Identification of UV stellar point sources using NIR colour cut method

Abstract

For the first time, we have come up with a new idea of identifying the UV stellar point sources from the extra-galactic sources by choosing a suitable IR colour, J-W1 < 1.2 (W1 is a WISE band at 3.4 micron and J is a 2MASS band). We have used this method to identify the stars and then compared the observed star counts with Besancon model of stellar population synthesis. We have shown that our IR colour cut method is better than the SDSS morphological classification in providing a clean catalog of stellar sources. GALEX covers almost 75% of the sky, whereas the WISE+2MASS covers almost the entire sky. We have analyzed the entire GALEX data to identify the white dwarf candidates (WDs) of the disk and blue horizontal branch star candidates (BHBs) of halo from the observed sample by selecting suitable UV colour FUV - NUV colour ranges. In order to substantiate our identification of the WD and BHB candidates using GALEX FUV-NUV colour, we have also compared them with their 2MASS colours. We aim to make a more quantitative estimate of the space densities of these objects in our Galaxy.