Emission-Line Galaxies from the NICMOS/HST GRISM Parallel Survey release_dsf7n2d7cjhofdrmvwg2zk5jd4

Abstract

We present the first results of a survey of random fields with the slitless G141 (λ_c = 1.5μ, Δλ=0.8μ) grism on NICMOS. Approximately 64 square arcminutes have been observed at intermediate and high galactic latitudes. The 3σ limiting line and continuum fluxes in each field vary from 7.5 × 10^-17 to 1 × 10^-17 erg/cm^2/sec and from H = 20 to 22, respectively. Our median and area weighted 3σ limiting line fluxes within a 4 pixel aperture are nearly identical at 4.1 × 10^-17 erg/cm^2/sec and are 60 imaging surveys from the ground. We have identified 33 emission-line objects and derive their observed wavelengths, fluxes and equivalent widths. We argue that the most likely line identification is Hα and that the redshift range probed is from 0.75 to 1.9. The 2σ rest-frame equivalent width limits range from 9Å to 130Å with an average of 40Å. The survey probes an effective co-moving volume of 10^5 h_50^-3 Mpc^3 for q_0=0.5. Our derived co-moving number density of emission line galaxies in the range 0.7 < z < 1.9 is 3.3×10^-4 h_50^3 Mpc^-3, very similar to that of the bright Lyman break objects at z ∼ 3. The objects with detected emission-lines have a median F160W magnitude of 20.4 (Vega scale) and a median Hα luminosity of 2.7 × 10^42 erg/sec. The implied star formation rates range from 1 to 324 M_/yr, with an average [NII]6583,6548 corrected rate of 21 M_/yr for H_0=50 km/s/Mpc and q_0=0.5 (34 M_/yr for q_0=0.1).
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