Welcome to the MAST access site for browsing and retrieving GALEX Releases 2 and 3 data. The Galaxy Evolution Explorer (GALEX) is a NASA mission led by the California Institute of Technology aimed at investigating 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 spectroscopy.

During its mission (ongoing) GALEX is also identifying celestial objects for further study in ongoing and future missions. GALEX data is populating a large, unprecedented archive available to the entire astronomical community and to the general public via the MultiMission Archive at Space Telescope Science Institute (MAST). Pipeline processed GALEX data are periodically sent to MAST and ingested into its database. These products can be accessed directly over the web in real time, or in the case of large volume requests by secure ftp.

GALEX was successfully launched on April 28, 2003. 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. These are, respectively, the Nearby Galaxy Survey, Deep, Medium, and All Sky Surveys (imaging) and a somewhat smaller Spectroscopic (imaging) survey. Although originally planned as a 29-month mission, the NASA Senior Review Panel in 2006 recommended that the mission lifetime be extended.

With its UV surveying capabilities, GALEX will complement the functions of the Hubble Space Telescope (HST) and the Far Ultraviolet Spectroscopic Explorer (FUSE), GALEX also complements the ground-based, optical Sloan Digital Sky Survey (SDSS) at optical wavelengths, which will ultimately cover 1/4 of the sky. (The GALEX AIS will cover some 3/4 of the sky.) Users can familiarize themselves with GALEX data products by selecting, browsing, and downloading them. A high-level description of data retrieval modes is provided on the Getting Started page. Help in navigating the website is provided by the GALEX/MAST tutorial.

During the course of the mission, the Project has been releasing data to the public through MAST at discrete times; these are known as "Galex Releases." Following the Early Release Observations the first release, GR1, was released in 2004/5. The GR2, a three-times larger dataset (about 1.5 TB in volume), was released in early 2006. This release superceded the GR1 in quality and sky coverage. A comparably sized GR3 was released recently in January of 2007. Because the GR3 contains only new tiles on the sky and was processed with the same pipeline software, it may be regarded as a supplement to the GR2. Other differences of GR3 with respect to GR2 include addition of Calibration file data ("CAI") and, for the first time, some GI Program data. Users should be aware that MAST will no longer routinely distribute GR1 data when GR4 becomes available, possibly in late 2007.

The Guest Investigator (GI) program complements the general mission objectives. Proposals for the GI Cycle 1 program were announced in the spring of 2004, and so far have continued annually. All GI products are proprietary for six months following the archiving date. The GI data for which proprietary periods have expired now lie in one of two databases. The first is a GI database containing data of mixed quality. These data are therefore not cominglable with other GR data. These data may be accessed at the url website. Note also that these data cannot be searched at the level of individual target names. The second database containing public GI data is the GR database. To differentiate between the two public GI datasets, we call the latter the "GII program" dataset. These data have the same quality as the survey data and one may search on individual target names.