Molecular Gas in 3C 293: The First Detection of CO Emission and Absorption in a Fanaroff‐Riley Type II Radio Galaxy

Abstract

The first detection of CO emission in a Fanaroff and Riley type II (i.e., edge-brightened radio lobe morphology) radio galaxy is presented. Multiwavelength (0.36-2.17 μm) imaging of 3C 293 shows it to be a disk galaxy with an optical jet or tidal tail extending toward what appears to be a companion galaxy 28 kpc away via a low surface brightness envelope. The molecular gas appears to be distributed in an asymmetric disk rotating around an unresolved continuum source, which is presumably emission from the active galactic nucleus (AGN). A narrow (Deltav_abs~60 km s^-1) absorption feature is also observed in the CO spectrum and is coincident with the continuum source. Assuming the standard CO conversion factor, the molecular gas (H_2) mass is calculated to be 1.5x10^10 M_solar, several times the molecular gas mass of the Milky Way. The high concentration of molecular gas within the central 3 kpc of 3C 293, combined with the multiwavelength morphological peculiarities, supports the idea that the radio activity has been triggered by a gas-rich galaxy-galaxy interaction or merger event.