The 172 ks Chandra exposure of the LALA Bootes field: X-ray source catalog

J. X. Wang, S. Malhotra, J. E. Rhoads, M. J.I. Brown, A. Dey, T. M. Heckman, B. T. Jannuzi, C. A. Norman, G. P. Tiede, P. Tozzi

Research output: Contribution to journalArticle

23 Scopus citations

Abstract

We present an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha survey (LALA) Bootes field, obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on board the Chandra X-Ray Observatory. This is one of the deepest Chandra images of the extragalactic sky; only the 2 Ms Chandra Deep Field North (CDF-N) and 1 Ms Chandra Deep Field South (CDF-S) are substantially deeper. In this paper we present the X-ray source catalog obtained from this image, along with an analysis of source counts and optical identifications. The X-ray image is composed of two individual observations obtained in 2002 and reaches 0.5-2.0 and 2.0-10.0 keV flux limits of 1.5 × 10 -16 and 1.0 × 10 -15 ergs cm -2 s -1, respectively, for point sources near the aim point. A total of 168 X-ray sources were detected: 160 in the 0.5-7.0 keV band, 132 in the 0.5-2.0 keV band, and 111 in the 2.0-7,0 keV band. The X-ray source counts were derived and compared with those from other Chandra deep surveys; the hard X-ray source density of the LALA Bootes field is 33% higher than that of CDF-S at the flux level of 2.0 × 10 -15 ergs cm -2 s -1, confirming the field-to-field variances of the hard-band source counts reported by previous studies. The deep exposure resolves ≳72% of the 2.0-10.0 keV X-ray background. Our primary optical data are R-band imaging from the NOAO Deep Wide-Field Survey (NDWFS), with a limiting magnitude of R = 25.7 (Vega, 3 σ, and 4″ diameter aperture). We have found optical counterparts for 152 of the 168 Chandra sources (90%); 144 of these are detected in the R-band image, and eight have optical counterparts in other bands (either B W, V, I, or z′). Among the R-band nondetected sources, not more than 11 of them can possibly be at z > 5, based on the hardness ratios of their X-ray emission and nondetections in bluer bands (B W V). The majority (∼76%) of the X-ray sources are found to have log(f X/f R) within 0.0 ± 1; these are believed to be AGNs. Most of the X-ray-faint/optically bright sources [log(f X/f R) < -1.0] are optically extended; these are low-z normal galaxies or low-luminosity AGNs. There is also a population of sources that are X-ray overluminous for their optical magnitudes [log(f X/f R) > 1.0], which are harder in X-ray and are probably obscured AGNs.

Original languageEnglish (US)
Pages (from-to)213-229
Number of pages17
JournalAstronomical Journal
Volume127
Issue number1 1777
StatePublished - Jan 1 2004
Externally publishedYes

Keywords

  • Catalogs
  • Galaxies: active
  • Galaxies: high-redshift
  • X-rays: difluse background
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Wang, J. X., Malhotra, S., Rhoads, J. E., Brown, M. J. I., Dey, A., Heckman, T. M., Jannuzi, B. T., Norman, C. A., Tiede, G. P., & Tozzi, P. (2004). The 172 ks Chandra exposure of the LALA Bootes field: X-ray source catalog. Astronomical Journal, 127(1 1777), 213-229.