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Register a new userGalaxy Counts at 24 Microns in the SWIRE Fields
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This paper presents galaxy source counts at 24 microns in the six Spitzer Wide-field InfraRed Extragalactic (SWIRE) fields. The source counts are compared to counts in other fields, and to model predictions that have been updated since the launch of Spitzer. This analysis confirms a very steep rise in the Euclidean-normalized differential number counts between 2 mJy and 0.3 mJy. Variations in the counts between fields show the effects of sample variance in the flux range 0.5-10 mJy, up to 100% larger than Poisson errors. Nonetheless, a shoulder in the normalized counts persists at around 3 mJy. The peak of the normalized counts at 0.3 mJy is higher and narrower than most models predict. In the ELAIS N1 field, the 24 micron data are combined with Spitzer-IRAC data and five-band optical imaging, and these bandmerged data are fit with photometric redshift templates. Above 1 mJy the counts are dominated by galaxies at z less than 0.3. By 300 microJy, about 25% are between z ~ 0.3-0.8, and a significant fraction are at z ~ 1.3-2. At low redshifts the counts are dominated by spirals, and starbursts rise in number density to outnumber the spirals contribution to the counts below 1 mJy.
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We present initial results of galaxy clustering at 24um by analyzing statistics of the projected galaxy distribution from counts-in-cells. This study focuses on the ELAIS-N1 SWIRE field. The sample covers ~5.9 square-degrees and contains 24,715 sources detected at 24um to a 5.6-sigma limit of 250 micro-Jy (in the lowest coverage regions). We have explored clustering as a function of 3.6 - 24um color and 24um flux density using angular-averaged two-point correlation functions derived from the variance of counts-in-cells on scales 0.05-0.7 degrees. Using a power-law parameterization, $w_{2}(theta)=A(theta/deg)^{1-gamma}$, we find [A,gamma] = [(5.43pm0.20)times10^{-4},2.01pm0.02] for the full sample (1-sigma errors throughout). We have inverted Limbers equation and estimated a spatial correlation length of $r_{0}=3.32pm0.19 h^{-1}$Mpc for the full sample, assuming stable clustering and a redshift model consistent with observed 24um counts. We also find that blue [f(24)/f(3.6)<=5.5] and red [f(24)/f(3.6)>=6.5] galaxies have the lowest and highest $r_{0}$ values respectively, implying that redder galaxies are more clustered (by a factor of ~3 on scales >0.2 degree). Overall, the clustering estimates are smaller than those derived from optical surveys, but in agreement with results from IRAS and ISO in the mid-infrared. This extends the notion to higher redshifts that infrared selected surveys show weaker clustering than optical surveys.
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.
Emission at far-infrared wavelengths makes up a significant fraction of the total light detected from galaxies over the age of Universe. Herschel provides an opportunity for studying galaxies at the peak wavelength of their emission. Our aim is to provide a benchmark for models of galaxy population evolution and to test pre-existing models of galaxies. With the Herschel Multi-tiered Extra-galactic survey, HerMES, we have observed a number of fields of different areas and sensitivity using the SPIRE instrument on Herschel. We have determined the number counts of galaxies down to ~20 mJy. Our constraints from directly counting galaxies are consistent with, though more precise than, estimates from the BLAST fluctuation analysis. We have found a steep rise in the Euclidean normalised counts at <100 mJy. We have directly resolved 15% of the infrared extra-galactic background at the wavelength near where it peaks.
We have imaged a $sim$6 arcminute$^2$ region in the Bootes Deep Field using the 350 $mu$m-optimised second generation Submillimeter High Angular Resolution Camera (SHARC II), achieving a peak 1$sigma$ sensitivity of $sim$5 mJy. We detect three sources above 3$sigma$, and determine a spurious source detection rate of 1.09 in our maps. In the absence of $5sigma$ detections, we rely on deep 24 $mu$m and 20 cm imaging to deduce which sources are most likely to be genuine, giving two real sources. From this we derive an integral source count of 0.84$^{+1.39}_{-0.61}$ sources arcmin$^{-2}$ at $S>13$ mJy, which is consistent with 350 $mu$m source count models that have an IR-luminous galaxy population evolving with redshift. We use these constraints to consider the future for ground-based short-submillimetre surveys.
We present galaxy counts at 15 microns using the Japanese AKARI satellites NEP-deep and NEP-wide legacy surveys at the North Ecliptic Pole. The total number of sources detected are approximately 6700 and 10,700 down to limiting fluxes of 117 and 250 microJy (5 sigma) for the NEP-deep and NEP-wide survey respectively. We construct the Euclidean normalized differential source counts for both data sets (assuming 80 percent completeness levels of 200 and 270 microJy respectively) to produce the widest and deepest contiguous survey at 15 microns to date covering the entire flux range from the deepest to shallowest surveys made with the Infrared Space Observatory (ISO) over areas sufficiently significant to overcome cosmic variance, detecting six times as many sources as the largest survey carried out with ISO.We compare the results from AKARI with the previous surveys with ISO at the same wavelength and the Spitzer observations at 16 microns using the peek-up camera on its IRS instrument. The AKARI source counts are consistent with other results to date reproducing the steep evolutionary rise at fluxes less than a milliJansky and super-Euclidean slopes. We find the the AKARI source counts show a slight excess at fluxes fainter than 200 microJanskys which is not predicted by previous source count models at 15 microns. However, we caution that at this level we may be suffering from the effects of source confusion in our data. At brighter fluxes greater than a milliJansky, the NEP-wide survey source counts agree with the Northern ISO-ELAIS field results, resolving the discrepancy of the bright end calibration in the ISO 15 micron source counts.
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