Search

We present new and archival Chandra X-ray Observatory observations of $\mathsf {X}$-shaped radio galaxies (XRGs) within z [?] 0.1 alongside a comparison sample of normal double-lobed FR I and II radio galaxies. By fitting elliptical distributions to the observed diffuse hot X-ray emitting atmospheres (either the interstellar or intragroup medium), we find that the ellipticity and the position angle of the hot gas follow that of the stellar light distribution for radio galaxy hosts in general. Moreover, compared to the control sample, we find a strong tendency for $\mathsf {X}$-shaped morphology to be associated with wings directed along the minor axis of the hot gas distribution. Taken at face value, this result favors the hydrodynamic backflow models for the formation of XRGs which naturally explain the geometry; the merger-induced rapid reorientation models make no obvious prediction about orientation.

We report on Combined Array for Research in Millimeter-Wave Astronomy and James Clerk Maxwell Telescope observations toward the Einstein source 1E 1740.7-2942, a low-mass X-ray binary commonly known as the "Great Annihilator." The Great Annihilator is known to be near a small, bright molecular cloud in a region largely devoid of emission in 12CO surveys of the Galactic center. This region is of interest because it is interior to the dust lanes which may be the shock zones where atomic gas from the HI nuclear disk is converted into molecular gas. We find that the region is populated with a large number of dense (n [?] 105 cm-3) regions of excited gas with small filling factors. The gas appears to have turbulent support and may be the result of sprays of material from collisions in the shock zone. We estimate that [?](1-3) x 105 M of shocked gas resides in our r [?] 3', Dv LSR = 100 km s-1 field. If this gas has recently shocked and is interior to the inner Lindblad resonance of the dominant bar, it is in transit to the x 2 disk, suggesting that a significant amount of mass may be transported to the disk by a low filling factor population of molecular clouds with low surface brightness in larger surveys.

We present three-dimensional hydrodynamic models of radio galaxies interacting with initially relaxed hot atmospheres and explore the significant off-axis radio lobe structures that result under certain conditions. With a focus on the "winged" and "X-shaped" radio galaxy population, we confirm the importance of observed trends such as the connection of wing formation with jets co-aligned with the major axis of the surrounding atmosphere. These wings are formed substantially by the deflection of lobe plasma flowing back from the hot spots (backflow) and develop in two stages: supersonic expansion of an overpressured cocoon at early times followed by buoyant expansion at later times. We explore a limited parameter space of jet and atmosphere properties and find that the most prominent wings are produced when a decaying jet is injected into a small, dense, highly elliptical atmosphere. On the basis of this search, we argue that the deflection of backflow by gradients in the hot atmosphere is a strong candidate for forming observed wings but must work in tandem with some other mechanism for forming the initial wing channels. Our models indicate that lobe interaction with the hot atmosphere may play a dominant role in shaping the morphology of radio galaxies.