GALEXLOG Catalog
This table contains the Galaxy Evolution Explorer (GALEX) observation
log of the extant and planned observations to be made by this satellite
observatory. The Galaxy Evolution Explorer (GALEX) is a NASA Small Explorer
Mission launched on April 28, 2003. GALEX has been performing the first
Space Ultraviolet sky survey. Five imaging surveys in each of two bands
(FUV: 1350-1750 Angstroms and NUV: 1750-2800 Angstroms) range from an all-sky
survey (limiting mAB ~ 20 - 21) to an ultra-deep survey of 4 square degrees
(limiting mAB ~ 26). Three spectroscopic grism surveys (spectral resolution
R = 100 - 300) are underway with various depths (mAB ~ 20 - 25) and sky
coverage (100 to 2 square degrees) over the 1350 - 2800 Angstroms spectral
range. The instrument includes a 50-cm modified Ritchey-Chretien telescope,
a dichroic beam splitter and astigmatism corrector, two large, sealed-tube
microchannel plate detectors to simultaneously cover the two bands and
the 1.2-degree field of view. A rotating wheel provides either imaging or
grism spectroscopy with transmitting optics.
The GALEX mission also includes an Associate Investigator program for
additional observations and supporting data analysis which supports a
wide variety of investigations made possible by the first UV sky survey.
The HEASARC provides this table of GALEX observations as an assistance to
the high-energy astrophysics community, e.g., to enable cross-correlations
of GALEX with X-ray observations. The GALEX data are available via MAST at
http://galex.stsci.edu/. More information about GALEX can be found at
http://www.galex.caltech.edu/ and https://asd.gsfc.nasa.gov/archive/galex/.
GALEXTDSC Catalog
This table contains results from the selection and classification of over a
thousand ultraviolet (UV) variable sources discovered in ~ 40 deg2 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-2 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-2 yr-1 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 mAB(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.
GLXSDSSQS2 Catalog
A sample of ~60,000 objects from the combined Sloan Digital Sky Survey-Galaxy
Evolution Explorer (SDSS-GALEX) database with UV-optical colors that should
isolate QSOs in the redshift range 0.5 to 1.5 is discussed. The authors use
SDSS spectra of a subsample of ~ 4,500 to remove stellar and galaxy
contaminants in the sample to a very high level, based on the 7-band
photometry. In their paper, they discuss the distributions of redshift,
luminosity, and reddening of the 19,100 QSOs (~96%) that they estimate to be
present in their final sample of 19,812 point sources. This latter catalog is
available in the present table.
This paper is based on archival data from the Galaxy Evolution Explorer
(GALEX) which is operated for NASA by the California Institute of Technology
under NASA contract NAS5-98034, and on data from the SDSS.
GLXSDSSQSO Catalog
This table contains the result of an analysis of the broad-band UV and
optical properties of z ~< 3.4 quasars matched in the Galaxy Evolution
Explorer (GALEX) General Data Release 1 (GR1) and the Sloan Digital Sky
Survey (SDSS) Data Release 3 (DR3). Of the 6371 SDSS DR3 quasars covered by
204 GALEX GR1 tiles and listed in this table, 5380 (84%) have near-UV
detections, while 3034 (48%) have both near-UV and far-UV detections using a
matching radius of 7 arcseconds. Most of the DR3 sample quasars are detected
in the near-UV until z ~ 1.7, with the near-UV detection fraction dropping to
~50% by z ~ 2. Statistical tests performed on the distributions of
non-detections indicate that the optically selected quasars missed in the UV
tend to be optically faint or at high redshift. The GALEX positions are shown
to be consistent with the SDSS astrometry to within an rms scatter of 0.6 -
0.7 arcsecs in each coordinate, and the empirically determined photometric
errors from multi-epoch GALEX observations significantly exceed the Poissonian
errors quoted in the GR1 object catalogs. The UV-detected quasars are well
separated from stars in UV-optical color-color space, with the UV-optical
relative colors suggesting a marginally detected population of reddened
objects due to absorption along the line of sight or dust associated with the
quasar. The resulting spectral energy distributions (SEDs) cover ~350 - 9000
Angstroms (rest frame), where the overall median SED peaks near the
Lyman-Alpha emission line, as found in other UV quasar studies. The large
sample size allows the authors to construct median SEDs in small bins of
redshift and luminosity, and they find that the median SED becomes harder
(bluer) at UV wavelengths for quasars with lower continuum luminosity. The
detected UV-optical flux as a function of redshift is qualitatively
consistent with attenuation by intervening Lyman-absorbing clouds.
MDWF10PCUX Catalog
M dwarfs are the most numerous stars in the galaxy. They are characterized by
strong magnetic activity. The ensuing high-energy emission is crucial for the
evolution of their planets and the eventual presence of life on them. The
authors systematically study the X-ray and ultraviolet emission of a
subsample of M dwarfs from a recent proper-motion survey, selecting all M
dwarfs within 10 pc to obtain a nearly volume-limited sample (~90%
completeness). Archival ROSAT, XMM-Newton and GALEX data are combined with
published spectroscopic studies of H-alpha emission and rotation to obtain a
broad picture of stellar activity on M dwarfs. The authors make use of
synthetic model spectra to determine the relative contributions of
photospheric and chromospheric emission to the ultraviolet flux. They also
analyze the same diagnostics for a comparison sample of young M dwarfs in the
TW Hya association (~10 Myr old). The authors find that generally the
emission in the GALEX bands is dominated by the chromosphere but the
photospheric component is not negligible in early-M field dwarfs. The surface
fluxes for the H-alpha, near-ultraviolet, far-ultraviolet and X-ray emission
are connected via a power-law dependence. The authors present in the
reference paper for the first time such flux-flux relations involving
broad-band ultraviolet emission for M dwarfs. Activity indices are defined as
the flux ratios between the activity diagnostics and the bolometric flux of
the star in analogy to the Ca II R'(HK) index. For a given spectral type,
these indices display a spread of 2-3 dex which is largest for M4-type stars.
