The WISE 3-Band Cryo Source Working Database (WDB) contains astrometry and photometry for 261,418,479 sources detected on the 3-Band Cryo Atlas Intensity Images. Positions, magnitudes, astrometric and photometric uncertainties, flags indicating the quality of the source characterizations, and associations with the WISE All-Sky Release Catalog and the 2MASS Point and Extended Source Catalog sources are presented for each source.
A summary of the properties of the 3-Band Cryo WDB and detailed column descriptions are presented below. More detailed descriptions of photometric and astrometric characteristics of the WDB are presented in section VII.5. Descriptions of processing algorithms used to generate the WDB can be found in sections IV and VII.3.Users are strongly encouraged to read the Cautionary Notes before using the 3-Band Cryo Source WDB.
The 3-Band Cryo Source WDB contains measurements of all detections made on the coadded Atlas Images during second-pass Multiframe Pipeline processing. The database is analogous to the one generated from the Multiframe processing of the full cryogenic mission data. However, the 3-Band Cryo WDB has not been split into a separate Catalog and Reject Table, as was done for the All-Sky Data Release.
Consequently, the 3-Band Cryo WDB is not a well-vetted list of reliable mid-infrared source detections like the WISE All-Sky Release Catalog. The WDB contains detections of real astrophysical sources, along with low SNR noise excursions, spurious detections of image artifacts and transient pixel events, and duplicate, redundant entries of source detections in Atlas Tile overlap regions. The general reliability of the 3-Band Cryo WDB is described in VII.5.e. Tips for selecting reliable and unique detections the the WDB are given in VII.1.d.iii.
As is the case with the All-Sky Release Catalog, the reliable detections in the 3-Band Cryo WDB are not restricted to point sources such as stars and unresolved galaxies. The WDB contains point-like objects, close multiple sources, detections on the disks and spiral arms of resolved galaxies and clumps or filaments in Galactic nebulosity. Many of the objects that are well-resolved with respect to the WISE PSF are identified by having extended source flag values of ext_flg=1.
The 3-Band Cryo WDB is best used as as a source of supplemental information for objects that are found in the WISE All-Sky Release Source Catalog. Because the 3-Band Cryo observations provide independent, second-epoch of measurements of approximately 30% of the sky, the WDB can be used to search for potential proper motions and flux variability of All-Sky Catalog sources. The reliability of a faint source from the All-Sky Catalog can be verified if it appears in the 3-Band Cryo WDB, particularly for those with detections in W1 and W2 where the sensitivity is close to the full-cryo mission phase. Finally, the 3-Band Cryo WDB provides potential source information for regions with low or even no-coverage in the All-Sky Catalog. To facilitate such comparisons, the 3-Band Cryo WDB and All-Sky Release Catalog have been positionally cross-correlated, and the the identification, position offsets and 4-band magnitudes of the closest Catalog entry within 3 arcseconds are included in each 3-Band Cryo WDB source record.
The number of sources in the 3-Band Cryo WDB with >2σ flux measurements in each of WISE W1, W2 and W3 bands, and with measurement in the different combinations of bands, are listed in Tables 1 and 2, respectively. Compare these with the same statistics for the All-Sky Release Catalog given in Tables 2 and 3 in II.2.c. 4.4% (11,479,336) of the entries in the 3-Band Cryo WDB were nominally detected on the Atlas Images, but do not have >2σ flux measurements in any band (det_bit=0). These are most likely spurious detections of artifacts and noise. Such objects were filtered out of the All-Sky Release Catalog.
As for the All-Sky Catalog, the majority of objects in the 3-Band Cryo WDB 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 at the shorter wavelengths. Because WISE source detection and characterization is done on all bands simultaneously, and because the majority of objects are detected in W1, detections of real objects in W1 often pull along faint extractions in the other bands that may not otherwise have been detected on their own.
