TheSpitzer Space TelescopeExtragalactic First Look Survey: 24 μm Data Reduction, Catalog, and Source Identification

We present the reduction of the 24 micron data obtained during the firstcosmological survey performed by the Spitzer Space Telescope (First LookSurvey, FLS). The survey consists of a shallow observation of 2.5x2 sq degcentered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sqdeg centered at 17h17m +59d45m(verification survey). Issues with the reductionof the 24 micron MIPS data are discussed and solutions to attenuateinstrumental effects are proposed and applied to the data. Approximately 17000sources are extracted with a SNR greater than five. The photometry of the pointsources is evaluated through PSF fitting using an empirical PSF derived fromthe data. Aperture corrections and the absolute calibration have been checkedusing stars in the field. Astrometric and photometric errors depend on the SNRof the source varying between 0.35-1 arcsec and 5-15%, respectively, forsources detected at 20-5 sigma. The flux of the 123 extended sources have beenestimated through aperture photometry. The extended sources cover less than0.3% of the total area of the survey. Based on simulations, the main andverification surveys are 50% complete at 0.3 and 0.15 mJy, respectively.Counterparts have been searched for in optical and radio catalogs. More than80% of the 24 micron sources have a reliable optical counterpart down toR=25.5. 16% of the sources have a 20 cm counterpart down to 0.1 mJy and ~ 80%of the radio-infrared associations have a reliable optical counterpart. Aresidual map is obtained by subtracting point sources detected at the 3-sigmalevel and interpolating the regions occupied by extended sources. Severalgalactic clouds with low and intermediate velocities are identified bycomparison with neutral Hydrogen data from this field.