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1. Modeling Ionized Gas in the Small Magellanic Cloud: The Wolf–Rayet Nebula N76

   https://doi.org/10.3847/1538-4357/ad3def  

   Tarantino, Elizabeth; Bolatto, Alberto D; Indebetouw, Rémy; Rubio, Mónica; Sandstrom, Karin M; Smith, J-D T; Stapleton, Daniel; Wolfire, Mark (July 2024, The Astrophysical Journal)

   Abstract We presentCloudymodeling of infrared emission lines in the Wolf–Rayet (WR) nebula N76 caused by one of the most luminous and hottest WR stars in the low metallicity Small Magellanic Cloud. We use spatially resolved mid-infrared Spitzer/InfRared Spectrograph and far-infrared Herschel/PACS spectroscopy to establish the physical conditions of the ionized gas. The spatially resolved distribution of the emission allows us to constrain properties much more accurately than using spatially integrated quantities. We construct models with a range of constant hydrogen densities between n_H= 4–10 cm⁻³and a stellar wind-blown cavity of 10 pc, which reproduces the intensity and shape of most ionized gas emission lines, including the high ionization lines [Oiv] and [Nev], as well as [Siii], [Siv], [Oiii], and [Neiii]. Our models suggest that the majority of [Siii] emission (91%) is produced at the edge of the Hiiregion around the transition between ionized and atomic gas while very little of the [Cii] (<5%) is associated with the ionized gas. The physical conditions of N76 are characterized by a hot HII region with a maximum electron temperature ofT_e∼ 24,000 K, electron densities that range fromn_e∼ 4 to 12 cm⁻³, and high ionization parameters of $\log \left(U\right)\sim -1.15\mathrm{to}-1.77.$ By analyzing a low-metallicity WR nebula with a single ionization source, this work gives valuable insights into the impact WR stars have on the galaxy-integrated ionized gas properties in nearby dwarf galaxies. 

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2. Imaging nuclear shape through anisotropic and radial flow in high-energy heavy-ion collisions

   https://doi.org/10.1088/1361-6633/ae0fc3  

   Collaboration, The STAR (October 2025, Reports on Progress in Physics)

   Abstract Most atomic nuclei exhibit ellipsoidal shapes characterized by quadrupole deformationβ₂and triaxialityγ, and sometimes even a pear-like octupole deformationβ₃. The STAR experiment introduced a new ‘imaging-by-smashing’ technique ((STAR Collaboration) 2024Nature63567; Jia 2025Rep. Prog. Phys.88092301) to image the nuclear global shape by colliding nuclei at ultra-relativistic speeds and analyzing outgoing debris. Features of nuclear shape manifest in collective observables like anisotropic flowv_nand radial flow via mean transverse momentum $\left[p_{\mathrm{T}}\right]$ . We present new measurements of the variances ofv_n(n = 2, 3, and 4) and $\left[p_{\mathrm{T}}\right]$ , and the covariance of $v_n^2$ with $\left[p_{\mathrm{T}}\right]$ , in collisions of highly deformed²³⁸U and nearly spherical¹⁹⁷Au. Ratios of these observables between the two systems effectively suppress common final-state effects, isolating the strong impact of uranium’s deformation. By comparing results with state-of-the-art hydrodynamic model calculations, we extract ${\beta }_{2\mathrm{U}}$ and ${\gamma }_{\mathrm{U}}$ values consistent with those deduced from low-energy nuclear structure measurements. Measurements ofv₃and its correlation with $\left[p_{\mathrm{T}}\right]$ also provide the first experimental suggestion of a possible octupole deformation for²³⁸U. These findings provide significant support for using high-energy collisions to explore nuclear shapes on femtosecond timescales, with implications for both nuclear structure and quark-gluon plasma studies. 

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3. Massive Extremely High-velocity Outflow in the Quasar J164653.72+243942.2

   https://doi.org/10.3847/1538-4357/adef0d  

   Rodríguez_Hidalgo, Paola; Choi_최, Hyunseop 현섭; Hall, Patrick B; Leighly, Karen M; Flores, Liliana; Charles, Mikel M; DeFrancesco, Cora; Hlavacek-Larrondo, Julie; Perreault-Levasseur, Laurence (September 2025, The Astrophysical Journal)

