- ID:
- ivo://CDS.VizieR/J/ApJ/798/41
- Title:
- GALEX NUV observations of bright M-type stars
- Short Name:
- J/ApJ/798/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Planets orbiting within the close-in habitable zones of M dwarf stars will be exposed to elevated high-energy radiation driven by strong magnetohydrodynamic dynamos during stellar youth. Near-ultraviolet (NUV) irradiation can erode and alter the chemistry of planetary atmospheres, and a quantitative description of the evolution of NUV emission from M dwarfs is needed when modeling these effects. We investigated the NUV luminosity evolution of early M-type dwarfs by cross-correlating the Lepine & Gaidos catalog (2011, J/AJ/142/138) of bright M dwarfs with the Galaxy Evolution Explorer (GALEX) catalog of NUV (1771-2831{AA}) sources. Of the 4805 sources with GALEX counterparts, 797 have NUV emission significantly (>2.5{sigma}) in excess of an empirical basal level. We inspected these candidate active stars using visible-wavelength spectra, high-resolution adaptive optics imaging, time-series photometry, and literature searches to identify cases where the elevated NUV emission is due to unresolved background sources or stellar companions; we estimated the overall occurrence of these "false positives" (FPs) as ~16%. We constructed an NUV luminosity function that accounted for FPs, detection biases of the source catalogs, and GALEX upper limits. We found the NUV luminosity function to be inconsistent with predictions from a constant star-formation rate and simplified age-activity relation defined by a two-parameter power law.
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- ID:
- ivo://CDS.VizieR/J/ApJ/766/9
- Title:
- GALEX observations of exoplanet host stars
- Short Name:
- J/ApJ/766/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the far-UV (FUV) and near-UV (NUV) photometry from the NASA Galaxy Evolution Explorer (GALEX), we searched for evidence of increased stellar activity due to tidal and/or magnetic star-planet interactions (SPI) in the 272 known FGK planetary hosts observed by GALEX. With the increased sensitivity of GALEX, we are able probe systems with lower activity levels and at larger distances than what has been done to date with X-ray satellites. We compared samples of stars with close-in planets (a<0.1AU) to those with far-out planets (a>0.5AU) and looked for correlations of excess activity with other system parameters. This statistical investigation found no clear correlations with a, M_p_, or M_p_/a, in contrast to some X-ray and CaII studies. However, there is tentative evidence (at a level of 1.8{sigma}) that stars with radial-velocity-(RV)-detected close-in planets are more FUV-active than stars with far-out planets, in agreement with several published X-ray and Ca II results. The case is strengthened to a level of significance to 2.3{sigma} when transit-detected close-in planets are included. This is most likely because the RV-selected sample of stars is significantly less active than the field population of comparable stars, while the transit-selected sample is similarly active. Given the factor of 2-3 scatter in fractional FUV luminosity for a given stellar effective temperature, it is necessary to conduct a time-resolved study of the planet hosts in order to better characterize their UV variability and generate a firmer statistical result.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A101
- Title:
- GALEX observations of Herschel Reference Survey
- Short Name:
- J/A+A/544/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) as well as SDSS g, r, i photometry and structural parameters for the Herschel Reference Survey, a magnitude-, volume-limited sample of nearby galaxies in different environments. We use this unique dataset to investigate the ultraviolet (UV) structural scaling relations of nearby galaxies and to determine how the properties of the UV disk vary with atomic hydrogen content and environment.
- ID:
- ivo://CDS.VizieR/J/ApJ/733/74
- Title:
- GALEX - SDSS properties of local galaxies
- Short Name:
- J/ApJ/733/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of the first unbiased search for extended ultraviolet (XUV)-disk galaxies undertaken to determine the space density of such galaxies. Our sample contains 561 local (0.001<z<0.05) galaxies that lie in the intersection of available Galaxy Evolution Explorer (GALEX) deep imaging (exposure time >1.5x10^4^s) and Sloan Digital Sky Survey DR7 footprints. We explore modifications to the standard classification scheme for our sample that includes both disk- and bulge-dominated galaxies. Visual classification of each galaxy in the sample reveals an XUV-disk frequency of up to 20% for the most nearby portion of our sample. On average over the entire sample (out to z=0.05) the frequency ranges from a hard limit of 4%-14%. The GALEX imaging allows us to detect XUV disks beyond 100 Mpc. The XUV regions around XUV-disk galaxies are consistently bluer than the main bodies. We find a surprisingly high frequency of XUV emission around luminous red (NUV-r>5) and green valley (3<NUV-r<5) galaxies. The XUV-disk space density in the local universe is >(1.5-4.2)x10^-3^Mpc^-3^. Using the XUV emission as an indicator of recent gas accretion, we estimate that the cold gas accretion rate onto these galaxies is >(1.7-4.6)x10^-3^M_{sun}_/Mpc^3^/yr. The number of XUV disks in the green valley and the estimated accretion rate onto such galaxies points to the intriguing possibility that 7%-18% of galaxies in this population are transitioning away from the red sequence.
