arXiv subjects

Hsiang-Yi Karen Yang

Publications and source records attributed to Hsiang-Yi Karen Yang.

9 recordsLinked to original sources

arXiv2026

Cool-Core Destruction in Merging Clusters with AGN Feedback and Radiative Cooling

The origin of cool-core (CC) and non-cool-core (NCC) dichotomy of galaxy clusters remains uncertain. Previous simulations have found that cluster mergers are effective in destroying CCs but fail to prevent overcooling in cluster cores when radiative cooling is included. Feedback from active galactic nuclei (AGN) is a promising mechanism for balancing cooling in CCs; however, the role of AGN feedback in CC/NCC transitions remains elusive. In this work, we perform three-dimensional binary cluster merger simulations incorporating AGN feedback and radiative cooling, aiming to investigate the heating effects from mergers and AGN feedback on CC destruction. We vary the mass ratio and impact parameter to examine the entropy evolution of different merger scenarios. We find that AGN feedback is essential in regulating the merging clusters, and that CC destruction depends on the merger parameters. Our results suggest three scenarios regarding CC/NCC transitions: (1) CCs are preserved in minor mergers or mergers that do not trigger sufficient heating, in which cases AGN feedback is crucial for preventing the cooling catastrophe; (2) CCs are transformed into NCCs by major mergers during the first core passage, and AGN feedback is subdominant; (3) in major mergers with a large impact parameter, mergers and AGN feedback operate in concert to destroy the CCs.

astro-ph.CO↗

arXiv2026

Equatorially Asymmetric Magnetic Fields and Their Impact on Black Hole Accretion Dynamics

We investigate the impact of equatorial asymmetry in the magnetic field geometry on accretion dynamics around a spinning black hole using axisymmetric general relativistic magnetohydrodynamic simulations. We consider a Fishbone--Moncrief torus orbiting a Kerr black hole with spin parameter $a = 0.9375$, threaded by large-scale magnetic fields that are asymmetric about the equatorial plane. The degree of equatorial asymmetry in the magnetic field is parametrized by an angle, with values of $30^\circ$, $45^\circ$, and $60^\circ$. We examine how this equatorially asymmetric initial magnetic field configuration influences the magnetic field structure, accretion flow morphology, and angular momentum transport across a range of initial plasma beta values ($β= 0.007, 0.005, 0.001$). We find that such deformation in the magnetic field leads to noticeable changes in the inner disk structure, asymmetric outflow patterns in the poloidal plane, and time-dependent variations in accretion rates. These effects are generally more pronounced at lower beta values, where magnetic pressure dominates; in particular, the $30^\circ$ case at $β= 0.001$ exhibits strong and persistent asymmetric inflows and outflows. Our results demonstrate that equatorially asymmetric magnetic field configurations can significantly influence the structure and variability of relativistic accretion flows. These findings motivate future extensions to full three-dimensional studies, where black hole magnetosphere can be explored in a more general setting.

astro-ph.HE↗

arXiv2025

Exploring the Role of Vector Potential and Plasma-$β$ in Jet Formation from Magnetized Accretion Flows

In this work, we investigate how the choice of initial vector potential and plasma parameters influences the development of accretion columns and jet formation in magnetized accretion flows. Using general relativistic magnetohydrodynamic simulations, we explore two different configurations of the vector potential $A_ϕ$ and three plasma beta values $β$ = 50, 100, 500. We analyze how variations in the poloidal magnetic field strength and plasma magnetization affect magnetic flux accumulation near the black hole and the subsequent growth of the accretion column. Our results highlight the dependence of jet launching efficiency and accretion dynamics on the initial magnetic field topology and plasma beta, offering insight into the conditions that favor magnetically arrested disk or standard and normal evolution states.

astro-ph.HE↗

arXiv2025

Impact of Jet Density on Intracluster Medium Heating in Self-Regulated AGN Feedback Simulations

Active galactic nucleus (AGNs) feedback is widely accepted as the key mechanism to suppress cooling flows in galaxy clusters. However, the dependence of heating efficiency on jet properties is not fully understood. In this work, we present three-dimensional hydrodynamic simulations of a Perseus-like cluster, including both single-jet and self-regulated models, to investigate how jet density affects bubble evolution and the thermal balance of the intracluster medium. Our results confirm previous findings that lighter jets inflate more spherical bubbles and are more easily deflected by cold gas, enabling isotropic energy deposition throughout the cluster core. However, despite their broader spatial impact, lighter jets display lower overall heating efficiency, requiring higher average jet power to maintain self-regulation compared to heavier jets. We also find that the distribution and amount of cold gas significantly influence the effectiveness of jet heating. These results highlight jet density as a critical parameter in AGN feedback and emphasize the need to incorporate additional physical processes such as magnetic fields, viscosity, and cosmic rays in future studies for realistic comparisons with observations.

