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Notes on CrossID

The CrossID form allows users to match a list of coordinates with objects in a VSA source and detection tables.

VSA users should select the survey/database release they wish to cross-match with.

table: Then choose the table against which the pairing is to be done. Typically this will be source or detection. See the data overview for a description of source and detection.

Select: Next enter the parameters you wish to extract from the table, the default entry represents the anticipated set of most useful attributes for a given table (Info on defaults). You can append to the default set by adding extra parameters, separated by commas, after default e.g. enter default,htmID,cx,cy,cy in the attributes to select box. If you do not wish the default list to be returned enter your own comma separated list in place of default e.g enter htmID,cx,cy,cy
The schema browser can be used to explore the attributes for a given table. The fewer attributes selected to be returned the quicker requests will run.

Where: The contraints/where box can be used to refine your coss-match, for example you might only want to find galaxies brighter than a a given magnitude, e.g. if querying the LAS source table you might enter mergedClass=1 and j_1mag < 16 and j_1mag > 0 . Note the j_1mag > 0 excludes those objects with default (unmeasured) magnitudes = -0.9999995e9
When you select source as the table to query (priOrSec<=0 or priOrSec=framesetID) should automatically appear in the where box. This clause ensures that objects considered duplicates in the overlap regions are removed. This is typically what users will want but delete as required. So the full where entry for the above example would be
(priOrSec<=0 or priOrSec=framesetID) and mergedClass=1 and j_1mag < 16 and j_1mag > 0 . If the box is submitted empty all objects meeting the proximity criteria will be returned.

Pairing radius: Enter the pairing radius in arcseconds.

Pairing option: Choose whether you want all objects within the pairing radius returned (all nearby objects) or just the closest one (nearest object only). Note if you choose nearest and have statements in the where box then if an object is returned it will be the nearest object that satisfies the where clause rather then necessarily the nearest object.

File: enter the path/filename of the file containing the list of coordinates only, not comments or names. The supplied file should contain the J2000 RA/Dec coordinates of your objects (one object per line) in decimal degrees or sexagesimal. Values in the file should be separated by spaces or commas, for example the following lines will be parsed correctly

117.000, -25.444
118.123 23.34
11 12 13.4 -30 20 10.0

Results: As well as the attributes chosen in Select the results also contain a running ID for the uploaded positions, the uploaded RA and Dec and the angular distance in arcsecs to the matching VSA object: upload_ID,upload_RA,upload_Dec,distance. If you want your results saved to file rather than just the html table summary of the first N rows then choose the file format required. Enter your email address if you wish the job to be placed into the background if it doesn't return after 30 seconds. If you do supply an email please wait until the message appears saying the job has been placed in the background. Note that if no matching objects are found for a given user supplied position a row is still returned but all the table attributes will be set to zero.



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WFAU, Institute for Astronomy,
Royal Observatory, Blackford Hill
Edinburgh, EH9 3HJ, UK

vsa-support@roe.ac.uk
24/1/2014