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Abstract Magnetic fields and turbulence are fundamental to the evolutions of galaxies, yet their precise measurement and analysis present significant challenges. The recently developed Velocity Gradient Technique (VGT), which capitalizes on the anisotropy inherent in magnetohydrodynamic (MHD) turbulence, represents a new method for mapping magnetic fields in galaxies using spectroscopic observations. Most validations of VGT thus far have relied upon idealized MHD turbulence simulations, however, which lack the more complex dynamics found in galaxies and galaxy mergers. In this study, we scrutinize VGT using an AREPO-based cosmological galaxy merger simulation, testing its effectiveness across pre-merger, merging, and post-merger stages. We examine the underlying assumptions of VGT and probe the statistics of gas density, velocity, and magnetic fields over time. We find that the velocity fluctuations are indeed anisotropic at each stage, being larger in the direction perpendicular to the local magnetic field, as required by VGT. We find additionally that galaxy mergers substantially intensify the velocity and density fluctuations and amplify the magnetic fields at all scales. The observed scaling of the velocity fluctuations shows a steeper trend thanr1/2between 0.6 and 3 kpc and a shallower trend at larger scales. The scaling of the magnetic field and density fluctuations at scales ≲1.0 kpc also predominantly aligns withr1/2. Finally, we compare results from VGT to those derived from polarization-like mock magnetic field measurements, finding consistent and statistically significant global agreement in all cases.
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This content will become publicly available on August 13, 2026
Impact of Magnetic-field-driven Anisotropies on the Equation of State Probed in Neutron Star Mergers
Abstract Binary neutron star mergers can produce extreme magnetic fields, some of which can lead to strong magnetar-like remnants. While strong magnetic fields have been shown to affect the dynamics of outflows and angular momentum transport in the remnant, they can also crucially alter the properties of nuclear matter probed in the merger. In this work, we provide a first assessment of the latter, determining the strength of the pressure anisotropy caused by Landau-level quantization and the anomalous magnetic moment. To this end, we perform the first numerical relativity simulation with a magnetic polarization tensor and a magnetic-field-dependent equation of state using a new algorithm we present here, which also incorporates a mean-field dynamo model to control the magnetic field strength present in the merger remnant. Our results show that—in the most optimistic case—corrections to the anisotropy can be in excess of 10% and are potentially largest in the outer layers of the remnant. This work paves the way for a systematic investigation of these effects.
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- PAR ID:
- 10628472
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- The Astrophysical Journal Letters
- Volume:
- 989
- Issue:
- 2
- ISSN:
- 2041-8205
- Page Range / eLocation ID:
- L29
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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