Article
Astronomy & Astrophysics
Karol Fulat, Artem Bohdan, Gabriel Torralba Paz, Martin Pohl
Summary: This study investigates electron acceleration and heating processes at nonrelativistic high-Mach-number shocks in electron-ion plasma with a turbulent upstream medium using 2D3V particle-in-cell simulations. The results indicate that fluctuations in the upstream turbulent medium have little influence on the behavior of electrons in perpendicular shocks.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
James Juno, Collin R. Brown, Gregory G. Howes, Colby C. Haggerty, Jason M. TenBarge, Lynn B. Wilson, Damiano Caprioli, Kristopher G. Klein
Summary: Examining the energization of kinetic plasmas in phase space has become an increasingly important topic. By applying the field-particle correlation (FPC) technique and numerical integration of the plasma kinetic equation, we have studied the energization of ions in oblique collisionless shocks. Our analysis in phase space allows for the characterization of distinct populations of energized ions, including those reflecting multiple times off the shock front through shock-drift acceleration. We further demonstrate the applicability of the FPC technique in more realistic collisionless shock environments.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Domenico Trotta, Timothy S. Horbury, David Lario, Rami Vainio, Nina Dresing, Andrew Dimmock, Joe Giacalone, Heli Hietala, Robert F. Wimmer-Schweingruber, Lars Berger, Liu Yang
Summary: This study reports novel observations of irregular enhancements of the suprathermal particle population upstream of a high-Mach-number interplanetary shock and interprets the observed behavior as irregular injections of suprathermal particles resulting from shock front irregularities. Comparing the findings to self-consistent simulation results, important insights are provided for the study of remote astrophysical systems where shock structuring is often neglected.
ASTROPHYSICAL JOURNAL LETTERS
(2023)
Article
Astronomy & Astrophysics
Naveen Kumar, Brian Reville
Summary: This study investigates the nonthermal acceleration of electrons and ions at an oblique, nonrelativistic shock using large-scale particle-in-cell simulations in one spatial dimension. The simulation results reveal early onset of the diffusive shock acceleration for both electrons and ions at a highly oblique subluminal shock. Ion acceleration efficiencies of less than or similar to 5% are measured at later times, although this is not the saturated value.
ASTROPHYSICAL JOURNAL LETTERS
(2021)
Article
Physics, Multidisciplinary
Qile Zhang, Fan Guo, William Daughton, Hui Li, Xiaocan Li
Summary: Research shows that the flux-rope kink instability leads to strong field-line chaos in weak-guide-field regimes, allowing particles to transport more efficiently out of flux ropes and undergo acceleration. The results are highly relevant to observations of nonthermal particle acceleration in space and astrophysics.
PHYSICAL REVIEW LETTERS
(2021)
Article
Astronomy & Astrophysics
Allard Jan van Marle, Artem Bohdan, Paul J. Morris, Martin Pohl, Alexandre Marcowith
Summary: This article investigates the occurrence of diffusive shock acceleration (DSA) in oblique high Mach number shocks. Using particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique, the study examines the formation of the shock and determines the fraction of particles involved in DSA. The researchers also use PIC-MHD simulations to model the plasma and magnetic field surrounding the shock and determine whether reflected particles can generate upstream turbulence and trigger DSA. The results show that the feasibility of this process in oblique shocks depends strongly on the Alfvenic Mach number, with high Mach number shocks being more likely to trigger DSA.
ASTROPHYSICAL JOURNAL
(2022)
Article
Physics, Fluids & Plasmas
Xiaocan Li, Fan Guo, Yi-Hsin Liu
Summary: Magnetic reconnection plays a key role in accelerating particles in space and astrophysical plasmas. Research on how particles are accelerated and the resulting particle energy spectra is a central topic. Recent advances in nonrelativistic reconnection focus on particle acceleration mechanisms, particle transport, and the formation of power-law particle energy spectra. Challenges in studying particle acceleration and transport in a large-scale reconnection layer are highlighted, with relevant issues to be addressed in the future.
PHYSICS OF PLASMAS
(2021)
Article
Physics, Fluids & Plasmas
J. Plank, I. L. Gingell
Summary: The energy cascade in turbulent plasmas like the solar wind and magnetosheath occurs across different scales, and recent observations of Earth's bow shock provide insight into the turbulent dissipation and magnetic fluctuations in this region. Through analysis of magnetic spectra and correlation lengths, researchers found power-law scaling and changes in kurtosis in the shock transition region, with differences observed between quasi-perpendicular and quasi-parallel shocks. These findings contribute to a better understanding of plasma turbulence and its dynamics.
