of these differences, for a continuousJdistribution across the surface,B_potand ${\mathit{B}}_{\tilde{S}}$are linear combinations of ${\mathit{B}}_{\mathrm{P}}^{<}$and ${\mathit{B}}_{\mathrm{P}}^{>}$. We demonstrate that, similar to the Gaussian method, our decomposition allows one to identify the footprints and projected surface-location of MFRs in the solar corona, as well as the direction and connectivity of their currents. 

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2. Planck Dust Polarization Power Spectra Are Consistent with Strongly Supersonic Turbulence

   https://doi.org/10.3847/1538-4357/ad571b  

   Stalpes, Kye_A; Collins, David_C; Huffenberger, Kevin_M (August 2024, The Astrophysical Journal)

   Abstract The polarization of the cosmic microwave background is rich in information but obscured by foreground emission from the Milky Way’s interstellar medium (ISM). To uncover relationships between the underlying turbulent ISM and the foreground power spectra, we simulated a suite of driven, magnetized, turbulent models of the ISM, varying the fluid properties via the sonic Mach number, ${\mathcal{M}}_{\mathcal{S}}$, and magnetic (Alfvén) Mach number, ${\mathcal{M}}_{\mathrm{A}}$. We measure the power spectra of density (ρ), velocity (v), magnetic field (H), total projected intensity (T), parity-even polarization (E), and parity-odd polarization (B). We find that the slopes of all six quantities increase with ${\mathcal{M}}_{\mathcal{S}}$. Most increase with ${\mathcal{M}}_{\mathrm{A}}$, while the magnetic field spectrum steepens with ${\mathcal{M}}_{\mathrm{A}}$. By comparing spectral slopes ofEandBto those measured by Planck, we infer typical values of ${\mathcal{M}}_{\mathcal{S}}$and ${\mathcal{M}}_{\mathrm{A}}$for the ISM. As the fluid velocity increases, ${\mathcal{M}}_{\mathcal{S}}>4$, the ratio of BB power to EE power increases to approach a constant value near the Planck-observed value of ∼0.5, regardless of the magnetic field strength. We also examine correlation coefficients between projected quantities, and find thatr^TE≈ 0.3, in agreement with Planck, for appropriate combinations of ${\mathcal{M}}_{\mathcal{S}}$and ${\mathcal{M}}_{\mathrm{A}}$. Finally, we consider parity-violating correlationsr^TBandr^EB. 

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3. Relationships between Polycyclic Aromatic Hydrocarbons, Small Dust Grains, H ₂ , and H i in Local Group Dwarf Galaxies NGC 6822 and WLM Using JWST, ALMA, and the VLA

   https://doi.org/10.3847/1538-4357/add73a  

   Chown, Ryan; Leroy, Adam K; Bolatto, Alberto D; Chastenet, Jérémy; Glover, Simon_C O; Indebetouw, Rémy; Koch, Eric W; Donovan_Meyer, Jennifer; Pingel, Nickolas M; Rosolowsky, Erik; et al (July 2025, The Astrophysical Journal)

