Molecular gas and nuclear activity in radio galaxies detected by IRAS

This paper reports the latest results from a millimeter-wave (CO) spectroscopic survey of IRAS-detected radio galaxies with L-1.4 (GHz) similar to 10(23)-10(28) W Hz(-1) in the redshift range z similar to 0.02-0.15. The IRAS flux-limited sample contains 33 radio galaxies with different radio morphologies and a broad range of infrared luminosities (L-IR = 10(9)-10(12) L-.), allowing for an investigation of ( 1) whether low-z radio-selected active galactic nuclei (AGNs) reside in molecular gas-rich host galaxies and ( 2) whether the CO properties are correlated with the properties of the host galaxy or the AGN. All of the radio galaxies in Mazzarella et al. and Mirabel et al. have been reobserved. Three new CO detections have been made, raising the total number of CO detections to nine and setting the survey detection rate at similar to 25%. Many of the CO lines have double-peaked profiles, and the CO line widths are broad ( average Delta v(FWHM) similar to 500 +/- 130 km s(-1)), exceeding the average CO widths of both ultraluminous infrared galaxies ( 300 +/- 90 km s(-1)) and Palomar-Green QSOs ( 260 +/- 160 km s(-1)), and thus being indicative of massive host galaxies. The CO luminosities translate into molecular gas masses of similar to(0.4-7) x 10(9) M-., however, the 3 sigma CO upper limits for nondetections do not rule out a molecular gas mass as high as that of the Milky Way ( similar to 3 x 10(9) M-.). Optical images of eight out of nine molecular gas-rich radio galaxies show evidence of close companions and/or tidal features. Finally, there is no obvious correlation between radio power and molecular gas mass. However, it is notable that only one F-R II galaxy out of 12 is detected in this CO survey; the remaining detections are of galaxies hosting F-R I and compact radio jets.