- ID:
- ivo://CDS.VizieR/J/AJ/157/107
- Title:
- GALEX spectral database correction with IUE SEDs
- Short Name:
- J/AJ/157/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CALSPEC database of absolute spectral energy distributions (SEDs) from the Hubble Space Telescope is based on pure hydrogen model atmosphere calculations for three unreddened white dwarf stars and represents the current UV flux calibration standard with a precision approaching 1% for well observed stars. Following our previous work to correct International Ultraviolet Explorer (IUE) fluxes, this paper provides an average correction for the Galaxy Evolution Explorer (GALEX) spectral database that places GALEX fluxes on the current CALSPEC scale. Our correction is derived by comparing GALEX spectroscopic flux distributions with CALSPEC and corrected IUE SEDs. This recalibration is relevant for any project based on GALEX archival spectroscopic data, e.g., UV or multi-wavelength analyses, correlating GALEX spectra with other existing or future databases, and planning of new observations. The recalibration will be applied to our planned catalog of corrected GALEX SEDs.
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- ID:
- ivo://CDS.VizieR/J/ApJS/173/572
- Title:
- GALEX/Spitzer photometry in NGC 7331
- Short Name:
- J/ApJS/173/572
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images of NGC 7331 obtained with GALEX and Spitzer, tracing UV and IR signatures of star formation. NGC 7331's morphology at 8-850um is dominated by a central dust ring. This structure is a vigorous site of star formation (hosting one-third of the present activity) but remains inconspicuous in our GALEX UV imagery. Radial profile analysis and photometry for discrete UV- and UV+IR-selected substructures indicate a decline in UV extinction with increasing galactocentric distance, although highly attenuated star-forming regions can be found throughout the disk. UV-optical surface brightness profiles suggest a recent birthrate parameter (b_8_) that is highest in the outer part of the disk, even though the local star formation intensity peaks in the ring. Bolometric luminosity and UV attenuation are correlated in substructures on 0.4kpc scales, with a relationship similar to that established for starburst galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/2180
- Title:
- GALEX survey subdwarf atmospheric parameters
- Short Name:
- J/MNRAS/427/2180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an update of our low-resolution spectroscopic follow-up and model atmosphere analysis of hot subdwarf stars from the Galaxy Evolution Explorer (GALEX) survey. Targets were selected on the basis of colour indices calculated from the GALEX GR6 N_UV_, Guide Star Catalogue (GSC2.3.2) Vand the Two Micron All Sky Survey (2MASS) J and H photometry. High signal-to-noise ratio spectra were obtained at the European Southern Observatory (ESO) and the Kitt Peak National Observatory (KPNO) over the course of three years. Detailed H, He and CNO abundance analysis helped us improve our T_eff_, logg and He abundance determination and to constrain CNO abundances. We processed 191 observations of 180 targets and found 124 sdB and 42 sdO stars in this sample while some blue horizontal branch stars were also found in this programme. With quantitative binary decomposition of 29 composite spectra we investigated the incidence of A, F and G type companions. The incidence of late G and K type companions and their effects on subdwarf atmospheric parameters were also examined.
- ID:
- ivo://nasa.heasarc/galextdsc
- Title:
- GALEX Time Domain Survey Catalog
- Short Name:
- GALEXTDSC
- Date:
- 27 Sep 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This table contains results from the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~ 40 deg<sup>2</sup> 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. The authors 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. They measure the statistical properties of the UV variability, including the structure function on timescales of days and years, and 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. The authors 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). They detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |Delta-M| = 4.6 and 2.9 magnitudes, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. 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 a dormant super-massive black hole. The authors 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<sup>-2</sup> for quasars, AGN, and RR Lyrae stars, respectively, and 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<sup>-2</sup> yr<sup>-1</sup> for M dwarfs and extragalactic transients, respectively. The GALEX observations were made using the NUV detector which has an 1.25 degree diameter field of view and an effective wavelength of 2316 Angstroms. During the window of observing visibility of each GALEX TDS field (from two to four weeks, one to two times per year), they were observed with a cadence of 2 days, and a typical exposure time per epoch of 1.5 ks (or a 5-sigma point-source limit of m<sub>AB</sub>(NUV) ~ 23.3 magnitude), with a range from 1.0 to 1.7 ks. Table 2 in the reference paper lists the RA and Dec of their centers, the Galactic extinction E(B - V ) for each field from the Schlegel et al. (1998, ApJ, 500, 525) dust maps, and the number of epochs per field. This table was created by the HEASARC in May 2013 based on a machine-readable version of Table 4 from the paper which was obtained from the ApJ web site. This is a service provided by NASA HEASARC .
