6.7 GHz methanol absorption toward the Seyfert 2 galaxy NGC 3079

Abstract

The detection of the 6.7 GHz line of methanol (CH3OH) is reported for the first time toward an object beyond the Magellanic Clouds. Using the Effelsberg 100 m telescope, two absorption features were identified toward the Seyfert 2 galaxy NGC 3079. Both components probably originated on lines-of-sight toward the central region, presumably absorbing the radio continuum of the nuclear sources A, B, and E of NGC 3079. One absorption feature, at the systemic velocity, is narrow and may arise from gas not related to the nuclear environment of the galaxy. The weaker blue-shifted component is wider and may trace outflowing gas. Total A-type CH3OH column densities are estimated to be between a few times 10^13 and a few times 10^15 cm^-2. Because of a highly frequency-dependent continuum background, the overall similarity of HI, OH, and CH3OH absorption profiles hints at molecular clouds that cover the entire area occupied by the nuclear radio continuum sources ~ 4 pc.