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SPICESCXO - SPICES Lynx Field Chandra X-Ray Source Catalog

HEASARC
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Overview

This table contains the first results on field X-ray sources detected in a deep, 184.7 ks observation with the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-Ray Observatory. The observations target the Lynx field (J2000.0 RA = 08h 48m and Dec = +44d 54') of SPICES, the Spectroscopic Photometric Infrared-Chosen Extragalactic Survey, which contains three known X-ray-emitting clusters at redshifts of z = 0.57, 1.26, and 1.27. Not including the known clusters, in the 17' x 17' ACIS-I field the authors detect 132 sources in the 0.5 - 2 keV (soft) X-ray band down to a 2.1-sigma limiting flux of ~ 1.7 x 10^-16 erg/cm^2/s and 11 sources in the 2 - 10 keV (hard) X-ray band down to a 2.1-sigma limiting flux of ~ 1.3 x 10^-15 erg/cm^2/s. The combined catalog contains a total of 153 X-ray sources, of which 42 are detected only in the soft band and 21 are detected only in the hard band.

Confirming previous Chandra results, the authors find that the fainter sources have harder X-ray spectra, providing a consistent solution to the long-standing "spectral paradox". From deep optical and near-infrared follow-up data, 77% of the X-ray sources have optical counterparts to I = 24, and 71% of the X-ray sources have near-infrared counterparts to K_s = 20. Four of the 24 sources in the near-IR field are associated with extremely red objects (EROs; I - K_s >= 4). The authors have obtained spectroscopic redshifts with the Keck telescopes of 18 of the Lynx Chandra sources. These sources comprise a mix of broad-lined active galaxies, apparently normal galaxies, and two late-type Galactic dwarfs. Intriguingly, one Galactic source (number 72) is identified with an M7 dwarf exhibiting nontransient, hard X-ray emission. Thirteen of the Chandra sources are located within regions for which the authors have Hubble Space Telescope imaging. Nine of the sources are detected, showing a range of morphologies: several show compact cores embedded within diffuse emission, while others are spatially extended showing typical galaxy morphologies. Two of the Chandra sources in this subsample appear to be associated with mergers.

ACIS-I observations of the Lynx field were obtained on 2000 May 3 (65 ks; OBS-ID 1708) and 2000 May 4 (125 ks; OBS-ID 927). Time intervals with background rates larger than 3 sigma over the quiescent value of ~ 0.30 counts s^-1 per chip in the 0.3 - 10 keV band were removed. This procedure gave 60.7 ks of effective exposure out of the first observation and 124 ks out of the second, for a total of 184.7 ks. The two observations are almost coincident on the sky, so that the total coverage is 298 arcmin^2. The aim point for the observations was RA = 08h 48m 54.79s, Dec = +44d 54' 32.9" (J2000.0), and both exposures were obtained in the faint mode when ACIS was at a temperature of -120 C. The Galactic absorbing column for this field is N_H = 2 x 10^20 cm^-2. The position angle of the observations was 258.45 degrees.

Cosmology-dependent parameters are calculated for two models: an Einstein-de Sitter (EdS) universe consistent with previous work in this field (H_0 = 50 h_50 km s^-1 Mpc^-1, Omega_M = 1, and Omega_Lambda = 0) and the dark energy cosmology (DEC) universe favored by recent work on high-redshift supernovae and fluctuations in the cosmic microwave background (H_0 = 65 km s^-1 Mpc^-1, Omega_M = 0.35, and Omega_Lambda = 0.65).


Catalog Bibcode

2002AJ....123.2223S

References

SPICES II: optical and near-infrared identifications of faint X-ray sources
from deep CHANDRA observations of Lynx.
    Stern D., Tozzi P., Stanford S.A., Rosati P., Holden B., Eisenhardt P.,
    Elston R., Wu K.L., Connolly A., Spinrad H., Dawson S., Dey A.,
    Chaffee F.H.
   <Astron. J. 123, 2223 (2002)>
   =2002AJ....123.2223S

Provenance

This table was created by the HEASARC in April 2007 based on CDS catalog J/AJ/123/2223 files table1.dat, table2.dat and table3.dat.

Parameters

Source_Number
A running sequential identification number for the X-ray source which uniquely identifies it.

Name
The designation for the X-ray source, using the prefix '[STS2002]' (for Stern, Tozzi, Stanford 2002) and the source number, e.g., '[STS2002] 72', as recommended by the CDS Dictionary of Nomenclature of Celestial Objects. Note that the X-ray sources are referred to in the paper using a shorthand form with the prefix 'CXO', e.g., 'CXO 72'.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table. Astrometric positions were initially determined from the ACIS-I aspect solution. Following comparison of X-ray source positions with the deep, ground-based imaging discussed in Section 4 of the reference paper, the authors refined the absolute pointing of the X-ray data with an offset of 1.09" west, 1.35" south, and no rotation. These offsets were determined by matching X-ray sources with greater than 25 total counts (0.5 - 7 keV) to 17.5 < I < 22.5 sources. The positions presented therefore match the astrometric frame of the SPICES survey.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table. Astrometric positions were initially determined from the ACIS-I aspect solution. Following comparison of X-ray source positions with the deep, ground-based imaging discussed in Section 4 of the reference paper, the authors refined the absolute pointing of the X-ray data with an offset of 1.09" west, 1.35" south, and no rotation. These offsets were determined by matching X-ray sources with greater than 25 total counts (0.5 - 7 keV) to 17.5 < I < 22.5 sources. The positions presented therefore match the astrometric frame of the SPICES survey.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

