Studying the Evolution of Field Galaxies Using NICMOS/HST Parallel Imaging and Grism Data

Abstract

We present results from our analysis of F160W NICMOS Parallel images. These data cover $\sim$~9~sq. arcminutes and reach 3$σ$ depths of H$=$ 24.3 $-$ 25.5 in a $0.6&#39;&#39;$ diameter aperture with integration times of 2,000 to 13,000 seconds. We derive the first deep H band galaxy counts. The slope of the counts for H$<$ 20 is 0.31, consistent with various K-band measurements from the Keck telescopes. The measured number counts vs. magnitude relation is reasonably well fitted with no-evolution models with a low $Ω$ value. The half-light radii of the galaxies declines steeply with apparent magnitude and reaches the NIC3 resoltion limit at H$=$23.5. Deep ground-based VRI imaging of one NICMOS field has revealed an extremely red galaxy with R$-$H $=$ 6 and H of 18.8. Our analyses of the grism data show that we can reach 3$σ$ flux limits of of $1\times 10^{-16}$ to $2\times10^{-17}$ ergs/sec/cm$^2$ for integration times of 2,000 to 21,000~seconds. We have detected a total of 33 emission line galaxies. The comoving number density is $\rm \sim 2\times 10^{-4} Mpc^{-3}$. The detected emission lines are probably H$_α$~6563Å. Thus, the derived star formation rates, without extinction correction, are $10 - 163 M\odot$ per year for galaxies at redshifts between 0.7 and 1.9.