The Results From The NICMOS Parallel Imaging and Grism Survey

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We present the results of a survey which utilizes the NICMOS Camera 3 Parallel grism and imaging observations of random fields. We have identified 33 Hα emission-line galaxies at 0.75<z<1.9. The inferred co-moving number density of these objects is 3.3×10⁻⁴ h₅₀³ Mpc⁻³, very similar to that of the bright Lyman break objects at z 3. The mean star formation rate of these galaxies 21 M yr⁻¹ for H₀=50 km/s/Mpc. Using this sample, we derived the Hα luminosity function (LF) at z=1.3. The integrated Hα luminosity density at z 1.3 is 1.64× 10⁴⁰ h₅₀ erg/s Mpc⁻³, approximately 14 times greater than the local value reported by Gallego et al. (1995). The volume averaged star formation rate at z=1.3 ± 0.5 is 0.13 M yr⁻¹ Mpc⁻³ without correction for extinction. The SFR derived at 6500 Åis a factor of 3 higher than that deduced from 2800 Åcontinua. We believe that this difference is largely due to dust extinction. The implied total extinction at 2800Åis in the range of 2 - 4 magnitude. However, the precise determination of the total extinction is sensitive to the model assumptions. Deep ground-based VRI images of the NICMOS fields have revealed roughly a dozen of extremely red objects (EROs) with R - H > 5 and H brighter than 20.6. The surface density of these objects is around 0.6 per square arcminutes.