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CHANSEXAGN - Chandra Serendipitous Extragalactic X-Ray Source ID (SEXSI)/Spitzer AGN Catalog

HEASARC
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Overview

The authors compare the relative merits of active galactic nuclei (AGN) selection at X-ray and mid-infrared wavelengths using data from moderately deep fields observed by both Chandra and Spitzer. The X-ray-selected AGN sample and associated photometric and spectroscopic optical follow-up are drawn from a subset of fields studied as part of the Serendipitous Extragalactic X-ray Source Identification (SEXSI) program. Mid-infrared data in these fields are derived from targeted and archival Spitzer imaging, and mid-infrared AGN selection is accomplished primarily through application of the Infrared Array Camera (IRAC) color-color AGN "wedge" selection technique. Nearly all X-ray sources in these fields which exhibit clear spectroscopic signatures of AGN activity have mid-infrared colors consistent with IRAC AGN selection. These are predominantly the most luminous X-ray sources. X-ray sources that lack high-ionization and/or broad lines in their optical spectra are far less likely to be selected as AGNs by mid-infrared color selection techniques. The fraction of X-ray sources identified as AGN in the mid-infrared increases monotonically as the X-ray luminosity increases. Conversely, only 22% of mid-infrared-selected AGN are detected at X-ray energies in the moderately deep (t_exp_n~ 100 ks) SEXSI Chandra data.

The authors have expanded the multiwavelength data available for six SEXSI fields by obtaining Spitzer imaging observations. All six fields have deep Chandra X-ray images, optical imaging, and extensive, deep optical spectroscopy -- all of which has been published in Harrison et al. (2003, ApJ, 596, 944), Eckart et al. (2005, ApJS, 156, 35), and Eckart et al. (2006, ApJS, 165, 19). The authors obtained mid-infrared imaging through both archival and targeted Spitzer programs which include imaging at 3.6, 4.5, 5.8, and 8 micron (um) from IRAC (PID 00017, 00064, 20694 and 20808), and imaging at 24 um from MIPS (PID 20808 and 00083). This table contains mid-IR photometric data for 290 hard X-ray-selected SEXSI sources. Each of the four IRAC catalogs as well as the MIPS catalog was individually matched to the SEXSI X-ray source positions using a 2.5 arcseconds search radius. To calculate a false match rate, the authors shifted the X-ray source catalog by 1' and matched to the IRAC and MIPS catalogs; this entire procedure was repeated 6 times using different 1' shifts. The resulting false match rates were 10.1% (3.6 um), 7.2% (4.5 um), 3.7% (5.8 um), 2.6% (8.0 um), 1% (24 um), and <1% for four-band-detected IRAC sources.


Catalog Bibcode

2010ApJ...708..584E

References

A comparison of X-ray and mid-infrared selection of obscured active galactic
nuclei.
    Eckart M.E., McGreer I.D., Stern D., Harrison F.A., Helfand D.J.
   <Astrophys. J., 708, 584-597 (2010)>
   =2010ApJ...708..584E

Provenance

This table was created by the HEASARC in Match 2012 based on CDS Catalog J/ApJ/708/584 file table2.dat.

Parameters

Name
The name of the Chandra SEXSI source using the approved designation, viz. 'CXOSEXSI JHHMMSS.s+DDMMSS'.

RA
The Right Ascension of the infrared counterpart to the Chandra source as determined by SExtractor from Spitzer astronomy.

Dec
The Declination of the infrared counterpart to the Chandra source as determined by SExtractor from Spitzer astronomy.

LII
The Galactic Longitude of the infrared counterpart to the Chandra source.

BII
The Galactic Latitude of the infrared counterpart to the Chandra source.

Offset_RA
The difference between the corrected X-ray Right Ascension as determined from SEXSI II (CDS Cat. J/ApJS/156/35, available in the HEASARC database as the CHANSEXOID table) and the Spitzer Right Ascension. This is greater than zero if the Spitzer RA is greater than the Chandra RA.

Offset_Dec
The difference between the corrected X-ray Declination as determined from SEXSI II (CDS Cat. J/ApJS/156/35, available in the HEASARC database as the CHANSEXOID table) and the Spitzer Declination. This is greater than zero if the Spitzer Dec is greater than the Chandra Dec.

HB_Flux
The Galactic-absorption-adjusted 2-10 keV flux of the Chandra SEXSI source, in erg s-1 cm-2.

Hardness_Ratio
The hardness ratio HR of the Chandra SEXSI source, defined as HR = (H-S)/(H+S) where H is the corrected counts in the 2.0 - 10 keV band and S is the corrected counts in the 0.5 - 2.0 keV band extracted at the position of the hard band detection.

Rmag_Limit
This parameter is set to '>' if the quoted R magnitude is an upper limit rather than an actual value.

Rmag
The R-band magnitude of the optical counterpart to the Chandra SEXSI source.

Rmag_Flag
This flag parameter indicates the security and other properties of the optical identification, coded as follows:

      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = bright source - magnitude taken from Guide Star Catalog II;
      2 = upper limit;
      1 = optical identification;
      0 = no optical coverage.
  

