Correlations between H α equivalent width and galaxy properties at z = 0.47: Physical or selection-driven?

The H alpha equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H alpha EW strongly anticorrelates with stellar mass as M-0.25 similar to the sSFR - stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H alpha EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H alpha emitters from the Ly alpha Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg(2) area of COSMOS with a survey comoving volume of 1.1 x 10(5) Mpc(3). We assume an intrinsic EW distribution to form mock samples of H alpha emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H alpha EW intrinsically correlates with stellar mass as W-0 proportional to M-0.16 +/- 0.03 and decreases by a factor of similar to 3 from 10(7) M-circle dot to 10(10) M-circle dot, while not correcting for selection effects steepens the correlation as M-025 +/- 0.04, We find low-mass H alpha emitters to be similar to 320 times more likely to have rest-frame EW > 200 angstrom compared to high-mass H alpha emitters. Combining the intrinsic W-0-stellar mass correlation with an observed stellar mass function correctly reproduces the observed H alpha luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W-0-stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H alpha emitters and not a byproduct of selection effects.