The GALEX science data archive, and the discovery potential from multi-wavelength surveys Alberto Conti(1), Luciana Bianchi(2), Lino Rodriguez(2) , Bernie Shiao(1) (1) Space Telescope Science Institute, (2) Johns Hopkins University

Abstract: We present the main features of the GALEX (Galaxy Evolution Explorer) science data archive, hosted by MAST at STScI. GALEX catalogs of UV sources, images in two UV bands (near-UV and far-UV), and spectra are accessible in a VO type format. The SQL query language allows flexible browsing of the data. An interesting scientific application is the possibility of correlating catalogs from different archives, to build selected samples of sources and new catalogs of objects by astrophysical classes. We show one example of such application: using the matched GALEX (2 UV bands) plus SDSS (Sloan Digital Sky Survey - 5 optical bands) photometry of about 2 Million sources, by comparison with synthetic colors of astrophysical objects across their physical parameters ranges, we extract catalogs of hot stars in the MW, binaries containing WDs, low red-shift QSO candidates, and other interesting classes of objects. In some cases, the catalogs of objects found from the GALEX surveys are orders of magnitude larger than previous ones.

The GALEX Archive Results: The Multi mission Archive at Space CALCULATION of TOTAL Overlap Area : The Hierarchical Telescope (MAST) delivers GALEX Triangular Mesh (HTM) partition of the SDSS/GALEX data (ultimately ~5TB) to the entire archive cannot be used to compute an accurate area astronomical community and to the Scientific application: matching UV coverage taking into account overlap between GALEX general public. GALEX data products fields, and common areas of GALEX-SDSS fields. For this include near-UV and far-UV medium, and optical surveys. purpose, we have built a different partition of the sky deep and all-sky surveys in imaging using a more convenient geometry, and determined the areas of unique sky coverage of our matched catalogs. mode and partial sky surveys in This tool may have wide applications. Details in Bianchi spectroscopic mode. et al. (2005b) The Data The GALEX archive at MAST is built In this example of scientific use of the around a core set of web applications GALEX database, we analyze 2 Million Statistics of Matched Sources - LF and xml web services that mine matched sources from the GALEX GALEX data stored in a Microsoft imaging surveys MIS (Medium Imaging SQL Server database. Interoperability Sky Survey, mag limit ~25) and AIS with other data centers is achieved by (All Sky Imaging Survey, mag lim ~ 23), and the SDSS (five photometric offering many VO compliant services. bands, u g r i z). The GALEX GR1.0 Together with other MAST surveys and SDSS DR3 releases overlap over a such as GOODS, UDF and HDFN/S, total of 86 (MIS) and 363 (AIS) square the GALEX archive is an integral part degrees, at high Galactic latitudes. of OpenSkyQuery: the VO SkyNode portal. The Figure shows the sky coverage of From Bianchi et al , 2005b : The luminosity function of hot stars (in three the GALEX surveys in May 2005 and temperature ranges) and QSO candidates, classified from the multi-band Pink: SDSS overlap with GALEX MIS photometry. The total density of point-like and extended sources is also shown. MAST is in the process of completing the overlap with SDSS. Red: SDSS overlap with GALEX AIS AIS left, MIS right. In the MIS LF, the solid-line histograms are obtained applying error cuts also in the SDSS r-band (thus limiting the sample to brighter magnitudes the GALEX Multi-mission Archive than the deeper GALEX data). GALEX-only LF are shown with dashed lines, and Cross-Correlation tool (GMAX): a extend to fainter objects. proof of concept application Study of the Milky Way Structure specifically developed to utilize the Analysis: Classification of Sources large collection of services available We compare colors, from GALEX far-UV and near-UV, and SDSS u g r i z under VO. GMAX uses the VO bands, to model colors of different astrophysical objects. We restrict the Registry to locate ConeSearch and sample to objects with photometric accuracy adequate to separate SIAP VO services from surveys that classes of objects. overlap the GALEX footprint. The GALEX image cutout service uses the sample Color-Color results of the ConeSearch to display figures from Bianchi et al (2005a, b): objects from these surveys onto a GALEX image. Cross-correlation with From Bianchi et al , 2005b: The object density, In different bands of galactic Data latitude. AIS left, MIS right. The number of very hot stars (WD and SD) is GALEX data is achieved using the Black dots: Extended orders of magnitude higher than in previous catalogs. Follow-up Hierarchical Triangular Mesh (HTM) sources(galaxies) spectroscopic surveys are under-way. Blue dots: Point-Like index or the VO SkyNode service. sources (stars, QSOs) Model Colors Low Redshift QSO Candidates Red triangles: ms stars as a function of Teff (max From Bianchi et al , 2005a 50,000k) (ApJL , 619, L27; these data Red square: WD (only are from GALEX IR02 + SDSS 100,000K shown) DR1) Several thousand new QSO Green: SSP as a function candidates found by Bianchi of age et al. (2005b) in the new data Purple: CSP as a function release. of age Solid histogram: GALEX low- Cyan: QSO as a function of z QSOs, dashed histogr: QSO redshift candidates from previous Arrows indicate SDSS catalogs. E(B-V) = 0.5 For more information: http://dolomiti.pha.jhu.edu (see list of publications) or email: [email protected]

Acknowledgements: We acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiales of France and the Korean Ministry of Science and Technology.