Chandra Deep Field South: The 1 Ms Catalog

Abstract

In this paper we present the source catalog obtained from a 942 ks exposure of the Chandra Deep Field South (CDFS), using the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. Eleven individual pointings made between 1999 October and 2000 December were combined to generate the final image used for object detection. Catalog generation proceeded simultaneously using two different methods; a method of our own design using a modified version of the SExtractor algorithm, and a wavelet transform technique developed specifically for Chandra observations. The detection threshold has been set in order to have less than 10 spurious sources, as assessed by extensive simulations. We subdivided the catalog into four sections. The primary list consists of objects common to the two detection methods. Two secondary lists contain sources which were detected by (1) the SExtractor algorithm alone and (2) the wavelet technique alone. The fourth list consists of possible diffuse or extended sources. The flux limits at the aimpoint for the soft (0.5-2 keV) and hard (2-10 keV) bands are 5.5 × 10-17 erg s-1 cm-2 and 4.5 × 10-16 erg s-1 cm-2, respectively. The total number of sources is 346; out of them, 307 were detected in the 0.5-2 keV band, and 251 in the 2-10 keV band. We also present optical identifications for the cataloged sources. Our primary optical data are R band imaging from VLT/FORS1 to a depth of R ~ 26.5 (Vega). In regions of the field not covered by the VLT/FORS1 deep imaging, we use R-band data obtained with the Wide Field Imager (WFI) on the ESO-MPI 2.2 m telescope, as part of the ESO Imaging Survey (EIS), which cover the entire X-ray survey. We found that the FORS1/Chandra offsets are small, ~1''. Coordinate cross-correlation finds 85% of the Chandra sources covered by FORS1 R to have counterparts within the 3 σ error box (15 depending on off-axis angle and X-ray signal-to-noise). The unidentified fraction of sources, approximately ~10%-15%, is close to the limit expected from the observed X-ray flux to R-band ratio distribution for the identified sample.