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We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~ 40 deg^2 of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of ~ 3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. We characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5\sigma level in at least one epoch. We measure the statistical properties of the UV variability, including the structure function on timescales of days and years. We report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by dormant supermassive black hole. We calculate a surface density for variable sources in the UV with NUV < 23 mag and |\Delta m| > 0.2 mag of ~ 8.0, 7.7, and 1.8 deg^-2 for quasars, AGNs, and RR Lyrae stars, respectively. We also calculate a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ~ 15 and 52 deg^-2 yr^-1 for M dwarfs and extragalactic transients, respectively. (Abridged.), Comment: Accepted for publication in ApJ, 14 pages, 19 figures, 4 tables

We investigate the use of MIR PAH bands, continuum and emission lines as probes of star-formation and AGN activity in a sample of 100 'normal' and local (z~0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer Space Telescope Infrared Spectrograph (IRS) as part of the Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) which includes multi-wavelength photometry from the UV to the FIR and optical spectroscopy. The continuum and features were extracted using PAHFIT (Smith et al. 2007), a decomposition code which we find to yield PAH equivalent widths up to ~30 times larger than the commonly used spline methods. Despite the lack of extreme objects in our sample (such as strong AGNs, low metallicity galaxies or ULIRGs), we find significant variations in PAH, continuum and emission line properties and systematic trends between these MIR properties and optically derived physical properties such as age, metallicity and radiation field hardness. We revisit the diagnostic diagram relating PAH equivalent widths and [Ne II]12.8micrometers/[O IV]25.9micrometers line ratios and find it to be in much better agreement with the standard optical star-formation/AGN classification than when spline decompositions are used, while also potentially revealing obscured AGNs. The luminosity of individual PAH components, of the continuum, and with poorer statistics, of the neon emission lines and molecular hydrogen lines, are found to be tightly correlated to the total IR luminosity, making individual MIR components good gauges of the total dust emission in SF galaxies. Like the total IR luminosity, these individual components can be used to estimate dust attenuation in the UV and in Halpha lines based on energy balance arguments. We also propose average scaling relations between these components and dust corrected, Halpha derived star-formation rates., Accepted for publication in ApJ

We present the analysis of the Polycyclic Aromatic Hydrocarbon (PAH) spectra of a sample of 92 typical star forming galaxies at 0.03

We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a sample of intermediate-redshift (0.2 ≤ z ≤ 0.7) UV-selected galaxies from the ELAIS N1 and ELAIS N2 fields by fitting a multi-wavelength data set to a library of GRASIL templates. Star formation related properties of the galaxies are derived from the library of models by using Bayesian statistics. We find a decreasing presence of galaxies with low attenuation and low total luminosity as redshift decreases, which does not hold for high total luminosity galaxies. In addition, the dust attenuation of low-mass galaxies increases as redshift decreases, and this trend seems to disappear for galaxies with M_* ≥ 10^(11) M_⊙. This result is consistent with a mass-dependent evolution of the dust-to-gas ratio, which could be driven by a mass-dependent efficiency of star formation in star-forming galaxies. The specific star formation rates (SSFR) decrease with increasing stellar mass at all redshifts, and for a given stellar mass the SSFR decreases with decreasing redshift. The differences in the slope of the M^*-SSFR relation found between this work and others at similar redshift could be explained by the adopted selection criteria of the samples, which for a UV-selected sample, favors blue, star-forming galaxies.

The ELAIS S1 field was observed by GALEX in both its Wide Spectroscopic and Deep Imaging Survey modes. This field was previously observed by the Infrared Space Observatory and we made use of the catalogue of multi-wavelength data published by the ELAIS consortium to select galaxies common to the two samples. Among the 959 objects with GALEX spectroscopy, 88 are present in the ELAIS catalog and 19 are galaxies with an optical spectroscopic redshift. The distribution of redshifts covers the range $0, Comment: This paper has been published as part of the GALEX ApJL Special Issue (ApJ 619, L63)

We present multiband photometric observations of three spiral galaxies selected in a sample suited for the study of young stellar groupings and their relationship with the parent galaxy and the galactic environment. Star forming regions have been identified using an objective technique based on a multivariate statistical analysis. Maps of young star groupings are given for each galaxy. The luminosity functions of the young star group populations show a remarkable similarity with a slope in the range -1.52 to -1.33 range. The size distributions peak around the classical 100pc value of the Local Group associations for two out of the three galaxies. NGC 1058 shows smaller associations (peak at about 50pc). The total number of young groups per unit B absolute luminosity of the galaxy is significantly greater in UGC 12732. The activity of star formation is in all three galaxies clearly stronger in the central regions., Comment: 7 pages, 7 figures, 3 tables (enclosed as single postscript file). Paper accepted for publication in A&A main journal

We use the GALEX (Galaxy Evolution Explorer) Medium Imaging Survey (MIS) and All-Sky Imaging Survey (AIS) data available in the first internal release, matched to the SDSS catalogs in the overlapping regions, to classify objects by comparing the multi-band photometry to model colors. We show an example of the advantage of such broad wavelength coverage (GALEX far-UV and near-UV, SDSS ugriz) in classifying objects and augmenting the existing samples and catalogs. From the MIS [AIS] sample over an area of 75 [92] square degrees, we select a total of 1736 [222] QSO candidates at redshift less than 2, significantly extending the number of fainter candidates, and moderately increasing the number of bright objects in the SDSS list of spectroscopically confirmed QSO. Numerous hot stellar objects are also revealed by the UV colors, as expected., This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Full paper available from http://dolomiti.pha.jhu.edu . Links to the full set of papers available at http://www.galex.caltech.edu/PUBLICATIONS/ after Nov.22, 2004

In a companion paper (Arnouts et al. 2004) we presented new measurements of the galaxy luminosity function at 1500 Angstroms out to z~1 using GALEX-VVDS observations (1039 galaxies with NUV0.2) and at higher z using existing data sets. In this paper we use the same sample to study evolution of the FUV luminosity density. We detect evolution consistent with a (1+z)^{2.5+/-0.7} rise to z~1 and (1+z)^{0.5+/-0.4} for z>1. The luminosity density from the most UV-luminous galaxies (UVLG) is undergoing dramatic evolution (x30) between 025%) of the total FUV luminosity density at z, Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004