Seminarios de Astrofísica en el INAOE

Statistical Properties of the GALEX/SDSS Matched Source Catalogs, and Classification of the UV Sources.

We use the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey (MIS) and All-Sky Imaging Survey (AIS) data from the first public data release (GR1), matched to the Sloan Digital Sky Survey (SDSS) DR3 catalog in the overlapping areas to perform classification of the sources. The GALEX surveys provide photometry in two UV bands (far-Ultraviolet and near-Ultraviolet) and the SDSS in five optical bands (u, g, r, i, z). The overlapping areas are 363 deg2 for the GALEX AIS (622 fields) and 86 deg2 for the GALEX MIS (122 fields), when we restrict the analysis to sources within the central area of the GALEX fields (0.5 degree radius). The present sample covers mostly high galactic latitudes (|b| > 30 deg). We present statistical properties of the GALEX/SDSS matched sources catalog, containing a total of over 2 million objects detected in at least one UV band. At the AIS depth, the number of Galactic and extragalactic objects are comparable, but the latter become increasingly predominant at fainter magnitudes. We classify the matched sources by comparing the seven-band photometry to model colors, constructed for different classes of astrophysical objects. If the catalogs are restricted to sources with photometric errors better than 0.3 mag, the corresponding typical magnitude limits in the GALEX bands are mFUV < 21.5 , mNUV < 22.5 for AIS, and mFUV < 24 , mNUV < 24.5 for MIS (AB magnitude system). Based on our stellar models, we estimate that the GALEX surveys can detect hot White Dwarfs throughout the MW halo (down to an estimated radius of 0.04R at the MIS depth), providing an unprecedented improvement on the census of such objects in the Galaxy. This is confirmed by the good agreement between Luminosity Functions for hot stellar objects selected from the GALEX photometry and predicted by MW models. Archival SDSS spectra confirm the stellar classification for 97% of our hot-star candidate sample selected from the GALEX photometry and for which spectroscopy is available. Binaries containing a hot star and a cooler companion can be selected photometrically with a purity estimated at 45%(AIS)/31%(MIS). We also derive the LF for low-redshift QSO candidates selected from the GALEX surveys. The GALEX-selected QSO candidates extend the sample of known QSOs at faint magnitudes, and provide the ideal selection for detailed follow-up investigations of QSOs with redshift around 1. Archival optical spectra indicate that the purity of the QSO selected sample is ~85%.