Revealing the nature of star forming blue early-type galaxies at low
  redshift
  Context: Star forming early-type galaxies with blue optical colours at low
redshift can be used to test our current understanding of galaxy formation and
evolution. Aims: We want to reveal the fuel and triggering mechanism for star
formation in these otherwise passively evolving red and dead stellar systems.
Methods: We undertook an optical and ultraviolet study of 55 star forming blue
early-type galaxies, searching for signatures of recent interactions that could
be driving the molecular gas into the galaxy and potentially triggering the
star formation. Results: We report here our results on star forming blue
early-type galaxies with tidal trails and in close proximity to neighbouring
galaxies that are evidence of ongoing or recent interactions between galaxies.
There are 12 galaxies with close companions with similar redshifts, among which
two galaxies are having ongoing interactions that potentially trigger the star
formation. Two galaxies show a jet feature that could be due to the complete
tidal disruption of the companion galaxy. The interacting galaxies have high
star formation rates and very blue optical colours. Galaxies with no companion
could have undergone a minor merger in the recent past. Conclusions: The recent
or ongoing interaction with a gas-rich neighbouring galaxy could be responsible
for bringing cold gas to an otherwise passively evolving early-type galaxy. The
sudden gas supply could trigger the star formation, eventually creating a blue
early-type galaxy. The galaxies with ongoing tidal interaction are blue and
star forming, thereby implying that blue early-type galaxies can exist even
when the companion is on flyby so does not end up in a merger.
