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CANDELSCXO - CANDELS H-Band Selected Chandra Source Catalog

HEASARC
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Overview

Improving the capabilities of detecting faint X-ray sources is fundamental to increase the statistics on faint high-z AGN and star-forming galaxies. The authors performed a simultaneous maximum likelihood point-spread function (PSF) fit in the 0.5-2 keV and 2-7 keV energy bands of the 4 Ms Chandra Deep Field South (CDFS) data at the position of the 34,930 CANDELS H-band selected galaxies. For each detected source, they provide X-ray photometry and optical counterpart validation. The authors validated this technique by means of a ray-tracing simulation, and detected a total of 698 X-ray point-sources with a likelihood L > 4.98 (i.e.> 2.7sigma). They show that the prior knowledge of a deep sample of Optical-NIR galaxies leads to a significant increase of the detection of faint (i.e. ~ 10-17 erg s-1 cm-2 in the 0.5-2 keV band) sources with respect to "blind" X-ray detections. By including previous catalogs, this work increases the total number of X-ray sources detected in the 4 Ms CDFS, CANDELS area to 793, which represents the largest sample of extremely faint X-ray sources assembled to date. These results suggest that a large fraction of the optical counterparts of our X-ray sources determined by likelihood ratio actually coincides with the priors used for the source detection. Most of the newly detected sources are likely star-forming galaxies or faint absorbed AGN. The authors identified a few sources with putative photometric redshift z > 4. Despite the low number statistics, this sample significantly increases the number of X-ray selected candidate high-z AGN.

The 4-Ms CDFS consists of 23 observations described in Table 1 of Luo et al. (2008, ApJS, 179, 19) plus 31 other pointings described in Xue et al. (2011, ApJS, 195, 10, hereafter X11) for a total exposure of ~4 Ms. For the purpose of this paper, the authors employed only observations taken with a focal temperature of <= -120 C, since at higher temperatures the background cannot be modeled with their technique.


Catalog Bibcode

2016ApJ...823...95C

References

Chandra counterparts of CANDELS GOODS-S sources.
    Cappelluti N., Comastri A., Fontana A., Zamorani G., Amorin R.,
    Castellano M., Merlin E., Santini P., Elbaz D., Schreiber C., Shu X.,
    Wang T., Dunlop J.S., Bourne N., Bruce V.A., Buitrago F., Michalowski M.J.,
    Derriere S., Ferguson H.C., Faber S.M., Vito F.
    <Astrophys. J. 823, 95 (2016)>
    =2016ApJ...823...95C        (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in July 2016 based on CDS Catalog J/ApJ/823/95 file catalog.dat.

Parameters

Source_Number
A unique identification source number for the X-ray source.

Can_Prior_Source_Number
The CANDELS identification of the optical source whose position was used as a prior for the X-ray detection.

Prior_Flag
This parameter contains a flag (called FLAG_PRIOR) in the reference paper) to determine the reliability of the association of the X-ray source with the optical prior. It has the value of 1 for off-axis angles < 4 arcminutes,, or detection likelihood > 10, and 2 for off-axis angles > 4 arcminutes, detection likelihood < 10. If the value is 1, one can safely use the prior source as the actual counterpart.

Can_Best_Source_Number
The CANDELS identification of the "best" optical counterpart of X-Ray Source from the likelihood ratio (LR) test.

Can_2nd_Source_Number
The CANDELS identification of the "second best" optical counterpart of X-Ray Source from the likelihood ratio (LR) test.

ID_Flag
This parameter contains a flag (called FLAG_ASSOC in the reference paper) to determine the quality of the identification of the X-ray source with the CANDELS source. Secure identifications are flagged with FLAG_ASSOC = 1, while for 90 sources the authors did not have a significant counterpart association and they are flagged with FLAG_ASSOC = 2 in the catalog. However, in many cases, having multiple counterparts does not imply that the identification is not secure. In order to resolve multiple associations, the authors computed the distribution of the likelihood ratios LR among the possible counterparts of the same X-ray source (Civano et al. 2012, ApJS, 201, 30). If such a ratio is larger than the median, then the authors define the association as secure. In other cases the association is flagged with FLAG_ASSOC = -1 which means ambiguous and the CANDELS ID numbers of all the candidate counterparts are listed in the catalog in LR order.

Name
The standard source designation in the style recommended by the Dictionary of Nomenclature of Celestial Objects for unregistered Chandra X-ray source, which was created by the HEASARC using the prefix 'CXOU' and the J2000.0 Right Ascension and Declination truncated to 0.1 seconds of time in RA and to 1 arcsecond in Declination. This can sometimes lead to ambiguity for close sources. In this catalog, two sources (source numbers 449 and 607) have been given the same name (CXOU J033205.7-274447) due to their proximity.

RA
The Right Ascension of the best-fit X-ray source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

Dec
The Declination of the best-fit X-ray source centroid in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

LII
The Galactic Longitude of the best-fit X-ray source centroid.

BII
The Galactic Latitude of the best-fit X-ray source centroid.

Error_Radius
The one-dimensional error in the X-ray source centroid position, in arcseconds.

Offset
The angular distance of the X-ray source centroid from the position of the best optical counterpart, in arcseconds.

FB_Counts
The X-ray source counts in the 0.5-7 keV band. The full band count rate, counts, and fluxes are the sums of those in the two sub-bands, respectively

FB_Counts_Error
The 1-sigma error in the X-ray source counts in the 0.5-7 keV band.

SB_Counts
The X-ray source counts in the 0.5-2 keV band.

SB_Counts_Error
The 1-sigma error in the X-ray source counts in the 0.5-2 keV band.

HB_Counts
The X-ray source counts in the 2-7 keV band.

