How to use the 2QZ catalogue search
With the exception of RA,dec position (see below),
all search criteria and combined with an AND operation. That is, the returned
objects will satisfy all the specified criteria.
There are no compulsory criteria which must be filled in. You could
if you wished run a search with no criteria set at all and it would return
all objects in the catalogue. This is strongly discouraged though as it
would take a very long time and when the results finally came back, your
browser probably would not be able to display it all anyway. The
only constraint made on the parameters you fill in is that if a search
around a position is made, all three parameters, RA, DEC and RADIUS must
All RA and dec positions may be input in either decimal degrees (ddd.ddd
-dd.ddd) or hours, minutes, seconds (hh mm ss.ss -dd mm ss.ss)
There are two positional search mechanisms.
By position and radius:
A position must be specified in RA,dec coordinates and all objects within
a certain radius of that point are returned. Radius is given in
minutes of arc.
RA format: hours, minutes and seconds (hh mm ss.ss) or decimal
degrees (d.ddd) e.g.:
12 30 00 or 187.6380
DEC format: degrees, minutes and seconds (+/-dd mm ss.s) or
decimal degrees (+/-d.ddd). e.g.:
-30 30 00 or -30.50
RADIUS format: this is always in arcminutes. e.g.:
By maximum/minimum RA and/or declination:
Objects are selected if they have positions within the specified limits.
J2000 coordinates are assumed. Any number of the limits may be input
(none to all). There are special cases to consider when using RA
minimum and/or maximum.
If only one RA limit (minimum or maximum) is entered this is assume
to be bounded at
RA=0/24h, so a search with only:
ramax=00 30 0
will be interpretted as
ramin=00 00 0 ramax=00
If both RA limits are used (minimum and maximum) then the search is
done between the limits. In the special case of a search spanning
RA=0h, the search algorithm will also perform a valid search.
ramin=23 30 0 ramax=00 30 0
will result in sources around RA=0h being selected.
Here you can search for an specific 2QZ object name (IAU format) or some
substring of a name. For example searching for J235935.4-313344 would find
just this object, while searching for J2359 would find all objects which
have names beginning with this string. The 2QZ at the beginning of the
full name is not required.
There are six different object classes listed in the 2QZ catalogue:
||spectrum with one of more broad lines (>1000 km/s)
||spectrum with one or more narrow lines (<1000 km/s)
||galaxy spectrum with no emission lines
||galactic star spectrum
||high signal to noise spectrum (S/N>10) with no identifiable emission
or absorption features
There are also a number of sub classes, which are placed after the main
classification in parentheses:
||broad absorption line QSO
||DA white dwarf (hydrogen Balmer line dominated)
||DB white dwarf (neutral helium dominated)
||DO white dwarf (singly ionized helium dominated)
||DZ white dwarf (calcium H,K dominated)
||DA - M dwarf binary
||DB - M dwarf binary
For a fuller description of the classification scheme see Croom
et al. (2001) - Paper V. or Croom
et al. (2003) - Paper XII.
Magnitudes and colours
You may also select objects based on both their aparent magnitudes and
colours. The survey is flux limited in the bJ band with
18.25<bJ <20.85. Therefore a selection in either
u or r will not be complete to any given flux limits, but will depend on
the colour distribution of the sources. When selecting on the basis
of colour it should also be noted that objects were included in the catalogue
which have only upper limits on their r-band magnitudes from the photographic
r plates. These objects are indicated by given them a colour which
is based on their bJ and the r plate limit. For r plate
upper limits the (bJ-r) colour is defined as:
The -10 is used to differentiate between normal colours and
colours constructed with only an upper limit in the r-band. Any sources
with (bJ-r) < -9 will have only upper limits
in r. When constraining a search with a maximum or minimum r-band
magnitude for r-plate non-detections the r plate limits are used (without
Specify redshift range to select.
Two data quality criteria are available:
Quality Flag: The quality flag contains information
on both the reliabilty of the object's type identification and the assigned
Quality = 10 × ID_quality + redshift_quality
ID_quality and redshift_quality are 1, 2 or 3 meaning
`Good', `Poor' and `Too poor to classify' respectively. Therefore
the best quality objects have a 11 quality flag, while the worst
have a 33 quality flag.
Signal-to-noise ratio: Signal-to-noise is calculated
in the 4000 - 5000 Å band.
Data output format
The data are available in a number of formats. The catalogue is a single
ASCII file with ~50000 lines, one for each object in the catalogue. The
search tool will output a page containing the basic details of each object
selected (name, position, object type, redshift). There are also links
provided for the following:
These links are from the coloured balls on the left hand side of the results
table. In a number of cases we have repeat observation of an object.
There will then be two or more coloured balls for each data type
with the numbers 1, 2... printed on them. Data are sorted by quality rather than
observation date. The first spectrum is the best available observation.
If a coloured ball has a red cross through it, that
data/image is not available on-line. This is typically the case for non-2dF/6dF data.
The full catalogue entry of the object.
FITS spectra in simple or multiple extension format.
Gzipped postscript and PNG plots of the spectra.
2x2 arcmin JPEG and FITS postage stamps from the SuperCOSMOS
Lastly, when setting the maximum number of records, we recommend that
the user doesn't set this value to be too large (> 1000), as the browser will
struggle to display the table. In all cases the catalogue file produced
as output from the search (there is a link to this at the bottom of the
results page) contains all the selected objects, not only those up to the
maximum number of rows.
WWW and CD-ROM formats
The data presented here are available via the world-wide-web at
and on CD-ROM. For ease of use, we have endeavoured to keep both formats
as similar as possible. There are minor differences however, enforced by
the different capabilities of the two media. Most notably, lack of space
on the CD, means that it contains only the simple version of the FITS files
(without extenstions) and does not contain postscript images of the spectra
or SuperCOSMOS postage stamp
If you require the data which is unavailable on the CD you can obtain them
from the 2QZ website.
Back to 2QZ home
Back to Spectroscopic catalogue home
The 2QZ team (July 2003)