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1. Toward Robustness across Cosmological Simulation Models I llustris TNG, SIMBA, A strid , and S wift -E agle

   https://doi.org/10.3847/1538-4357/adec78  

   Jo, Yongseok; Genel, Shy; Sengupta, Anirvan; Wandelt, Benjamin; Somerville, Rachel; Villaescusa-Navarro, Francisco (September 2025, The Astrophysical Journal)

   Abstract The rapid advancement of large-scale cosmological simulations has opened new avenues for cosmological and astrophysical research. However, the increasing diversity among cosmological simulation models presents a challenge to therobustness. In this work, we develop the Model-Insensitive ESTimator (Miest), a machine that canrobustlyestimate the cosmological parameters, Ω_mandσ₈, from neural hydrogen maps of simulation models in the Cosmology and Astrophysics with MachinE Learning Simulations project—IllustrisTNG,SIMBA, Astrid, and SWIFT-Eagle. An estimator is consideredrobustif it possesses a consistent predictive power across all simulations, including those used during the training phase. We train our machine using multiple simulation models and ensure that it only extracts common features between the models while disregarding the model-specific features. This allows us to develop a novel model that is capable of accurately estimating parameters across a range of simulation models, without being biased toward any particular model. Upon the investigation of the latent space—a set of summary statistics, we find that the implementation ofrobustnessleads to the blending of latent variables across different models, demonstrating the removal of model-specific features. In comparison to a standard machine lackingrobustness, the average performance of Mieston the unseen simulations during the training phase has been improved by ∼17% for Ω_mand 38% forσ₈. By using a machine learning approach that can extractrobust, yet physical features, we hope to improve our understanding of galaxy formation and evolution in a (subgrid) model-insensitive manner, and ultimately, gain insight into the underlying physical processes responsible forrobustness. 

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2. Modeling the Reverberation Response of the Broad-line Region in Active Galactic Nuclei. II. Incorporating Photoionization Models

   https://doi.org/10.3847/1538-4357/adf109  

   Rosborough, Sara A; Robinson, Andrew; Almeyda, Triana; Humphrey, Daniel; Noll, Madison (September 2025, The Astrophysical Journal)

   Abstract The broad emission lines (BELs) emitted by active galactic nuclei respond to variations in the ionizing continuum emission from the accretion disk surrounding the central supermassive black hole (SMBH). This reverberation response provides insights into the structure and dynamics of the broad-line region (BLR). In 2024, we introduced a new forward-modeling tool, the Broad Emission Line Mapping Code (BELMAC), which simulates the velocity-resolved reverberation response of the BLR to an input light curve. In this work, we describe a new version of BELMAC, which uses photoionization models to calculate the cloud luminosities for selected BELs. We investigated the reverberation responses of Hα, Hβ, MgIIλ2800, and CIVλ1550 for models representing a disk-like BLR with Keplerian rotation, radiatively driven outflows, and inflows. The line responses generally provide a good indication of the respective luminosity-weighted radii. However, there are situations where the BLR exhibits a negative response to the driving continuum, causing overestimates of the luminosity-weighted radius. The virial mass derived from the models can differ dramatically from the actual SMBH mass, depending mainly on the disk inclination and velocity field. In single-zone models, the BELs exhibit similar responses and profile shapes; two-zone models, such as a Keplerian disk and a biconical outflow, can reproduce observed differences between high- and low-ionization lines. Radial flows produce asymmetric line profile shapes due to both anisotropic cloud emission and electron scattering in an intercloud medium. These competing attenuation effects complicate the interpretation of profile asymmetries. 

