We report the detection of ^ { 12 } CO ( 1 \rightarrow 0 ) and ^ { 12 } CO ( 2 \rightarrow 1 ) emission from the central regions ( \lesssim 5 – 10 { kpc } ) of the two powerful radio galaxies 3C 31 and 3C 264 .
Their individual CO emission exhibits a double-horned line profile that is characteristic of an inclined rotating disk with a central depression at the rising part of its rotation curve .
The inferred disk or ring distributions of the molecular gas is consistent with the observed presence of dust disks or rings detected optically in the cores of both galaxies .
For a CO to H _ { 2 } conversion factor similar to that of our Galaxy , the corresponding total mass in molecular hydrogen gas is ( 1.3 \pm 0.2 ) \times 10 ^ { 9 } { M _ { \odot } } in 3C 31 and ( 0.31 \pm 0.06 ) \times 10 ^ { 9 } { M _ { \odot } } in 3C 264 .
Despite their relatively large molecular-gas masses and other peculiarities , both 3C 31 and 3C 264 , as well as many other powerful radio galaxies in the ( revised ) 3C catalog , are known to lie within the fundamental plane of normal elliptical galaxies .
We reason that if their gas originates from the mergers of two gas-rich disk galaxies , as has been invoked to explain the molecular gas in other radio galaxies , then both 3C 31 and 3C 264 must have merged a long time ( a few billion years or more ) ago but their remnant elliptical galaxies only recently ( last tens of millions of years or less ) become active in radio .
Instead , we argue that the cannibalism of gas-rich galaxies provides a simpler explanation for the origin of molecular gas in the elliptical hosts of radio galaxies .
Given the transient nature of their observed disturbances , these galaxies probably become active in radio soon after the accretion event when sufficient molecular gas agglomerates in their nuclei .