PHYSICS OF PLASMAS
(2023)
Article
Astronomy & Astrophysics
Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang
Summary: Cosmology models predict the formation of external accretion shocks in the outer region of galaxy clusters due to supersonic gas infall from filaments and voids. These shocks are expected to efficiently accelerate cosmic rays, but nonthermal signatures of shock-accelerated cosmic rays have not been confirmed, and the physics of acceleration at such shocks is not well understood.
ASTROPHYSICAL JOURNAL
(2023)
Article
Astronomy & Astrophysics
Sunjung Kim, Ji-Hoon Ha, Dongsu Ryu, Hyesung Kang
Summary: Microinstabilities have been found to play crucial roles in entropy generation and particle acceleration in collisionless shocks. Analysis of these microinstabilities in the high-beta region of the intercluster medium has revealed that ion and electron temperature anisotropies can induce various instabilities, leading to the generation of plasma waves with different scales and properties.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Bjorn Eichmann, Joerg P. Rachen
Summary: The study investigates the nonthermal source abundances of elements in cosmic ray phenomena, systematically describing the change of abundances from thermal to nonthermal states through diffusive shock acceleration by a evolving shock. The results show excellent agreement in warm ionized ISM environments, indicating efficient injection of dust grains in the acceleration process.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Krzysztof Stasiewicz, Zbigniew Klos
Summary: The analysis of four-point measurements by NASA's Magnetospheric Multiscale spacecraft reveals that the formation of quasi-parallel shocks is consistent with the counter-streaming ion-ion resonant right-handed instability. The onset of the instability is initiated by 30-second period oscillations, which steepen to shorter wavelengths and higher frequencies. The instability produces large amplitude magnetic field and plasma density shocklets with specific scale lengths.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Geosciences, Multidisciplinary
Li-Jen Chen, Shan Wang, Jonathan Ng, Naoki Bessho, Jian-Ming Tang, Shing F. Fung, Guan Le, Daniel Gershman, Barbara Giles, Christopher T. Russell, Roy Torbert, James Burch
Summary: The study investigates the formation of solitary magnetic structures known as SLAMS using measurements from the magnetospheric multiscale mission combined with fully kinetic simulations. The results indicate that gyro-resonance between solar wind ions and electromagnetic waves leads to magnetic field amplification, while the solitary nature of SLAMS is attributed to a specific magnetic field envelope.
GEOPHYSICAL RESEARCH LETTERS
(2021)
Article
Astronomy & Astrophysics
Oleh Kobzar, Jacek Niemiec, Takanobu Amano, Masahiro Hoshino, Shuichi Matsukiyo, Yosuke Matsumoto, Martin Pohl
Summary: Using large-scale fully kinetic two-dimensional particle-in-cell simulations, the effects of shock rippling on electron acceleration at low-Mach-number shocks propagating in high-beta plasmas were investigated. It was found that the electron-acceleration rate increases considerably when the rippling modes appear, with the main acceleration mechanism being stochastic shock-drift acceleration. Multiscale magnetic turbulence at the shock transition and the region behind the main shock overshoot are essential for electron energization, leading to wide-energy non-thermal electron distributions formed both upstream and downstream of the shock. The downstream electron spectrum was shown for the first time to have a power-law form with index p approximate to 2.5, consistent with observations.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Z. Wang, H. S. Fu, X. H. Chen, J. B. Cao, Y. Y. Liu, Y. Yu, R. J. He, Z. Z. Guo
Summary: By investigating the spiral magnetic nulls in the diffusion region of turbulent reconnection in the magnetotail, this study reveals the relationship between currents and the topology of magnetic nulls, with a focus on the role of background currents in determining the direction and orientation of the currents and null structures.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
T. Thomas, C. Pfrommer
Summary: Cosmic ray hydrodynamics is important for understanding the dynamical evolution of interstellar, circumgalactic, and intracluster medium. This paper investigates the impact of different closure relations on the resulting solutions and finds that the three presented hydrodynamical models produce similar results when cosmic ray scattering is neglected.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Martin Sparre, Joseph Whittingham, Mitali Damle, Maan H. Hani, Philipp Richter, Sara L. Ellison, Christoph Pfrommer, Mark Vogelsberger
Summary: This study explores the gas dynamics in and around merging galaxies, finding that the gas bridge connecting them is dominated by supersonic turbulence, making it an ideal candidate for studying the impact of extreme environments on star formation. Gas accreted from the circumgalactic medium significantly contributes to the star formation rate pre-merger and reignites star formation in the merger remnant.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Philipp Girichidis, Christoph Pfrommer, Ruediger Pakmor, Volker Springel
Summary: Studied the role of cosmic rays in galaxy formation, introduced a spectrally resolved cosmic ray model and compared it to a grey cosmic ray model, and found differences between the two models in galaxy morphology, star formation rate, and characteristics of outflows.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Ali Kurmus, Sownak Bose, Mark Lovell, Francis-Yan Cyr-Racine, Mark Vogelsberger, Christoph Pfrommer, Jesus Zavala
