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Getting Started with GALEX

All GALEX observations are made through a beam-splitter allowing light to be recorded by far-UV and near-UV detectors in either direct-imaging and spectroscopic (grism) modes. The wavelength bandpasses of these detectors are in the near-UV (1800-2800 Angstroms) and far-UV (in the range 1400-1800 Angstroms). Comprehensive technical information can be obtained at the GALEX/Caltech website or through a FAQ pages. The direct-imaging All Sky Survey, (direct imaging, completed in 2007) covers about 2/3 of the sky from (generally) short single visits of a few hundred seconds). Users should be aware that some regions of the Galactic Plane, the Magellanic Clouds, and bright stars (m(AB) < 9) were not observed in order to prevent damage to the detectors.

Data Searches:
Data selection, browsing, and retrieval proceeds by making queries in the "Search and Retrieval" tab in the left gutter. By far the most popular is the GalexView site, which operates with Flash technology and offers a wide range of options for data browsing, searching and downloads not available with other MAST tools. In the past MAST has offered several options to browse and download data through its pages.

A second, though, dated method is to use the "Simple Form. MAST has discontinued updating of this form, although many users still find it useful because it mimics the functionalities of data search pages for other MAST missions. Also, we have deprecated but otherwise allow access to a partially dated GALEX tutorial site.

A second search form is the SQL search form. This form allows one to find data to customized queries on GALEX fields that may or may not be visible on our other forms. Search queries are written by SQL syntax, and a text box is provided for this purpose. SQL-challenged users may consult a drop-down menu and submit customized requests on objects or sky tiles by modifying any of these programmed queries. [If you would like to use this form and are not SQL-savvy, drop us a line ( and we will help you construct a specialized request in this form.] Clicking on "Execute" returns a table embedded in the search results form; the user is free to choose the format of this table as html (default), Comma Separated Value, or VOTable.

GR data discovery may be executed in yet another manner by clicking on one of the Search Tile Catalog selections in the Search and Retrieval tab, for example the All Surveys selection. The user is able either to enter coordinates for a search or to load a full table of all tiles in the survey. The resulting tile list permits one to browse the far-UV, near-UV jpeg images of a tile of interest and/or to download individual products for the tile. In the latter case, the user may decide whether to download only selected data products (FITS format), a designated set of "minimum recommended files" suggested by the project, all files, or only a catalog of the files. The user should be cautioned that the products downloaded will include those for all objects in the sky tile.

Text descriptions of GALEX pipeline file types:
The array of files generated by the GALEX pipeline can be baffling to the uninitiated and even experienced users. MAST has ingested all files delivered to it by the GALEX pipeline processing software. Most files have been given "one line" definitions, and occasionally more developed descriptions. Several files have been ingested that have no meaning other than to the pipeline processing staff at Caltech. In the former category, we have listed the file names in TABLE 1 of the Documentation/MAST/General tab of the left menu of our web pages. Additional (though often obsolete) descriptions can be found on the Goddard GI office until they are removed in the spring of 2012. For succinct descriptions of GALEX files one has a choice of either going to the SQL query page and typing into the open box "select * from fileDescriptions" (then clicking on "Execute") or finding file descriptions by following the "description" columns links in a "Files available for download" table for either image (image example) or grism (grism example) files, which one can get to through the surveys search form referred to above.

Finding descriptions of column headers (keywords):
The columns in the database that the user sees on the Files Available for download page, particularly those of the mcat ("master catalog") file are taken from the FITS header keywords of the datafiles. These keywords are renamed in the database. These names can be found in the Database Info--> Tables pages. Succinct definitions of these columns can be obtained on line either by looking in the FITS keyword headers in the datafiles or by entering an appropriate "select" query the SQL Search Form, and clicking "Execute." This will return a list of Tables containing the column name of interest. For detailed explanations of the column names please consult the Caltech column description page. Caltech has provided an excellent series of pages of Technical Documentation on GALEX.

All comments concerning GALEX data should be sent to MAST or the GI office and not to the Caltech project office directly. Questions that MAST can not or should not answer will be immediately directed to the Project or GI office, as appropriate.

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4/26/2022 3:14:49 PM