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Latest articles for The Astrophysical Journal
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The JADES Mass–Metallicity and Fundamental Metallicity Relations at z ≳ 2 Using New High-redshift Metallicity Calibrations
We present measurements of the mass–metallicity relation (MZR) and fundamental metallicity relation (FMR) at 1.4 < z < 7.0 using stacked JWST/NIRSpec spectra of 601 star-forming galaxies from the JWST Advanced Deep Extragalactic Survey (JADES). Using the most up-to-date strong-line metallicity calibrations based on high-redshift galaxies, we derive gas-phase metallicities from composite spectra binned by stellar mass, redshift, and star-forming main sequence (SFMS) offset. We find that the MZR slope evolves weakly from z ∼ 0 out to ∼5, with γ ∼ 0.21 ± 0.03, while the normalization decreases smoothly with redshift at a rate of out to z ∼ 4. Beyond z ≳ 5, the low-mass end continues to decline in metallicity while the high-mass end remains broadly consistent with lower-redshift relations, producing a steeper overall MZR. We additionally find evidence for a shallow anticorrelation between deviations from the MZR and SFMS at fixed stellar mass at z ∼ 1.4−5. This anticorrelation, albeit with weaker star formation rate coupling than observed locally, suggests that an FMR is already beginning to emerge by z ∼ 5. Comparisons with recent observations and cosmological simulations show broad agreement, though no single simulation simultaneously reproduces the observed slopes and normalizations across all redshifts. Our results support a picture in which bursty star formation and strong stellar feedback increasingly shape the regulation of galaxy growth at high redshift, while also highlighting the need for substantially larger spectroscopic samples to robustly constrain the evolution of galaxy scaling relations at high redshift.
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Collisionless Electron Heat Flux for the Nonequilibrium Solar Wind Plasma: Revisiting Hollweg’s Parameter
Here, we discuss an extension of the modelling of the collisionless heat flux and the related parameter α, derived by Hollweg for a truncated Maxwellian to distributions with suprathermal tails. In the collisionless solar wind plasma, electrons and ions are described by a multitude of non-Maxwellian (nonequilibrium) velocity distributions, such as the standard, regularized κ, and Druyvesteyn distributions. We show that for these nonidealized distributions, the heat flux and the related parameter α can deviate significantly from the Maxwellian values derived by Hollweg. It is also shown that the heat flux is best described using a form that does not directly involve the truncation speed. Furthermore, we discuss the applicability of these distribution models for the nonrelativistic case, which constrains the κ values for the standard κ distribution to values above 4. In addition, we provide the possibility to easily obtain the heat flux parameter for a given solar wind environment.
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Exploring Magnetic Reconnection in a Sub-A-class Microflare Using Data-constrained Numerical Simulation and Multi-instrument Observations
Solar flares are intermittent events that convert free magnetic energy into heat and kinetic energy of charged particles, along with a rearrangement of magnetic field lines (MFLs) through magnetic reconnection. This work investigates an active-region sub-A-class microflare detected by the Solar X-ray Monitor on board Chandrayaan-2. The MFL topology, its evolution, and the associated magnetic reconnection in the flaring region are investigated. The coronal magnetic field is constructed using the nonlinear force-free field (NLFFF) extrapolation model, indicating the presence of a magnetic flux rope (MFR) at the flaring location. Notably, this MFR exhibits regions of high magnetic field gradient and a nonuniform distribution of twist along its axis. Furthermore, the dynamics of the MFR is explored using a three-dimensional data-constrained magnetohydrodynamics simulation performed using the EULAG-MHD code. The simulation shows overall untangling of the MFLs that constitute the MFR, along with changes in their connectivity, which suggests underlying magnetic reconnection. Further, a few representative MFLs belonging to the MFR over a given time span are advected with the plasma flow to maintain their identity. These field lines show a change in connectivity, and such reconnections can contribute to the unfurling of the MFR. The overall scenario is generally consistent with the concept of braiding reconnection in an MFR.
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The Relation between Magnetic-field Intensity and Size of the Emission Region in the High-synchrotron-peaked BL Lacertae Object Mrk 421
Magnetic effects are thought to dominate the formation of BL Lac object jets, but the role and influence of large-scale magnetic fields within the jets remains incompletely understood. We utilize a one-zone synchrotron-self-Compton (SSC) model with broken-power-law electron injection to reproduce multiwavelength spectral energy distributions (SEDs) of the high-synchrotron-peaked BL Lac object Mrk 421 for 73 activity states, constraining six key physical parameters. We investigate the correlation between magnetic-field strength B and emission-region size R and estimate the powers of relativistic electrons, cold protons, magnetic fields, and total jet power. We find a significant anticorrelation . The derived slope close to −1 is compatible with theoretical expectations for a toroidal magnetic geometry, though parameter couplings inherent to the leptonic model cannot be fully excluded. Markov Chain Monte Carlo (MCMC) posterior analyses demonstrate that this B–R scaling is not merely an artefact of intra-epoch parameter degeneracy. On emission-region scales the jet is particle-kinetic-energy dominated; distinct electron-acceleration mechanisms (shocks, magnetic reconnection) operate across different activity states, and the conventional Poynting-flux-dominated scenario cannot account for the observed radiative power.
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Can Magnetic Reconnection Accelerate Energetic Particles in the Heliosheath?
The mechanism for accelerating energetic particles in the outer heliosphere is still under debate. The termination shock, turbulence, and magnetic reconnection have all been proposed as viable mechanisms. We investigate compression-driven particle acceleration during magnetic reconnection in the heliospheric current sheet using the MHD–SDE framework that incorporates energetic particle feedback into the MHD evolution. For the heliosheath conditions considered here, we find that reconnection-driven acceleration is inefficient downstream of the termination shock, whereas reconnection near the heliopause can generate stronger compression and produce a power-law differential intensity spectrum J(ε) ∝ ε−5.4. However, even the hardest spectrum achieved during magnetic reconnection remains much steeper than the typical J(ε) ∝ ε−1.5 spectrum observed in the heliosheath. This indicates that magnetic reconnection alone is insufficient to explain the acceleration of energetic particles in the heliosheath.