Starting in DR19, we created sdss_id to be a unique identifier for targets within SDSS surveys. Every object on the sky identified as a target for SDSS-V or which has been spectroscopically observed in previous SDSS phases receives an sdss_id. This identifier should be used to match targets between different SDSS products and data releases.
Motivation
As we describe in the cross-match page, SDSS-V cross-matches earlier SDSS data releases as well as a number of other public data releases (e.g., Gaia, 2MASS, WISE, Pan-STARRS, etc.). There are several versions of the cross-match, which themselves need to be linked. We therefore created sdss_id as an overarching identifier, which is unique to individual objects on the sky and can be used to track down their SDSS targeting information, SDSS spectra, and other observations from other surveys included in any of our cross-matches.
Where to find sdss_id
There are two sdss_id tables released in DR19: mos_sdss_id_stacked and mos_sdss_id_flat. mos_sdss_id_stacked matches the catalogids between cross-match versions. These catalogids refer to rows in the mos_catalog table, as described on the cross-match page.
mos_sdss_id_stacked has one row for each and every sdss_id, and has a column for each version of the cross-match indicating which catalogid the given object corresponds to in each cross-match. Importantly, a given catalogid can appear in multiple rows of this table (for example, a TESS Input Catalog source can be resolved into two sources in Gaia eDR3). In general, these issues are rare but can occur.
mos_sdss_id_flat provides a pivoted version of the sdss_id table, for which each row contains a unique sdss_id/catalogid pair. When a catalogid matches to multiple sdss_ids, we recommend selecting the lowest numerical value as the chosen sdss_id. This information is stored in the rank column of mos_sdss_id_flat, where rank==1 is preferred.
Using sdss_id
We provide a tutorial to demonstrate how to use sdss_id.