Star formation history in the NICMOS northern Hubble Deep Field

We present the results of an extensive analysis of the star formation rates determined from the NICMOS deep images of the northern Hubble Deep Field. We use SED template fitting photometric techniques to determine both the re dshift and the extinction for each galaxy in our field. Measurement of the individual extinctions provides a correction for star formation hidden by d ust obscuration. We determine star formation rates for each galaxy based on the 1500 Angstrom UV flux and add the rates in redshift AZ bins of width 1 .0 centered on integer redshift values. We find a rise in the star formatio n rate from a redshift of 1 to 2 then a falloff from a redshift of 2 to 3. However, within the formal limits of the error bars this could also be inte rpreted as a constant star formation rate from a redshift of 1 to 3. The st ar formation rate from a redshift of 3 to 5 is roughly constant followed by a possible drop in the rate at a redshift of 6. The measured star formatio n rate at a redshift of 6 is approximately equal to the present day star fo rmation rate determined in other work. The high star formation rate measure d at a redshift of 2 is due to the presence of two possible ULIRGs in the f ield. If real, this represents a much higher density of ULIRGs than measure d locally. We also develop a new method to correct for faint galaxies or fa int parts of galaxies missed by our sensitivity limit, based on the assumpt ion that the star formation intensity distribution function is independent of redshift. We measure the 1.6 mum surface brightness due to discrete sour ces and predict the 850 mum brightness of all of our galaxies based on the determined extinction. We find that the far-infrared fluxes predicted in th is manner are consistent with the lack of detections of 850 mum sources in the deep NICMOS HDF, the measured 850 mum sky brightness due to discrete so urces and the ratio of optical-UV sky brightness to far-infrared sky bright ness. From this we infer that we are observing a population of sources that contributes significantly to the total star formation rate and these sourc es are not overwhelmed by the contribution from sources such as the extreme ly superluminous galaxies represented by the SCUBA detections. We have esti mated the errors in the star formation rate due to a variety of sources inc luding photometric errors, the near-degeneracy between reddening and intrin sic spectral energy distribution as well as the effects of sampling errors and large-scale structure. We have tried throughout to give as realistic an d conservative an estimate of the errors in our analysis as possible.