The equivalent width (EW) of the Lyman Alpha (Lya) line is directly related
to the ratio of star formation rates determined from Lya flux and UV flux
density [SFR(Lya)/SFR(UV)]. We use published data --in the literature EW and
SFR(Lya)/SFR(UV) are treated as independent quantities-- to show that the
predicted relation holds for the vast majority of observed Lya emitting
galaxies (LAEs). We show that the relation between EW and SFR(Lya)/SFR(UV)
applies irrespective of a galaxy's `true' underlying star formation rate, and
that its only source of scatter is the variation in the spectral slope of the
UV continuum between individual galaxies. The derived relation, when combined
with the observed EW distribution, implies that the ratio SFR(UV)/SFR(Lya) is
described well by a log-normal distribution with a standard deviation of
~0.3-0.35. This result is useful when modelling the statistical properties of
LAEs. We further discuss why the relation between EW and SFR(Lya)/SFR(UV) may
help identifying galaxies with unusual stellar populations.Comment: 6 pages, 4 figures, accepted to MNRA
