The Galaxy Evolution Explorer (GALEX) imaged the sky in the Ultraviolet (UV) for almost a decade, delivering the first sky surveys at these wavelengths. Its database contains far-UV (FUV,
λ
eff
...∼1528 Å) and near-UV (NUV,
λ
eff
∼2310 Å) images of most of the sky, including deep UV-mapping of extended galaxies, over 200 million source measurements, and more than 100,000 low-resolution UV spectra. The GALEX archive will remain a long-lasting resource for statistical studies of hot stellar objects, QSOs, star-forming galaxies, nebulae and the interstellar medium. It provides an unprecedented road-map for planning future UV instrumentation and follow-up observing programs in the UV and at other wavelengths.
We review the characteristics of the GALEX data, and describe final catalogs and available tools, that facilitate future exploitation of this database. We also recall highlights from the science results uniquely enabled by GALEX data so far.
The Galaxy Evolution Explorer (GALEX) imaged the sky in two ultraviolet (UV) bands, far-UV (FUV, λeff ∼ 1528 ), and near-UV (NUV, λeff ∼ 2310 ), delivering the first comprehensive sky surveys at ...these wavelengths. The GALEX database contains FUV and NUV images, ∼500 million source measurements and over 100,000 low-resolution UV spectra. The UV surveys are a unique resource for statistical studies of hot stellar objects, z 2 QSOs, star-forming galaxies, nebulae and the interstellar medium, and provide a roadmap for planning future UV instrumentation and follow-up observing programs. We present science-enhanced, "clean" catalogs of GALEX UV sources, with useful tags to facilitate scientific investigations. The catalogs are an improved and expanded version of our previous catalogs of UV sources (BCScat). With respect to BCScat, we have patched 640 fields for which the pipeline had improperly coadded non-overlapping observations, and we provide a version with a larger sky coverage (about 10%) by relaxing the restriction to the central area of the GALEX field to 1 1 diameter (GUVcat_AIS_fov055), as well as the cleaner, more restrictive version using only the 1° central portion of each field as in BCScat (GUVcat_AIS_fov050). We added new tags to facilitate selection and cleaning of statistical samples for science applications: we flag sources within the footprint of extended objects (nearby galaxies, stellar clusters) so that these regions can be excluded for estimating source density. As in our previous catalogs, in GUVcat duplicate measurements of the same source are removed, so that each astrophysical object has only one entry. Such a unique-source catalog is needed to study the density and distributions of sources, and to match UV sources with catalogs at other wavelengths. The catalog includes all observations from the All-Sky Imaging Survey (AIS), the survey with the largest area coverage, with both FUV and NUV detectors exposed: over 28,700 fields, made up of a total of 57,000 observations ("visits"). The total area covered, when overlaps are removed and gaps are accounted for, is 24,790 square degrees for GUVcat_AIS_fov055 (GUVcat_AIS_fov055) and 22,125 square degrees for (GUVcat_AIS_fov050). The total numbers of "unique" AIS sources (eliminating duplicate measurements) are 82,992,086 ( ) and 69,772,677 ( ). The typical depth of the GUVcat_AIS catalog is FUV = 19.9, NUV = 20.8 AB mag.
We extend the PARSEC library of stellar evolutionary tracks by computing new models of massive stars, from 14 to 350 M⊙. The input physics is the same used in the PARSEC V1.1 version, but for the ...mass-loss rate from considering the most recent updates in the literature. We focus on low metallicity, Z = 0.001 and Z = 0.004, for which the metal-poor dwarf irregular star-forming galaxies, Sextans A, the Wolf–Lundmark–Melotte galaxy and NGC 6822, provide simple but powerful workbenches. The models reproduce fairly well the observed colour-magnitude diagrams (CMDs) but the stellar colour distributions indicate that the predicted blue loop is not hot enough in models with a canonical extent of overshooting. In the framework of a mild extended mixing during central hydrogen burning, the only way to reconcile the discrepancy is to enhance the overshooting at the base of the convective envelope (EO) during the first dredge-up. The mixing scales required to reproduce the observed loops, EO = 2H
P or EO = 4H
P, are definitely larger than those derived from, e.g. the observed location of the red-giant-branch bump in low mass stars. This effect, if confirmed, would imply a strong dependence of the mixing scale below the formal Schwarzschild border, on the stellar mass or luminosity. Reproducing the features of the observed CMDs with standard values of envelope overshooting would require a metallicity significantly lower than the values measured in these galaxies. Other quantities, such as the star formation rate and the initial mass function, are only slightly sensitive to this effect. Future investigations will consider other metallicities and different mixing schemes.
