The UV Sky


GALEX (The Galaxy Evolution Explorer) performed the first extensive sky surveys at Ultraviolet wavelengths, filling the last gap in our view of the sky across the electromagnetic spectrum.
The imaging surveys resulted in about 300 million measurements of sources in two UV bands, far-UV and near-UV.
What are these sources? How many are Milky Way stars, galaxies and Quasars? How are they distributed across the sky, and in color, magnitude, luminosity? How to extract samples of UV sources by astrophysical class? What peculiar classes of objects can be discovered from the GALEX data? The "UV sky" project and the papers below seek to answer these questions. The project also provides several science-ready catalogs and useful model grids and tools to facilitate science exploitation of the GALEX data, matched to surveys at other wavelengths.

Here you will find:

  1. relevant publications describing data, catalogs, science tools
  2. NEW! revised, final catalogs of GALEX UV sources: GUVcat

  3. previous catalogs of GALEX UV sources (BCScat) and matched UV-optical-IR catalogs
  4. catalogs of hot stars selected from GALEX-SDSS matched catalogs (from earlier release: GR5)
  5. catalogs of 19000 QSO candidates at redshift ~ 1 from GALEX-SDSS matched catalogs
  6. catalog of matched GALEX AIS sources with GSC2
  7. GALEX photometry of Magellanic Clouds souurces

1) Relevant publications for using GALEX data and catalogs (for publications on science results, go to the entire list )

* final GALEX catalogs of UV sources, with added useful tags: GUVcat ( coming soon)
Bianchi, L., Shiao, B. and Thilker, D. 2017, in prep.

* Bianchi, L., Shiao, B., Barstow, M., Keller, G., 2016: 41st COSPAR Scientific Assembly, 41E.198B
Characterization of the hot white dwarfs population in the Milky Way with GALEX, SDSS, PanSTARRS, and HST, to understand post-AGB evolution

* Invited Review paper on GALEX data
Bianchi, L. 2014, in "Challenges in UV Astronomy", ApSS, 354, 103:112, DOI: 10.1007/s10509-014-1935-6 ; arXiv:1404.4882
The Galaxy Evolution Explorer (GALEX). Its legacy of UV surveys, and science highlights
you may download pdf manuscript here or see the Springer online article here (open source)

* GALEX catalogs of UV sources, BCScat including GR7 additions: (new version coming soon)
Bianchi, L., Conti, A., and Shiao, B. 2014, J. Adv. Space Res. 53 (2014), pp. 900-912, DOI: http://dx.doi.org/10.1016/j.asr.2013.07.045 ; astro-ph 1312.3281
The ultraviolet sky: An overview from the GALEX surveys. link to ASR article or download manuscript pdf or go to astro-ph 1312.3281

* First Catalog of GALEX serendipitous UV variables:
Conti, A., Bianchi, L., Chopra, N., Orio, M., and Shiao, B. 2014, J. Adv. Space Res. 53 (2014), pp. 967-972; DOI: http://dx.doi.org/10.1016/j.asr.2013.07.022
A database of UV Variables from the GALEX survey link to online article in Advances in Space Research or download pdf here

* Catalog of UV sources in the Magellanic Clouds : (part I)
Simons, R., Thilker, D., and Bianchi, L., 2014, J. Adv. Space Res. 53 (2014), pp.939-949 ; DOI: http://dx.doi.org/10.1016/j.asr.2013.07.016
The Ultraviolet View of the Magellanic Clouds from GALEX: A First Look at the LMC Source Catalog. link to online article in Advances in Space Research or download pdf here

* Review paper on GALEX results: includes useful tables for converting magntiudes and for extinction corrections for GALEX, SDSS, and other photometric systems, and GALEX results highlights
Bianchi, L., 2011, ApSS, 335, 51; DOI: 10.1007/s10509-011-0612-2 ( download pdf )
this is an invited review in "The UV Universe 2010" (St. Petersburg June 2010), editors B. Shustov, A.I. Gomez de Castro, and M. Sachkov
"GALEX and star formation"

