Publication Details

This article was originally published as: Machacek, M, Jones, C, Forman, WR & Nulsen, P, Chandra Observations of Gas Stripping in the Elliptical Galaxy NGC 4552 in the Virgo Cluster, The Astrophysical Journal, 2006, 644(1), 155-166. Copyright 2006 University of Chicago Press. The journal can be found here.


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 keV) tail with mean density ne ∼ (5.4±1.7) × 10-3 cm-3 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 keV) and denser (ne ∼ 0.010 cm-3) than the surrounding Virgo ICM [kT = 2.2 keV and ne = (3.0 ± 0.3) × 10-4 cm-3]. The resulting pressure ratio between the free-streaming ICM and cluster gas at the stagnation point is ∼7.6 for galaxy gas metallicities of 0.5 Z⊙, which suggests that NGC 4552 is moving supersonically through the cluster with a velocity v ∼ 1680 km s-1 (Mach 2.2) at an angle ξ ∼ 35o ± 7o toward us with respect to the plane of the sky.

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