   Abstract We present 0.6–3.2 pc resolution mid-infrared (MIR) JWST images at 7.7μm (F770W) and 21μm (F2100W) covering the main star-forming regions of two of the closest star-forming low-metallicity dwarf galaxies, NGC 6822 and Wolf–Lundmark–Melotte (WLM). The images of NGC 6822 reveal filaments, edge-brightened bubbles, diffuse emission, and a plethora of point sources. By contrast, most of the MIR emission in WLM is pointlike, with a small amount of extended emission. Compared to solar-metallicity galaxies, the ratio of 7.7μm intensity ( $I_{\nu }^{\mathrm{F770W}}$), tracing polycyclic aromatic hydrocarbons (PAHs), to 21μm intensity ( $I_{\nu }^{\mathrm{F2100W}}$), tracing small, warm dust grain emission, is suppressed in these low-metallicity dwarfs. Using Atacama Large Millimeter/submillimeter Array CO(2–1) observations, we find that detected CO intensity versus $I_{\nu }^{\mathrm{F770W}}$at ≈2 pc resolution in dwarfs follows a similar relationship to that at solar metallicity and lower resolution, while the CO versus $I_{\nu }^{\mathrm{F2100W}}$relationship in dwarfs lies significantly below that derived from solar-metallicity galaxies at lower resolution, suggesting more pronounced destruction of CO molecules at low metallicity. Finally, adding in Local Group L-Band Survey 21 cm Hiobservations from the Very Large Array, we find that $I_{\nu }^{\mathrm{F2100W}}$and $I_{\nu }^{\mathrm{F770W}}$versus total gas ratios are suppressed in NGC 6822 and WLM compared to solar-metallicity galaxies. In agreement with dust models, the level of suppression appears to be at least partly accounted for by the reduced galaxy-averaged dust-to-gas and PAH-to-dust mass ratios in the dwarfs. Remaining differences are likely due to spatial variations in dust model parameters, which should be an exciting direction for future work in local dwarf galaxies. 

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4. KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6

   https://doi.org/10.3847/1538-4357/ac7400  

   Lehner, Nicolas; Kopenhafer, Claire; O’Meara, John M.; Howk, J. Christopher; Fumagalli, Michele; Prochaska, J. Xavier; Acharyya, Ayan; O’Shea, Brian W.; Peeples, Molly S.; Tumlinson, Jason; et al (September 2022, The Astrophysical Journal)

   Abstract We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲z≲ 3.6 in 202 Hi-selected absorbers with 14.6 ≤ $\log N_{\mathrm{H}\mathrm{I}}$< 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with $14.6\le \log N_{\mathrm{H}\mathrm{I}}<20$at 2.2 ≲z≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyαabsorbers (DLAs); it can also be very metal-poor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For $16<\log N_{\mathrm{H}\mathrm{I}}<20$absorbers, the frequency of pristine absorbers is about 1%–10%, while for $14.6\le \log N_{\mathrm{H}\mathrm{I}}\le 16$absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv< 500 km s⁻¹imply that the metals are poorly mixed in $14.6\le \log N_{\mathrm{H}\mathrm{I}}<20$gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲z≲ 3.6. We find that the mean metallicity increases withN_Hi, consistent with what is found inz< 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲z≲ 3.6 toz< 1, but the contribution of the $14.6\le \log N_{\mathrm{H}\mathrm{I}}<19$absorbers to the total metal budget of the universe atz< 1 is a quarter of that at 2.2 ≲z≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] withN_Hi, which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 atz∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows. 

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5. Noise in the LIGO livingston gravitational wave observatory due to trains

   https://doi.org/10.1088/1361-6382/acf01f  

   Glanzer, J.; Soni, S.; Spoon, J.; Effler, A.; González, G. (September 2023, Classical and Quantum Gravity)

   Abstract Environmental seismic disturbances limit the sensitivity of LIGO gravitational wave detectors. Trains near the LIGO Livingston detector produce low frequency (0.5– $10\mathrm{H}\mathrm{z}$) ground noise that couples into the gravitational wave sensitive frequency band (10– $100\mathrm{H}\mathrm{z}$) through light reflected in mirrors and other surfaces. We investigate the effect of trains during the Advanced LIGO third observing run, and propose a method to search for narrow band seismic frequencies responsible for contributing to increases in scattered light. Through the use of the linear regression tool Lasso (least absolute shrinkage and selection operator) and glitch correlations, we identify the most common seismic frequencies that correlate with increases in detector noise as 0.6– $0.8\mathrm{H}\mathrm{z}$, 1.7– $1.9\mathrm{H}\mathrm{z}$, 1.8– $2.0\mathrm{H}\mathrm{z}$, and 2.3– $2.5\mathrm{H}\mathrm{z}$in the LIGO Livingston corner station. 

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