SB_Counts
The X-ray source net counts S in the soft band (0.5 - 2 keV). Source counts were measured with simple aperture photometry within a radius R_S = 2.4 FWHM_PSF, where FWHM_PSF is the modeled PSF full width at half-maximum, determined as a function of off-axis angle to reproduce the broadening of the PSF. A minimum R_S = 5" was used in the central regions. The background for each source was calculated locally within an annulus of inner radius R_S + 2" and an outer radius of R_S + 12". Numerical simulations show that this aperture photometry systematically underestimates the net counts by 4%.

SB_Counts_Error
The RMS uncertainty in the soft-band counts.

HB_Counts
The X-ray source net counts H in the hard band (2 - 7 keV). Source counts were measured with simple aperture photometry within a radius R_S = 2.4 FWHM_PSF, where FWHM_PSF is the modeled PSF full width at half-maximum, determined as a function of off-axis angle to reproduce the broadening of the PSF. A minimum R_S = 5" was used in the central regions. The background for each source was calculated locally within an annulus of inner radius R_S + 2" and an outer radius of R_S + 12". Numerical simulations show that this aperture photometry systematically underestimates the net counts by 4%.

HB_Counts_Error
The RMS uncertainty in the hard-band counts.

Hardness_Ratio
The hardness ratio (H-S)/(H+S) of the X-ray source, where H is the net hard counts and S is the net soft counts.

SNR
The signal-to-noise ratio of the X-ray detection in the 0.5 - 7 keV band.

Off_Axis
The off-axis angle of the X-ray source from the nominal pointing direction, in arcminutes.

SB_Flux
The flux in the soft Band (0.5 - 2 keV), in erg/s/cm^2. The net count rate was transformed into the energy flux in the soft 0.5 - 2 keV band and in the hard 2 - 10 keV band. The conversion factors used were (4.52 +/- 0.3) x 10^-12 ergs cm^-2 count^-1 in the soft band and (2.79 +/- 0.3) x 10^-11 ergs cm^-2 count^-1 in the hard band, assuming an absorbing column of 2 x 10^20 cm^-2 (Galactic value) and a photon index Gamma = 1.4. The uncertainties in the conversion factors reflect the range of possible values for the photon index, Gamma = 1.1 - 1.8. As suggested by the spectral analysis of the stacked spectra, these values are representative of this sample. Since the conversion factors were computed at the aim point, where the effective area of Chandra/ACIS is at its maximum, the count rate of each source was corrected for vignetting. Namely, the net count rate was multiplied by the ratio of the exposure map at the aim point to the value of the exposure map averaged within the extraction region. Such a correction was done in the soft and hard bands separately.

HB_Flux
The flux in the hard band (2 - 10 keV), in erg/s/cm^2. The net count rate was transformed into the energy flux in the soft 0.5 - 2 keV band and in the hard 2 - 10 keV band. The conversion factors used were (4.52 +/- 0.3) x 10^-12 ergs cm^-2 count^-1 in the soft band and (2.79 +/- 0.3) x 10^-11 ergs cm^-2 count^-1 in the hard band, assuming an absorbing column of 2 x 10^20 cm^-2 (Galactic value) and a photon index Gamma = 1.4. The uncertainties in the conversion factors reflect the range of possible values for the photon index, Gamma = 1.1 - 1.8. As suggested by the spectral analysis of the stacked spectra, these values are representative of this sample. Since the conversion factors were computed at the aim point, where the effective area of Chandra/ACIS is at its maximum, the count rate of each source was corrected for vignetting. Namely, the net count rate was multiplied by the ratio of the exposure map at the aim point to the value of the exposure map averaged within the extraction region. Such a correction was done in the soft and hard bands separately.

Source_Flag
This flag parameter is set to 'a' to indicate that the host is more than 1.5 arcseconds away from the faint X-ray source.

RA_Offset
The X-ray to optical Right Ascension offset, in arcseconds.

Dec_Offset
The X-ray to optical Declination offset, in arcseconds.

Bmag
The Harris B-band magnitude (lambda_c = 4313 A(ngstrom), delta lambda = 1069 A) of the optical counterpart to the X-ray source. X-ray sources whose positions were outside the optical field, objects within the optical field with non-detections in this band, and sources within the optical field but havibg bad photometry, due either to source saturation or contamination from the stellar bleed trail of a nearby bright source, are all listed with null values.To distinguish these 3 cases for which there are no quoted magnitude values, the HEASARC has created a parameter (called optical_field_flag) which is set to 'Y' for all sources in the optical field having good photometry (whether detected or not), to 'C' for sources in the optical field with bad photometry in at least one of the optical bands (BRIz), and 'N' for sources outside the optical field.