* Early version of UV source catalogs with description of recipe and caveats, (available at this site or MAST or Vizier ;) matched GALEX-SDSS catalog, and analysis hot-star sub-catalogs with Milky Way models:
Bianchi, L., Efremova, B., Herald, J., Girardi, L, Zabot, A., Marigo, P., Martin, C, 2011, MNRAS, 411, 2770, ( doi:10.1111/j.1365-2966.2010.17890.x) , (astro-ph: http://arxiv.org/abs/1011.1733 )
Catalogs of Milky Way Hot White Dwarf Candidates from GALEX's Ultraviolet Sky Surveys. Constraining Stellar Evolution.
download manuscript pdf or get the published paper: link to MNRAS paper or go to preprint in ADS (http://arxiv.org/abs/1011.1733 )

* Additional statistical properties of the UV catalogs, biases of sample selections, GALEX-GSC2 matched catalog:
Bianchi, L. , Herald, J., Efremova, B., Girardi, L., Zabot, A., Marigo, P., Conti, A., Shiao, B. 2011, ApSS, 335, 161, DOI: 10.1007/s10509-010-0581-x, ``GALEX Catalogs of UV sources: Statistical properties and sample science applications: Hot White Dwarfs in the Milky Way'' link to paper in ADS or go to ApSS link download pdf here

* Catalog of z~1 QSO candidates extracted from the Bianchi+2011 catalogs:
Hutchings, J.B., and Bianchi, L. , 2010, AJ, 140, 1987
A sample of 19000 QSO Caldidates with redshift 0.5 to 2.0 download pdf or link to the AJ catalog

* Overview of GALEX's UV surveys and source classification by astrophysical class:
Bianchi, L. 2009, in "Space Astronomy: The UV Window to the Universe", APSS, 320, 11 ( DOI: 10.1007/s10509-008-9761-3 )
The Ultraviolet Sky Surveys: Filling the Gap in our View of the Universe
download the poscript file or the pdf file or get the article from www.spirngerlink.com

* Discovery of QSOs with anomalous FUV-NUV color: Ly_alpha enhanced?
Bianchi, L., Hutchings, J.B., Efremova, B. et al. 2009, AJ, 137, 3761 ( astro-ph arXiv:0901.1896 )
Ultraviolet Quasi Stellar Objects download pdf file

* Early analysis of the Bianchi et al. 2011 MNRAS sample:
Bianchi, L., Efremova, B., Herald, J. et al. 2009, in "Future Directions in Ultraviolet Spectroscopy", eds.Van Steenberg et al AIPC, 1135, 326
The UV sky surveys: a roadmap for future UV missions download ps file

* On the classification of GALEX UV sources (several color-color diagrams):
Bianchi, L., et al. 2007, ApJS, 173, 659
Statistical Properties of the GALEX/SDSS Matched Source Catalogs, and Classification of the UV Sources
download: [paper ps gzip file]

* First work on classification of GALEX UV sources from early data release:
Bianchi, L. et al. 2005, ApJ, 619, L27 [pdf file] or [link to ApJ]
Classification and Characterization of Objects from the Galaxy Evolution Explorer Survey and the Sloan Digital Sky Survey

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GALEX CATALOGS of UV SOURCES

The GALEX database in MAST contains about 300 million UV source measurements; same sources have repeated measurements (useful to search for variability, for example), due to repeated observations of the same field or overlap between fields.
To estimate density of sources across the sky or the number of sources with given magnitude or color ranges, or to match UV sources with other catalogs, a source catalog is needed in which each astronomical source is counted only once.

We therefore constructed catalogs of clean, unique (i.e. only one entry for each object) sources. One also must weed out artifacts and bad measurements from any extracted sample: flags are included. And, we included other flags useful for science analysis of the catalog sources, for example flags indicating whether a source is within the footprint of a large galaxy, or stellar cluster (see Bianchi et al. 2017).

We constructed catalogs from the two GALEX surveys with the largest sky coverge (see maps):
MIS (Medium Imaging Survey, depth about 22.7 ABmag in FUV/NUV)
AIS (All-Sky Imaging Survey, depth about 19.9/20.8 FUV/NUV ABmag).

