We use the combined photometric SDSS + GALEX database to look for populations of luminous blue star-forming galaxies. These were initially identified from such a sample at redshifts near 0.4, using SDSS spectra. We make use of the colour index previo
usly defined to separate stars and QSOs, to locate more of these unusual galaxies, to fainter limits. They are found in significant numbers in two different regions of the related colour-magnitude plot. Within these regions, we use the ensemble 7-colour photometry to estimate the populations of blue star-forming galaxies at redshift near 0.4, and at redshift near 1, from a full photometric sample of over half a million, composed mostly of normal galaxies and QSOs.
We describe calibration data, and discuss performance of the photon-counting flight detectors for the Ultraviolet Imaging Telescopes on the Astrosat observatory. The paper describes dark current, flat field and light-spot images for FUV, NUV, and Vis
ible band detectors at more than one wavelength setting for each. We also report on nominal gain and low-gain operations, full- and sub-window read rates, and non-photon-counting modes of operation, all expected to be used in flight. We derive corrections to the event centroids from the CMOS readout arrays, for different centroid algorithms. We derive spatial resolution values for each detector and plots of point-source signal saturation for different flux levels. We also discuss ways to correct for saturation in extended object images.
An asymmetry index is derived from ellipse-fitting to galaxy images, that gives weight to faint outer features and is not strongly redshift-dependent. These measures are made on a sample of 13 2MASS QSOs and their neighbour galaxies, and a control sa
mple of field galaxies from the same wide-field imaging data. The QSO host galaxy asymmetries correlate well with visual tidal interaction indices previously published. The companion galaxies have somewhat higher asymmetry than the control galaxy sample, and their asymmetry is inversely correlated with distance from the QSO. The distribution of QSO-companion asymmetry indices is different from that for matched control field galaxies at the $sim95%$ significance level. We present the data and discuss this evidence for tidal and other disturbances in the vicinity of QSOs.
