Searching for Images by Object Name or Coordinates

(Latest Revision: 4 June 2009)

Image Searches by Name

Image Searches by Coordinates

How to Retrieve Compressed FITS Images

Images in NED

NED includes images at various wavelengths of about 2.3 million extragalactic objects of all types. Most of the images are 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.

Digitized Sky Survey images also exist for most optical galaxies and IRAS sources in NED, as well as for many radio sources. The DSS images have been been centered on the NED positions. If errors exist in the positions, the objects may not be centered in the image, or may even be outside the boundaries of the image. We are replacing these images, and revising the NED positions, as we become aware of these problems. Should you find such an error, please send us a message about it so that we can fix the image.

For objects without cutouts from 2MASS or DSS, NED provides images "on-the-fly" from the DSS. After your image search has been completed, you may resize DSS images if they are too small or too large.

Many FITS images have not had World Coordinate System (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 returned by your query if the WCS keywords are missing. Note that all 2MASS and DSS images include the correct WCS information.


Images Searches by Name

NED's name interpreter recognizes most of the well-known prefixed names used in the literature (e.g. NGC 224, IRAS F00400+4059, 1ES 0039+409). NED Standard Names has more information on NED's naming conventions.

Data Entry

Type the name of the object you wish to search for in the "Object name:" box. The NED interface allows substantial freedom in formats and conventions for names, so type the name in any format you wish. When you submit your search, NED's name interpreter will attempt to translate your input into a name that NED recognizes.

If it cannot interpret the name you typed, a page will appear with a message explaining the most likely problem with your input. These usually fall into three categories, all explained in the message. In all three cases, click your browser's "Back" button to go back to the search page, and enter another object name.

(1) If the name you entered has an acceptable catalog name, but the object number within the catalog is not within the range of numbers for that catalog, the page will tell you this. An example is "M111"; there are only 110 entries in the Messier catalog.

(2) If the catalog name itself is ambiguous, the page will list the acceptable possibilities. An example is "A123"; this could be "Abell 123", "Arakelian 123", "Arp 123", "Asiago1 023", or "[RC1] A1203".

(3) If the name interpreter does not recognize the catalog, the page will sometimes suggest alternative catalogs, sometimes not. In either case, click the "Back" button and try another name.

After you have typed in the name of your object, click the "Submit Query" button to initiate the image search.

Results

When a search has completed successfully, the interface opens a new page with a summary listing of the available images for the object. Each listing is accompanied by a small "postage stamp" representation. Click on that to have your browser open a new window showing the image at full resolution (this assumes that your browser supports viewing of GIF files, either internally, or via a helper application). FITS formatted versions of the images may be downloaded by clicking on "Retrieve" in the "FITS File" column of the table. You may also view the "FITS Header", and use Aladin to manipulate the image and overlay catalogs on it. Other information given includes the waveband (in astronomical jargon) used for the image, the image dimensions in arcminutes, the image resolution in arcseconds, the telescope used to obtain the image, and the reference to a published description of the image. You may also change the image size for DSS images.

Digitized Sky Survey images in NED appear courtesy of AURA/STScI.


Images Searches by Coordinates

Through a collaboration with IRSA and the VAO, FITS images archived in NED can now be queried by celestial coordinates and areal coverage. Clicking on the link will take you to a documented page where you may search for images by coordinate or by areal coverage on the sky via a map.


Retrieving Compressed FITS Images

To save disk space and transmission time, the FITS (Flexible Image Transport System) images in NED are compressed using "gzip", a standard UNIX compression utility. We have found that some older versions of Netscape Navigator on UNIX systems remove the ".gz" suffix from these compressed image files during downloading. This will leave a compressed FITS file with a truncated name like "[filename].FITS" instead of the proper "[filename].FITS.gz".

If you encounter this problem, there are several ways to restore the missing suffix:

(A) Exit Navigator, go to the directory where the image was saved, and add the ".gz" suffix to the filename. The file can then be uncompressed using "gunzip" as usual.

(B) Change your Version 3 and earlier Navigator setup as follows:

     1) Click:  "Options"
                "General Preferences"
                "Helpers"

     2) If there is not an entry in the table headed "MIME
        Configuration Files" reading something like "image/x-fits", 
        create one:

        a) click "New",

        b) type in the "Description" box:  FITS Images
                in the "Type" box:         image/x-fits
                in the "Suffix" box:       fits fit fts FITS FIT

        c) in the large "Handle By" box, choose the
           "Unknown: PromptUser" radio button

        d) click "OK".

     3) If there is an entry in the table reading something like 
        "image/x-fits", make sure it matches the set up outlined 
        in Step 2 above by clicking on the entry to highlight it, 
        then click "Edit", and check the table entries.  Click
        "OK" or "Cancel" to close the Edit window.

     4) Click "OK" to close the "Options" window.

     5) Click "Options" again, and finally

     6) If your browser has a "Save Options" menu entry, click it,
        then click "OK" when Navigator says "Options have been saved."

(C) Exit Navigator, go to the directory where your Navigator setup files are stored (usually your home directory) and add the following line to the ".mime.types" file:

image/x-fits                   fit fits fts FIT FITS

While any of these options should correct the problem, the second and third are "permanent" fixes.

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NED Standard Names

Object names are separated into catalog identifier and member identifier. The name interpreter checks the catalog identifier to certify that it points uniquely to a catalog recognized by the database. The name interpreter then checks the member identifier to certify that it corresponds to the conventions of the catalog identified (e.g. is it a sequential number, or a combination of numbers and letters, etc?), and that it does not exceed certain limits (e.g. the number of objects in catalog). The left hand column of the following table contains examples of input names recognized by the interpreter. The right hand column shows the NED standard formats.
n33 NGC 0033
U 12 UGC 00012
M81 MESSIER 081
mk1000 MRK 1000
M 3-4-5 MCG +03-04-005
ZW23.1 CGCG 023-001
1zw23 I Zw 023
PKS0350+23 PKS 0350+23
4C23.7 4C +23.07

Names with square bracket prefixes (e.g. "[HB89]" and "[WB92]") usually come from papers published in journals, while those names with unbracketed prefixes (e.g. "NGC" and "IRAS") usually come from separately published catalogs. There are exceptions, however; examples include "[RC2]" and "87GB". Some names have combination prefixes (e.g. "87GB[BWE91]" and "ABELL 400:[D80]").

Objects in multiple systems without existing unique names are formed by the name of the system itself followed by "NEDnn", where "nn" is a decimal number starting with "01" (example: "ARP 294 NED01" and "ARP 294 NED02"). Similarly, objects found only in catalog notes are given names beginning with the name of the cataloged object followed by "NOTESnn" (example: "UGC 01562 NOTES01" and "UGC 01562 NOTES02"). Sources named in non-optical catalogs or lists, which are later found to be coincident with galaxies but which are not renamed, have "ID" appended to their original names (example: "IRAS 04356+3412 ID"). In this case, the Preferred Object Type is also changed to "Galaxy".

Note that the recognition by the interface of the nomenclature used for the object name does not guarantee that the name exists in the Database. This recognition signals that at present parts of the catalog are in the Database, and that the intent is to eventually include the extragalactic portion of that catalog in NED.

Back to the Image Search Input Page.
Return to beginning of this help page.

Return to NED's Home Page.