NED Frequently Asked Questions -- NED Database


  • Q.: What kind of magnitude is listed in the Basic Data?

    These are usually optical magnitudes taken from the astronomical literature, and should be understood as being indicative only. We are adding letters after the magnitudes indicating the band pass to which the magnitude applies. For example, we use "U", "B", "V", "R", and "I" for the standard Johnson and/or Cousins magnitudes in the optical; "p" for photographic magnitudes from e.g. IIa-O or 103a-O plates, "g" for Gunn g-band magnitudes, "j" for magnitudes from III-aJ plates, "J" for 2MASS near-IR magnitudes, and so on.

    We will eventually have all of NED's Basic Data magnitudes flagged with the band passes. In the meantime, the magnitude may have already been included in NED's table of of referenced Photometric Data.

  • Q.: How do I read a 19-digit REFCODE?

    A.: NED reference codes are 19-character strings of the form:


    Unused characters are padded with dots ".". The fields within the string are as follows:

    YYYYThe four digits of the year of publication
    PUBLNThe journal code, left-justified within the five-digit field
    The codes for those journals regularly entered into NED are:
    A&A..Astronomy and Astrophysics
    A&AS.Astronomy and Astrophysics Supplement Series
    AJ...Astronomical Journal
    ApJ..Astrophysical Journal
    ApJS.Astrophysical Journal Supplement Series
    ARep.Astronomy Reports (formerly Soviet Astronomy)
    AstL.Astronomy Letters (formerly Soviet Astronomy Letters)
    IAUC.IAU Circulars
    MNRASMonthly Notices of the Royal Astronomical Society
    PASP.Publications of the Astronomical Society of the Pacific
    PASJ.Publications of the Astronomical Society of Japan

    VVVVVolume number of the journal, right-justified within the four-digit field
    MTie-breaker code. Where ambiguity is possible (e.g. between the main journal section,
    and the "letters" section of a journal), the following characters or digits in this field break the ambiguity:

    LLetters sections in various journals
    pPink pages in MNRAS. (changed to "L" in 1993)
    1, 2, ..., 9,Issue numbers 1 through 9, then "a" through "o", within the same volume of a journal
    0, a, b, c, (e.g. Sky and Telescope, Physics Today).
    ..., o
    A, B, ...Issue designations used by the publisher within the same volume, where each issue starts with page one.
    Two or more articles appearing on the same page within a single issue of a journal
    (e.g. Nature, IAU Circulars) are lettered successively beginning with A - Z.

    PPPPStarting page number of the article, right-justified
    AFirst letter of the first author's last name, or a ":" when no authors are specified for a reference

    More information on reference codes is available in a paper by the NED group.

  • Q.: What do the notations like "NED01", "ID", and "NOTES02" mean?

    A.: These are suffixes which we add to a root name to distinguish physically separate objects which do not otherwise carry separate names. For example, UGC 01562 is a double galaxy, but has only one entry in UGC. In order to include both galaxies in NED with unique names, we add the notation "NED01" and "NED02" to "UGC 01562".

    Similarly, we add "NOTES01" to UGC 01562 to refer to a galaxy included only in the UGC Notes for UGC 01562.

    We typically use the "ID" suffix to indicate that a non-optical source (e.g. an infrared source) has been associated with an otherwise unnamed physical object, usually a galaxy. An example is "IRAS 00182+1130". This has been identified as a galaxy, but not given a separate name. The "ID" notation makes it clear that the object has been reclassified from its original type.

    Other suffixes that we use include "COM" for a nearby companion, not necessarily physically connected to the main object (e.g. "3C 227 COM01"), "ABS" for an absorption line system seen along the line of sight to a background object (e.g. "[HB89] 1727+502 ABS01"), and "ARC" for gravitationally-lensed arcs usually found in rich clusters (e.g. "ABELL 0164 ARC01").

  • Q.: How often is NED updated?

    A.: Usually three or four times a year. A backup working copy of the database is continually updated and checked for problems and errors before being released.

  • Q.: How complete is NED?

    A.: We have tried to get all data published since 1988 into the database, but we invariably miss some and probably have errors as well. We are also constantly changing and refining the Basic Data so you may not always see the same data from month to month (although if the change is large we will generally include a note to that effect).

    Also, we scan the refereed literature only in the larger professional journals. Thus, if data are published only in an observatory monograph, only in preprint, only in a conference proceeding, or only in a thesis, we may well not see it. In these cases, we are happy to add the data to NED when you bring it to our attention.