Strikingly, at mid-M spectral types, the spread of rotation rates is also at
its highest level. The mean activity index for fast rotators, likely
representing the saturation level, decreases from X-rays over the FUV to the
NUV band and H-alpha, i.e. the fractional radiation output increases with
atmospheric height. The comparison to the ultraviolet and X-ray properties of
TW Hya members shows a drop of nearly three orders of magnitude for the
luminosity in these bands between ~10 Myr and a few Gyr age. A few young
field dwarfs (<1 Gyr) in the 10-pc sample bridge the gap indicating that the
drop in magnetic activity with age is a continuous process. The slope of the
age decay is steeper for the X-ray than for the UV luminosity. This sample is
based on the All-Sky Catalog of bright M dwarfs published by Lepine & Gaidos
(2011, AJ, 142, 138, CDS Cat. J/AJ/142/138, available at the HEASARC as the
MDWARFASC table). The authors selected all 163 stars from this reference that
are within 10pc. Four of these stars that were discovered to be actually late
K-type stars were removed from this initial sample, leaving a final sample of
159 stars.
NUVBEMDCAT Catalog
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. The authors investigated the NUV
luminosity evolution of early M-type dwarfs by cross-correlating the Lepine &
Gaidos (LG11: 2011, AJ, 142, 138) catalog of bright M dwarfs (available at
the HEASARC as the MDWARFASC table) with the Galaxy Evolution Explorer
(GALEX) catalog of NUV (1771-2831 Angstrom) sources. Of the 4,805 sources
with GALEX counterparts, 797 have NUV emission significantly (> 2.5 sigma) in
excess of an empirical basal level. The authors 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; they estimated the overall occurrence of these "false
positives" (FPs) as ~ 16%. The authors constructed an NUV luminosity function
that accounted for FPs, detection biases of the source catalogs, and GALEX
upper limits. They 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.
UVQS Catalog
This table contains data from the first data release (DR1) from the UV-bright
Quasar Survey (UVQS) for new z ~ 1 active galactic nuclei (AGN) across the
sky. Using simple GALEX UV and WISE near-IR color selection criteria, the
authors generated a list of 1,450 primary candidates with FUV < 18.5 mag,
that is contained in the HEASARC table (entries with source_sample = 'P').
They obtained discovery spectra, primarily on 3m-class telescopes, for 1,040
of these candidates and confirmed 86% as AGN, with redshifts generally at z >
0.5. Including a small set of observed secondary candidates, the authors
report the discovery of 217 AGN with GALEX FUV magnitudes < 18 mag that
previously had no reported spectroscopic redshifts. These are excellent
potential targets for UV spectroscopy before the end of the Hubble Space
Telescope mission. The main data products of UVQS are publicly available
through the Mikulski Archive for Space Telescopes (MAST).
The authors have performed an all-sky survey for z ~ 1, FUV-bright quasars
selected from GALEX and WISE photometry. In several of the observing runs,
conditions were unexpectedly favorable and we exhausted the primary
candidates at certain right ascension ranges. To fill the remaining observing
time, they generated a secondary candidate list. This secondary set of 2,010
candidates is also contained in this HEASARC table (entries with
source_sample = 'S').
The authors proceeded to obtain discovery-quality long-slit spectra (i.e.,
low-dispersion, large-wavelength coverage, modest signal-to-noise ratio (S/N)
of their UV-bright Quasar Survey (UVQS) candidates in one calendar year. The
principal facilities were: (i) the dual Kast spectrometer on the 3m Shane
telescope at the Lick Observatory; (ii) the Boller & Chivens (BCS)
spectrometer on the Irenee du Pont 100-inch telescope at the Las Campanas
Observatory; and (iii) the Calar Alto Faint Object Spectrograph on the CAHA
2.2-meter telescope at the Calar Alto Observatory (CAHA). They acquired an
additional ~20 spectra on larger aperture telescopes (Keck/ESI, MMT/MBC,
Magellan/MagE) during twilight or under poor observing conditions. Typical
exposure times were limited to < ~200s, with adjustments for fainter sources
or sub-optimal observing conditions. Table 3 in the reference paper provides
a list of the details of the observations of these candidates. From the total
candidates list of 3,460 objects, the authors measured high-quality redshifts
(redshift quality flag values of 3 or greater) for 1,121 sources. They
assumed that every source with a recessional velocity vr = z * c < 500 km
s-1 was "Galactic", which they associate with the Galaxy and members of the
Local Group. This included sources where the eigenspectra fits were poor yet
a low vr was indisputable (e.g., stars). Many of these were assigned z = 0
exactly. The remainder of the UVQS sources were assumed to be extragalactic
AGN, and the derived redshift information for these sources (which was given
in Table 4 of the reference paper) has been incorporated into this HEASARC
representation of UVQS. Finally, there were 93 sources with good-quality
spectra for which we cannot the authors could not recover a secure redshift.
The majority of these have been previously cataloged as blazars (or BL Lac
objects). Table 6 in the reference paper lists the sample of these unknown or
insecure redshift objects.
