Fueling the central engine of radio galaxies. III. Molecular gas and
  star formation efficiency of 3C 293
  Aims. We investigate the different manifestations of AGN feedback in the
evolved, powerful radio source 3C293 and their impact on the molecular gas of
its host galaxy, which harbors young star-forming regions and fast outflows of
HI and ionized gas. Methods. We study the distribution and kinematics of the
molecular gas of 3C293 using high spatial resolution observations of the
CO(1-0) and CO(2-1) lines, and the 3 and 1mm continuum taken with the IRAM
PdBI. We mapped the molecular gas of 3C293 and compared it with the dust and
star-formation images of the host. We searched for signatures of outflow
motions in the CO kinematics, and reexamined the evidence of outflowing gas in
the HI spectra. We also derived the star formation rate (SFR) and efficiency
(SFE) of the host with all available SFR tracers from the literature, and
compared them with the SFE of young and evolved radio galaxies and normal
star-forming galaxies. Results. The CO(1-0) emission line shows that the
molecular gas in 3C293 is distributed along a massive (2.2E10 Msun) warped disk
with diameter of 21 kpc that rotates around the AGN. Our data show that the
dust and the star formation are clearly associated with the CO disk. The
CO(2-1) emission is located in the inner 7 kpc (diameter) region around the
AGN, coincident with the inner part of the CO(1-0) disk. Both the CO(1-0) and
CO(2-1) spectra reveal the presence of an absorber against the central regions
of 3C293 that is associated with the disk. We do not detect any fast (>500
km/s) outflow motions in the cold molecular gas. The host of 3C293 shows an SFE
consistent with the Kennicutt-Schmidt law. The apparently low SFE of evolved
radio galaxies may be caused by an underestimation of the SFR and/or an
overestimation of the molecular gas densities in these sources. We find no
signatures of AGN feedback in the molecular gas of 3C293.
