# The Infall of the Virgo Elliptical Galaxy M60 toward M87 and the Gaseous Structures Produced by Kelvin-Helmholtz Instabilities

## TL;DR

This study uses Chandra X-ray observations to analyze gas stripping and Kelvin-Helmholtz instabilities in the infalling Virgo galaxy M60, revealing detailed gas structures and motion parameters during its merger with M87.

## Contribution

First detailed X-ray analysis of M60's gas stripping and Kelvin-Helmholtz instabilities during its infall into the Virgo cluster.

## Key findings

- Identified a sharp cold front indicating M60's motion through Virgo ICM.
- Measured gas temperature, density, and velocity of M60 during infall.
- Detected gaseous wings consistent with Kelvin-Helmholtz instability simulations.

## Abstract

We present Chandra observations of hot gas structures, characteristic of gas stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located $1$ Mpc east of M87. $0.5-2$ keV Chandra X-ray images show a sharp leading edge in the surface brightness $12.4 \pm 0.1$ kpc north and west of the galaxy center in the direction of M87 characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of $1.00 \pm 0.02$ keV for abundance $0.5 Z_\odot$ inside the edge and $1.37^{+0.35}_{-0.19}$ keV for abundance $0.1 Z_\odot$ in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio of $6.44^{+1.04}_{-0.67}$ between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of $4.7^{+1.7}_{-1.4}$ and Mach number $1.7 \pm 0.3$. For 1.37 keV Virgo gas we find a total infall velocity for M60 of $1030 \pm 180$ kms$^{-1}$. We calculate the motion in the plane of the sky to be $1012^{+183}_{-192}$ km$^{-1}$ implying an inclination angle $\xi = 11 \pm 3$ degrees. Surface brightness profiles show the presence of a faint diffuse gaseous tail. We identify filamentary, gaseous wing structures caused by the galaxy's motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin-Helmholtz instabilities as expected if the gas stripping is close to inviscid.