Because of the greatly reduced W3 sensitivity during 3-Band Cryo observations, sources detected only in W3 are largely unreliable extractions of artifacts, scattered moonlight features and noise events. See VII.5.e.v for more details.
|Band||Number of Objects||Percentage of Total|
|Band-Combination||det_bit||Number||Percentage of Total|
The WISE 3-Band Cryo observations covered approximately 30.3% of the sky in two broad ecliptic longitude ranges: 42.2°<λ<98.0° and 228.5°<λ<281.7°. The 3-Band Cryo Atlas Images and Source Working Database were constructed by combining the Single-exposure images that fall within 5,649 Atlas Tiles and that meet minimum quality criteria, and extracting sources from the coadded images. These Tiles were not required to be completely filled by the Single-exposure images. Figures 1 below shows the realized 3-Band Cryo Atlas depth-of-coverage around the sky in W1, W2 and W3 after all static and dynamic filtering of Single-exposure images during the Multiframe Pipeline processing. Depth-of-coverage ranges from ~12 along the ecliptic plane, and increases to several hundred near the ecliptic poles. The median coverage depth in the 3-Band Cryo survey area is 13.7, 13.9 and 13.8 in W1, W2 and W3, respectively. The strip of missing coverage in the W3 map is caused by the saturation in that band during the 4.4 sec exposure observations.
Figure 2 contains sky maps that show the number of 3-Band Cryo WDB sources in 12'x12' spatial bins in W1, W2 and W3. 3-Band Cryo WDB sources are concentrated towards the Galactic plane. The gap in the W3 count maps corresponding to the period of W3 saturation is clearly visible. Density enhancements are visible along "spokes" running between the Ecliptic poles that correspond to regions that were scanned twice as many times as normal during moon avoidance maneuvers. Note that the W3 saturation coverage gap on one side of the sky was partially filled in by the extra scans in a moon avoidance maneuver. The surface density enhancement near the south Ecliptic pole is the Large Magellanic Cloud.
|Figure 1 - Hammer galaction projection sky maps showing the realized Single-exposure depth-of-coverage in the W1, W2 and W3 bands for the WISE 3-Band Cryo Release Atlas and Source Working Database. Colors encode the average frame depth-of-coverage in 14'x14' spatial bins as indicated by the legends on the left.||Figure 2 - Hammer galactic projection grey-scale maps showing the total counts of >2-σ detections computed in 12'x12' spatial bins, in the WISE 3-Band Cryo Release WDB, by band. These maps have the same projection and orientation as the depth-of-coverage maps in Figure 1.|
The photometric sensitivity of the 3-Band Cryo Source WDB is discussed in more detail in VII.5.b.ii. In general, the sensitivity of W1 and W2 measurements during the 3-Band Cryo phase is similar to that during the full cryogenic mission phase. W3 sensitivity is 0.5 to 4 magnitudes poorer relative to the full cryogenic survey, and varies in a complex way because of the increasing telescope thermal emission and reduced exposure times.
The depth of the 3-Band Cryo Release Source WDB relative to the All-Sky Release Source Catalog is illustrated by the diagrams in Figure 3. These diagrams show the 3-Band Cryo WDB and All-Sky Catalog differential source counts and profile-fit photometry signal-to-noise ratios plotted as a function of source magnitude in two different 2°x2° regions selected to have been observed at the beginning and near the end of the 3-Band Cryo survey operations.
In W1 and W2, the 3-Band Cryo WDB source count curves extend to fainter magnitudes than the All-Sky Catalog because sources were required to have an SNR>5 in at least one band to be included in the All-Sky Catalog. The 3-Band Cryo WDB contains all extractions down to the detection limit near SNR~3.5, so no SNR filtering has been applied. The W3 source counts from the 8.8 sec 3-Band Cryo observations begin to roll off approximately one magnitude brighter than the counts in the All-Sky Catalog because of the higher thermal background emission during the 3-Band Cryo period. In the 1.1 sec W3 3-Band Cryo observations, the 3-Band Cryo WDB counts roll off 3-4 magnitudes brighter than the All-Sky Catalog because of both the shorter exposure times and higher backgrounds. The excess of sources in the 3-Band Cryo WDB fainter at W3>8 mag relative to the All-Sky Catalog indicates the presence significant numbers of of spurious W3 noise detections at SNR≤10 in that band.
