Central star formation in double-peak gas rich radio galaxies
  The respective contributions of gas accretion, galaxy interactions, and
mergers to the mass assembly of galaxies, their morphological transformations,
and the changes in their molecular gas content and star formation activity are
still not fully understood. Galaxies with two kinematic components which are
manifested as a double-peak (DP) in their emission lines, have been identified
in a recent work to play a major role in the morphological transformation
towards larger bulges. Notably, star-forming DP galaxies display a central star
formation enhancement and are thought to be associated with a sequence of
recent minor mergers. In order to probe merger induced star formation, we
conducted observations of the molecular gas content of star-forming DP galaxies
in the upper part of the main sequence (MS) with the IRAM 30m telescope. In
combination with existing molecular gas observations from the literature, we
gathered a sample of 41 such galaxies. We succeed in fitting the same kinematic
parameters to the optical ionised and molecular gas emission lines for 24
(59\,\%) galaxies. We find a central star formation enhancement which is most
likely the result of a galaxy merger or galaxy interactions which is indicated
by an excess of gas extinction found in the centre. This star formation is
traced by radio continuum emissions of 150 MHz, 1.4 GHz and 3 GHz, which are
all three linearly correlated with the CO luminosity described by the same
slope. We find a significantly larger amount of molecular gas in the present DP
galaxies and larger depletion times. We discard a scenario of large scale
instabilities driving gas into the centre and find no direct link between the
measured kinematic signatures and inclination. This leads us to conclude that
the observed DP galaxies are mostly the result of a recent merger that
funnelled molecular gas towards the centre and triggered star formation there.