Log_HB_Over_Opt_Flux
The logarithm of the ratio of the hard-band flux (2 - 10 keV) to the optical flux.

Object_Type
The optical-spectroscopic classification of the source, where sources marked as 'unid' have no spectroscopic classification or redshift:

    BLAGN = Broad-Line Active Galactic Nucleus;
    NLAGN = Narrow-Line Active Galactic Nucleus;
      ELG = Emission-Line Galaxy;
      ALG = Absorption-Line Galaxy;
     unid = No Spectroscopic Observations;
     cont = Continuum Only Spectrum;
     star = any type of star.
  

Redshift
The redshift of the object, if available.

Log_HB_Lx
The logarithm of the observed 2 - 10 keV luminosity of the Chandra SEXSI source, in erg s-1, as given in SEXSI III (CDS Cat. J/ApJS/165/19, available in the HEASARC database in the CHANSEXOID table).

Log_NH
The logarithm of the best-fit H I column density n_H as determined from the X-ray data, in atoms cm-2. When the best-fit value of n_H is 0.0, a value of 0.0 is given for log n_H. See Eckart et al. (2006, ApJS, 165, 19) for details of these calculations.

IRAC_3p6_um_Flux
The flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 3.6um image, in microJansky (uJy). The value is blank if the source was not observed in this band.

IRAC_3p6_um_Flux_Error
The associated error in the flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 3.6um image, in microJansky (uJy). The errors are >~ 10% of the source flux density owing to the authors' conservative estimate of the systematic uncertainties in the Spitzer data.

IRAC_3p6_um_Flux_Flag
This parameter flags the associated flux density for the source, coded as follows:

      8 = below nominal 5-sigma detection limit;
      7 = likely counterpart outside formal match radius;
      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = not used;
      2 = upper limit;
      1 = infrared identification;
      0 = no infrared coverage.
  

IRAC_4p5_um_Flux
The flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 4.5um image, in microJansky (uJy). The value is blank if the source was not observed in this band.

IRAC_4p5_um_Flux_Error
The associated error in the flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 4.5um image, in microJansky (uJy). The errors are >~ 10% of the source flux density owing to the authors' conservative estimate of the systematic uncertainties in the Spitzer data.

IRAC_4p5_um_Flux_Flag
This parameter flags the associated flux density for the source, coded as follows:

      8 = below nominal 5-sigma detection limit;
      7 = likely counterpart outside formal match radius;
      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = not used;
      2 = upper limit;
      1 = infrared identification;
      0 = no infrared coverage.
  

IRAC_5p8_um_Flux
The flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 5.8um image, in microJansky (uJy). The value is blank if the source was not observed in this band.

IRAC_5p8_um_Flux_Error
The associated error in the flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 5.8um image, in microJansky (uJy). The errors are >~ 10% of the source flux density owing to the authors' conservative estimate of the systematic uncertainties in the Spitzer data.

IRAC_5p8_um_Flux_Flag
This parameter flags the associated flux density for the source, coded as follows:

      8 = below nominal 5-sigma detection limit;
      7 = likely counterpart outside formal match radius;
      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = not used;
      2 = upper limit;
      1 = infrared identification;
      0 = no infrared coverage.
  

IRAC_8p0_um_Flux
The flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 8.0um image, in microJansky (uJy). The value is blank if the source was not observed in this band.

IRAC_8p0_um_Flux_Error
The associated error in the flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/IRAC 8.0um image, in microJansky (uJy). The errors are >~ 10% of the source flux density owing to the authors' conservative estimate of the systematic uncertainties in the Spitzer data.

IRAC_8p0_um_Flux_Flag
This parameter flags the associated flux density for the source, coded as follows:

      8 = below nominal 5-sigma detection limit;
      7 = likely counterpart outside formal match radius;
      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = not used;
      2 = upper limit;
      1 = infrared identification;
      0 = no infrared coverage.
  

MIPS_24_um_Flux
The flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/MIPS 24um image, in microJansky (uJy). The value is blank if the source was not observed in this band.

MIPS_24_um_Flux_Error
The associated error in the flux density of the infrared counterpart to the Chandra SEXSI source in the Spitzer/MIPS 24um image, in microJansky (uJy). The errors are >~ 10% of the source flux density owing to the authors' conservative estimate of the systematic uncertainties in the Spitzer data.

MIPS_24_um_Flux_Flag
This parameter flags the associated flux density for the source, coded as follows:

      8 = below nominal 5-sigma detection limit;
      7 = likely counterpart outside formal match radius;
      6 = non-detection but near bright source (limiting mag will be incorrect);
      5 = unclear which source is optical counterpart;
      4 = near bright source (magnitude affected);
      3 = not used;
      2 = upper limit;
      1 = infrared identification;
      0 = no infrared coverage.
  

Class
The HEASARC Browse object classification, based on the value of the object_type parameter.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 16-Mar-2012