  • Q.: Are the redshifts reported in NED spectroscopic or photometric? And what do the codes following the redshift mean?

    A.: We adopt spectroscopic redshifts whenever they are available. Sometimes, however, only a photometric redshift is available for an object, or the source of a redshift is not clearly stated in the published paper. In those cases, we flag the redshifts if we know that they are not from spectroscopy. It is still possible, however, for photometric redshifts to slip in unflagged. In cases of doubt, we urge you to go back to the published paper to check the source of the redshifts.

    When we can determine from the reference the Quality of a Basic Data redshift, we attach a code to it. Here is a list of the codes:

    [blank] usually a reliable spectroscopic value
    : an uncertain value
    :: a highly uncertain value
    ? a very uncertain (questionable) value
    1LIN a spectroscopic value from a single line, assuming the line is known
    AVGnn average, based on nn measurements
    CONT continuum, based on Balmer/4000A break (e.g., Kriek et al. 2008ApJ...677..219K)
    EST an estimated value
    FoF Friends-of-Friends (velocity of near neighbor)
    LUM estimated from assumed luminosity for a brightest cluster galaxy (Nelson et al. ApJ 563, 629, 2001)
    MFA a value from a matched filter algorithm (see Postman et al. AJ 111, 615, 1996)
    MOD a modelled value
    PAH redshift determined from PAH features
    PHOT estimated using photometry
    PEAK determined from peak of Gaussian distribution (e.g., Krick et al. 2009ApJ...700..123K)
    PRED a predicted value
    SED a value from a spectral energy distribution
    SPEC an explicitly declared spectroscopic value
    TENT a tentative value
    TOMO a tomographic redshift for a lensing object (see e.g. Hennawi and Spergel ApJ 624, 59, 2005)
    SN the redshift of a host galaxy determined from the expansion velocity of a supernova

  • Q.: What is the source of the morphological types in the NED database? Is there a way to find out where the classifications for each galaxy came from?

    A.: Many of the morphological types in NED come from the Third Reference Catalog of Bright Galaxies (RC3). This is essentially the same system as described in the RC2. Both of these texts should be available from your library.

    We have also added physical classifications from spectroscopy when available (e.g. "Sy1", "BLLAC", "HII", and so forth). These and other classifications come from the literature, but are not yet specifically referenced.

  • Q.: The "Morphology" line of NED's Basic Data sometimes contains abbreviations such as "BCD" and "Sbrst". What exactly do these mean?

    A.: These are usually "standard" abbreviations, taken from the literature, for various sorts of nuclear activity in galaxies. Occasionally, they are simply descriptive abbreviations relating to the morphology of the galaxy.

    Here is a list:

    AGN active galactic nucleus
    BAL broad absorption line
    BEL broad emission line
    BBG Balmer-break galaxy
    BCDG blue compact dwarf galaxy
    BH black hole
    BLAGN broad-line active galactic nucleus
    BLLAC BL Lacertae-type object
    BLAZAR Strongly variable and optically-polarized QSO or BL Lac object, often with strong gamma- and X-ray emission
    BlueCG blue compact galaxy (may be called BCG in the literature)
    BLR broad line region
    BLRG broad line radio galaxy
    BrClG brightest cluster galaxy (may be called BCG in the literature)
    cD supergiant galaxy with an extensive envelope in a cluster
    CNELG compact narrow emission line galaxy
    DANS dwarf amorphous nuclear starburst
    DLA damped Lyman-alpha
    DLyA damped Lyman-alpha
    DOG dust-obscured galaxy
    ELG emission line galaxy
    ERO extremely red object
    FSRQ flat spectrum radio QSO
    HEG high-excitation narrow-line radio galaxy
    HEX high excitation line galaxy
    HII HII-type object
    HPQ high polarization QSO
    IFRS infrared faint radio source
    LAE Lyman-alpha emitter
    LBG Lyman-break galaxy
    LCBG luminous compact blue galaxy
    LCG luminous compact galaxy
    LEG low-excitation narrow-line radio galaxy
    LERG low-excitation radio galaxy (not to be confused with LIRG)
    LEX low excitation line galaxy
    LINER low-ionization nuclear emission-line region
    LIRG luminous infrared galaxy (not to be confused with LERG)
    LPQ low-polarization QSO
    LSB low surface brightness
    NELG narrow-emission-line galaxy
    NLAGN narrow-line active galactic nucleus
    NLRG narrow-line radio galaxy
    NLSy1 narrow-line Seyfert 1
    OFRG Optically-faint radio galaxy
    PAS passive nucleus
    PEG passive elliptical galaxy
    QSO Quasi-stellar object
    RET retired nucleus
    RLG radio-loud galaxy
    RLQ radio-loud quasar
    RQQ radio-quiet quasar
    Sbrst starburst object
    SFRG Submillimeter-faint, star-forming radio galaxy
    Sy1 Seyfert 1
    Sy1.2 Seyfert 1.2
    Sy1.5 Seyfert 1.5
    Sy1.8 Seyfert 1.8
    Sy1.9 Seyfert 1.9
    Sy2 Seyfert 2
    Sy3 Seyfert 3
    ULIRG ultra-luminous infrared galaxy
    XBONG X-ray bright/optically normal galaxy
    XMPG eXtremely Metal-Poor Galaxy

