The Spitzer Space Telescope extragalactic first look survey:: 24 μm data reduction, catalog, and source identification

We present the reduction of the 24 mu m data obtained during the first cosmological survey performed by the Spitzer Space Telescope. Images of a region of sky at moderately high Galactic latitude (l = 88.degrees 3, b = 34.degrees 9) were obtained on 2003 December 9-11. The survey consists of a shallow observation of 2.degrees 5 x 2 degrees centered at 17(h)18(m), + 59 degrees 30' (main survey) and a deeper observation of 1 degrees x 0.degrees 5 centered at 17(h)17(m), + 59 degrees 45' (verification survey). Issues with the reduction of the 24 mu m MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17,000 sources are extracted with a signal-to-noise ratio (S/N) greater than 5. The photometry of the point sources is evaluated through point-spread function (PSF) fitting using an empirical PSF derived from the data. Aperture corrections and the absolute calibration have been checked using stars in the field. Astrometric and photometric errors depend on the S/N of the source varying between 0."35-1" and 5%-15%, respectively, for sources detected at 20-5 sigma. The fluxes of the 123 extended sources have been estimated through aperture photometry. The extended sources cover less than 0.3% of the total area of the survey. Based on simulations, the main and verification surveys are 50% complete at 0.3 and 0.15 mJy, respectively. Counterparts have been searched for in optical and radio catalogs. More than 80% of the 24 mu m sources have a reliable optical counterpart down to R 25: 5; 16% of the sources have a 20 cm counterpart down to 0.1 mJy and similar to 80% of the radio-IR associations have a reliable optical counterpart. A residual map is obtained by subtracting point sources detected at the 3 sigma level and interpolating the regions occupied by extended sources. Several Galactic clouds with low and intermediate velocities are identified by comparison with neutral hydrogen data from this field.