arXiv subjects

J. A. Zuhone

Publications and source records attributed to J. A. Zuhone.

3 recordsLinked to original sources

arXiv2019

Effects of Anisotropic Viscosity on the Evolution of Active Galactic Nuclei Bubbles in Galaxy Clusters

The interaction between jets from active galactic nuclei (AGNs) and the intracluster medium (ICM) provides key constraints on the feeding and feedback of supermassive black holes. Much understanding about AGN feedback is gained from purely hydrodynamic models; however, whether such an approximation is adequate for the magnetized, weakly collisional ICM needs to be critically examined. For example, AGN-blown bubbles in hydrodynamic simulations are easily disrupted by fluid instabilities, making it difficult to explain the coherence of observed bubbles such as the northwest ghost bubble in Perseus. In order to investigate whether magnetic tension and viscosity in realistic conditions could preserve the bubble integrity, we performed the first Braginskii-magnetohydrodynamic simulations of jet-inflated bubbles in a medium with tangled magnetic field. We find that magnetic tension alone is insufficient to prevent bubble deformation due to large velocity shear at early stage of the evolution. Although unsuppressed anisotropic viscosity in tangled magnetic field can have similar effects as isotropic viscosity, when the pressure anisotropy is bounded by microscopic plasma instabilities, the level of viscosity is substantially limited, thereby failing to prevent bubble deformation as in the inviscid case. Our results suggest that Braginskii viscosity is unlikely to be the primary mechanism for suppressing the fluid instabilities for AGN bubbles, and it remains a challenging task to reproduce smooth and coherent bubbles as observed. Because the dynamical influence and heating of the ICM critically depend on the bubble morphology, our study highlights the fundamental role of "microphysics" on the macroscopic properties of AGN feedback processes.

astro-ph.HE↗

arXiv2015

Deep Chandra, HST-COS, and Megacam Observations of the Phoenix Cluster: Extreme Star Formation and AGN Feedback on Hundred Kiloparsec Scales

We present new ultraviolet, optical, and X-ray data on the Phoenix galaxy cluster (SPT-CLJ2344-4243). Deep optical imaging reveals previously-undetected filaments of star formation, extending to radii of ~50-100 kpc in multiple directions. Combined UV-optical spectroscopy of the central galaxy reveals a massive (2x10^9 Msun)), young (~4.5 Myr) population of stars, consistent with a time-averaged star formation rate of 610 +/- 50 Msun/yr. We report a strong detection of OVI(1032,1038) which appears to originate primarily in shock-heated gas, but may contain a substantial contribution (>1000 Msun/yr) from the cooling intracluster medium. We confirm the presence of deep X-ray cavities in the inner ~10 kpc, which are amongst the most extreme examples of radio-mode feedback detected to date, implying jet powers of 2-7 x10^45 erg/s. We provide evidence that the AGN inflating these cavities may have only recently transitioned from "quasar-mode" to "radio-mode", and may currently be insufficient to completely offset cooling. A model-subtracted residual X-ray image reveals evidence for prior episodes of strong radio-mode feedback at radii of ~100 kpc, with extended "ghost" cavities indicating a prior epoch of feedback roughly 100 Myr ago. This residual image also exhibits significant asymmetry in the inner ~200 kpc (0.15R500), reminiscent of infalling cool clouds, either due to minor mergers or fragmentation of the cooling ICM. Taken together, these data reveal a rapidly evolving cool core which is rich with structure (both spatially and in temperature), is subject to a variety of highly energetic processes, and yet is cooling rapidly and forming stars along thin, narrow filaments.

astro-ph.GA↗

arXiv2009

A Line-Of-Sight Galaxy Cluster Collision: Simulated X-Ray Observations

Several lines of evidence have suggested that the the galaxy cluster Cl~0024+17, an apparently relaxed system, is actually a collision of two clusters, the interaction occurring along our line of sight. In this paper we present a high-resolution $N$-body/hydrodynamics simulation of such a collision. We have created mock X-ray observations of our simulated system using MARX, a program that simulates the on-orbit performance of the Chandra X-ray Observatory. We analyze these simulated data to generate radial profiles of the surface brightness and temperature. At later times, $t = 2.0-3.0$ Gyr after the collision, the simulated surface brightness profiles are better fit by a superposition of two $β$-model profiles than a single profile, in agreement with the observations of Cl~0024+17. In general, due to projection effects, much of the post-collision density and temperature structure of the clusters is not seen in the observations. In particular, the observed temperatures from spectral fitting are much lower than the temperature of the hottest gas. We determine from our fitted profiles that if the system is modeled as a single cluster, the hydrostatic mass estimate is a factor $\sim$2-3 less than the actual mass, but if the system is modeled as two galaxy clusters in superposition, a hydrostatic mass estimation can be made which is accurate to within $\sim$10%. We examine some implications of these results for galaxy cluster X-ray surveys.

astro-ph↗