We investigate the relationship between H \alpha and [ O II ] ( \lambda 3727 ) emission in faint star-forming galaxies at z = 1.47 with dust uncorrected star formation rates ( SFRs ) down to 1.4 M _ { \odot } yr ^ { -1 } , using data in two narrow-bands from WFCAM/UKIRT and Suprime-Cam/Subaru .
A stacking analysis allows us to investigate H \alpha emission flux from bright [ O II ] emitters as well as faint ones for which H \alpha is not individually detected , and to compare them with a large sample of local galaxies .
We find that there is a clear , positive correlation between the average H \alpha and [ O II ] luminosities for [ O II ] emitters at z = 1.47 , with its slope being consistent with the local relation .
[ O II ] emitters at z = 1.47 have lower mean observed ratios of H \alpha / [ O II ] suggesting a small but systematic offset ( at 2.8 \sigma significance ) towards lower values of dust attenuation , A _ { H \alpha } \sim 0.35 , than local galaxies .
This confirms that [ O II ] selection tends to pick up galaxies which are significantly less dusty on average than H \alpha selected ones , with the difference being higher at z = 1.47 than at z = 0 .
The discrepancy of the observed line ratios between [ O II ] emitters at z = 1.47 and the local galaxies may in part be due to the samples having different metallicities .
However , we demonstrate that metallicity is unlikely to be the main cause .
Therefore , it is important to take into account that the relations for the dust correction which are derived using H \alpha emitter samples , and frequently used in many studies of high- z galaxies , may overestimate the intrinsic SFRs of [ O II ] -selected galaxies , and that surveys of [ O II ] emission galaxies are likely to miss dusty populations .