Summary: Observations of the high redshift universe offer a promising approach to understand the nature of dark matter. Through simulations, it has been found that different dark matter models show significant differences in the formation and development of high redshift galaxies, which has important implications for studying the essence of dark matter.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
K. Ehlert, R. Weinberger, C. Pfrommer, R. Pakmor, V Springel
Summary: Heating from active galactic nuclei (AGNs) is believed to stabilize cool-core clusters and limit star formation and cooling flows. This study used radiative magnetohydrodynamic (MHD) simulations to investigate light AGN jet feedback with different accretion modes in an idealized Perseus-like cluster. The results showed that the cluster self-regulates to form central entropies and cooling times consistent with observed cool-core clusters.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Thales A. Gutcke, Christoph Pfrommer, Greg L. Bryan, Ruediger Pakmor, Volker Springel, Thorsten Naab
Summary: The ability of galaxies to continue forming stars after reionization is related to their host halo's mass, growth history, UV background, and retained metals.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Matthias Weber, Timon Thomas, Christoph Pfrommer
Summary: Cosmic rays (CRs) have an important role in astrophysical systems and are usually modelled as a fluid. In this study, two different methods, the energy-based and entropy-conserving schemes, for evolving CRs were compared and tested in various scenarios. The entropy-conserving scheme performed better in purely adiabatic CR cases, while both methods yielded similar results at lower resolution. In more realistic applications, both methods produced almost identical results.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Christine M. Simpson, Ruediger Pakmor, Christoph Pfrommer, Simon C. O. Glover, Rowan Smith
Summary: In this study, the impact of diffusive cosmic rays (CRs) on the evolution of the interstellar medium (ISM) is explored under varying assumptions of supernova explosion environment. It is found that CR pressure and transport are important factors that strongly influence the ISM's solution state. Observable signatures such as gamma-ray emission and H i gas are also investigated, with the gamma-ray luminosity being consistent with observations but the thickness of the H i gas layer potentially being too compact.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Correction
Astronomy & Astrophysics
Philipp Girichidis, Christoph Pfrommer, Ruediger Pakmor, Volker Springel
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Rainer Weinberger, Kung-Yi Su, Kristian Ehlert, Christoph Pfrommer, Lars Hernquist, Greg L. Bryan, Volker Springel, Yuan Li, Blakesley Burkhart, Ena Choi, Claude-Andre Faucher-Giguere
Summary: Feedback from hydrodynamic jets is believed to reduce cooling flows in cool-core galaxy clusters. Our simulations show that the choices of jet properties within a given model are the dominant uncertainties. Light, thermal jets with low momentum flux can delay the onset of a cooling flow more efficiently than heavy, kinetic jets. The delay originates from a displacement and boost in entropy of the central gas.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Rudiger Pakmor, Volker Springel, Jonathan P. Coles, Thomas Guillet, Christoph Pfrommer, Sownak Bose, Monica Barrera, Ana Maria Delgado, Fulvio Ferlito, Carlos Frenk, Boryana Hadzhiyska, Cesar Hernandez-Aguayo, Lars Hernquist, Rahul Kannan, Simon D. M. White
Summary: In this study, the MillenniumTNG (MTNG) project is introduced, which provides high-resolution, large-volume simulations of cosmic structure formation. The focus is on the MTNG740 simulation, which produces galaxy clusters consistent with observational constraints. It is found that the mass estimates of Planck clusters may be underestimated.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Maria Werhahn, Philipp Girichidis, Christoph Pfrommer, Joseph Whittingham
Summary: Gamma-ray observations are used to constrain the interaction and transport properties of cosmic rays in the interstellar medium. Simulations show that energy-dependent spatial diffusion of cosmic rays leads to a more extended distribution of high-energy gamma rays compared to a steady-state model, but the total gamma-ray spectra can still be approximated by the steady-state model.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Joseph Whittingham, Martin Sparre, Christoph Pfrommer, Ruediger Pakmor
Summary: The role of magnetic fields in galaxy evolution is crucial and alters the outcome of mergers, modifies the transport of angular momentum, suppresses bar-instability, and decreases the influence of stellar feedback.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Review
Astronomy & Astrophysics
Mateusz Ruszkowski, Christoph Pfrommer
Summary: Understanding the physical mechanisms that control galaxy formation is a fundamental challenge in contemporary astrophysics. Recent advances suggest that cosmic rays (CRs) may be crucially important for our understanding of cosmological galaxy formation and evolution. CRs play important roles in driving galactic winds, influencing pressure in the circumgalactic medium, and addressing the cooling flow problem in galaxy clusters.
ASTRONOMY AND ASTROPHYSICS REVIEW
(2023)