The NEWFIRM Medium-Band Survey: Filter Definitions and First Results
  Deep near-infrared imaging surveys allow us to select and study distant
galaxies in the rest-frame optical, and have transformed our understanding of
the early Universe. As the vast majority of K- or IRAC-selected galaxies is too
faint for spectroscopy, the interpretation of these surveys relies almost
exclusively on photometric redshifts determined from fitting templates to the
broad-band photometry. The best-achieved accuracy of these redshifts
Delta(z)/(1+z) ~ 0.06 at z>1.5, which is sufficient for determining the broad
characteristics of the galaxy population but not for measuring accurate
rest-frame colors, stellar population parameters, or the local galaxy density.
We have started a near-infrared imaging survey with the NEWFIRM camera on the
Kitt Peak 4m telescope to greatly improve the accuracy of photometric redshifts
in the range 1.5<z<3.5. The survey uses five medium-bandwidth filters, which
provide crude "spectra" over the wavelength range 1-1.8 micron for all objects
in the 27.6 x 27.6 arcmin NEWFIRM field. In this first paper, we illustrate the
technique by showing medium band NEWFIRM photometry of several galaxies at
1.7<z<2.7 from the near-infrared spectroscopic sample of Kriek et al. (2008).
The filters unambiguously pinpoint the location of the redshifted Balmer break
in these galaxies, enabling very accurate redshift measurements. The full
survey will provide similar data for ~8000 faint K-selected galaxies at z>1.5
in the COSMOS and AEGIS fields. The filter set also enables efficient selection
of exotic objects such as high redshift quasars, galaxies dominated by emission
lines, and very cool brown dwarfs; we show that late T and candidate "Y" dwarfs
could be identified using only two of the filters.
