G359.87+0.18, an FR II radio galaxy 15' from Sagittarius A: Implications for the scattering region in the galactic center

Abstract

G359.87+0.18 is an enigmatic object located 15' from Sgr A. It has been variously classified as an extragalactic source, a Galactic jet source, and a young supernova remnant. We present new observations of G359.87+0.18 between 0.33 and 15 GHz and an H I absorption spectrum and use these to argue that this source is an FR II radio galaxy. We are able to place a crude limit on its redshift of z≥0.1. The source has a spectral index of α←1 (S∝v^α), suggestive of a radio galaxy with a redshift z≥2. The scattering diameters of Sgr A and several nearby OH masers (≈1" at 1 GHz) indicate that a region of enhanced scattering is along the line of sight to the Galactic center. If the region covers the Galactic center uniformly, the implied diameter for a background source is at least 600" at 0.33 GHz, which is in contrast with the observed 20" diameter of G359.87+0.18. Using the scattering diameter of a nearby OH maser OH 359.762+0.120 and the widths of two nearby nonthermal threads, G0.08+0.15 and G359.79+0.17, we show that a uniform scattering region should cover G359.87+0.18. We therefore conclude that the Galactic center scattering region is inhomogeneous on a scale of 5' (1≈0 pc at a distance of 8.5 kpc). This scale is comparable with the size scale of molecular clouds in the Galactic center. The close agreement between these two length scales is an indication that the scattering region is linked intimately to the Galactic center molecular clouds.