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 stronglyinteracting dumbbell galaxies NGC4782(3C278) and NGC4783 that constrain thekinematics of the interaction and models for bending the radio jets associatedwith NGC4782. The galaxies are embedded in an approximately sphericaldistribution of group gas, centered on NGC4782,that is nearly isothermal withmean kT ~ 1.4+/- 0.4 keV. The X-ray morphology suggests that NGC4783 isinfalling into a single, massive galaxy group (LGG316) with NGC4782 nearly atrest at the center of the group potential.NGC4783 shows a sharp X-ray surfacebrightness edge (cold front) to the east and a ~15 kpc ram-pressure-strippedtail to the west. Analysis of this cold front indicates NGC4783 is moving eastwith a total velocity ~870+270-400 km/s (Mach ~1.4+0.5-0.7) at an inclinationangle ~46 deg.(>33 deg.)towards us with respect to theplane of the sky. A~45Myr old X-ray cavity, with enthalpy of 4.4 x 10^{57}ergs, coincides with theeastern radio lobe of 3C278. X-ray knots are found on both the radio jet andcounter-jet, coincident with peaks in the radio emission. Assuming a light,mildly relativistic jet in 3C278, ram pressure velocities of 100-200 km/simpacting the eastern jet and ~170 km/s acting on the western radio lobe aresufficient to produce their observed bending. These velocities may be caused bybulk motions established in the IGM by the high velocity interaction betweenthe galaxies, by the motion of NGC4782 relative to the IGM, or both.