How to use the 2SLAQ LRG catalogue search

General comments

This search engine for the 2SLAQ LRG catalogue and spectral database is based on the 2QZ search engine. Much of the text below is taken from this, with modifications where appropriate.

With the exception of RA,dec position (see below), all search criteria are 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. 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 interpreted 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

Here you can search for an specific 2SLAQ 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 2SLAQ at the beginning of the full name is not required.

Sample

The LRGs in 2SLAQ were targeted using colour selection criteria based on the SDSS imaging. The table below summarises these selection criteria where

d_perp = (r-i) - (g-r)/8.0

and

c_para = 0.7(g-r) + 1.2(r-i - 0.18).

Sample	d_perp	c_para	i_deV	g-r	r-i
8	> 0.65	>= 1.6	< 19.8	0.5 - 3.0	< 2.0
9	0.55 - 0.65	>= 1.6	< 19.8	0.5 - 3.0	< 2.0
3	> 0.55	>= 1.6	< 19.5	1.0 - 3.0	< 2.0
4	0.45 - 0.55	>= 1.6	< 19.5	1.0 - 3.0	< 2.0
5	0.25 - 0.45	>= 1.6	< 19.5	1.0 - 3.0	< 2.0
6	> 0.55	>= 1.6	< 20.0	1.0 - 3.0	< 2.0

Samples 8 and 9 define the primary and secondary samples and comprise 67% and 27% respectively. 4% of the objects are in Samples 3-6, observed in March and April 2003. Sample 0 consists of the remainder that lie out side the selection boundaries. Further details are given in Cannon et al. (2006).

Magnitudes and colours

You may also select objects based on both their apparent magnitudes and colours. The magnitudes are SDSS model mags and have had a galactic extinction correction applied (based on the work of Schlegel et al. (1998)).

Redshift

Specify redshift range to select.

Data quality

Quality Flag: The quality flag (Q) indicates the reliability of the assigned redshift.
Objects with Q = 1 have no reliable redshift, with Q = 2, 3, or 4 having reliabilities of ~50%, 95% and >99% respectively.

Signal-to-noise ratio: Signal-to-noise is calculated as an average over the entire spectrum.

Data output format

The data are available in a number of formats. The catalogue is a single ASCII file with ~18000 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:

The full catalogue entry of the object.
FITS spectra in a multiple extension format (including spectrum and variance).
Gzipped postscript and PNG plots of the spectra.
40x40 arcsec JPEG postage stamps from the SDSS DR7 cutout server.

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. The spectra are sorted by observation date, but the redshift listed in the table is from the best spectrum (which is listed in the main catalogue file). 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-2SLAQ data, or unobserved objects.

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.

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The 2SLAQ team (Nov 2008)