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XBOOTESOID - XBOOTES: NDWFS Bootes Field Optical & Near IR Counterparts

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Overview

The XBootes Survey is a 5 ks Chandra survey of the Bootes Field of the NOAO Deep Wide-Field Survey (NDWFS). This survey is unique in that it is the largest (9.3 square degrees) contiguous region imaged in X-ray with complementary deep optical and near-infrared (near-IR) observations. The authors present a catalog of the optical counterparts to the 3213 X-ray point sources detected in the XBootes survey. Using a Bayesian identification scheme, they successfully identified optical counterparts for 98% of the X-ray point sources. The optical colors suggest that the optically detected galaxies are a combination of z < 1 massive early-type galaxies and bluer star-forming galaxies whose optical AGN emission is faint or obscured, whereas the majority of the optically detected point sources are likely quasars over a large redshift range. This large-area, X-ray-bright, optically deep survey enables the authors to select a large subsample of sources (773) with high X-ray to optical flux ratios (fX/fo > 10). These objects are likely high-redshift and/or dust-obscured AGNs. These sources have generally harder X-ray spectra than sources with 0.1 < fX/fo < 10. Of the 73 X-ray sources with no optical counterpart in the NDWFS catalog, 47 are truly optically blank down to R ~ 25.5 (the average 50% completeness limit of the NDWFS R-band catalogs). These sources are also likely to be high-redshift and/or dust-obscured AGNs.

The 9.3 square degrees region of sky chosen to match the area covered with the NDWFS was observed by ACIS-I on the Chandra X-Ray Observatory over a 2 week time interval in 2003 March and April. The data were taken in 126 separate pointings, each observed for ~ 5 ks. The CIAO 3.0.2 wavelet detection algorithm (wavdetect; Freeman et al. 2002) was used to detect X-ray sources in the total (0.5 - 7.0 keV) band data. A probability threshold of 5 x 10-5 was chosen as the best compromise between maximizing the completeness while minimizing the number of spurious detections. The X-ray catalog comprises 3293 unique X-ray sources with >= 4 counts in the total-band images (Paper II). The authors expect only ~ 35 of these sources to be spurious in the full survey (Paper II). For the matching with cataloged optical counterparts, the authors only considered the 3213 X-ray sources that overlap with the NDWFS area. The authors include all multiply matched sources with >1% probability of being the correct optical counterpart.

This table contains the X-ray and optical characteristics of the matched optical/X-ray catalog for the Chandra sources in the XBootes and NDWFS survey, and is Version 1.0, dated 21st June 2005.


Catalog Bibcode

2006ApJ...641..140B

References

The Chandra XBootes Survey. III. Optical and Near-Infrared Counterparts
     Brand K., Brown M.J.I., Dey A., Jannuzi B.T., Kochanek C.S., Kenter A.T.,
     Fabricant D., Fazio G.G., Forman W.R., Green P.J., Jones C.J.,
     McNamara B.R., Murray, S.S., Najita J.R., Rieke M., Shields J.C.,
     Vikhlinin, A.
    <Astrophys. J. 641, 140 (2006)>
    =2006ApJ...641..140B

This table is the full matched X-ray and optical/IR catalog of the XBootes catalog (Murray et al. 2005, ApJS, 161,1; Kenter et al. 2005, ApJS, 161,9) and the NDWFS catalogs (Data release 3; Jannuzi & Dey 1999, ASP, 191, 111). The optical data is available at http://www.noao.edu/noao/noaodeep and http://archive.noao.edu/nsa/ and will be described by Jannuzi et al. (in prep.). The near-IR data will be described by Dey et al. (in prep.). The matched optical catalogs are reproduced from Brand et al. (2006). The X-ray data in this table is reproduced from Kenter et al. 2005, ApJS, 161, 9. We request that any use of this dataset should reference both these papers (Kenter et al. 2005 and Brand et al. 2006).


Provenance

This table was created in November 2006 by the HEASARC based on the file xbootes_cat_xray_opt_IR_21jun_v1.0.txt obtained from the NOAO ftp area ftp://archive.noao.edu/pub/catalogs/xbootes/ .

Parameters

Xray_Name
The IAU-registered name for the X-ray source, based on the J2000 equatorial coordinates and the 'CXOXB' prefix (for Chandra X-Ray Observatory XBootes survey).

RA_Xray
The Right Ascension of the X-ray source in fixed J2000 coordinates. The RA was given in J2000 equatorial coordinates and to a precision of 0.01 seconds of time in the original source table. The positions were estimated by iteratively centroiding the counts within the 50% encircled energy radius of the Chandra ACIS point-spread function (PSF).

