| Abstract | We present R-band images covering more than 11 square degrees of sky that were obtained in preparation for the Spitzer Space Telescope First-Look Survey (FLS). The FLS was designed to characterize the mid-infrared sky at depths 2 orders of magnitude deeper than previous surveys. The extragalactic component is the first cosmological survey done with Spitzer. Source catalogs extracted from the R-band images are also presented. The R-band images were obtained using the Mosaic-1 camera on the 4 m Mayall Telescope of the Kitt Peak National Observatory. Two relatively large regions of the sky were observed to modest depth: the main FLS extragalactic field (17h18m00s, +59°30'00.0" [J2000]; l=88.3d, b=+34.9d) and the ELAIS-N1 field (16h10m01s, +54°30'36.0" l=84.2d, b=+44.9d). While both these fields were in early plans for the FLS, only a single deep-pointing test observation was made at the ELAIS-N1 location. The larger Legacy program SWIRE will include this region among its surveyed areas. The data products of our KPNO imaging (images and object catalogs) are made available to the community through the World Wide Web (via the Spitzer Science Center and NOAO Science Archive). The overall quality of the images is high. The measured positions of sources detected in the images have rms uncertainties in their absolute positions on the order of 0.35" with possible systematic offsets on the order of 0.1", depending on the reference frame of comparison. The relative astrometric accuracy is much better than 1/10 of an arcsecond. Typical delivered image quality in the images is 1.1" full width at half-maximum. The images are relatively deep, since they reach a median 5 σ depth limiting magnitude of R=25.5 (Vega) as measured within a 1.35FWHM aperture, for which the signal-to-noise ratio (S/N) is maximal. Catalogs have been extracted with SExtractor, using thresholds in area and flux for which the number of false detections is below 1% at R=25. Only sources with S/N>3 have been retained in the final catalogs. Comparing the galaxy number counts from our images with those of deeper R-band surveys, we estimate that our observations are 50% complete at R=24.5. These limits in depth are sufficient to identify a substantial fraction of the infrared sources that will be detected by Spitzer. |
