  In a recent work, a large sample of double-peak (DP) emission line galaxies
have been identified from the SDSS. While the two peaks could represent two
kinematic components, they may be linked to the large bulges which their host
galaxies tend to have. Star-forming DP galaxies display a central star
formation enhancement and have been discussed to be compatible with a sequence
of recent minor mergers. In order to probe merger induced star formation
mechanisms, we conducted observations of the molecular gas content of 35
star-forming DP galaxies in the upper part of the main sequence (MS) of star
formation with the IRAM 30m telescope. Including similar galaxies 0.3 dex above
MS and with existing molecular gas observations from the literature, we finally
obtain a sample of 52 such galaxies. We succeed in fitting the same kinematic
parameters to the optical ionised and molecular gas emission lines for 10 (19%)
galaxies. We find a central star formation enhancement resulting most likely
from a galaxy merger or galaxy interaction, which is indicated by an excess of
gas extinction found in the centre. This star formation is traced by radio
continuum emissions at 150MHz, 1.4 and 3GHz, which are all three linearly
correlated in log with the CO luminosity with the same slope. The 52 DP
galaxies are found to have a significantly larger amount of molecular gas and
larger depletion times, hence a lower star formation efficiency, than the
expected values at their distance of the MS. This is consistent with a scenario
of minor mergers increasing the mass of bulges and driving gas to the centre.
We also exclude the inwards directed gas migration and central star formation
enhancement to be the origin of a bar morphology. Hence, these 52 DP galaxies
could be the results of recent minor mergers that funnelled molecular gas
towards their centre, triggering star formation, but with a moderate
efficiency.
