Extragalactic Source Counts at 24 Microns in the Spitzer First Look Survey

We present the Spitzer MIPS 24 micron source counts in the Extragalactic First Look Survey main, verification and ELAIS-N1 fields. Spitzers increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 micron band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The First Look Survey observations cover areas of, respectively, 4.4, 0.26 and 0.015 sq.deg. and reach 3-sigma depths of 0.11, 0.08 and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index alpha=-2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peaks displacement in the 24 micron counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 micron deep counts.

The Spitzer Space Telescope Extra-Galactic First Look Survey: 24 micron data reduction, catalog, and source identification

We present the reduction of the 24 micron data obtained during the first cosmological survey performed by the Spitzer Space Telescope (First Look Survey, FLS). The survey consists of a shallow observation of 2.5x2 sq deg centered at 17h18m +59d30m (main survey) and a deeper observation of 1x0.5 sq deg centered at 17h17m +59d45m(verification survey). Issues with the reduction of the 24 micron MIPS data are discussed and solutions to attenuate instrumental effects are proposed and applied to the data. Approximately 17000 sources are extracted with a SNR greater than five. The photometry of the point sources is evaluated through 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 SNR of the source varying between 0.35-1 arcsec and 5-15%, respectively, for sources detected at 20-5 sigma. The flux 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 micron 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 ~ 80% of the radio-infrared 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.

The HDF-North SCUBA Super-map I: Submillimetre maps, sources and number counts

We investigate the emission of sub-millimetre-wave radiation from galaxies in a 165 square arcminute region surrounding the Hubble Deep Field North. The data were obtained from dedicated observing runs from our group and others using the SCUBA camera on the James Clerk Maxwell Telescope, and combined using techniques specifically developed for low signal-to-noise source recovery. The resulting `Super-map is derived from about 60 shifts of JCMT time, taken in a variety of observing modes and chopping strategies, and combined here for the first time. At 850 micron we detect 19 sources at >4 sigma, including 5 not previously reported. We also list an additional 15 sources between 3.5 and 4.0 sigma (where 2 are expected by chance). The 450 micron map contains 5 sources at >4 sigma. We present a new estimate of the 850 micron and 450 micron source counts. The number of sub-mm galaxies we detect account for approximately 40% of the 850 micron sub-mm background, and we show that mild extrapolations can reproduce it entirely. A clustering analysis fails to detect any significant signal in this sample of SCUBA detected objects. A companion paper describes the multiwavelength properties of the sources.

The SCUBA-2 Cosmology Legacy Survey: 850um maps, catalogues and number counts

We present a catalogue of nearly 3,000 submillimetre sources detected at 850um over ~5 square degrees surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850um, probing a meaningful cosmic volume at the peak of star formation activity and increasing the sample size of submillimetre galaxies selected at 850um by an order of magnitude. We describe the wide 850um survey component of S2CLS, which covers the key extragalactic survey fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1-sigma depth of S2CLS is 1.2 mJy/beam, approaching the SCUBA-2 850um confusion limit, which we determine to be ~0.8 mJy/beam. We measure the single dish 850um number counts to unprecedented accuracy, reducing the Poisson errors on the differential counts to approximately 4% at S_850~3mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5-1 degree scales are generally within 50% of the S2CLS mean for S_850>3mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2-sigma) density enhancement in the GOODS-North field. The observed number counts are in reasonable agreement with recent phenomenological and semi-analytic models. Finally, the large solid angle of S2CLS allows us to measure the bright-end counts: at S_850>10mJy there are approximately ten sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850um emission and strongly lensed high-redshift galaxies. Here we describe the data collection and reduction procedures and present calibrated maps and a catalogue of sources; these are made publicly available.