2006MNRAS.371..945H

We present multifrequency radio continuum as well as Hi observations of the composite galaxy NGC6764, which has a young, circumnuclear starburst and also harbours an active galactic nucleus (AGN). These observations have been made at a number of frequencies ranging from ∼600MHz to 15GHz using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). They reveal the structure of the bipolar bubbles of non-thermal radio emission which are along the minor axis of the galaxy and extend up to ∼1.1 and 1.5kpc on the northern and southern sides, respectively. Features in the radio bubbles appear to overlap with filaments of Hα emission. The high-resolution observations reveal a compact source, likely to be associated with the nucleus of the galaxy, and a possible radio jet towards the south-west. We have compiled a representative sample of galaxies with bubbles of non-thermal radio emission and find that these are found in galaxies with an AGN.

The Hi observations with the GMRT show two peaks of emission on both ends of the stellar bar and depletion of Hi in the central region of the galaxy. We also detect Hi in absorption against the central radio peak at the systemic velocity of the galaxy. The Hi absorption spectrum also suggests a possible weak absorption feature blueshifted by ∼120km/s, which requires confirmation. A similar feature has also been reported from observations of CO in emission, suggesting that the circumnuclear starburst and nuclear activity affect the kinematics of the atomic and molecular gas components, in addition to the ionized gas seen in Hα and [Nii].