Continuum and spectral-line observations of the OH megamaser galaxy IRAS 01298-0744

Abstract

We present Very Long Baseline Array observations of radio continuum and OH line emission toward the OH megamaser (OHM) galaxy IRAS 01298$-$0744. We recover over 82<!PCT!> of the OH line emission seen in single-dish observations, including multiple strong OH line components and the broad shallow line profile spanning over 1000 The OH emission spatially has four compact components, as well as diffuse emission, and the 3 sigma signals are distributed in a rectangular region with size of sim 40times 30 mas. The spatial--velocity structure is complex and is consistent with that from HCN and HCO$^+$ lines in the literature, indicating that the nuclear region of this source is likely still in the merging process characterized by intense nuclear activities. The multiple strong OH peaks are blue-shifted compared to dense millimetre-wave molecular gas tracers, but similar to optical Na I absorption. This suggests that the compact masers might be in an outflow driven by an active galactic nucleus or starburst. We have detected compact radio continuum emissions adjacent to the maser positions with a brightness temperature of around $3 10^6$ K, similar to other OHM galaxies with very-long-baseline interferometry observations in the literature, which is consistent with a starburst origin.