The GALEX Mission

Welcome to the MAST public access site for browsing and retrieving GALEX Release 6 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 the operations of the GALEX satellite will be terminated on December 31, 2011.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 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 GALEX AIS, which was completed with the GR4 in 2008, covers over 2/3 of the sky. However, in general GALEX has avoided observing near the Galactic plane and Magellanic clouds in order to safeguard the detectors from excessive stellar and/or background UV fluxes.

GALEX Surveys

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 Surveys (AIS:imaging). A somewhat smaller grism (spectroscopic) is also included. More details on each survey can be found in Chapter 2 of the GALEX technical documentation page. STScI Archive Manual. Although originally planned as a 29-month mission, past NASA Senior Senior Review Panels have recommended mission extensions.

Public GALEX Releases

During the course of the mission Project has 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). The GALEX catalog of discrete sources, "GCAT," will be released in the fall of 2011. Several small GR7 releases will be distributed in late 2011 and early 2012. These will be the last new data products of the mission. Various documentation and archived software of various new data products (including the photon list files) are planned for 2012.

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 MAST pages, including this one (as of October 2011).

Close out deliverables (the "GR7")

In early 2011 NASA mandated that the project continue observing through December 31, 2011, while quickly planning on closing out all other ground based activities meant that the project must deliver plan its final deliveries of data products before overall termination of the project in 2012. These products, defined largely by observations made since 2010 February 1 - and in all cases only for observations made with the NUV camera - comprise the GR7. The GR7 consists of the subdeliveries in the third and following bullets. Note again that all observations are carried out using the only the NUV camera.

• A pair of GCAT catalogs. The catalogs are called the ASC and MSC, and they are taken from data in 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 a astronomical source.

• MCAT files for the Kepler Field of View in Cygnus-Lyra. These files (but not the underlying image files) are being delivered early for them to be available through the MAST Kepler/GALEX search page at http://archive.stsci.edu/kepler/kgmatch/search.php
  in support of the Kepler GO proposal Cycle 4. The initial release in October 2011 will have magnitudes extracted that in some cases may have a residual "smear" (noncircular PSF). This may influence the extracted fluxes by a few percent.

• All files associated with new Kepler field observations (previous bullet) will be released as part of the GR7. The smear problem just referred to should be corrected in this final delivery.

• Processing of observations made subsequent to 2010 February 1.

• New observations of the Galactic bulge and of low Galactic latitudes at many new Galactic longitudes.

• Observations of the Magellanic Clouds.

• New observations of M31. These will complement ongoing ground-based observations by the PanSTARRS project.

• Final GII (formerly known as "GI") program observations.

These products will use an improved pipeline system rather with updated calibrations to handle changes in the response of the NUV detector in 2010 and 2011. MAST will post News Corner items that pertain to any changes from GR6 processing. This section will be updated when these deliveries and ingests are completed.

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.