Abstract
We present near-infrared emission line counts and luminosity functions from
the HST WFC3 Infrared Spectroscopic Parallels (WISP) program for 29 fields
observed using both the G102 and G141 grism. Altogether we identify 1048
emission line galaxies with observed equivalent widths greater than 40
Angstroms, 467 of which have multiple detected emission lines. The WISP survey
is sensitive to fainter flux levels (3-5x10^-17 ergs/s/cm^2) than the future
space near-infrared grism missions aimed at baryonic acoustic oscillation
cosmology (1-4x10^-16 ergs/s/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 are in rough agreement with the corrected count
predictions of H-alpha emitters from Geach et al. (2010), reaching 10,000
deg^-2 above an H-alpha flux of 2x10^-16 ergs/s/cm^2. H-alpha-emitting
galaxies with comparable OIII flux are roughly 5 times less common than
galaxies with just H-alpha emission at those flux levels. Galaxies with low
H-alpha/OIII ratios are very rare at the brighter fluxes that future
near-infrared grism surveys will probe; our survey finds no galaxies with
H-alpha/OIII<0.95 that have H-alpha flux greater than 3x10^-16 ergs/s/cm^2.
We also find that our high redshift (z=0.9-1.5) counts are slightly higher
(factors of 1.3-2) than the high redshift (z=1.47) narrow band H-alpha survey
of HiZELS (Sobral et al. 2012), although our lower redshift luminosity function
(z=0.3-0.9) is consistent with their z=0.84 result. The evolution in the OIII
luminosity function from z=0.7-2.3 is almost entirely in the L* parameter,
which steadily increases with redshift over that range.
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