Emission‐Line Galaxies from the NICMOS/ Hubble Space Telescope Grism Parallel Survey

Abstract

We present the first results of a survey of random fields with the slitless G141 (lambda_c=1.5 mum, Deltalambda=0.8 μm) grism on the near-IR camera and multiobject spectrometer (NICMOS) on board the Hubble Space Telescope (HST). Approximately 64 arcmin^2 have been observed at intermediate and high Galactic latitudes. The 3 sigma limiting line and continuum fluxes in each field vary from 7.5x10^-17 to 1x10^-17 ergs cm^-2 s^-1, and from H=20 to 22, respectively. Our median and area-weighted 3 sigma limiting line fluxes within a 4 pixel aperture are nearly identical at 4.1x10^-17 ergs cm^-2 s^-1 and are 60% deeper than the deepest narrowband 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 2 sigma rest-frame equivalent width limits range from 9 to 130 Å, with an average of 40 Å. The survey probes an effective comoving volume of 10^5 h^-3_50 Mpc^3 for q_0=0.5. Our derived comoving number density of emission-line galaxies in the range 0.7