The NEWFIRM Medium-Band Survey: Filter Definitions and First Results

Abstract

ABSTRACTDeep 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 are too faint for spectroscopy, the interpretation of these surveys relies almost exclusively on photometric redshifts determined from fitting templates to the broadband photometry. The best-achieved accuracy of these redshifts, Δz/(1 + z) ≳ 0.06 at z > 1.5, 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 4-m 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 μm for all objects in the 27.6′ × 27.6′ 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 recent near-infrared spectroscopic sample of Kriek et al.. 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.