Molecular Gas in Powerful Radio Galaxies Detected by IRAS

May 1993 • 1993ApJ...409..170M

Authors • Mazzarella, J. M. • Graham, J. R. • Sanders, D. B. • Djorgovski, S.

Abstract • Results are presented from the first phase of a CO(J = 1 - 0) line survey of powerful radio galaxies (log P_408 MHz_ >~ 23.5 W Hz^-1^) Eight radio galaxies detected by IRAS have been observed to a sensitivity limit of ~1.0 mK rms (45 km s^-1^ resolution) using the new 3 mm SIS receiver on the NRAO 12 m telescope; five sources were detected. These observations include the CO detection of the highly variable, compact flat-spectrum radio galaxy 3C 120, detections of four galaxies from the Bologna B2 radio sample, and establishment of sensitive upper limits on the molecular gas content of the very powerful radio galaxies 4C 29.30, 3C 321, and Cygnus A (3C 405). These data have doubled the number of CO detections of powerful radio galaxies, allowing us to begin exploration of the full range of CO luminosities characteristic of this class of objects. The range of computed molecular gas masses, log M(H_2_)/M_sun_ = 9.42 - 10.34, is ~1-7 times the H_2_ mass of the Milky Way and is in stark contrast to the low molecular gas masses found in radio-quiet far-infrared-selected elliptical galaxies, log M(H_2_)/M_sun_ ~ 7-8. The relatively high CO detection rate for the current sample suggests that rich supplies of molecular gas may be ubiquitous in powerful radio-selected galaxies detected by IRAS. The infrared-luminosity to molecular gas mass ratio, L_ir_/M(H_2_), in powerful radio galaxies observed in CO is in the range ~15 L_sun_ M_sun_^-1^ to > 100 L_sun_ M_sun_^-1^, typical of the range of values found in infrared-luminous nuclear starbursts and AGNs. The CO(J = 1 - 0) line widths of 3C 120, B2 0722+300, and B2 1318 + 343 are very broad (FWZI >~ 500 km s^-1^) compared to normal galaxies, but consistent with previously observed interacting/merging galaxies. The CO profile for B2 1506+345 is bimodal; both components of this galaxy pair each contain ~10^10^ M_sun_ of molecular gas. The new CO observations support the hypothesis that powerful radio galaxies originate in colliding disk galaxies which evolve into gas-rich, peculiar E/S0 galaxies during the merger process.

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Joe Mazzarella

Senior Scientist