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 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 GammaS Gamma ray source GClstr Cluster of galaxies GGroup Group of galaxies GPair Galaxy pair GTrpl Galaxy triple G_Lens Lensed 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 QGroup Group of QSOs QSO Quasi-stellar object Q_Lens Lensed image of a QSO RadioS Radio 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 !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 Return to beginning of this page. 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