HB_Counts_Error
The 1-sigma error in the X-ray source counts in the 2-7 keV band.

FB_Detect_Likelihood
The detection likelihood L = -ln(p), where p is the probability for a random Poissonian fluctuation to have caused the observed source counts, determined in the 0.5-7 keV band.

SB_Detect_Likelihood
The detection likelihood L = -ln(p), where p is the probability for a random Poissonian fluctuation to have caused the observed source counts, determined in the 0.5-2 keV band.

HB_Detect_Likelihood
The detection likelihood L = -ln(p), where p is the probability for a random Poissonian fluctuation to have caused the observed source counts, determined in the 2-7 keV band.

SB_Exposure
The effective exposure time at the source position in the soft 0.5-2 keV band, in seconds.

HB_Exposure
The effective exposure time at the source position in the hard 2-7 keV band, in seconds.

FB_Flux
The observed source flux in the 0.5-10 keV band, in erg s-1 cm-2. Count rates were converted into fluxes by assuming a simple power-law spectrum with slope = 1.4 plus a Galactic absorption NH = 7 x 1019 cm-2 (Dickey & Lockman 1990, ARA&A, 28, 215). The energy conversion factors (ECFs) were computed with the online Chandra PIMMS tool. The response of the ACIS-I detector varied significantly across the Chandra lifetime; for this reason, the authors computed the ECFs for every pointing's epoch and then weight-averaged them according to the exposure time. As a result, they obtained a count rate to flux ECF of 5.32 x 10-12 erg cm-2 in the 0.5-2 keV band and 2.71 x 10-12 erg cm-2 to convert the 2-7 keV count rate into a 2-10 keV flux. The full band count rate, counts, and fluxes are the sums of those in the two sub-bands, respectively.

FB_Flux_Error
The 1-sigma error in the observed source flux in the 0.5-10 keV band, in erg s-1 cm-2.

SB_Flux
The observed source flux in the 0.5-2 keV band, in erg s-1 cm-2. Count rates were converted into fluxes by assuming a simple power-law spectrum with slope = 1.4 plus a Galactic absorption NH = 7 x 1019 cm-2 (Dickey & Lockman 1990, ARA&A, 28, 215). The energy conversion factors (ECFs) were computed with the online Chandra PIMMS tool. The response of the ACIS-I detector varied significantly across the Chandra lifetime; for this reason, the authors computed the ECFs for every pointing's epoch and then weight-averaged them according to the exposure time. As a result, they obtained a count rate to flux ECF of 5.32 x 10-12 erg cm-2 in the 0.5-2 keV band and 2.71 x 10-12 erg cm-2 to convert the 2-7 keV count rate into a 2-10 keV flux.

SB_Flux_Error
The 1-sigma error in the observed source flux in the 0.5-2 keV band, in erg s-1 cm-2

HB_Flux
The observed source flux in the 2-10 keV band, in erg s-1 cm-2. Count rates were converted into fluxes by assuming a simple power-law spectrum with slope = 1.4 plus a Galactic absorption NH = 7 x 1019 cm-2 (Dickey & Lockman 1990, ARA&A, 28, 215). The energy conversion factors (ECFs) were computed with the online Chandra PIMMS tool. The response of the ACIS-I detector varied significantly across the Chandra lifetime; for this reason, the authors computed the ECFs for every pointing's epoch and then weight-averaged them according to the exposure time. As a result, they obtained a count rate to flux ECF of 5.32 x 10-12 erg cm-2 in the 0.5-2 keV band and 2.71 x 10-12 erg cm-2 to convert the 2-7 keV count rate into a 2-10 keV flux.

HB_Flux_Error
The 1-sigma error in the observed source flux in the 2-10 keV band, in erg s-1 cm-2.

FB_Count_Rate
The count rate in the 0.5-7 keV band, in counts per second. The full band count rate, counts, and fluxes are the sums of those in the two sub-bands, respectively.

FB_Count_Rate_Error
The 1-sigma error in the count rate in the 0.5-7 keV band, in counts per second.

SB_Count_Rate
The count rate S in the 0.5-2 keV band, in counts per second.

SB_Count_Rate_Error
The 1-sigma error in the count rate in the 0.5-2 keV band, in counts per second.

HB_Count_Rate
The count rate H in the 2-7 keV band, in counts per second.

HB_Count_Rate_Error
The 1-sigma error in the count rate in the 2-7 keV band, in counts per second.

Hardness_Ratio
The hardness ratio HR of the Chandra X-ray source defined as HR = (H - s)/(H + S)m where H and S are the count rates in the 2-7 keV and 0.5-2 keV bands, respectively.

Hardness_Ratio_Error
The error in the hardness ratio HR of the Chandra X-ray source.

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

Candels_RA
The best-fit Right Ascension of the best CANDELS counterpart to the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

Candels_Dec
The best-fit Declination of the best CANDELS counterpart to the X-ray source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

F160W_Mag
The F160W AB (H band) magnitude of the best CANDELS counterpart to the X-ray source.

Redshift
The spectroscopic redshift of the best CANDELS counterpart to the X-ray source from Santini et al. (2015, ApJ, 801, 97).

Phot_Redshift_1
The photometric redshift of the best CANDELS counterpart to the X-ray source from Santini et al. (2015, ApJ, 801, 97).

Phot_Redshift_2
The photometric redshift of the best CANDELS counterpart to the X-ray source from Hsu et al. (2014, ApJ, 796, 60).

Xue_Source_Number
The source identification of the corresponding X-ray source in the Xue et al. (2011, ApJS, 195, 10) catalog.


Contact Person

Questions regarding the CANDELSCXO database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 09-Aug-2016 00:12:02 EDT