X - Ray Constraints on Galaxy - Gas - Jet Interactions in the Dumbbell Galaxies Ngc 4782 and Ngc 4783 in the Lgg 316 Galaxy Group

We present results from a 49.3 ks Chandra X-ray observation of the strongly interacting dumbbell galaxies NGC 4782(3C278) and NGC 4783 that constrain the kinematics of the interaction and models for bending the radio jets associated with NGC 4782. The galaxies are embedded in an approximately spherical distribution of group gas, centered on NGC 4782, that, away from the interaction region, is nearly isothermal with kT ∼ 1.4 keV. NGC 4783 shows a sharp X-ray surface brightness edge (cold front) to the east and a ∼ 15 kpc rampressure-stripped tail to the west. Analysis of this cold front indicates NGC 4783 is moving east with a total velocity 930+100 −190 km s −1 (Mach 1.4+0.3 −0.4) at an inclination angle 42 +15 −5 deg. towards us with respect to the plane of the sky. A ∼ 45 Myr old X-ray cavity, with enthalpy of 4.4× 1057 ergs, coincides with the eastern radio lobe of 3C278. If we assume a light, mildly relativistic jet in 3C278, then ram pressure velocities of 100 − 200 km s−1 impacting the eastern jet and ∼ 170 km s−1 acting on the western radio lobe are sufficient to produce their observed bending. These velocities may be caused by bulk motions established in the IGM by the high velocity interaction between the galaxies, by the motion of the host galaxy NGC 4782 relative to the IGM, or both. However, the X-ray morphology suggests that NGC 4783 is infalling into a single, massive galaxy group (LGG 316) with NGC 4782 nearly at rest at the center of the group potential, such that bulk gas motions likely dominate in bending the radio lobes. Subject headings: galaxies: groups: general – galaxies:individual (NGC 4782, NGC 4783) – galaxies: intergalactic medium – X-rays: galaxies