- ID:
- ivo://CDS.VizieR/J/ApJS/216/26
- Title:
- GALEX search for T Tauri in Taurus-Auriga
- Short Name:
- J/ApJS/216/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we identify 63 bona fide new candidates to T Tauri stars (TTSs) in the Taurus-Auriga region, using its ultraviolet excess as our baseline. The initial data set was defined from the GALEX all sky survey (AIS). The GALEX satellite obtained images in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands where TTSs show a prominent excess compared with main-sequence or giants stars. GALEX AIS surveyed the Taurus-Auriga molecular complex, as well as a fraction of the California Nebula and the Perseus complex; bright sources and dark clouds were avoided. The properties of TTSs in the ultraviolet (GALEX), optical (UCAC4), and infrared (2MASS) have been defined using the TTSs observed with the International Ultraviolet Explorer reference sample. The candidates were identified by means of a mixed ultraviolet-optical-infrared excess set of colors; we found that the FUV-NUV versus J-K color-color diagram is ideally suited for this purpose. From an initial sample of 163313 bona fide NUV sources, a final list of 63 new candidates to TTSs in the region was produced. The search procedure has been validated by its ability to detect all known TTSs in the area surveyed: 31 TTSs. Also, we show that the weak-lined TTSs are located in a well-defined stripe in the FUV-NUV versus J-K diagram. Moreover, in this work, we provide a list of TTSs photometric standards for future GALEX-based studies of the young stellar population in star forming regions.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/18
- Title:
- GALEX/S4G surface brightness profiles. I.
- Short Name:
- J/ApJS/234/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spatially resolved surface photometry in the far-ultraviolet (FUV) and near-ultraviolet (NUV) from images obtained by the Galaxy Evolution Explorer (GALEX) and IRAC1 (3.6{mu}m) photometry from the Spitzer Survey of Stellar Structure in Galaxies (S^4^G). We analyze the radial surface brightness profiles {mu}FUV, {mu}NUV, and {mu}[3.6], as well as the radial profiles of (FUV-NUV), (NUV-[3.6]), and (FUV-[3.6]) colors in 1931 nearby galaxies (z<0.01). The analysis of the 3.6 {mu}m surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos (2000MNRAS.312..398B). The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two of those obtained via direct kinematic measurements. We find that at a surface brightness fainter than {mu}[3.6]=20.89mag arcsec^-2^, or below 3x10^8^M_{sun}_/kpc^2^ in stellar mass surface density, the average specific star formation rate (sSFR) for star-forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies show a radial decrease in sSFR. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star-forming galaxies toward the red sequence of quiescent galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/728/23
- Title:
- GALEX UV-bright high-redshift quasars
- Short Name:
- J/ApJ/728/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the small population of high-redshift (z_em_>2.7) quasars detected by the Galaxy Evolution Explorer(GALEX), whose far-UV emission is not extinguished by intervening HI Lyman limit systems. We correlate almost all verified z_em_>2.7 quasars to the GALEX GR4 source catalog covering ~25000deg^2^, yielding 304 sources detected at signal-to-noise ratio (S/N)>3. However, ~50% of these are only detected in the GALEX NUV band, signaling the truncation of the FUV flux by low-redshift optically thick Lyman limit systems. We regard 52 quasars detected at S/N>3 to be most promising for Hubble Space Telescope follow-up, with an additional 114 quasars if we consider S/N>2 detections in the FUV. Combining the statistical properties of HI absorbers with the Sloan Digital Sky Survey (SDSS) quasar luminosity function, we predict a large all-sky population of ~200 quasars with z_em_>2.7 and i<~19 that should be detectable at the HeII edge at m_304_<21. However, SDSS provides just half of the NUV-bright quasars that should have been detected by SDSS and GALEX. With mock quasar photometry we revise the SDSS quasar selection function, finding that SDSS systematically misses quasars with blue u-g<~2 colors at 3<~z_em_<~3.5 due to overlap with the stellar locus in color space.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/643
- Title:
- GALEX UV photometry of M31 Globular Clusters
- Short Name:
- J/ApJS/173/643
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ultraviolet (UV) photometry of M31 globular clusters (GCs) found in 23 Galaxy Evolution Explorer (GALEX) images covering the entirety of M31. We detect 485 and 273 GCs (and GC candidates) in the near-ultraviolet (NUV) and far-ultraviolet (FUV), respectively. The UV properties of GCs have been analyzed using various combinations of UV-optical and optical-optical colors. Comparing M31 data with those of Galactic GCs in the UV with the aid of population models, we find that the age ranges of old GCs in M31 and the Galactic halo are similar. Three metal-rich ([Fe/H]>-1) GCs in M31 produce significant FUV flux making their FUV-V colors unusually blue for their metallicities. These are thought to be analogs of the two peculiar Galactic GCs, NGC 6388 and NGC 6441, with extended blue HB stars. We detect 12 (10) intermediate-age GC candidates in NUV (FUV) identified by previous spectroscopic observations. On the basis of comparing our UV photometry to population models, we suggest that some of spectroscopically identified intermediate-age GCs may not be truly intermediate in age, but rather older GCs that possess developed HB stars which contribute to enhanced UV flux as well as Balmer lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/715/572
- Title:
- GOALS UV and FIR properties
- Short Name:
- J/ApJ/715/572
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS; Sanders et al. 2003, Cat. J/AJ/126/1607). The galaxies span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (~2"-6"), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0+/-0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9x10^-10^/yr) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess-UV slope (IRX-{beta}) diagram as a function of galaxy properties, including IR luminosity and interaction stage.
- ID:
- ivo://CDS.VizieR/J/PASJ/70/S10
- Title:
- GOLDRUSH I. UV magnitudes
- Short Name:
- J/PASJ/70/S10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the UV luminosity functions (LFs) at z~4, 5, 6, and 7 based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP). On the 100 deg^2^ sky of the HSC SSP data available to date, we take enormous samples consisting of a total of 579565 dropout candidates at z~4-7 by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at z~4-7 that span a very wide UV luminosity range of ~0.002-100L^*^_UV_(-26<M_UV_<-14mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, {Phi}^*^, M_UV_, and {alpha}, of the UV LFs in the magnitude range where the active galactic nucleus (AGN) contribution is negligible, and find that and {Phi}^*^ decrease from z~4 to 7 with no significant evolution of M_UV_. Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided by spectroscopy or the best-fit AGN UV LFs. We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at >2{sigma} significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.