Abstract
We have performed the first systematic search of the full Galaxy Evolution Explorer (GALEX) data archive for astrophysical variability on timescales of seconds to minutes by rebinning data ...across the whole mission to 30 s time resolution. The result is the GALEX Flare Catalog (GFCAT), which describes 1426 ultraviolet variable sources, including stellar flares, eclipsing binaries,
δ
Scuti and RR Lyrae variables, and active galactic nuclei. Many of these sources have never previously been identified as variable. We have also assembled a table of observations of ultraviolet flares and accompanying statistics and measurements, including energies, and of candidate eclipsing stars. This effort was enabled by a significantly enhanced version of the gPhoton software for analyzing time-domain GALEX data; this “gPhoton2” package is available to support follow-on efforts.
New low-resolution UV spectra of a sample of reddened OB stars in M31 were obtained with the Hubble Space Telescope/STIS to study the wavelength dependence of interstellar extinction and the nature ...of the underlying dust grain populations. Extinction curves were constructed for four reddened sightlines in M31 paired with closely matching stellar atmosphere models. The new curves have a much higher signal-to-noise ratio than previous studies. Direct measurements of N(H i) were made using the Ly alpha absorption lines enabling gas-to-dust ratios to be calculated. The sightlines have a range in galactocentric distance of 5-14 kpc and represent dust from regions of different metallicities and gas-to-dust ratios. The metallicities sampled range from solar to 1.5 solar. The measured curves show similarity to those seen in the Milky Way and the Large Magellanic Cloud. The Maximum Entropy Method was used to investigate the dust composition and size distribution for the sightlines observed in this program, finding that the extinction curves can be produced with the available carbon and silicon abundances if the metallicity is super-solar.
Summary
The aim of the present study was to compare the information provided by a discrete and continuous data analysis of two emotions (disgust and joy), elicited by bitter‐tasting beverages ...(coffee, yerba mate infusion and grapefruit juice) in two groups with different body mass index (BMI): overweight group (25 < BMI < 30), and healthy‐weight control group (18.5 < BMI ≤ 25). Participants (n = 66; 34 females, 32 males) evaluated a total of three consecutive sips of the same beverage (taking one sip every 20 s and registering a continuous video for 60 s). The Wilcoxon test (continuous analysis) showed some changes generated as the drinks were being consumed. The biggest difference was the expression of disgust for coffee in the high BMI group, at the first sip (0–10 s). It represented 27% compared to 2% in normal BMI. The continuous analysis allowed to observe the periods where the differences were greater (0–10 and 40–50 s).
Discrete & continuous analysis of facial expression in overweight and healthy‐weight individuals
UV Star Formation Rates in the Local Universe Salim, Samir; Rich, R. Michael; Charlot, Stéphane ...
The Astrophysical journal. Supplement series,
12/2007, Volume:
173, Issue:
2
Journal Article
Peer reviewed
Open access
We measure star formation rates (SFRs) of approximately 50,000 optically selected galaxies in the local universe (z approximately 0.1)--from gas-rich dwarfs to massive ellipticals. We obtain ...dust-corrected SFRs by fitting the GALEX (ultraviolet) and SDSS photometry to a library of dust-attenuated population synthesis models. For star-forming galaxies, our UV-based SFRs compare remarkably well with those from SDSS-measured emission lines (H alpha ). Deviations from perfect agreement are shown to be due to differences in the dust attenuation estimates. In contrast to H alpha measurements, UV provides reliable SFRs for galaxies with weak H alpha , and where H alpha is contaminated with AGN emission (1/2 of the sample). Using full-SED SFRs, we calibrate a simple prescription that uses GALEX far- and near-UV magnitudes to produce dust-corrected SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGNs, (2) those hosting an AGN, and (3) galaxies without Ha emission. We find that the three have distinct star formation histories, with AGNs lying Intermediate between the star-forming and the quiescent galaxies. Star-forming galaxies without an AGN lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. On the other hand, weak AGNs, while also massive, have lower SFRs, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent galaxies via strong and weak AGNs. We confirm that some galaxies with no H alpha show signs of star formation in the UV. We derive a cosmic star formation density at z = 0.1 with significantly smaller total error than previous measurements.
