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

We present Chandra observations of hot gas structures, which are characteristic of gas-stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. Chandra X-ray images at 0.5–2 keV show a sharp leading edge in the surface brightness that is 12.4 ± 0.1 kpc north and west of the galaxy center in the direction of M87 and characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00 ± 0.02 keV for an abundance of $0.5Z_{\odot }$ inside the edge and ${1.37}_{-0.19}^{+0.35}keV$ for an abundance of $0.1Z_{\odot }$ in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio $n_{in}/n_{out}={6.44}_{-0.67}^{+1.04}$ 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 ${4.7}_{-1.4}^{+1.7}$ and Mach number of ${1.7}_{-0.3}^{+0.3}$. For 1.37 keV Virgo gas, we find a total infall velocity for M60 of $v_{M60}=1030\pm 180km{s}^{-1}$. We calculate the motion in the plane of the sky to be $v_{tran}={1012}_{-192}^{+183}km{s}^{-1}$, implying an inclination angle of $\xi ={11}_{-3}^{+3}$°. Surface brightness profiles also 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.