The SNR curves illustrate that the sensitivity of the W1 and W2 photometric measurements early in the 3-Band Cryo phase is very similar to those represented in the All-Sky Catalog. Near the end of the 3-Band Cryo phase when temperatures had risen to approximately 44 K, the W1 and W2 observations are at most a few tenths of a magnitude less sensitive than those from the full cryogenic survey phase. The sensitivity of the 3-Band Cryo W3 measurements ranges from ~0.5 mag below the full cryo phase at the beginning of the 3-Band Cryo survey, to 3.5-4 mag near the end of the 3-Band Cryo period.
|Figure 3 - The top panels in each diagram show the W1, W2 and W3 source count curves in 4 deg2 regions in the WISE All-Sky Release Catalog (blue lines) and the 3-Band Cryo Source Working Database (hashed green lines). The bottom panels show the profile-fit photometry measurement signal-to-noise ratio (w?snr) plotted as a function of profile-fit magnitude for the All-Sky Release Catalog (blue points) and 3-Band Cryo Working Database (green points). The red horizontal lines indicate SNR=5. The top row of plots show the counts and SNR for a region at l,b=171.5°,-43.1° in which the 3-Band Cryo W3 exposure time was 8.8 sec. The bottom row represents a region at l,b=186.5°,-14.0° in which the W3 exposure time was 1.1 sec.|
The spatial variation of 3-Band Cryo WDB photometric sensitivity is illustrated in Figures 4a-c which contain sky maps that show the magnitude at which the mean profile-fit photometric measurement uncertainty in each band is equal to 0.217 mag, corresponding to 5σ. In W1 and W2, the variations are similar to those seen in the All-Sky Release Catalog shown in Figure 1 in VI.3.a. Source confusion drives down sensitivity in the high density regions near the Galactic plane. Sensitivity increases away from the Galactic plane, and as the Single-exposure depth-of-coverage increases towards the Ecliptic poles. In W3, the sensitivity variations are dominated by the decreasing exposure times and increasing telescope temperature at the beginning of the 3-Band Cryo observations. The W3 sensitivity stabilized approximately 40% of the way into the 3-Band Cryo period when the telescope temperature settled near 44 K.
|Figure 4a - W1||Figure 4b - W2|
|Figure 4c - W3|
|False-color galactic projection sky maps showing the spatial variation of average magnitude at which the flux SNR=5 in the 3-Band Cryo WDB (see VII.5.b.ii). The colors denote the mean SNR=5 magnitude per Tile, according to the color bars in each Figure. The longitude axes are reversed in these figures relative to those in Figures 1 and 2.|
Figures 5a-c show differences between the profile-fit photometry of the same sources in the 3-Band Cryo WDB and All-Sky Release Catalog in three ~100 deg2 regions with different source surface densities. In the lowest density region, shown in Figure 5a, the 3-Band Cryo W1 and W2 measurements for non-saturated sources (W1>8 mag and W2>7 mag) are approximately 0.01-0.02 mag fainter than in the All-Sky Release Catalog. Roughly half of this offset is caused by the photometric zero point that was applied as part of the photometric calibration. In the higher source density regions shown in Figures 5b and 5c, a systematic, flux-dependent bias between 3-Band Cryo WDB and All-Sky Catalog becomes apparent. In the high density regions, 3-Band Cryo WDB measurements become increasingly fainter than those in the All-Sky Catalog towards fainter flux levels. The amplitude of this bias strengthens with increasing source surface density. For example, at a fiducial magnitude of W1=15 mag, 3-Band Cryo photometry is 0.02, 0.10 and 0.30 mag fainter than that in the All-Sky Catalog in the fields with 1,900, 7,200 and 24,200 sources deg-2, respectively.
