ar X iv : a st ro - p h / 98 09 04 4 v 1 4 S ep 1 99 8 Studying the Evolution of Field Galaxies Using NICMOS / HST Parallel Imaging And Grism Data

We present results from our analysis of F160W NICMOS Parallel images. These data cover ∼ 9 sq. arcminutes and reach 3σ depths of H= 24.3 − 25.5 in a 0.6 ′′ 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 3σ flux limits of of 1 × 10 −16 to 2 × 10 −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 ∼ 2 × 10 −4 Mpc −3. The detected emission lines are probably H α 6563Å. Thus, the derived star formation rates, without extinction correction, are 10 − 163M ⊙ per year for galaxies at redshifts between 0.7 and 1.9.