Dec_Xray
The Declination of the X-ray source in fixed J2000 coordinates. This was given in J2000 equatorial coordinates and to a precision of 0.01 arcseconds in the original source table. The positions were estimated by iteratively centroiding the counts within the 50% encircled energy radius of the Chandra ACIS point-spread function (PSF).

RA_Xray_Adj
The Right Ascension of the X-ray source in fixed J2000 coordinates, shifted to the NDWFS astrometric frame. This parameter was given in J2000 equatorial coordinates and to a precision of 0.01 seconds of time in the original source table.

Dec_Xray_Adj
The Declination of the X-ray source in fixed J2000 coordinates, shifted to the NDWFS astrometric frame. This parameter was given in J2000 equatorial coordinates and to a precision of 0.01 arcseconds in the original source table.

Error_Radius
The positional unceratinty in the X-Ray source position, in arcseconds.

FB_Counts
The counts in the X-ray source in the full band (0.5 - 7 keV). The total counts from each X-ray source were determined within the 90% encircled energy radius (see Paper I for details). No corrections were made for the remaining flux expected to fall outside this radius.

SB_Counts
The counts in the X-ray source in the soft-band (0.5 - 2 keV). The total counts from each X-ray source were determined within the 90% encircled energy radius (see Paper I for details). No corrections were made for the remaining flux expected to fall outside this radius. The counts in the soft band were determined in the soft-band image using the position and 90% encircled energy radius from the total-band image.

HB_Counts
The counts in the X-ray source in the hard-band (2 - 7 keV). The total counts from each X-ray source were determined within the 90% encircled energy radius (see Paper I for details). No corrections were made for the remaining flux expected to fall outside this radius. The counts in the hard band were determined in the hard-band image using the position and 90% encircled energy radius from the total-band image.

FB_Flux
The X-Ray flux in the full band (0.5 - 7 keV). To estimate the X-ray flux for each source, a local background was calculated and subtracted from the net counts. Telescope vignetting results in an effective exposure time that varies with X-ray energy and position on the image (dropping to ~ 20% near the edges of the field). To account for this, the authors multiply the background-subtracted counts by the ratio of the average exposure time (5 ks) to the effective exposure time at the source position. They also divide by the fractional effective area at the source position. Assuming a power-law spectrum with photon index Gamma = 1.7 and the Galactic H I column density of 1 x 10^20 cm^-2 (Stark et al. 1992), a 4 count source in this survey corresponds to 7.8 x 10^-15, 4.7 x 10^-15, and 1.5 x 10^-14 ergs cm^-2 s^-1 in the 0.5 - 7, 0.5 - 2, and 2 - 7 keV bands, respectively. This corresponds to a total-band X-ray luminosity of L_x = 2 x 10^41, 4 x x 10^43, and 6 x 10^44 ergs s^-1, at z = 0.1, 1, and 3, respectively.

FB_Flux_Error
The uncertainty in the full-band X-Ray flux.

SB_Flux
The X-Ray flux in the soft band (0.5 - 2 keV). To estimate the X-ray flux for each source, a local background was calculated and subtracted from the net counts. Telescope vignetting results in an effective exposure time that varies with X-ray energy and position on the image (dropping to ~ 20% near the edges of the field). To account for this, the authors multiply the background-subtracted counts by the ratio of the average exposure time (5 ks) to the effective exposure time at the source position. They also divide by the fractional effective area at the source position. Assuming a power-law spectrum with photon index Gamma = 1.7 and the Galactic H I column density of 1 x 10^20 cm^-2 (Stark et al. 1992), a 4 count source in this survey corresponds to 7.8 x 10^-15, 4.7 x 10^-15, and 1.5 x 10^-14 ergs cm^-2 s^-1 in the 0.5 - 7, 0.5 - 2, and 2 - 7 keV bands, respectively. This corresponds to a total-band X-ray luminosity of L_x = 2 x 10^41, 4 x x 10^43, and 6 x 10^44 ergs s^-1, at z = 0.1, 1, and 3, respectively.

SB_Flux_Error
The uncertainty in the soft-band X-Ray flux.

