NED Database
- 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.
Return to NED's FAQ Page.
Back to "About NED".
Back to the NED Feature List.
|