Steep-spectrum radio lobes near the galactic centre

Abstract

In a previous paper¹ we reported the discovery of an extended steep-spectrum radio lobe located ∼34 arc min north-east of the galactic centre (the northern galactic centre lobe). Based on the similarity of the observed properties of this object to the radio lobes observed in the nuclei of Seyfert galaxies², we suggested that this source may be a manifestation of nuclear activity associated with the compact non-thermal source³ located at the galactic centre. However, no clear evidence for a second opposing lobe was evident from the 80-MHz observations. Here we report observations at 110.6 and 123.0MHz which confirm the existence of a second steep-spectrum feature, first discovered by Yusef-Zadeh et al.⁴ at 160 MHz, which extends ∼10 arc min to the south-east of the radio source Sagittarius-A. These new observations are in the only frequency range in which it is possible to view both of these features simultaneously and to display their morphology as a function of frequency. At lower frequencies the features are obscured by thermal absorption; at higher frequencies they blend into the background emission. Based on this unique perspective, we propose that these radio sources are related, and associated with activity at the galactic nucleus.