On how leakage can affect the Star Formation Rate estimation using Halpha luminosity

TL;DR

This study provides observational evidence that leakage of ionising photons from star-forming regions can significantly bias star formation rate estimates derived from Halpha luminosity, especially in dwarf galaxies and shell structures.

Contribution

It demonstrates that photon leakage affects SFR estimates from Halpha, highlighting the need to account for this effect in galactic star formation studies.

Findings

Leakage can reduce SFR(Ha)/SFR(FUV) ratio by up to 25%

Lower SFR(Ha)/SFR(FUV) ratios are observed in shell structures

Differences in ratios are statistically significant (1.1-1.4 sigma)

Abstract

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.