Rmag
The Harris R-band magnitude (lambda_c = 6458 A, delta lambda = 1472 A) of the optical counterpart to the X-ray source. X-ray sources whose positions were outside the optical field, objects within the optical field with non-detections in this band, and sources within the optical field but havibg bad photometry, due either to source saturation or contamination from the stellar bleed trail of a nearby bright source, are all listed with null values.To distinguish these 3 cases for which there are no quoted magnitude values, the HEASARC has created a parameter (called optical_field_flag) which is set to 'Y' for all sources in the optical field having good photometry (whether detected or not), to 'C' for sources in the optical field with bad photometry in at least one of the optical bands (BRIz), and 'N' for sources outside the optical field.

Rmag_Flag
This flag parameter is set to ':' to indicate that the measured R magnitude was somewhat affected by a nearby stellar bleed trail on the CCD.

Imag
The Harris I-band magnitude (lambda_c = 8204 Angstrom, delta lambda = 1821 A) of the optical counterpart to the X-ray source. X-ray sources whose positions were outside the optical field, objects within the optical field with non-detections in this band, and sources within the optical field but havibg bad photometry, due either to source saturation or contamination from the stellar bleed trail of a nearby bright source, are all listed with null values.To distinguish these 3 cases for which there are no quoted magnitude values, the HEASARC has created a parameter (called optical_field_flag) which is set to 'Y' for all sources in the optical field having good photometry (whether detected or not), to 'C' for sources in the optical field with bad photometry in at least one of the optical bands (BRIz), and 'N' for sources outside the optical field.

Zmag
The RG850 long-pass z-band magnitude of the optical counterpart to the X-ray source. X-ray sources whose positions were outside the optical field, objects within the optical field with non-detections in this band, and sources within the optical field but havibg bad photometry, due either to source saturation or contamination from the stellar bleed trail of a nearby bright source, are all listed with null values.To distinguish these 3 cases for which there are no quoted magnitude values, the HEASARC has created a parameter (called optical_field_flag) which is set to 'Y' for all sources in the optical field having good photometry (whether detected or not), to 'C' for sources in the optical field with bad photometry in at least one of the optical bands (BRIz), and 'N' for sources outside the optical field.

Jmag
The J-band magnitude (lambda_c = 1.14 micron, delta lambda = 0.29 micron)of the near-infrared counterpart to the X-ray source. X-ray sources whose positions were outside the optical field have been given magnitude values of -99.00 by the HEASARC.

Ks_Mag
The K_s-band magnitude (lambda_c = 2.16 micron, delta lambda = 0.33 micron)of the near-infrared counterpart to the X-ray source. X-ray sources whose positions were outside the optical field have been given magnitude values of -99.00 by the HEASARC.

Redshift
The spectroscopic redshift of the optical/near-IR counterpart to the X-ray source.

Spices_ID
The SPICES identification of the optical/near-IR counterpart to the X-ray source.

Abs_Bmag_Eds
The EdS cosmology (see overview for more details) rest-frame absolute B magnitude of the optical/near-IR counterpart to the X-ray source (only available for the 18 X-ray sources with known redshifts).

Log_SB_Lx_Eds
The EdS cosmology (see overview for more details) rest-frame 0.5 - 2 keV luminosity of the X-ray source, using an adopted X-ray power-law spectral index Gamma of 1.4 (only available for the 18 X-ray sources with known redshifts).

Log_HB_Lx_Eds
The EdS cosmology (see overview for more details) rest-frame 2 -10 keV luminosity of the X-ray source, using an adopted X-ray power-law spectral index Gamma of 1.4 (only available for the 18 X-ray sources with known redshifts).

Abs_Bmag_Dec
The Dark Energy cosmology (see overview for more details) rest-frame absolute B magnitude of the optical/near-IR counterpart to the X-ray source (only available for the 18 X-ray sources with known redshifts).

Log_SB_Lx_Dec
The Dark Energy cosmology (see overview for more details) rest-frame 0.5 - 2 keV luminosity of the X-ray source, using an adopted X-ray power-law spectral index Gamma of 1.4 (only available for the 18 X-ray sources with known redshifts).

Log_HB_Lx_Dec
The Dark Energy cosmology (see overview for more details) rest-frame 2 - 10 keV luminosity of the X-ray source, using an adopted X-ray power-law spectral index Gamma of 1.4 (only available for the 18 X-ray sources with known redshifts).

Source_Type
The galaxy or AGN class (or spectral type for X-ray sources associated with stars): this is only available for the 18 X-ray sources with known redshifts.

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

Optical_Field_Flag
The HEASARC created this parameter to indicate whether or not the X-ray source position was within ('Y') the optical field of view (FOV), outside ('N') of the optical FOV, or within the optical FOV but for which bad photometry was obtained for at least one of the B, R, I or z bands ('C'), either due to the source being saturated or to it being severely affected by a stellar `bleed trail'. Objects which were within the optical FOV but had bad photometry were listed in Table 2 of the reference paper with values of 99.00 or 99.99 for the affected magnitudes: the HEASARC set such values to nulls in this implementation.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 30-Apr-2007