We present near-infrared emission line counts and luminosity functions from the HST WFC3 Infrared Spectroscopic Parallels ( WISP ) program for 29 fields ( 0.037 deg ^ { 2 } ) observed using both the G102 and G141 grism .
Altogether we identify 1048 emission line galaxies with observed equivalent widths greater than 40 Å , 467 of which have multiple detected emission lines .
We use simulations to correct for significant ( > 20 % ) incompleteness introduced in part by the non-dithered , non-rotated nature of the grism parallels .
The WISP survey is sensitive to fainter flux levels ( 3-5 \times 10 ^ { -17 } ergs s ^ { -1 } cm ^ { -2 } ) than the future space near-infrared grism missions aimed at baryonic acoustic oscillation cosmology ( 1-4 \times 10 ^ { -16 } ergs s ^ { -1 } cm ^ { -2 } ) , allowing us to probe the fainter emission line galaxies that the shallower future surveys may miss .
Cumulative number counts of 0.7 < z < 1.5 galaxies reach 10,000 deg ^ { -2 } above an H \alpha flux of 2 \times 10 ^ { -16 } ergs s ^ { -1 } cm ^ { -2 } .
H \alpha -emitting galaxies with comparable [ O iii ] flux are roughly 5 times less common than galaxies with just H \alpha emission at those flux levels .
Galaxies with low H \alpha / [ O iii ] ratios are very rare at the brighter fluxes that future near-infrared grism surveys will probe ; our survey finds no galaxies with H \alpha / [ O iii ] < 0.95 that have H \alpha flux greater than 3 \times 10 ^ { -16 } ergs s ^ { -1 } cm ^ { -2 } .
Our H \alpha luminosity function contains a comparable number density of faint line emitters to that found by the NICMOS near-infrared grism surveys , but significantly fewer ( factors of 3-4 less ) high luminosity emitters .
We also find that our high redshift ( z =0.9-1.5 ) counts are in agreement with the high redshift ( z =1.47 ) narrow band H \alpha survey of HiZELS ( Sobral et al .
2013 ) , while our lower redshift luminosity function ( z =0.3-0.9 ) falls slightly below their z =0.84 result .
The evolution in both the H \alpha luminosity function from z =0.3–1.5 and the [ O iii ] luminosity function from z =0.7–2.3 is almost entirely in the L _ { \star } parameter , which steadily increases with redshift over those ranges .