This behavior is similar to the bias observed between photometry from the WISE All-Sky Release Catalog and from Spitzer Space Telescope Observations in selected regions (see VI.3.c.i.2). That bias is believed to result from slight overestimation of the background levels during WISE measurements because of the effects of source crowding and a small bias introduced in the pixel distributions during the Single-exposure image calibration step. The origin of the 3-Band Cryo vs. All-Sky Catalog bias likely has a similar origin.
3-Band Cryo WDB measurements of non-saturated sources in W3 are typically ~3% fainter than those in the All-Sky Release Catalog. At least a part of this offset is also attributable to difficulty in determining the photometric zero point for calibration. The time-variable zero point residuals in the W3 Single-exposures were corrected during 3-Band Cryo Atlas Image Generation, but it is likely a small net offset remained.
Photometry of saturated sources in the 3-Band Cryo WDB and the All-Sky Catalog show significant discrepancies in all bands (W1<8, W2<7 and W3<4 mag). As described in VII.1.a.iii, on-board saturated pixel encoding during the 3-Band Cryo phase was intermittent in W1 and W2, and inactive in W3 following the first exposure time reduction, so the identification and handling of saturated sources by the pipeline photometry modules was degraded. Therefore, photometry of very bright sources in the 3-Band Cryo WDB should be used with caution.
|Figure 5a - l,b=63.7°,+34.3°
|Figure 5b - l,b=162.1°,-4.3°
|Figure 5c - l,b=338.3°,-0.7°
|Profile-fit photometric residuals between the 3-Band Cryo WDB and the All-Sky Release Source Catalog. The small black dots represent individual sources. The larger green points and error bars are the trimmed average and RMS differences between 3-Band Cryo WDB and All-Sky Release Catalog magnitudes computed in 0.5 magnitude bins (0.2 magnitude bins in W3).|
The astrometric quality of the 3-Band Cryo WDB is described in VII.5.c. Because position reconstruction is based primarily on W1 detections that have similar sensitivity in the 3-Band Cryo observations, the absolute accuracy of 3-Band Cryo WDB astrometry is comparable to that of the All-Sky Release Catalog (VI.4). Bright, non-saturated sources in the 3-Band Cryo WDB have position residuals <0.2 arcsec with respect to the 2MASS Point Source Catalog, and the residual increases to approximately 0.4 arcsec for SNR~20 sources.
The relative agreement between astrometry in the 3-Band Cryo WDB and All-Sky Release Catalog is slightly better than the absolute accuracy which makes the WDB a resources for searching for candidate high proper motion objects. An example of this is illustrated in Figure 6 that shows the RA and Dec position differences in the 3-Band Cryo WDB and All-Sky Release Catalog plotted as function of 3-Band Cryo W1 magnitude for isolated, point-like sources in a 4 deg2 region centered on the position of Teegarden's star (α,δ=43.2643°+16.8701°). The green curves show ±5 times the RMS of the average position residuals. Teegarden's star RA and Dec residuals, as derived from the 3-Band Cryo WDB r_allsky and pa_allsky values, are indicated by the large blue points. The WISE-measured proper motion is 5.36 arcsec/year measured over the 195 days separating the All-Sky Release Catalog and 3-Band Cryo WDB observations, slightly larger than the published motion of 5.05 arcsec/year (Lepine and Shara, 2005, AJ, 129, 1483).
|Figure 6 - RA and Dec differences reported for the same sources in the WISE 3-Band Cryo WDB and All-Sky Release Catalog in the 4 deg2 region centered on Teegarden's star. Black points are non-blended sources (nb=1) that are not flagged as extended (ext_flg=0), The green lines show ±5 times the RMS of the average position residuals. The position residuals for Teegarden's star from the 3-Band Cryo WDB are the large blue points.|
Last Updated: 2012 July 26