GALEX SKY COVERAGE
Figures above: Final (GR6+GR7) sky coverage of GALEX AIS and MIS surveys (figures from Bianchi et al. 2014, J. ASR 53, 900; astro-ph 1312.3281 )

2) GUVcat , final GALEX CATALOGS of UV SOURCES (Bianchi et al. 2017)
This catalog expands, improves and replaces the previous catalog (BCScat). In particular, we patched some fields that had beed incorrectly merged by the pipeline (introducing some flawed sources and artifacts in the database and in previous catalogs), and added useful tags for science analysis.

Description of catalog, tags, useful advice and caveats:
Reference: Bianchi, L., Shiao, B., Thilker, D., 2017, in prep. (will be linked here)

Get the catalog:

GUVcat_AIS FOV_radius < 0.55deg (larger area, includes a few edge artifacts)

GUVcat_AIS FOV_radius < 0.50deg (area restricted to the good part of the fields, slightly less coverage, no edge artifacts)

tool for area coverage calculation (Bianchi and de la Vega 2017): compute area coverage in sky regions of your choice

Get the catalog from MAST casjobs: (coming soon)

Get the catalog from SIMBAD Vizier (coming soon)

Two new tags. inlargeobject and largeobjsize indicate whether a GUVcat source is within the footprint of an extended object: large galaxy or stellar clusters. For all known objects larger than 1arcmin which are partly or entirely in GUVcat, we provide information and finding charts in the following tables:

Globular Clusters in GUVcat

Open Clusters in GUVcat

Other (less specified) Clusters in GUVcat

Extended Galaxies in GUVcat

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3) BCScat, the previous version of GALEX CATALOGS of UV SOURCES:

Criteria for constructing the catalogs: (for more details, see the original papers: Bianchi et al. 2014, J. ASR 53, 900; Bianchi, L. et al. 2011, MNRAS, 411, 2770)
1) only observations with both FOV and NUV detectors turned on are included. This is useful for any science analysis where the fraction of sources with a given FUV-NUV color is of interest, or to estimate the fraction of sources with significant detection in both FUV and NUV over the total number of NUV detections. Note that the basic GALEX database gives FUV magnitude = -999 in both cases when the FUV detector was off, or the FUV detector was on but the source's FUV flux is below detection threshold.
More observations exist in the GALEX archive taken with one detector off (mostly FUV); those can be found in the galex.stsci.edu MAST database.

2) only sources within 0.5 degree of the field center are included, to avoid sources with poor photometry/astrometry near the edge, and rim artifacts. This makes the catalogs useful for statistical analysis of sources with homogeneous quality, without great loss of area coverage (also considering that overlap exist among several fields). Users interested in a particular source that happens to fall on the rim of a GALEX filed, should obtain its measurements from the main database and carefully examine the quality.

3) we retained sources with NUV magnitude errors less or equal 0.5mag (see Figure 4 of Bianchi et al. 2011 MNRAS , and Figures 2--4 of Bianchi et al. 2011 ApSS for effects of error cuts on the resulting sample statistics).

4) The general GALEX database contains all measurements for sources with repeated observations. We removed duplicate measurements to produce a unique source catalog as follows. GALEX sources within 2.5'' of each other, but from different observations, were considered duplicates. In such cases the object from the observation with the longest NUV exposure time was retained, and - in cases of equal exposure times - the object closest to the center of the field of view.

See also these review articles for useful information on GALEX data: Bianchi, L. 2009, 320, 11, DOI: 10.1007/s10509-008-9761-3 ; Bianchi, L. 2011 ApSS, 335, 51; DOI: 10.1007/s10509-011-0612-2 ) )


Reference: Bianchi, L., Conti, A., and Shiao, B. 2014, J. Adv. Space Res. Vol. 53 (2014), 900; DOI: 10.1016/j.asr.2013.07.045 ; astro-ph 1312.3281
The ultraviolet sky: An overview from the GALEX surveys. link to ASR article (open access, i.e. free) or download manuscript pdf or go to astro-ph 1312.3281