We present the Bayesian Extinction And Stellar Tool (BEAST), a probabilistic approach to modeling the dust extinguished photometric spectral energy distribution of an individual star while accounting ...for observational uncertainties common to large resolved star surveys. Given a set of photometric measurements and an observational uncertainty model, the BEAST infers the physical properties of the stellar source using stellar evolution and atmosphere models and constrains the line of sight extinction using a newly developed mixture model that encompasses the full range of dust extinction curves seen in the Local Group. The BEAST is specifically formulated for use with large multi-band surveys of resolved stellar populations. Our approach accounts for measurement uncertainties and any covariance between them due to stellar crowding (both systematic biases and uncertainties in the bias) and absolute flux calibration, thereby incorporating the full information content of the measurement. We illustrate the accuracy and precision possible with the BEAST using data from the Panchromatic Hubble Andromeda Treasury. While the BEAST has been developed for this survey, it can be easily applied to similar existing and planned resolved star surveys.
We introduce a new quantity, the mass flux density of galaxies evolving from the blue sequence to the red sequence. We propose a simple technique for constraining this mass flux using the ...volume-corrected number density in the extinction-corrected UV-optical color-magnitude distribution, the stellar age indexes H delta sub(A) and unk(4000), and a simple prescription for spectral evolution using a quenched star formation history. We exploit the excellent separation of red and blue sequences in the NUV - r band Hess function. The final value we measure, rho T = 0.033 m unk yr super(-1) Mpc super(-3), is strictly speaking an upper limit due to the possible contributions of bursting, composite, and extincted galaxies. However, it compares favorably with estimates of the average mass flux that we make based on the red luminosity function evolution derived from the DEEP2 and COMBO-17 surveys, rho R - +0034 M unk yr super(-1) Mpc super(-3). We find that the blue sequence mass has remained roughly constant since z = 1 ( rho B unk 0.01 M unk yr super(-1) Mpc super(-3), but the average on-going star formation of rho SF unk 0.037 M unk yr super(-1) Mpc super(-3) over 0 < z < 1 is balanced by mass flux off the blue sequence. We explore the nature of the galaxies in the transition zone with particular attention to the frequency and impact of active galactic nuclei (AGNs). The AGN fraction peaks in the transition zone. We find circumstantial, albeit weak evidence that the quench rates are higher in higher luminosity AGNs.
Abstract
We have matched the ultraviolet (UV) sources in
GUVcat
_AIS with optical databases that have similar depth and wide sky coverage.
GUVcat
_AIS has Galaxy Evolution Explorer (GALEX) far-UV ...(FUV,
λ
eff
∼ 1528 Å) and near-UV (NUV,
λ
eff
∼ 2310 Å) photometry of ≈83 million sources, covering 24,788 square degrees of the sky, with a typical depth of FUV = 19.9 and NUV = 20.8 AB mag. Matches with Gaia and the Sloan Digital Sky Survey (SDSS) databases are presented here. Gaia data release 2 (DR2), covering the entire
GUVcat
footprint, detected about one-third of the
GUVcat
_AIS sources. We found 31,925,294 Gaia DR2 counterparts to 30,024,791
GUVcat
_AIS unique sources, with photometry in the Gaia
G
band and often also in Gaia BP and RP bands; 26,275,572 matches have a parallax measurement, 21,084,628, 18,588,140, and 16,357,505 have a parallax error less than 50%, 30%, and 20%, respectively. The match with SDSS data release 14 (DR14) yields 23,310,532 counterparts to 22,207,563 unique
GUVcat
_AIS sources, 10,167,460 of which are pointlike, over a total overlap area of ≈11,100 square degrees (Bianchi et al. 2019). SDSS adds five optical magnitudes to the UV photometry :
u
,
g
,
r
,
i
,
z
, and optical spectra of 860,224 matched sources. We used a match radius of 3″, consistent with previous works, although the positions agree to ≲15 for the majority of (pointlike) matched sources, in order to identify possible multiple matches whose UV flux could be unresolved in GALEX imaging. The catalogs can be trimmed to a tighter match radius using the provided separation. The multiband photometry is used to identify classes of astrophysical objects that are prominent in UV, to characterize the content of the
GUVmatch
catalogs, where stars in different evolutionary stages, quasi-stellar objects, and galaxies can be separated.
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