NED Frequently Asked Questions -- NED Database

NED Database

What kind of magnitude is listed in the Basic Data?

How do I read that 19-digit REFCODE of yours?

What do the notations like "NED01", "ID", and "NOTES02" mean?

How often is NED updated?

How complete is NED?

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

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?

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

Is there any information which explains the jargon used in the photometry of objects in NED?

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

What are the object type codes that NED uses?

• Q.: What kind of magnitude is listed in the Basic Data?
  A.: 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 that 19-digit REFCODE of yours?

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

  YYYYPUBLNVVVVMPPPPA

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

  YYYY	The four digits of the year of publication
  PUBLN	The 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)
  Ast..	Astronomy
  IAUC.	IAU Circulars
  MNRAS	Monthly Notices of the Royal Astronomical Society
  Natur	Nature
  PASP.	Publications of the Astronomical Society of the Pacific
  PASJ.	Publications of the Astronomical Society of Japan

  VVVV	Volume number of the journal, right-justified within the four-digit field
  M	Tie-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:

  L	Letters sections in various journals
  p	Pink 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.
  	OR
  	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.

  PPPP	Starting page number of the article, right-justified
  A	First 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 redshift
  ?	a very uncertain (questionable) redshift
  1LIN	a spectroscopic value from a single line, assuming the line is known
  PHOT	estimated using photometry
  EST	an estimated value
  MOD	a modelled value

  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
  BLAGN	broad-line active galactic nucleus
  BlueCG	blue compact galaxy (may be called BCG in the literature)
  BLLAC	BL Lacertae-type object
  BLRG	broad line region
  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
  DLA	damped Lyman-alpha
  DLyA	damped Lyman-alpha
  ERO	extremely red object
  FSRQ	flat spectrum radio QSO
  HEG	high-excitation narrow-line radio galaxy
  HII	HII-type object
  HPQ	high polarization QSO
  LBG	Lyman-break galaxy
  LCG	luminous compact galaxy
  LEG	low-excitation narrow-line radio galaxy
  LINER	low-ionization nuclear emission-line region
  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
  PEG	passive elliptical galaxy
  RLG	radio loud galaxy
  RLQ	radio loud quasar
  RQQ	radio quite quasar
  Sbrst	starburst object
  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
  XBONG	X-ray bright/optically normal 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:

  • B_TC is a corrected total magnitude in the B-band
  • B_J is a B magnitude on the Johnson system
  • U_T is a total magnitude in the U-band
  • V_T is a total magnitude in the V-band
  • R_TC is a corrected total magnitude in the R-band
  • R₂₅C is a corrected R magnitude at the 25th mag arcsec^-2 isophote level

  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
  **	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*	Isolated star (not a member of a particular galaxy)
  Flare*	Flare star
  G	Galaxy
  GammaS	Gamma ray source
  GClstr	Cluster of galaxies
  GGroup	Group of galaxies
  GPair	Galaxy pair
  GTrpl	Galaxy triple
  G_Lens	Lensed 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
  QGroup	Group of QSOs
  QSO	Quasi-stellar object
  Q_Lens	Lensed QSO
  RadioS	Radio source
  Red*	Red star
  RfN	Reflection nebula
  SN	Supernova
  SNR	Supernova remnant
  UvES	Ultraviolet excess 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
  !EmObj	Galactic 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