Get the catalogs :

CATALOGS of UV sources( " BCScat" AIS and MIS )
==> download the catalogs HERE in csv files, or fits files:
==> from MAST casjobs : galex.stsci.edu/casjobs (Context: GALEXCatalogs, Tables: bcscat_ais, bcscat_mis )
==> from Vizier (see GUVcat above )

MATCHED CATALOGS UV-optical-IR
==> MATCHED with SDSS DR10: catalogs READY, will be posted soon
==> MATCHED with 2MASS: testing in progress, coming soon
==> MATCHED with GSC2: planned
==> MATCHED with Pan-STARRS: in progress

=> SUBCATALOGS: sources with significant detection in both FUV and NUV, from the above catalogs

Area coverage of BCScat and matched BCScatXoptical catalogs
Table with area coverage, total and at different latitudes
Compute area in sky regions of your choice

4) Previous Catalogs, from GALEX fifth data release (GR5)
The previous version of the final catalogs available above; these also include matched GALEXxSDSS catalogs, GALEXxGSC2 catalogs and extracted catalogs of hot stars and QSOs: go to the GR5 catalogs

Source/ reference: Catalogs can be used citing this ref.
Bianchi, L. et al. MNRAS, 2011 411, 2770 (open access) 2011, Catalogs of Milky Way Hot White Dwarf Candidates from GALEX's Ultraviolet Sky Surveys. Constraining Stellar Evolution.


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5) QSO samples extracted from the GALEX surveys

5a) CATALOG OF 19000 QSOs candidates at redshift about 1
Hutchings, J.B., and Bianchi, L., 2010, AJ, 140, 1987
A sample of 19000 QSO Candidates with redshift 0.5 to 2.0 download pdf or link to the AJ catalog

5b) QSOs with normal optical properties and unusual UV properties:
Bianchi, L., Hutchings, J.B., Efremova, B. et al. 2009, AJ, 137, 3761 ( astro-ph arXiv:0901.1896 )
Ultraviolet Quasi Stellar Objects download pdf file

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6) GALEX custom photometry of Magellanic Cloud sources


Safety constraints (countrate brightness) prevented observing of the bright LMC and SMC central regions during the main GALEX mission, but the survey was completed in NUV at the end of the mission. For an overview of area coverage and exposure level in FUV and NUV of the Magellanic Clouds, see Fig. 5 of Bianchi 2014, ApSS, 53 , 939 .

Sources are too crowded in the MC galaxies and their periphery for the standard GALEX pipeline to perform reliable source detection (the database photometry should be used with great caution!), therefore we performed custom photometry in the GALEX fields within 15 degrees of the LMC and and 10 deg of the SMC, covering also the Magellanic Bridge.

Current coverage with both FUV and NUV measurements includes ~550 square degrees in 1460 overlapping GALEX tiles with exposures typically at AIS depth (magnitude limit about 19.9[20.8] ABmag in FUV[NUV]), but occasionally reaching MIS level (about 2 mag deeper). The remaining area has NUV-only data. The catalogued GALEX detections are being matched to optical source catalogs to produce a multi-wavelength database.


Point source catalog (coming soon)
Extended source catalog (coming later)

References:

Thilker, D., Bianchi, L. Simons, R, 2015, poster at "Feedback in the magellanic Clouds" Conference, STScI, Oct.2015
The Ultraviolet Survey of the Magellanic Clouds with GALEX

Bianchi, L. 2014, ApSS, 354, 103:112 (DOI: 10.1007/s10509-014-1935-6; arXiv:1404.4882)
The Galaxy Evolution Explorer (GALEX). Its legacy of UV surveys, and science highlights
direct link to Springer online article

Simons, R., Thilker, D., and Bianchi, L.,, 2014, J. Adv. Space Res. 53 (2014), pp.939-949 ; DOI: http://dx.doi.org/10.1016/j.asr.2013.07.016 ( arXiv:1401.7286 )
The Ultraviolet View of the Magellanic Clouds from GALEX: A First Look at the LMC Source Catalog.
link to online article in Advances in Space Research (free online open-access)

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