Image Details
Caption: Figure 8.
Forced photometry with The Tractor code, using information from Legacy Surveys detections and light profiles, allows us to measure the mid-infrared flux from objects in the WISE images to below the WISE detection limit. Left panel: a comparison of the W1 photometric measurements in the Legacy Survey catalog (derived using The Tractor) with those in the ALLWISE catalog; the gray scale shows the relative density of points. The photometry agrees well for mid-infrared bright objects that are detected in the AllWISE catalog. The widening locus below W1 ∼ 14 is due to The Tractor photometry treating larger objects as truly extended, in contrast to the point-source-only assumptions in the public AllWISE catalog. Right panel: the number counts in the Legacy Survey catalog compared with those from AllWISE, demonstrating the increased depth made possible from using The Tractor. By using optical imaging from Legacy Surveys to detect objects, photometry is measured for objects that are well below the detection limit of the AllWISE catalog.
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