Near-Infrared Data Quality
The distribution of the median FWHMs (angular vs. physical) of all the J- (open blue circle; blue dashed line) and K-band (filled red circles; red full line) mosaics. The error bars show the RMS of the median seeing variation of each section of the mosaic. The dotted vertical line is the limit for quality requirements of WINGS survey spatial physical resolution, needed for reliable morphology classification and surface photometry. As it can be seen only three out of 47 co-added mosaics do not meet these quality requirements. In the histogram sections the black dotted lines are the total J and K distributions.
After the coadding of all the MEFs into a single mosaic, an additional astrometric
and photometric re-calibration check with point-like sources
from the 2MASS catalogue is performed. This figure is a visualization of the astrometric precision and accuracy for our entire cluster collection: upper panels show the overall spread of the right ascension and declination differences between the positions of common point-like sources in our catalogs and in 2MASS (left
panel) or UCAC2 (right panel). Only sources with a photometric error lower than 0.1 mag where considered. The overall zero point shift is negligible for all our applications, and the rms is consistent with UKIRT-WFCAM standard requirements, being of the order of 100mas (RMS=112mas).
Due to the WFCAM configuration and the way the observations are carried out, the final mosaics have global PSF variations in a chessboard pattern fashion. A ‘tile’ is composed by 4 exposures (i.e.,MEFs), of 4 detectors each, which gives the 16 sections of the mosaic shown here (pixel size is 0.2"). For each of the 16 sections, the median FWHM (in pixels) of well classified and non saturated stars is reported. During the 05A observing semester, besides experiencing poor seeing at the telescope, the imaging also suffers from a systematic broadening of the PSF caused by bad alignment of the camera.