astro-ph.GA↗

arXiv2025

Probing viscosity of the intracluster medium using ram-pressure stripping

Galaxies falling into galaxy clusters can leave imprints on both the corona of galaxies and the intracluster medium (ICM) of galaxy clusters. Throughout this infall process, the galaxy's atmosphere is subjected to ram pressure from a headwind, leading to the stripping morphology observed in its tail. The morphological evolution is affected by the properties of the surrounding ICM such as magnetic fields and viscosity. In this Letter, we perform 3D Braginskii-magnetohydrodynamic simulations using the FLASH code with varied ICM viscosity models. Specifically, we explore four models: an inviscid case, unsuppressed isotropic viscosity, unsuppressed anisotropic viscosity, and anisotropic viscosity suppressed by plasma instabilities. Our findings indicate that the isotropic viscosity case effectively suppresses hydrodynamic instabilities and shows strong viscous heating and the least mixing with the ICM, enabling the formation of long, coherent tails. The inviscid model has the shortest tail due to vigorous mixing, and the models with anisotropic viscosity are in between. The model with suppressed anisotropic viscosity due to plasma instabilities exhibits enhanced turbulence in the galactic tail and a concurrent limitation in viscous heating compared to the model neglecting plasma instabilities. These findings highlight the significant impact of ICM plasma physics on the processes of ram pressure stripping of galaxies.

astro-ph.GA↗

arXiv2025

Boosting Supermassive Black Hole Growth in the Early Universe by Fuzzy Dark Matter Solitons

Observations of massive supermassive black holes (SMBHs) in the early universe challenge existing black hole formation models. We propose that soliton cores in fuzzy dark matter (FDM) offer a potential solution to this timing problem. Our FDM cosmological zoom-in simulations confirm that for a particle mass $m_{\rm FDM}\sim 10^{-22}~{\rm eV}$, solitons are well developed at redshift $z \sim 7$ with masses of $\sim10^9~M_\odot$, comparable to the observed SMBHs. We then demonstrate using hydrodynamic simulations that, compared to cold dark matter, these high-$z$ massive FDM solitons with mass $M_s$ can provide additional gravitational potential to accrete gas and boost the Bondi accretion rate of a growing black hole seed with mass $M_{\rm BH}$ by up to two to four orders of magnitude, in the regime of efficient cooling and negligible radiation pressure. This accretion boosting mechanism is effective for $10^{-22}~{\rm eV} \lesssim m_{\rm FDM} \lesssim 10^{-20}~{\rm eV}$ and potentially beyond as long as $M_s > M_{\rm BH}$. The simulation code GAMER is accessible at https://github.com/gamer-project/gamer.

astro-ph.CO↗

arXiv2023

Recent Progress in Modeling the Macro- and Micro-Physics of Radio Jet Feedback in Galaxy Clusters

Radio jets and the lobes they inflate are common in cool-core clusters and are known to play a critical role in regulating the heating and cooling of the intracluster medium (ICM). This is an inherently multi-scale problem, and much effort has been made to understand the processes governing the inflation of lobes and their impact on the cluster, as well as the impact of the environment on the jet-ICM interaction, on both macro- and microphysical scales. Developments of new numerical techniques and improving computational resources have seen simulations of jet feedback in galaxy clusters become ever more sophisticated. This ranges from modelling ICM plasma physics processes such as the effects of magnetic fields, cosmic rays and viscosity to including jet feedback in cosmologically evolved cluster environments in which the ICM thermal and dynamic properties are shaped by large-scale structure formation. In this review, we discuss the progress made over the last ~decade in capturing both the macro- and microphysical processes in numerical simulations, highlighting both the current state of the field as well as open questions and potential ways in which these questions can be addressed in the future.

astro-ph.HE↗

arXiv2022

Curved accretion disks around rotating black holes without reflection symmetry

Rotating black holes without equatorial reflection symmetry can naturally arise in effective low-energy theories of fundamental quantum gravity, in particular, when parity-violating interactions are introduced. Adopting a theory-agnostic approach and considering a recently proposed Kerr-like black hole model, we investigate the structure and properties of accretion disk around a rotating black hole without reflection symmetry. In the absence of reflection symmetry, the accretion disk is in general a curved surface in shape, rather than a flat disk lying on the equatorial plane. Furthermore, the parameter $ε$ that controls the reflection asymmetry would shrink the size of the prograde innermost stable circular orbits, and enhance the efficiency of the black hole in converting rest-mass energy to radiation during accretion. The retrograde innermost stable circular orbits are stretched but the effects are substantially suppressed. In addition, we find that spin measurements based on the gravitational redshift observations of the disk, assuming a Kerr geometry, may overestimate the true spin values if the central object is actually a Kerr-like black hole with conspicuous equatorial reflection asymmetry. The qualitative results that the accretion disk becomes curved and the prograde innermost stable circular orbits are shrunk turn out to be generic in our model when the reflection asymmetry is small.

gr-qc↗

arXiv2019

Supermassive Black Hole Feedback

Understanding the processes that drive galaxy formation and shape the observed properties of galaxies is one of the most interesting and challenging frontier problems of modern astrophysics. We now know that the evolution of galaxies is critically shaped by the energy injection from accreting supermassive black holes (SMBHs). However, it is unclear how exactly the physics of this feedback process affects galaxy formation and evolution. In particular, a major challenge is unraveling how the energy released near the SMBHs is distributed over nine orders of magnitude in distance throughout galaxies and their immediate environments. The best place to study the impact of SMBH feedback is in the hot atmospheres of massive galaxies, groups, and galaxy clusters, which host the most massive black holes in the Universe, and where we can directly image the impact of black holes on their surroundings. We identify critical questions and potential measurements that will likely transform our understanding of the physics of SMBH feedback and how it shapes galaxies, through detailed measurements of (i) the thermodynamic and velocity fluctuations in the intracluster medium (ICM) as well as (ii) the composition of the bubbles inflated by SMBHs in the centers of galaxy clusters, and their influence on the cluster gas and galaxy growth, using the next generation of high spectral and spatial resolution X-ray and microwave telescopes.

astro-ph.HE↗