HB_Flux
The X-Ray flux in the hard band (2 - 7 keV). To estimate the X-ray flux for each source, a local background was calculated and subtracted from the net counts. Telescope vignetting results in an effective exposure time that varies with X-ray energy and position on the image (dropping to ~ 20% near the edges of the field). To account for this, the authors multiply the background-subtracted counts by the ratio of the average exposure time (5 ks) to the effective exposure time at the source position. They also divide by the fractional effective area at the source position. Assuming a power-law spectrum with photon index Gamma = 1.7 and the Galactic H I column density of 1 x 10^20 cm^-2 (Stark et al. 1992), a 4 count source in this survey corresponds to 7.8 x 10^-15, 4.7 x 10^-15, and 1.5 x 10^-14 ergs cm^-2 s^-1 in the 0.5 - 7, 0.5 - 2, and 2 - 7 keV bands, respectively. This corresponds to a total-band X-ray luminosity of L_x = 2 x 10^41, 4 x x 10^43, and 6 x 10^44 ergs s^-1, at z = 0.1, 1, and 3, respectively.

HB_Flux_Error
The uncertainty in the hard-band X-Ray flux.

Hardness_Ratio
The X-Ray hardness ratio HR defined as HR = (H-S)/(H+S) where H is the hard-band counts (hb_counts) and S is the soft-band counts (sb_counts).

Hardness_Ratio_Pos_Err
The positive error in the X-Ray hardness ratio HR.

Hardness_Ratio_Neg_Err
The negative error in the X-Ray hardness ratio HR,

ObsID
The Chandra Observation Identifer of the X-Ray pointing in which the source was detected.

Opt_Ctrpart_Prob
The probability of the X-Ray source having an optical counterpart.

Num_Opt_Ctrparts
Th number of optical sources with a > 1% probability of being associated with the X-Ray source.

Optical_Rank
The optical rank, where 1 = `Most Probable, in running order to the least probable, of the counterpart to the X-ray source.

Bayes_Match_Prob
The Bayesian probability that the optical source is the true optical counterpart to the X-ray source.

Opt_Id_Flag
The optical identification flag: 1 -- optical ID, -1 -- no optical ID. In cases of no optical ID being the most probable identification, the following flag values have been applied manually:

   -3 -- no optical ID, but source obscured by nearby star/missing data
   -2 -- no optical ID, but X-ray position is close to optically bright galaxy
         (source is either obscured by or associated with the galaxy
   -1 -- 'true' no optical ID (optical image is truly blank)
  

Name
The NDWFS optical name (null if no optical ID).

RA
The Right Ascension of the optical counterpart to the X-ray source in the selected equinox (null if no optical ID). This was given in J2000 equatorial coordinates and to a precision of 0.01 seconds of time in the original source table.

Dec
The Declination of the optical counterpart to the X-ray source in the selected equinox (null if no optical ID). This was given in J2000 equatorial coordinates and to a precision of 0.01 arcseconds in the original source table.

LII
The Galactic Longitude of the optical counterpart to the X-ray source.

BII
The Galactic Latitude of the optical counterpart to the X-ray source.

Offset
The offset between the optical and X-Ray positions, in arcseconds.

Bw_Mag
The B_W band magnitude (Vega; null if no optical ID; -1: no data in this band (this may occur for a small number of sources for which the position on the optical image coincides with a masked-out region due to a nearby bright star, cosmic ray, or other problem), 0: no detection in this band [but detected in another band]).

Rmag
The R-band magnitude (Vega; null if no optical ID; -1: no data in this band (this may occur for a small number of sources for which the position on the optical image coincides with a masked-out region due to a nearby bright star, cosmic ray, or other problem), 0: no detection in this band [but detected in another band]).

Imag
The I-band magnitude (Vega; null if no optical ID; -1: no data in this band (this may occur for a small number of sources for which the position on the optical image coincides with a masked-out region due to a nearby bright star, cosmic ray, or other problem), 0: no detection in this band [but detected in another band]).

Kmag
The K-band magnitude (Vega; null if no optical ID; -1: no data in this band (generally because there is no K-band image coverage); 0: no detection in this band).

Lim_Bw_Mag
The B_W band 50% completeness limit (-1: no data in this band).

Lim_Rmag
The R-band 50% completeness limit (-1: no data in this band).

Lim_Imag
The I-band 50% completeness limit (-1: no data in this band).

Lim_Kmag
The K-band 50% completeness limit (-1: no data in this band).

Stellarity
The optical stellarity parameter (taken from either the R-, B_W, or I-band catalogs in that order of preference; null if no optical ID).

Optical_Field
The name of the optical subfield in which the source was found.


Contact Person

Questions regarding the XBOOTESOID database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 1-Dec-2006