NED Processing Status

(Latest Revision: 19 December 2013)

Unprocessed Catalog Sources versus NED Objects

The Status column returned by the Search Objects, With Unprocessed Catalog Sources service indicates the NED processing status. A Status of S (catalog source) indicates an astronomical observation which has not yet been fully integrated into NED's representation of the hierarchy of the universe. A Status of O (NED object) indicates a physical thing or a group of things in the universe, or a region of space, which has been cross-identified or associated by NED with one or more vetted catalog sources.

Depending on the spatial resolution of the observations, a source of radiation represented by a catalog source entry (row) may contain emission originating from (1) a single astrophysical object (e.g., a galaxy or a star), (2) multiple astrophysical objects (e.g., a pair of galaxies), (3) a region inside a larger physical object (e.g., a star cluster within a galaxy), or (4) an instrumental artifact. The situation gets confusing when we consider that a catalog source name is often also used to identify an astrophysical object (case 1 above). For example, the radio catalog source "3C 84" is also recognized in NED as a physical object, a galaxy also called "NGC 1275". (But note that the NGC is a catalog, and thus NGC 1275 is also a catalog source.) The key point is that NGC 1275 and 3C 84 are both thought to represent visual and radio emission from the same physical object in space (although only approximately, since the radio emission may be more or less concentrated than the optical emission). Also, the universe is hierarchical, so compound objects (e.g., galaxy groups) contain other objects (galaxies), and objects within those objects (e.g., star clusters, stars), etc. NED attempts to keep this all sorted out as new data are published.

Depending on the outcome of an ongoing process involving cross-matching of catalog source parameters (positions, fluxes, diameters, beam size, etc.) with other data in NED, an S entry may later be flagged either as O, meaning it was cross-identified with a previously known NED object, or it had no match and thus became a new NED object (with or without associations to other NED objects). The string "S" or "O" in the Status field simply indicates the current status of the corresponding table row in NED. When you return to NED in the future, you may find that some entries previously identified as S have been promoted to O or added as cross-identifications to other entries, due to new runs or refinements of NED's cross-matching algorithms. If you do not want to see the unprocessed catalog sources (S) that NED knows about which have not yet been cross-matched (or may be artifacts, etc.), the user interface can be used to query only fully integrated NED objects (O) .

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