Welcome to the GALEX Public Archive
The GALEX Mission
Welcome to the MAST public access site for browsing and retrieving GALEX Release
7 data products. The Galaxy Evolution Explorer (GALEX)
satellite is a NASA mission led by the California
Institute of Technology to investigate how star formation in galaxies evolved
from the early Universe up to the present. GALEX uses microchannel plate detectors
to obtain direct images in the near-UV (NUV) and far-UV (FUV) and a grism to disperse light for low resolution spectroscopy.
Note that operations of the GALEX satellite will likely be terminated in Spring 2013. The GALEX data archive will continue to be available via the
MultiMission Archive at Space Telescope Science Institute (MAST), which is also the only NASA-sanctioned site that distributes GALEX data to the public. Pipeline-processed GALEX data are periodically sent to
MAST and ingested into the GALEX/MAST database. These products can be accessed directly
over the web in real time, or in the case of large volume requests, by ftp.
With its UV surveying capabilities, GALEX complements the functions of the Hubble
Space Telescope (HST) and the Far Ultraviolet
Spectroscopic Explorer (FUSE), GALEX likewise
complements the ground-based, optical Sloan Digital Sky Survey (SDSS)
at optical wavelengths, which covered about 1/4 of the sky. The original GALEX AIS, which was
completed with the GR4 in 2008, covers over 2/3 of the sky. However, in general GALEX originally avoided
observing near the Galactic plane and Magellanic clouds in order to safeguard the detectors from
excessive stellar and/or background UV fluxes. With the final data release (GR7), the AIS coverage of the sky
was greatly increased, in particular at lower Galactic latitudes, thanks to a lifting of this safeguard towards
the end of the mission.
Users can familiarize themselves with GALEX data products by selecting, browsing, and downloading
them from several search forms accessible from the Search and Retrieval tab on this page. For most
purposes we recommend use of the galexView tool. A high-level description of data retrieval modes
is provided on the Getting Started page.
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From its launch into low-Earth orbit on April 28, 2003 the GALEX NUV camera operated almost
continuously. The Project suspended operations of the FUV camera following an electrical
overcurrent in May 2009. GALEX data products include a series of all sky surveys and
deep sky surveys in the imaging mode, and partial surveys in the near and far UV spectroscopic modes.
The principal imaging studies are the Nearby Galaxy Survey (NGS), Deep (DIS), Medium (MIS), and All Sky
Imaging Surveys (AIS). A somewhat smaller grism (spectroscopic) survey
is also included. More details on each survey can be found in
Chapter 2 of the GALEX technical documentation page.
Although originally planned as a 29-month mission, past NASA Senior
Senior Review Panels have recommended mission extensions.
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GALEX Merged Catalog (MCAT)
The GALEX MCAT is the mission-produced catalog of sources. There is a catalog based on visits and another catalog based on coadds. You can read more about the contents of the MCAT tables in the GALEX wiki. You can search the MCAT at MAST in several ways, including via SQL using CasJobs. or through a web browser using GalexView. You can also use the MAST Portal to cross-match an uploaded list of targets against the MCAT.
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Public GALEX Releases
During the course of the mission, the GALEX team have released data to the public through
MAST at discrete times. The last complete release was
the GR6 (late 2010 through mid 2011 for imaging supplements and the
grism survey). A final release of GALEX data arrived in late 2012 at MAST. These included a number
of redelivered GR6 data (additional visits and associated coadds from 2003 onwards), along with new tiles within GR7,
which span approximately from Jan. 2010 through Feb. 2012. This data will be made available
through the various MAST search tools by Feb. 2013. The GALEX catalog of discrete sources, "GCAT",
will be made available through MAST at a later date. Various documentation, analysis tools, and new data
products (potentially including the photon list files) are planned for 2013 and beyond, so continue to
look for new data and analysis tools within MAST.
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Guest Investigator Program
Through year 2009 the GALEX mission committed about 1/3
of its observing program to carrying out observations for a
Guest Investigator (GI) program. This Program is now chiefly
of historical interest, except that the observations are
currently being reprocessed and posted under the name of
the "GII Survey" on these pages. Also, one may navigate to
the abstracts of accepted GI proposals via several links on
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Close out deliverables (the "GR7")
The final set of tiles, observed with the remaining NUV camera and predominantly observed
after 2010 February 1, comprise the GR7. These products will use an improved pipeline, with
updated calibrations, to handle changes in the response of the NUV detector in 2010 and 2011.
For an explanation of these changes, please visit the link entitled "GR7 Pipeline Description" at the
top of the page. With the lifting of bright star limits, a variety of areas
previously unexplored were targeted, including completion of the AIS survey within the plane of the
Milky Way. A sample of the GR7 subdeliveries are:
- Processing of observations made subsequent to 2010 February 1.
- New observations at low Galactic latitudes, including the Bulge area.
- Observations of the Magellanic Clouds (LMC/SMC/Bridge).
- New observations of M31, which will complement ongoing ground-based
observations by the PanSTARRS project,
- Increased coverage of the Kepler field. A search interface enabling access to the Kepler-GALEX
cross-matching is provided here, while the
GALEX fluxes are included (along with data from other cross-matched catalogs) in the Kepler Target Search
- Final GII (formerly known as "GI") program observations.
Later, a pair of GCAT catalogs, called the ASC and
MSC, will be provided based on the AIS and MIS surveys. The catalogs
are "NUV-centric", meaning that FUV parameters like FUV magnitudes
are determined from the positions of the corresponding NUV images.
Also, unlike the GR datasets, a unique identifer is assigned to each
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Scan Mode Data
In the post-NASA (or "CAUSE") phase of the GALEX mission, the spacecraft began
observing frequently in a mode known as "scan mode". In scan mode, the spacecraft
boresight would traverse and observe many degrees of sky, rapidly, in a long swath.
This was in contrast to the traditional boresight dither, known as the "petal pattern",
and to AIS modes in which the spacecraft hovered over single sky pointings and was reduced
to a low voltage (non-observing) state when orienting between pointings. The benefit
of scan mode was that it allowed the team to more rapidly complete the All Sky Survey
in the ultraviolet. But scan mode was performed at a time when the mission was operating
on both minimal staff and budget, so while nominal data products were produced, the
calibration pipeline was not optimized to handle these data, and no additional scientific
support was available. MAST provides access to the RAW6 and visit-level data products, but
we do not mix these data with other GALEX services (e.g., GALEXView), since the data are so
different from the rest of the mission. You can find documentation and access information by
visiting the MAST GALEX Scan Mode page.
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