This page is for the CSC 1.1 release. Please see the CSC home page for the latest release.

The CSC-SDSS Cross-match Catalog query interface provided by the CXC is a service which returns a table of sources common to both the Chandra Source Catalog and the Sloan Digital Sky Survey catalog, either all such matched sources or the subset of sources satisfying your (optional) input search criteria. The CSC-SDSS Catalog is essentially a large table of sources and a number of associated CSC and SDSS source properties, which resulted from cross-matching the lists of CSC and SDSS source positions. You may retrieve from the Cross-match Catalog both the CSC and SDSS source properties it includes, and may specify the order in which the search results should be sorted in the output table returned by a query. The available output table options are an HTML table, a tab-delimited ASCII file, or a fixed width ASCII file, with or without column names included.

The catalog was compiled by applying a Bayesian cross-match algorithm developed by Tamas Budavari and Alex Szalay (JHU) to the source lists of the Chandra Source Catalog, Release 1.1, and the Sloan Digital Sky Survey object list, Data Release 7. The algorithm takes into account the catalog positions, the position errors, and the coverage areas of the catalogs.

The Cross-match Catalog contains about 19,000 CSC(R1.1)-SDSS(DR7) source pairs, approximately 10,000 of which are classified as stars by the SDSS, and 9,000 as galaxies.

Questions about the CSC-SDSS Cross-match Catalog should be submitted to the CXC Helpdesk.

There are four steps involved in completing a CSC-SDSS Cross-match Catalog query:

• 1. Selecting the result set

• 2. Specifying optional search criteria

• 3. Specifying the sort order of the result set
• 4. Selecting the output table format

1. Selecting the result set

In the section of the query form titled Select items to be returned in the Result Set, you are to check the box next to each source property you would like returned for all sources found in the search. If you don't check any of the boxes, all source properties will be returned. The source properties are split into five categories: Source identification and matching properties, which lists the CSC and SDSS source identification properties (e.g., the CSC 'MSID' and SDSS 'OBJID' properties), as well as the source properties which describe the quality of the cross-match (e.g., the positional separation of the matched CSC and SDSS sources); the SDSS properties, which are source properties specific to the SDSS catalog; the general Chandra Source Properties contained in the CSC (such as positions); and Chandra Properties based on HRC data and Chandra Properties based on ACIS data which are instrument-specific properties (photometry and variability) for HRC and ACIS.

2. Specifying optional search criteria

If you do not wish to specify any search criteria in the section of the query form titled Enter Optional Search Criteria, i.e., you would like the source properties you selected in step 1 to be returned for all sources in the CSC-SDSS Cross-match Catalog, then leave this section blank. However if you are interested in a subset of the matched sources satisfying specific search criteria, e.g., all matched sources with a hard-to-soft hardness ratio less than zero, then you may enter search criteria of the form:

      A>0,   B=3.0,  C='string',  D!=4.3,  E between 5 and 6,  F in (1,2,3)  
     

   AND    OR    NOT
     

For example:

SDSS_TYPE=3 and SIGNIFICANCE > 3. and HARD_HS < 0. and SEPARATION < 0.04

This query locates all galaxies (classified as such by the SDSS) in the Cross-match Catalog which have a CSC hard-to-soft hardness ratio less than 0, a CSC significance (signal-to-noise ratio) greater than 3, and whose positions in the both catalogs agree to within 0.04 arcseconds. For those of you familiar with SQL: this is just the WHERE clause of an SQL query expression.

There is also a Cone Search feature which allows you to search for all matched sources within a given radius of a location on the sky, e.g., all sources within 10 arcminutes of an input RA and DEC in decimal degrees. Note that a specified cone search will be carried out in conjunction with any search criteria entered into the SQL query field.

3. Specifying the sort order of the result set

In the section of the query form titled Enter the order in which the Result Set is to be sorted, you may enter one or a comma-separated list of columns (corresponding to the source properties you selected in step 1) on which to sort the search results in the output table. For example, entering 'RA' in the provided field will sort the results on the Right Ascension recorded in the CSC, in ascending order. You may add 'DESC' after a column name to sort in descending order, e.g. 'RA DESC'. Leaving the field empty will yield an unsorted table.

4. Selecting the output table format

You can specify the format of the output table of search results in the section of the query form titled Output Format, either an HTML table, a tab-delimited ASCII file, or a fixed width ASCII file. Checking the "Data Only" box will remove the header with column names from the output table.