The SWIRE/Chandra Survey: The X-ray Sources

December 2009 • 2009ApJS..185..433W

Authors • Wilkes, Belinda J. • Kilgard, Roy • Kim, Dong-Woo • Kim, Minsun • Polletta, Mari • Lonsdale, Carol • Smith, Harding E. • Surace, Jason • Owen, Frazer N. • Franceschini, A. • Siana, Brian • Shupe, David

Abstract • We report a moderate-depth (70 ks), contiguous 0.7 deg² Chandra survey in the Lockman Hole Field of the Spitzer/SWIRE Legacy Survey coincident with a completed, ultra-deep VLA survey with deep optical and near-infrared imaging in-hand. The primary motivation is to distinguish starburst galaxies and active galactic nuclei (AGNs), including the significant, highly obscured (log N _H > 23) subset. Chandra has detected 775 X-ray sources to a limiting broadband (0.3-8 keV) flux ~4 × 10^-16 erg cm^-2 s^-1. We present the X-ray catalog, fluxes, hardness ratios, and multi-wavelength fluxes. The log N versus log S agrees with those of previous surveys covering similar flux ranges. The Chandra and Spitzer flux limits are well matched: 771 (99%) of the X-ray sources have infrared (IR) or optical counterparts, and 333 have MIPS 24 μm detections. There are four optical-only X-ray sources and four with no visible optical/IR counterpart. The very deep (~2.7 μJy rms) VLA data yield 251 (>4σ) radio counterparts, 44% of the X-ray sources in the field. We confirm that the tendency for lower X-ray flux sources to be harder is primarily due to absorption. As expected, there is no correlation between observed IR and X-ray fluxes. Optically bright, type 1, and red AGNs lie in distinct regions of the IR versus X-ray flux plots, demonstrating the wide range of spectral energy distributions in this sample and providing the potential for classification/source selection. Many optically bright sources, which lie outside the AGN region in the optical versus X-ray plots (f_r /f_x >10), lie inside the region predicted for red AGNs in IR versus X-ray plots, consistent with the presence of an active nucleus. More than 40% of the X-ray sources in the VLA field are radio-loud using the classical definition, R_L . The majority of these are red and relatively faint in the optical so that the use of R_L to select those AGNs with the strongest radio emission becomes questionable. Using the 24 μm to radio flux ratio (q ₂₄) instead results in 13 of the 147 AGNs with sufficient data being classified as radio-loud, in good agreement with the ~10% expected for broad-lined AGNs based on optical surveys. We conclude that q ₂₄ is a more reliable indicator of radio-loudness. Use of R_L should be confined to the optically selected type 1 AGN.

Links

• PREPRINT http://arxiv.org/abs/0910.2675
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2009ApJS..185..433W
• ELECTR https://doi.org/10.1088%2F0067-0049%2F185%2F2%2F433
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2009ApJS..185..433W
• PDF https://iopscience.iop.org/article/10.1088/0067-0049/185/2/433/pdf
• PDF https://stacks.iop.org/0067-0049/185/433/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/185/433
• DATA https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/185/433
• DATA https://cda.harvard.edu/chaser?obsid=5023,5024,5025,5026,5027,5028,5029,5030,5031
• DATA https://irsa.ipac.caltech.edu/bibdata/2009/W/2009ApJS..185..433W.html
• SPIRES http://inspirehep.net/search?p=find+eprint+arXiv:0910.2675