On how leakage can affect the Star Formation Rate estimation using
  Halpha luminosity
  We present observational evidence that leakage of ionising photons from
star-forming regions can affect the quantification of the star formation rate
(SFR) in galaxies. This effect could partially explain the differences between
the SFR estimates using the far ultraviolet (FUV) and the Halpha emission. We
find that leakage could decrease the SFR(Ha)/SFR(FUV) ratio by up to a 25 per
cent. The evidence is based on the observation that the SFR(Ha)/SFR(FUV) ratio
is lower for objects showing a shell Halpha structure than for regions
exhibiting a much more compact morphology. The study has been performed on
three object samples: low luminosity dwarf galaxies from the Local Volume
Legacy survey and star-forming regions in the Large Magellanic Cloud and the
nearby Local Group galaxy M33. For the three samples we find differences
(1.1-1.4sigma) between the SFR(Ha)/SFR(FUV) for compact and shell objects.
Although leakage cannot entirely explain the observed trend of SFR(Ha)/SFR(FUV)
ratios for systems with low SFR, we show the mechanism can lead to different
SFR estimates when using Halpha and FUV luminosities. Therefore, further study
is needed to constrain the contribution of leakage to the low SFR(Ha)/SFR(FUV)
ratios observed in dwarf galaxies and its impact on the Halpha flux as a SFR
indicator in such objects.
