Guide to NED Image Results Page

(Latest Revision: 4 June 2009)

This page displays the results of your image search, and shows the following information:

  • A summary line showing the name of the object you requested. This is linked to NED's object database, allowing you to retrieve the data and literature references currently stored by NED for the object.
  • A list, preceded by a header line, of the images and maps which NED currently has for your object. The information given in this list:
    • A "postage stamp" preview of the GIF or JPEG version of the image; clicking on this will retrieve the GIF or JPEG image and -- if your browser is configured to display GIF and/or JPEG images -- display it.
    • The size in KB of the corresponding FITS or JPEG file of the image, and a "Retrieve" option which allows you to download the FITS or JPEG image to your machine.
    • A "More Information" option which shows you the FITS header for FITS-formatted versions of the image, or the caption -- from the source article -- of the figure or map.
    • A "View and Overlay" option with a clickable icon to start the Aladin image tool, if the image supports this. This Java applets allows you to examine the NED image in detail, overlay catalogs on it, and retrieve data for objects in the field from NED, SIMBAD, VizieR, and other archives. If the FITS header does not contain enough information to allow Aladin to operate correctly, a warning message to that effect appears in this column. In particular, many images do not contain World Coordinate System (WCS) information, so cannot be used for any astrometric purpose, including derivation of accurate positions.
    • The waveband in which the image was obtained, in standard astronomical jargon, and the wavelength associated with that waveband.
    • The image size in arcminutes, and -- for Digitized Sky Survey images -- an option to change the image size.
    • The resolution (pixel size) of the image in arcseconds.
    • The telescope with which the image was obtained.
    • The literature reference which gives more information on the image. This is linked to NED's bibliographic database, allowing you to see the title and/or abstract for the paper.
  • Many FITS images have not had WCS information put into their headers and cannot be used for any astrometric work, including the derivation of accurate positions. NED includes a warning to that effect in the image list (see "View and Overlay" above) if the WCS keywords are missing.
    Please note that the optical images from Frei et al., AJ 111, 174, 1996 have had all foreground stars and background galaxies removed.

    NED includes images for extended sources from the final release of the The Two Micron All-Sky Survey. Here is a brief description of 2MASS, the extended source database, and the extended source images, courtesy of Tom Jarrett and the 2MASS Team.

    The Two Micron All-Sky Survey (2MASS) is a ground-based, all-sky survey that utilizes the near-infrared band windows of J (1.11 - 1.36 µm), H (1.50 - 1.80 µm) and Ks (2.00 - 2.32 µm). Two dedicated 1.3-m telescopes, one covering the most northern declinations one covering the most southern declinations, were designed specifically for 2MASS to provide all-sky uniformity. The 2MASS database includes both point and extended (i.e. resolved) sources extracted from "Atlas" images, each 8.5' X 16' in angular size with 1" pixels. Further information can be found in the 2MASS Data Release Documentation.

    2MASS extracts extended sources in both tabular and image format. Each extended source includes a small image data cube, representing the J, H and Ks-band "postage stamp" images (planes 1, 2 and 3, respectively), extracted from the full resolution Atlas images. The size of the cube is dynamically selected, scaled according to the measured angular size of the extended source, ranging from 21 to 101 pixels. The pixel scale is 1" per pixel, with a true PSF resolution of about 2.5" (FWHM). The size of the "postage stamp" images are adequate for most 2MASS galaxies, but for the largest galaxies (typically Ks < 9th mag) the images may not be large enough, resulting in clipped outer isophotes. The full-sized Atlas images should be consulted for the largest galaxies (size > 2'). The "stamp" image header contains the following information: catalog identification (e.g. NED name, if any), observation date and time, equatorial coordinate information, median background level before removal and the background "noise", PSF "shape" value (representing the radial extent of the PSF at the time of the observation), zero point calibration magnitudes and the airmass. Further information can be found in Jarrett et al., AJ 119, 2498, 2000 and in the on-line version of the paper.

    For quick viewing, the J, H, and Ks images have been combined to form a 3-color RGB jpeg image: the J-band image is assigned blue intensity levels, H green intensity levels and Ks red intensity levels. The color range was assigned such that a galaxy of color J-K = 1.0 and H-K = 0.28 appears white. Galaxies with colors J-K > 1 will appear correspondingly redder, and galaxies with J-K < 1 will appear correspondingly bluer. The basic near-infrared properties of galaxies separated by morphological type are illustrated and described in Jarrett, PASP 112, 1008, 2000 and in the on-line version of the paper.

    Questions, comments and suggestions regarding this publication may be directed to the 2MASS Help Desk or to Tom Jarrett.

    We gratefully acknowledge the many individuals who have already sent images in machine-readable formats for integration into NED. Digitized Sky Survey images in NED appear courtesy of AURA/STScI.

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