Stripped elliptical galaxies as probes of ICM physics: III. Deep Chandra Observation of NGC 4552 - Measuring the Viscosity of the Intracluster Medium

TL;DR

This study uses deep Chandra and XMM-Newton observations of NGC 4552 to analyze the galaxy's gas tail and compare it with hydrodynamical simulations, concluding that the intracluster medium's viscosity is negligible, indicating efficient mixing.

Contribution

It provides the first detailed comparison of deep X-ray observations with tailored hydrodynamical simulations to constrain ICM viscosity in a galaxy undergoing ram pressure stripping.

Findings

The observed tail morphology matches inviscid models.

ICM viscosity is constrained to be negligible.

Efficient mixing occurs in the stripped tail.

Abstract

We present results from a deep (200 ks) Chandra observation of the early-type galaxy NGC 4552 (M89) which is falling into the Virgo cluster. Previous shallower X-ray observations of this galaxy showed a remnant gas core, a tail to the South of the galaxy, and twin `horns' attached to the northern edge of the gas core [machacek05a]. In our deeper data, we detect a diffuse, low surface brightness extension to the previously known tail, and measure the temperature structure within the tail. We combine the deep Chandra data with archival XMM-Newton observations to put a strong upper limit on the diffuse emission of the tail out to a large distance (10$\times$the radius of the remnant core) from the galaxy center. In our two previous papers [roediger15a,roediger15b], we presented the results of hydrodynamical simulations of ram pressure stripping specifically for M89 falling into the Virgo cluster and investigated the effect of ICM viscosity. In this paper, we compare our deep data with our specifically tailored simulations and conclude that the observed morphology of the stripped tail in NGC 4552 is most similar to the inviscid models. We conclude that, to the extent the transport processes can be simply modeled as a hydrodynamic viscosity, the ICM viscosity is negligible. More generally, any micro-scale description of the transport processes in the high-$\beta$ plasma of the cluster ICM must be consistent with the efficient mixing observed in the stripped tail on macroscopic scales.