   Abstract We present analysis of one of the most extreme quasar outflows found to date in our survey of extremely high-velocity outflows (EHVOs). J164653.72+243942.2 (z_em ∼ 3.04) shows variable Civλλ1548,1551 absorption at speeds larger than 0.1c, accompanied by Siiv, Nv,and Lyα, and disappearing absorption at lower speeds. We perform absorption measurements using the apparent optical depth method and SimBAL. We find the absorption to be very broad (Δv ∼  35,100 km s⁻¹in the first epoch and 13,000 km s⁻¹in the second one) and fast (v_max ∼  –50,200 km s⁻¹and −49,000 km s⁻¹, respectively). We measure large column densities ( $\log N_{\mathrm{H}}>$ 21.6 (cm⁻²)) and are able to place distance estimates for the EHVO (5 ≲ R ≲ 28 pc) and the lower-velocity outflow (7 ≲ R ≲ 540 pc). We estimate a mass outflow rate for the EHVO to be ${\dot{M}}_{\mathrm{out}}\sim 50–290M_{\odot }{\mathrm{yr}}^{-1}$ and a kinetic luminosity of $\log L_{\mathrm{KE}}\sim 46.5–47.2\left(\mathrm{erg}{\mathrm{s}}^{-1}\right)$ in both epochs. The lower-velocity component has a mass outflow rate ${\dot{M}}_{\mathrm{out}}\sim 10–790M_{\odot }{\mathrm{yr}}^{-1}$ and a kinetic luminosity of $\log L_{\mathrm{KE}}\sim 45.3–47.2\left(\mathrm{erg}{\mathrm{s}}^{-1}\right)$ . We find that J164653.72+243942.2 is not an outlier among EHVO quasars in regard to its physical properties. While its column density is lower than typical BAL values, its higher outflow velocities drive most of the mass outflow rate and kinetic luminosity. These results emphasize the crucial role of EHVOs in powering quasar feedback, and failing to account for these outflows likely leads to underestimating the feedback impact on galaxies. 

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4. Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

   https://doi.org/10.1088/1367-2630/ace471  

   Jadbabaie, Arian; Takahashi, Yuiki; Pilgram, Nickolas H; Conn, Chandler J; Zeng, Yi; Zhang, Chi; Hutzler, Nicholas R (July 2023, New Journal of Physics)

   Abstract Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}\left(010\right)$ state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}\left(010\right)$ state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of ${}^{174}$ YbOH using high-resolution optical spectroscopy on the nominally forbidden $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}\left(010\right)$ $\to \tilde{A}{}^2{\mathrm{\Pi }}_{1/2}\left(000\right)$ transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}\left(010\right)$ state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the $\tilde{X}{}^2{\mathrm{\Sigma }}^{+}\left(010\right)$ state and fit the molecule-frame dipole moment to $D_{\mathrm{m}\mathrm{o}\mathrm{l}}=2.16\left(1\right)$ Dand the effective electrong-factor to $g_S=2.07\left(2\right)$ . Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excited $\tilde{A}{}^2{\mathrm{\Pi }}_{1/2}\left(000\right)$ state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules. 

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5. Can Broad-line Region Line Profile Shape Improve Single-epoch Black Hole Mass Estimates?

   https://doi.org/10.3847/1538-4357/ae69cf  

   Villafaña, Lizvette; Treu, Tommaso; Wang, Shu; Bentz, Misty C; Brewer, Brendon J; Barth, Aaron J; Woo, Jong-Hak; Malkan, Matthew A; Bennert, Vardha N; U, Vivian (June 2026, The Astrophysical Journal)

   Abstract The virial coefficient (f), which is meant to encapsulate broad-line region (BLR) geometry and kinematics, remains one of the largest sources of systematic uncertainty in black hole mass estimates for active galactic nuclei (AGNs). While the use of a sample average 〈f〉 enables black hole mass estimates across large samples and cosmological distances, individual AGNs may deviate from this average due to differences in BLR structure and viewing angle. In previous work, we reported marginal evidence for a correlation betweenfand the shape of the broad Hβemission line, ${\log }_{10}(\mathrm{FWHM}/\sigma )$ . In this work, we update our sample to include 10 new sources withCARAMELBLR dynamical modeling, increasing both the black hole mass range and statistical power of our analysis. We find marginal evidence for a correlation betweenfand ${\log }_{10}(\mathrm{FWHM}/\sigma )$ , with a slope and intrinsic scatter consistent with previous results. The confirmation of this trend across a larger sample further supports the idea that line profile shape may reflect BLR properties in a way that directly impactsf. If confirmed with future BLR dynamical modeling of sources within a wider range of ${\log }_{10}(\mathrm{FWHM}/\sigma )$ , this relationship could enable empirical estimates of the virial coefficient and improve single-epoch black hole mass estimates across cosmic time. 

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