How to use the 2QZ catalogue search

General comments

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 be used.

Target position:

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) format.

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.:
30.0

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=0/24^h, so  a search with only:
ramax=00 30 0
will be interpretted as ramin=00 00 0 ramax=00 30 0

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=0^h, the search algorithm will also perform a valid search.  For example
ramin=23 30 0 ramax=00 30 0
will result in sources around RA=0^h being selected.
 

Object Names:

Object identification:

There are also a number of sub classes, which are placed after the main classification in parentheses:
 

BAL	broad absorption line QSO
DA	DA white dwarf (hydrogen Balmer line dominated)
DB	DB white dwarf (neutral helium dominated)
DO	DO white dwarf (singly ionized helium dominated)
DZ	DZ white dwarf (calcium H,K dominated)
CV	Cataclysmic variable
DA/M	DA - M dwarf binary
DB/M	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 b_J band with 18.25<b_J <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 b_J and the r plate limit.  For r plate upper limits the (b_J-r) colour is defined as:
(b_J-r)=(b_J-r_lim)-10
The -10 is used to differentiate between normal colours and colours constructed with only an upper limit in the r-band.  Any sources with (b_J-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 the -10).

Redshift:

Specify redshift range to select.

Data quality

Quality Flag: The quality flag contains information on both the reliabilty of the object's type identification and the assigned redshift.
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 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 sky survey.

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