Chandra Source Catalog (CSC)

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Summary
Observational goals and requirements
Target selection and survey implementation
Targeting generations used in early FPS operations
Targeting generation used during SDSS-V plate operations
Spectroscopic data released in DR19

Summary

The Chandra Source Catalog (CSC) followup program uses SDSS-V spectroscopy to characterize the optical/NIR counterparts of Chandra X-ray sources. Spectra will provide redshifts and source classifications for AGN, galaxies and stars with active X-ray emission detected in the Chandra Source Catalog that have been matched to counterparts in the PanSTARRS-1, Gaia DR2, and 2MASS catalogs. Chandra X-ray imaging provides excellent sensitivity and unparalleled spatial resolution, unveiling a different population of sources than other X-ray missions.

For thousands of X-ray sources from Chandra (CSC2 catalog), plotted are the X-ray flux and optical magnitudes of positionally matching optical/IR counterparts. In this figure, plotted cases are restricted to those for which the counterpart also has an extant DR16/archival SDSS spectrum; color coding denotes the SDSS (pipeline) spectral classification of the likely optical/IR counterpart. The precise, arcsec-level Chandra X-ray positions insure added confidence in the X-ray/optical counterpart match, and the SDSS spectra then reveal the classifications/natures of the X-ray sources. In SDSS-V, the CSC program anticipates follow-up BOSS or APOGEE spectra to identify the natures/classifications of ~10^3.5 additional Chandra X-ray source counterparts. [Figure courtesy of Paul Green, CfA/SAO].

Observational goals and requirements

The BHM CSC project seeks to gather optical and IR spectroscopy for a large sample of X-ray selected sources discovered (mostly) serendipitously via uniform processing of the Chandra data archive – the Chandra Source Catalogue version 2.0.

For the majority of the CSC sources, the immediate goal is to obtain redshifts and classifications for the optical counterparts to the X-ray sources (selected from the PanSTARRS1 and Gaia DR2 catalogues). For a smaller subset of CSC sources, the X-ray detections are associated with NIR-bright 2MASS objects. For these targets, expected to be Galactic stars, we aim to collect APOGEE H-band spectroscopy for classification purposes.

Target selection and survey implementation

CSC targets require either optical BOSS spectroscopy, or APOGEE NIR spectroscopy.

CSC targets having existing SDSS archival spectroscopy are de-prioritized w.r.t. unobserved targets

BOSS exposure time requests (cadences) are determined according to apparent magnitude, based on past experience obtaining redshifts for counterparts to X-ray sources.

Further details of the algorithms and criteria used to select CSC target cartons are given in the links below.

Targeting generations used in early FPS operations

The ‘v0.5.2’, ‘v0.5.3’ and ‘v0.5.5’ targeting generations were used during initial SDSS-V/FPS science operations (2022-2023). These three generations are identical from the point of view of CSC targeting. In addition, an earlier targeting_generation (‘v0.5.epsilon-7-core-0’) was used for FPS commissioning observations, which contains earlier versions of the CSC cartons.

Below is a list of BHM CSC cartons that were considered in the ‘v0.5.2’, ‘v0.5.3’ and ‘v0.5.5’ targeting generations (the carton names link to detailed descriptions):

Below is a list of BHM CSC cartons that were considered in the ”v0.5.epsilon-7-core-0′ targeting generation (the carton names link to detailed descriptions):

Targeting generation used during SDSS-V plate operations

The ‘v0.plates’ targeting generation was used during the first year of SDSS-V operations at APO when the old plug plate system was still in place. We included early versions of the AQMES cartons during this phase, as listed below (the carton names link to detailed descriptions):

Spectroscopic data released in DR19

The numbers of BHM CSC BOSS spectra in DR19, and the sky distribution of observed CSC target are illustrated in the figure and table below.

The sky density of BHM CSC targets that have at least one spectrum in DR19.

(First)Carton name	“daily” coadd spectra	“epoch” coadd spectra	“allepoch” coadd spectra	Unique targets
bhm_csc_boss_dark	11392	7858	2891	2908
bhm_csc_boss	6930	5023	4149	4247
bhm_csc_boss_bright	749	344	184	198

Number of SDSS DR19 BOSS BHM Chandra Source Catalog spectra associated with each carton (considering only the FIRSTCARTON label for each spectrum). Target uniqueness is determined via SDSS_ID.

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