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3. High-resolution Spectra of Supernova Remnants in M83

   https://doi.org/10.3847/1538-4357/aca7f9  

   Winkler, P. Frank; Long, Knox S.; Blair, William P.; Points, Sean D. (January 2023, The Astrophysical Journal)

   Abstract In order to better characterize the rich supernova remnant (SNR) population of M83 (NGC 5236), we have obtained high-resolution (∼85 km s⁻¹) spectra of 119 of the SNRs and SNR candidates in M83 with Gemini/GMOS, as well as new spectra of the young SNRs B12-174a and SN 1957D. Most of the SNRs and SNR candidates have [Sii]:Hαratios that exceed 0.4. Combining these results with earlier studies we have carried out with MUSE and at lower spectroscopic resolution with GMOS, we have confirmed a total of 238 emission nebulae to be SNRs on the basis of their [Sii]:Hαratios, about half of which have emission lines that show velocity broadening greater than 100 km s⁻¹, providing a kinematic confirmation that they are SNRs and not Hiiregions. Looking at the entire sample, we find a strong correlation between velocity widths and the line ratios of [Oi]λ6300:Hα, [Nii]λ6584:Hα, and [Sii]λλ6716, 6731:Hα. The density-sensitive [Sii]λ6716:λ6731 line ratio is strongly correlated with SNR diameter, but not with the velocity width. We discuss these results in the context of previously published shock models. 

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4. Flavor at FASER: discovering light scalars beyond minimal flavor violation

   https://doi.org/10.1007/JHEP04(2025)071  

   Balkin, Reuven; Burger, Noam; Feng, Jonathan L; Shadmi, Yael (April 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We study a simple class offlavored scalarmodels, in which the couplings of a new light scalar to standard-model fermions are controlled by the flavor symmetry responsible for fermion masses and mixings. The scalar couplings are then aligned with the Yukawa matrices, with small but nonzero flavor-violating entries.D-meson decays are an important source of scalar production in these models, in contrast to models assuming minimal flavor violation, in whichBandKdecays dominate. We show that FASER2 can probe large portions of the parameter space of the models, with comparable numbers of scalars fromBandDdecays in some regions. If discovered, these particles will not only provide evidence of new physics, but they may also shed new light on the standard model flavor puzzle. Finally, the richness of theoretical models underscores the importance of model-independent interpretations. We therefore analyze the sensitivity of FASER and other experimental searches in terms of physical parameters: (i) the branching fractions of heavy mesons to the scalar, and (ii)τ/m, whereτandmare the scalar’s lifetime and mass, respectively. The results are largely independent of the new particle’s spin and can be used to extract constraints on a wide variety of models. 

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5. A New Constraint on the Relative Disorder of Magnetic Fields between Neutral Interstellar Medium Phases

   https://doi.org/10.3847/1538-4357/ad5ade  

   Lei, Minjie; Clark, S_E (August 2024, The Astrophysical Journal)

   Abstract Utilizing Planck polarized dust emission maps at 353 GHz and large-area maps of the neutral hydrogen (Hi) cold neutral medium (CNM) fraction (f_CNM), we investigate the relationship between dust polarization fraction (p₃₅₃) andf_CNMin the diffuse high latitude ( $\left(b\right)>30°$) sky. We find that the correlation betweenp₃₅₃andf_CNMis qualitatively distinct from thep₃₅₃–Hicolumn density (N_Hi) relationship. At low column densities (N_Hi< 4 × 10²⁰cm⁻²) wherep₃₅₃andN_Hiare uncorrelated, there is a strong positivep₃₅₃–f_CNMcorrelation. We fit thep₃₅₃–f_CNMcorrelation with data-driven models to constrain the degree of magnetic field disorder between phases along the line of sight. We argue that an increased magnetic field disorder in the warm neutral medium (WNM) relative to the CNM best explains the positivep₃₅₃–f_CNMcorrelation in diffuse regions. Modeling the CNM-associated dust column as being maximally polarized, with a polarization fractionp_CNM∼ 0.2, we find that the best-fit mean polarization fraction in the WNM-associated dust column is 0.22p_CNM. The model further suggests that a significantf_CNM-correlated fraction of the non-CNM column (an additional 18.4% of the Himass on average) is also more magnetically ordered, and we speculate that the additional column is associated with the unstable medium. Our results constitute a new large-area constraint on the average relative disorder of magnetic fields between the neutral phases of the interstellar medium, and are consistent with the physical picture of a more magnetically aligned CNM column forming out of a disordered WNM. 

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