The WISE All-Sky Release Source Catalog contains positions and four-band photometry for 563,921,584 objects detected in 18,240 Atlas Tiles. Each Catalog entry gives positions, magnitudes, astrometric and photometric uncertainties, flags indicating the reliability and quality of the source characterizations, and associations with any nearby 2MASS Point and Extended Source Catalog.
The All-Sky Release Catalog contains many types of sources, and is not restricted to point-like objects such as stars and unresolved galaxies. The Catalog contains both point-like objects and close multiple sources, detections on the disks and spiral arms of resolved galaxies and clumps or filaments in Galactic nebulosity if they meet the Catalog criteria described in sections II.2.b below and V.3.
A summary of the properties of the Source Catalog and a detailed Catalog format description are presented below. More detailed descriptions of photometric and astrometric characteristics of the Catalog are presented in section VI. Descriptions of processing algorithms used to generate the Source Catalog can be found in section IV.Users are strongly encouraged to read the Cautionary Notes before using the All-Sky Release Catalog.
Sources in the All-Sky Release Catalog were drawn from a Working Database (WDB) of all detections made on the coadded Atlas Images that was generated during second-pass Multiframe Pipeline processing. The WDB contains 847,809,235 entries, significantly more than the Source Catalog because many of the entries are spurious detections of noise and image artifacts. The reliability of the WISE Source Catalog was achieved by selecting entries in the WDB that satisfy the quality criteria that are described in V.3 and summarized in Table 1. WDB entries that were not selected for inclusion inthe All-Sky Release Source Catalog are contained in the Reject Table.
Extractions must have a "reliable" detection in at least one band. A reliable band-detection must satisfy all these criteria in that band.
|Signal-to-Noise Ratio (SNR)||Source must be detected with a SNR>5||Rejection of spurious detections of low SNR noise excursions.|
|Frame coverage||There must be five or more single-exposure images on which the source can be measured and characterized.||Rejection of single-exposure transient events that can persist into the coadded images because of low coverage.|
|Artifacts||Extraction must not
be identified as a spurious
detection of an image artifact from a bright source,
including one of the planets.
Sources believed to be real, but whose measurements are affected by artifacts, are included in the Catalog, and are flagged using the cc_flags parameter.
|Rejection of spurious detection of image artifacts.|
|Tile Boundaries||Extraction lies >50" from the edge of the Atlas Tile||To avoid truncation of the largest measurement aperture used for the source aperture photometry.|
|Duplicate Source Entries||For multiply-detected sources in Atlas Tile overlap regions, the apparition farthest from its respective Tile edge is selected. Sources in the overlap regions not multiply-detected are always included in the Source Catalog if they satisfy all other selection criteria.||To eliminate duplicate extractions of the same source|
The number of sources in the All-Sky Catalog with >2σdetections in each of four WISE bands, and with detections in combinations of bands, are listed in Tables 2 and 3, respectively. The overwhelming majority of objects in the Catalog have detections in the W1 band because that band has the best flux sensitivity (see VI.3.a) and because the spectral energy distributions of most objects on the sky favors detection in that band. Because WISE source detection and characterization is done on all bands simultaneously, the preponderance of detections in W1 means that source properties in this band will be weighted heavily in the measurements in all bands.
Although more than 99% of the All-Sky Release Catalog sources have W1 detections, there are over 5 million objects that aren't detected in W1. These rare objects may be among the most interesting measured by WISE (e.g. Kirkpatrick et al. 2011, ApJS, 197, 19; Liu et al. 2011; Eisenhardt et al. 2012).
|Band||Number of Objects||Percentage of Total|
|Band-Combination||det_bit||Number||Percentage of Total|
The approximate coverage of the All-Sky Release Source Catalog is 42,195 deg2, or 99.86% of the entire sky (VI.2). Although WISE imaged every point on the sky multiple times during its full cryogenic mission phase, some of the Single-exposure framesets had degraded quality and therefore were not utilized in the construction of the Source Catalog (V.2.c). Sources extracted by the Multiframe Processing pipeline were required to have at least five independent Single-exposures available for there measurement, so the loss of frame depth-of-coverage sometimes resulted in loss of Catalog effective sky coverage. Obscuration by the scattered light and other image artifacts from bright sources and nebulosity also diminishes the effective coverage of the Catalog. Some of the most prominent coverage gaps caused by degraded frame quality and losses due to bright sources and source confusion can be seen in the All-Sky Release Catalog source count map shown in Figure 1.
