2006ApJ...644..155M

We use a 54.4 ks Chandra observation to study ram pressure stripping in NGC 4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the 0.5-2 keV band show a sharp leading edge in the surface brightness 3.1 kpc north of the galaxy center, a cool (kT=0.51^+0.09_–0.06keV) tail with mean density n_e∼5.4±1.7x10^–3/cm3 extending ∼10 kpc to the south of the galaxy, and two 3-4 kpc horns of emission extending southward away from the leading edge. These are all features characteristic of supersonic ram pressure stripping of galaxy gas, due to NGC 4552's motion through the surrounding Virgo ICM. Fitting the surface brightness profile and spectra across the leading edge, we find the galaxy gas inside the edge is cooler (kT=0.43^+0.03_–0.02keV) and denser (n_e∼0.010/cm3) than the surrounding Virgo ICM [kT=2.2^+0.7_–0.4keV and n_e=(3.0±0.3)x10^–4/cm3]. The resulting pressure ratio between the free-streaming ICM and cluster gas at the stagnation point is ∼7.6^+3.4_–2.0for galaxy gas metallicities of 0.5^+0.5_–0.3Z_☉, which suggests that NGC 4552 is moving supersonically through the cluster with a velocity v∼1680⁺³⁹⁰_–220km/s (Mach 2.2^+0.5_–0.3) at an angle ξ∼35°±7° toward us with respect to the plane of the sky.