I. Introduction
4. Distribution Mode for 2MASS Products
a. On-Line Access
i. The NASA/IPAC Infrared Science Archive (IRSA)
- Catalogs:
Logical queries on the All-Sky Release Catalogs and Tables can be made via the General Catalog Query Engine on-line tool. The Catalog Query Engine enables searches on any Catalog attribute, such as position, brightness, color, quality flags, etc., or combinations thereof. Queries may be submitted using either a simple "Query-By-Table" form or with user-customizable SQL input.
Note - The Catalog Query Engine is not designed to support full-downloads of the 2MASS Catalogs. The Catalogs and Ancillary Tables are available in bulk distribution via electronic download and on a DVD-ROM set.
- Atlas and Quicklook Images:
FITS format images from the 2MASS All-Sky Release Image Atlas may be retrieved using the IRSA 2MASS Image Services.
The IRSA/2MASS Image Services are a suite of web-based services that allow users to view and download 2MASS J, H and/or Ks Atlas or Quicklook Images. Images may be requested individually or in a batch mode, and can be specifed by position, object name, region or other 2MASS-specific image attributes such as coadd_key or observation date and scan number.
Important Note - The Survey "Quicklook" Images returned by the 2MASS Image Service are FITS images that are expanded from lossy-compressed Atlas Images. These images are not recommended for quantitative brightness measurements of point or extended sources. Please use the full-fidelity Atlas Images or refer to the Source Catalogs for source photometry.
- Extended Source "Postage Stamp" Images:
Images centered on objects contained in the 2MASS All-Sky XSC can be retrieved using the IRSA 2MASS Extended Source Image Server . Users may specify the coordinate or name of the 2MASS XSC source and the service returns a 3-color JPEG image of the source, basic catalog information, and a 6-d FITS image cube containing the background-subtracted J, H and Ks images, and versions of the images in which foreground stars have been subtracted.
ii. NASA/IPAC Extragalactic Database (NED)
The names, positions and basic photometric information from the XSC have been integrated into the services of the NASA/IPAC Extragalactic Database. NED provides full cross-identification of XSC sources with other extragalactic holdings, and the 2MASS photometry is included in the NED Spectral Energy Distribution databases. 2MASS Extended Source images, including links to the IRSA 2MASS Quicklook Image Server Image Retrieval Service and jpeg previews, are also available in NED. For example, compare the 2MASS images with optical, radio and X-ray images of the NGC 253 galaxy.
b. Electronic Access to Full Catalogs
The 2MASS All-Sky Release Catalogs and Scan Information Table are available in compressed (gzipped) ascii form for bulk download from the NASA/IPAC Infrared Science Archive, at the following site:
https://irsa.ipac.caltech.edu/2MASS/download/allsky/Be aware that the catalog tables are extremely large. You will need approximately 43 GB of disk space to download all of the gzipped tables. Because the data volume is so large, it is not practical to access the data with screen editors. For this reason the tables have been formatted in a manner consistent with convenient loading into a database server. The formats of the Catalog and Tables, contents of the ftp site and useful database loading instructions and validation tests are described in the README_ftp.html and contents.html files available on the download site.
The PSC is divided into 92 separate files, each containing source records that fall in 0.1° declination bins starting with -90° declination. Within each declination bin source entries are ordered by increasing right ascension. The XSC is divided into two files, one containing sources with declination < 0° and the other containing sources with declination > 0°. Within each XSC file the source records are ordered by increasing declination. The Scan Information Table is contained in a single file ordered by increasing scan_key.
c. DVD-ROM Catalog Versions
The 2MASS All-Sky Catalogs and Scan Information Table is available on a limited edition DVD-ROM set. These disks contain only the Catalog Tables and are intended for use by professional astronomers and institutions. The DVD set does not contain the Image Atlas. If you are interested in ordering this product, please send us an email with your name, institution, and full mailing address.
[Last Update: 2015 May 5; R. Cutri, further revisions by S. Van Dyk.]
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