The Results From The NICMOS Parallel Imaging and Grism Survey

Abstract

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 H$α$ emission-line galaxies at 0.75<z<1.9. The inferred co-moving number density of these objects is $3.3\times10^{-4} h_{50}^{3} Mpc^{-3}$, very similar to that of the bright Lyman break objects at $z \sim 3$. The mean star formation rate of these galaxies 21 M$_{\odot} yr^{-1}$ for H_0=50 km/s/Mpc. Using this sample, we derived the H$α$ luminosity function (LF) at z=1.3. The integrated H$α$ luminosity density at $z \sim 1.3$ is $1.64\times 10^{40} h_{50} erg/s Mpc^{-3}$, approximately 14 times greater than the local value reported by Gallego et al. (1995). The volume averaged star formation rate at $z=1.3 \pm 0.5$ is 0.13 M_{\odot} yr^{-1} Mpc^{-3}$ without correction for extinction. The SFR derived at $\sim 6500$~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.