Infrared photometry Sample Clauses

Infrared photometry. All candidates have GALEX FUV/NUV and SDSS ugriz photometry. In order to extend the range of wavelengths, I determined photometry for the sample from the Widefield Infrared Space Explorer [WISE, Xxxxxx et al., 2010] and 2-Micron All Sky Survey [2MASS, Xxxxxxxxx et al., 2006] images, resulting in photometric data spanning a combined wavelength range of approximately 1500˚A to 22µm. For con- sistency I determined either measurements or limits on the galaxies’ magnitudes from the infrared imaging using fixed aperture photometry at the SDSS locations Band wavelength (µm) reference aperture (arcsec) zero-point (Xxxx) magnitude correction ∆m AB conversion J 1.235 4 20.9 0.05363 0.89 H 1.662 4 20.5 0.0572 1.37 Ks 2.159 4 20.0 0.0556 1.84 W1 3.4 8.25 20.5 0 2.683 W2 4.6 8.25 19.5 0 3.319 W3 12 8.25 18.0 0 5.242 W4 22 16.50 13.0 0 6.604 Table 2.1: The wavelength, reference aperture used, zero-point (in Xxxx magni- tudes), magnitude correction ∆m, and conversion between Xxxx and AB magnitudes for the 2MASS and WISE measurements. For 2MASS, the zero-point magnitude was found in the FITS header for each object individually, the quoted number gives the mean value. and the recommended aperture sizes appropriate to point sources. Using iraf I measured the flux interior to a series of apertures with 3, 4, 5, 7, 9, 11, 13, 15, and 20 arcseconds radius centred on the object location, and from this calculated the curve of growth correction for each source. The final magnitude in each in- frared band was determined as mAB,final = measured flux in reference aperture + magnitude zero-point - magnitude correction + AB conversion; the values for the last three quantities are shown in Table 2.1. By using a series of aperture sizes, it was possible to ensure that any potential nearby neighbours could be excluded. However, the sources had been selected to have no nearby neighbours in the optical or ultraviolet, and so did not require model-dependent deblending. In ∼10% of the sample, however, 2MASS photometry at the source location was unreliable due to blended sources or insufficient depth of the survey compared to the objects’ relative faintness. Approximately a third of the candidate objects are individually unde- tected above a 2σ detection limit in one or more infrared bands, where this limit is determined locally in each band.