- ID:
- ivo://CDS.VizieR/J/ApJ/766/60
- Title:
- GALEX Time Domain Survey I. UV variable sources
- Short Name:
- J/ApJ/766/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~40deg^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). We detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |{Delta}m|=4.6mag and 2.9mag, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. 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<23mag and |{Delta}m|>0.2mag of ~8.0, 7.7, and 1.8deg^-2^ for quasars, active galactic nuclei, 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 52deg^-2^/yr for M dwarfs and extragalactic transients, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/185
- Title:
- GALEX ultraviolet atlas of nearby galaxies
- Short Name:
- J/ApJS/173/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its far-ultraviolet (FUV; lambda_eff_=1516{AA}) and near-ultraviolet (NUV; lambda_eff_=2267{AA}) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate [SFR]) of galaxies in the local universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/13
- Title:
- GALEX ultraviolet halos around bright stars
- Short Name:
- J/ApJ/734/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have discovered ultraviolet (UV) halos extending as far as 5{deg} around four (of six) bright UV stars using data from the Galaxy Evolution Explorer satellite. These halos are due to scattering of the starlight from nearby thin, foreground dust clouds. We have placed limits of 0.58+/-0.12 and 0.72+/-0.06 on the phase function asymmetry factor (g) in the FUV (1521{AA}) and NUV (2320{AA}) bands, respectively. We suggest that these halos are a common feature around bright stars and may be used to explore the scattering function of interstellar grains at small angles.
- ID:
- ivo://CDS.VizieR/J/AJ/130/825
- Title:
- GALEX ultraviolet variability catalog
- Short Name:
- J/AJ/130/825
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present version 1.0 of the NASA Galaxy Evolution Explorer (GALEX) ultraviolet variability (GUVV) catalog, which contains information on 84 time-variable and transient sources gained with simultaneous near-ultraviolet (NUV) and far-ultraviolet (FUV) photometric observations. These time-variable sources were serendipitously revealed in the various 1.2{deg} diameter star fields currently being surveyed by the GALEX satellite in two ultraviolet bands (NUV 1750-2750{AA}, FUV 1350-1750{AA}) with limiting AB magnitudes of 23-25. The largest amplitude variable objects currently detected by GALEX are M dwarf flare stars, which can brighten by 5-10mag in both the NUV and FUV bands during short-duration (<500s) outbursts. Other types of large-amplitude ultraviolet variable objects include ab-type RR Lyrae stars, which can vary periodically by 2-5mag in the GALEX FUV band. This first GUVV catalog lists galactic positions and possible source identifications in order to provide the astronomical community with a list of time-variable objects that can now be repeatedly observed at other wavelengths.
- ID:
- ivo://CDS.VizieR/J/A+A/528/A107
- Title:
- GALEX Ultraviolet Virgo Cluster Survey (GUViCS)
- Short Name:
- J/A+A/528/A107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering ~40 sq. deg in the far UV (FUV, {lambda}_eff_=1539{AA}, {Delta}{lambda}=442{AA}) and ~120 sq. deg in the near UV (NUV, {lambda}_eff_=2316{AA}, {Delta}{lambda}=1060{AA}). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early- and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (alpha~-1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.
- ID:
- ivo://CDS.VizieR/J/A+A/570/A69
- Title:
- GALEX Ultraviolet Virgo Cluster Survey. IV.
- Short Name:
- J/A+A/570/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions that are selected from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) with the purpose of understanding the origin of the red sequence in dense environments. The sample spans a wide range in morphological types (from dwarf ellipticals to Im and BCD) and stellar masses (10^7^<=M_star_<=10^11.5^M_{sun}_). We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies, including UV, optical, mid- and far-infrared imaging data, as well as optical and HI spectroscopic data. We first identify the different dynamical substructures that compose the Virgo cluster, and we calculate the local density of galaxies using different methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the different cluster substructures or as a function of galaxy density. Our analysis indicates that all the most massive galaxies M_star_>=10^11^M_{sun}_) are slow rotators and are the dominant galaxies of the different cluster substructures, which are generally associated with a diffuse X-ray emission. They are probably the result of major merging events that occurred at early epochs, as also indicated by their very old stellar populations. Slow rotators of lower stellar mass (10^8.5^<=M_star_<=10^11^M_{sun}_) are also preferentially located within the different high-density substructures of the cluster. Their position in the velocity space indicates that they are virialised within the cluster; thus, they are Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later form the cluster (pre-processing). On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure stripping models consistently indicate that these star-forming systems can be rapidly deprived of their interstellar medium during their interaction with the intergalactic medium. The lack of gas quenches their star-formation activity transforming them into quiescent dwarf ellipticals. This mild transformation does not perturb the kinematic properties of these galaxies, which still have rotation curves typical of star-forming systems.