GALEX Mission

Welcome to the MAST public access site for browsing and retrieving GALEX Release 4 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 (ongoing) mission GALEX is also identifying celestial objects for further study in both active 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 Galex/MAST 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 Surveys 

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 (NGS), Deep (DIS), Medium (MIS), and All Sky Surveys (AIS:imaging) and a somewhat smaller Spectroscopic (SPECTRA:imaging or "grism") survey. More details on each survey can be found in the GALEX Observer's Guide and the StSci Archive Manual. 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 covers some 3/4 of the sky, and is close to completion.  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.

Public GALEX Releases

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 2004-2005. 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 in January of 2007. Because the GR3 contains only new tiles on the sky and was processed with the same GR2 pipeline software, it may be regarded as a supplement to the GR2.  Users should be aware that MAST will no longer distribute GR1 data, but database access is still available.  The GR4 data are processed with a pipeline processing system inaugurated in late 2007. The GALEX GR5 data release was delivered to MAST is early 2009.  It contains 870 new tiles of sky coverage from the primary mission surveys.  In addition, 266 GR4 tiles were delivered with extended exposure times. Since GR5 was processed with the same pipeline as GR4, it may be considered a supplement to GR4.

Guest Investigator Program

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 object 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 object names.