WISE All-Sky Release Catalog sky coverage is discussed in detail in VI.2.
|Figure 1 - Hammer galactic projection showing a grey-scale surface density map of All-Sky Release Source Catalog entries computed in 0.2°x0.2° spatial bins. The full range is 0 to 1166 per bin (0 to 29,150 deg-2). Galactic north is towards the top and galactic longitude increases to the left.|
As can be seen in Figure 1, the spatial distribution of All-Sky Release Catalog sources is concentrated towards the Galactic plane. Half of the Catalog entries are found within approximately ±25° of the plane, as shown in Table 4 which gives the cumulative Catalog source counts as a function of galactic latitude. However, the source density profile with galactic latitude, shown in Figure 2, flattens significantly beginning at ~40° from the plane. The nearly uniform source density at the high latitudes indicates that Catalog is dominated by extragalactic sources.
||b| < (deg)||Number||Percentage of Total|
|Figure 2 - Differential All-Sky Release Catalog source density measured in one degree wide bands of galactic latitude, plotted as a function of galactic latitude.|
The detailed distribution of Catalog sources on the sky is a complex function of brightness in each band because of the variation of source density on the sky, the survey depth-of-coverage, and the effects of confusion on source extraction. Figures 3-6 are animated GIF images that show sky maps of the surface density of Catalog sources in 0.5 magnitude bins in progressively fainter magnitude slices. Completeness in the Galactic Plane begins to fall off quickly in the short wavelength bands because of confusion in high source density regions. The distribution of sources at higher Galactic latitudes remains relative uniform until W1<17.0, W2>16.0, W3>12.5 and W4>9.0 mag. For fainter magnitudes, the non-uniform depth-of-coverage produced by survey strategy begins to dominate the distributions.
Another feature that is seen in the animations in Figures 5 and 6, is that the distributions of sources in W3 and W4 begin to trace the zodiacal dust bands and halos around bright stars at SNR<5-7. This is a by-product of the multiband source detection and extraction algorithms used in the WISE data reduction pipelines (c.f. IV.4.b and IV.v.c). The surface density of W1 and W2 sources is high over virtually the entire sky. When W1 and W2 sources fall on regions that have extended, structured background emission in W3 and W4, such as the dust bands, comet trails, or scattered light halos around very bright stars, the higher SNR W1 and W2 extractions will sometimes "pull along" apparent, albeit low SNR detections at the longer wavelengths. These low SNR "shadow" detections in W3 and W4 can be numerous, and thus standout in the cumulative count maps shown in the thumbnail images for Figures 5 and 6.
|Figure 3 - W1: Linear stretch; Range = 0-1057.3||Figure 4 - W2: Linear stretch; Range = 0-1005.3|
|Figure 5 - W3: Log stretch; Range = 0-1055.5||Figure 6 - W4: Loglog stretch; Range = 0-702.2|
|Hammer galactic projection grey-scale maps showing the cumulative counts >2-σ source densities computed in 0.2°x0.2° spatial bins, by band, in the WISE All-Sky Release Catalog. Click on the thumbnails to view animated GIF images that show the Catalog count maps for each band in slices of 0.5 mag intervals at progressively fainter levels. The center of the maps corresponds to galactic coordinates 0°,0°. Galactic north is towards the top of the maps and galactic longitude increases to the left.|
WISE Source Catalog is >95% complete for sources with SNR>20 in unconfused regions of the sky that have five or more Single-exposure depth-of-coverage (see VI.5). This corresponds approximately to magnitudes of W1=16.6, W2=16.0, W3=10.8 and W4=6.7 mag. The effective depth of the Catalog will vary around the sky, decreasing in regions with low depth-of-coverage or higher levels of confusion due to high source density or complex and bright emission backgrounds.
The variation of Catalog depth with source density is illustrated in the top panels of Figures 7 and 8 which show examples of source count log histograms for two representative regions in the All-Sky Release Source Catalog. Figures 7 shows the region within 10° of the north Galactic pole and 8 shows a region on the galactic plane. Although these two regions have similar survey depths-of-coverage, the peak of the source count curves (a proxy for the completeness level) occur at fainter magnitudes in the north Galactic pole field where source densities are much lower. The differences are most apparent in the W1 and W2 bands, and less prominent in the longer wavelength bands where the surface density of sources is lower all over the sky. The spatial distribution of the source count curve peak magnitudes are shown in Figures 9-12. The effect of survey-depth-of-coverage can be seen in all bands, with fainter completeness levels towards the ecliptic poles, and in the multiple-epoch coverage regions. The loss of depth due to confusion in the Galactic Plane is prominent in W1 and W2. In W3 and W4, there is an additional gradient in the depth with ecliptic latitude because of the varying impact of the zodiacal emission.
|Figure 7 - (top) Differential WISE Source Catalog counts in the 313 deg2 within 10° of the north Galactic pole. (bottom) Average photometric uncertainty as a function of source brightness in this region.||Figure 8 - (top) Differential WISE Source Catalog counts in a 10°x10° region centered on l,b=338°,0°. (bottom) Average photometric uncertainty as a function of source brightness in this region.|
|Figure 9 - W1||Figure 10 - W2|
|Figure 11 - W3||Figure 12 - W4|
|False-color maps showing the spatial distribution of the peak magnitude of the differential source count histograms computed in 0.2x0.2 deg spatial bins. The color scale in the images gives the peak magnitude color encoding for each band. The Maps are Hammer projections in galactic coordinates. The centers correspond to ecliptic coordinate 180°,0°. Galactic north is towards the top, and galactic longitude increases towards the left.|
Listed in Table 5 are the approximate magnitudes at which 50% of the sources in the All-Sky Release Source Catalog are saturated. Photometry is performed for sources brighter than the saturation limits by PSF-fitting to the non-saturated wings of the source profiles. The quality of the photometry for saturated sources is progressively degraded. Brighter than the extraction limit levels given in Table 5, saturation sources could no longer be reliably extracted and may be missing from the Catalog.