  • Q.: Is there any information which explains the jargon used in the photometry of objects in NED?

    A.: Again, we encourage you to go back to the original papers to fully understand the magnitudes adopted by NED.

    Here are a few examples of magnitudes currently found in NED's detailed photometric data:

    • u, g, r, i, or z usually refers to the five-band SDSS photometric system
    • B is a B-band magnitude on the Johnson system
    • BT is a total magnitude in the B-band
    • BT0 is a total magnitude in the B-band corrected to "face-on" (i.e. inclination = 0 degrees)
    • bj is approximately a B magnitude derived from photometry on a IIIa-J plate
    • R25 is an R magnitude at the 25th mag arcsec-2 isophote level
    • J, H, or Ks usually refers to the three-band 2MASS photometic system

  • Q.: The fields of view from the 2MASS Large Galaxy Atlas (LGA) do not agree between the FITS and GIF versions of the images. Which is correct?

    A.: Both; each is correctly labeled. The FITS images cover the entire image from the LGA, while the GIF images typically cover only the inner parts of the FITS images. The GIFs are used for the quick-look thumbnails in the image list; while the FITS images always cover the entire galaxy, and are suitable for scientific use.

  • Q.: What are the object type codes that NED uses?

    A.: Here is the current list of object types used in NED, listed alphabetically (objects within the Milky Way Galaxy have their types preceded by an exclamation point "!"):
    * Star or Point Source
    ** Double star
    *Ass Stellar association
    *Cl Star cluster
    AbLS Absorption line system
    Blue* Blue star
    C* Carbon star
    EmLS Emission line source
    EmObj Emission object
    exG* Extragalactic star (not a member of an identified galaxy)
    Flare*Flare star
    G Galaxy
    GammaSGamma ray source
    GClstrCluster of galaxies
    GGroupGroup of galaxies
    GPair Galaxy pair
    GTrpl Galaxy triple
    G_LensLensed image of a galaxy
    HII HII region
    IrS Infrared source
    MCld Molecular cloud
    Neb Nebula
    Nova Nova
    Other Other classification (e.g. comet; plate defect)
    PN Planetary nebula
    PofG Part of galaxy
    Psr Pulsar
    QGroupGroup of QSOs
    QSO Quasi-stellar object
    Q_LensLensed image of a QSO
    RadioSRadio source
    Red* Red star
    RfN Reflection nebula
    SN Supernova
    SNR Supernova remnant
    UvES Ultraviolet excess source
    UvS Ultraviolet source
    V* Variable star
    VisS Visual source
    WD* White dwarf
    WR* Wolf-Rayet star
    XrayS X-ray source
    !* Galactic star
    !** Galactic double star
    !*Ass Galactic star association
    !*Cl Galactic Star cluster
    !Blue*Galactic blue star
    !C* Galactic carbon star
    !EmObjGalactic emission line object
    !Flar*Galactic flare star
    !HII Galactic HII region
    !MCld Galactic molecular cloud
    !Neb Galactic nebula
    !Nova Galactic nova
    !PN Galactic planetary nebula
    !Psr Galactic pulsar
    !RfN Galactic reflection nebula
    !Red* Galactic red star
    !SN Galactic supernova
    !SNR Galactic supernova remnant
    !V* Galactic variable star
    !WD* Galactic white dwarf
    !WR* Galactic Wolf-Rayet star