1 Approximate values. Onset of saturation can vary by ~1mag depending on BG and sub-pixel location (see VI.3.d)
2 Approximate values. Sources brighter than these limits may not be present in the Catalog. (see VI.3.c.i)
Photometry of bright, non-saturated sources in the Preliminary Release Source Catalog has an accuracy of ~2-3% (VI.3.a). Photometric SNR>5 is achieved for sources with W1<16.6, W2<15.6, W3<11.2 and W4<8.0 mag in the unconfused regions of the sky with at least 8 independent coverages (VI.3.b).
The characteristic sensitivity of the Source Catalog varies significantly around the sky because of the variable depth-of-coverage, background emission levels and source confusion. The bottom panels of Figures 5 and 6 show the average quoted W1, W2, W3 and W4 profile-fitting photometric uncertainties in 0.2 magnitude bins for high and low galactic latitude regions in the Catalog, respectively. The vertical bars show the RMS dispersion in the mean uncertainties in each brightness. Photometric uncertainties increase at the bright end because of the onset of saturation. Uncertainties increase towards fainter flux levels as photon noise increasingly dominates the measurements.
The variation of photometric sensitivity around the sky is illustrated in Figures 13-16. These diagrams show sky maps of the magnitude for which the mean photometric measurement uncertainty in each band is equal to 0.217 mag, corresponding to 5σ, within each Atlas Tile. Sensitivities are lowest in the high source density regions of the Galactic plane. Sensitivities increase towards the Galactic poles, but also in regions with deeper Single-exposure coverage, such as in the portion of the sky surveyed twice during the full-cryogenic mission phase. There is also an ecliptic latitude-dependence in the achieved sensitivity because of the presence of the zodiacal background. The achieved sensitivity also varies along the "spokes" produced by the Moon avoidance maneuvers. It is minimized near the Ecliptic plane because of quality degradation due to scattered moonlight, but increases at high Ecliptic latitudes because of the double-coverage produced by the Moon avoidance maneuver. See VI.3.a for more details.
|Figure 13 - W1||Figure 14 - W2|
|Figure 15 - W3||Figure 16 - W4|
|False-color equatorial projection sky maps showing the spatial variation of average magnitude at which the average source SNR=5 in the All-Sky Release Source Catalog (see VI.3.a). The colors denote the mean SNR=5 magnitude per Tile, according to the color bars in each Figure.|
W1-W2-W3 (3.4-4.6-12 μm) color-color diagrams drawn from high and low galactic latitude regions in the All-Sky Release Source Catalog are shown in Figures 17 and 18, respectively. The locations in color-space for various classes of astrophysical objects are shown in the annotated version of Figure 17.
|Figure 17 - WISE 3.4-4.6-12 μm color-color diagram for a 116 deg2 region at l,b=225°,-55°. Green contours trace the density of sources in color bins. Click here for an annotated version of the color-color diagram showing the location of different classes of objects.||Figure 18 - WISE 3.4-4.6-12 μm color-color diagram for a 116 deg2 region at l,b=338°,-1°. Green contours trace the density of sources in color bins.|
The astrometric properties of the WISE All-Sky Release Source Catalog are discussed in detail in VI.4. Catalog source are reconstructed with respect to the 2MASS Point Source Catalog reference frame. The RMS accuracy of the reconstructed positions with respect to the 2MASS PSC for unsaturated sources with SNR>50 in unconfused regions of the sky is approximately 200 mas on each axis, with biases typically less than 50 mas. The accuracy is approximately 400 mas at SNR=20, and decreases towards fainter flux levels. Figures 19 and 20 illustrate the distribution of position differences between the WISE All-Sky Catalog and those in the USNO CCD Astrograph Catalog (UCAC3). WISE Catalog position reconstruction did not use any reference to UCAC3, so that Catalog provides a good independent check on the WISE astrometry.
Because of proper motion of 2MASS reference stars used by WISE in the ten years between the surveys, there can be systematic position biases between the WISE reference frame and the ICRS of up to approximately 150 mas depending on direction on the sky (see VI.4.f).
|Figure 19 - Histogram of RA (green) and Dec (blue) position residuals between UCAC3 and WISE All-Sky Catalog for sources with SNR(W1)>20 within 10° of the north Galactic pole.||Figure 20 - RMS of the UCAC3-WISE RA (green) and Dec (blue) position residuals as a function of WISE W1 source magnitude for sources within 10° of the north Galactic pole|
Last Updated: 2012 July 26