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CLSCAT - Chandra Legacy Survey (CLS) Catalog

HEASARC
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Overview

The COSMOS-Legacy survey is a 4.6-Ms Chandra program that has imaged 2.2 deg2 of the COSMOS field with an effective exposure of ~160 ks over the central 1.5 deg2 and of ~80 ks in the remaining area. The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. In the reference paper, the authors describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2 x 10-5. The authors also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4,016 point sources (3,814, 2,920 and 2,440 in the full, soft, and hard band). The limiting depths are 2.2 x 10-16, 1.5 x 10-15, and 8.9 x 10-16 erg/cm2/s in the 0.5-2, 2-10, and 0.5-10 keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density > 1022 cm-2 from the hardness ratio (HR) is ~ 50+17_-16_%. Given the large sample, the authors compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5% - 10%. For the first time, they compute number counts for obscured (HR > -0.2) and unobscured (HR < -0.2) sources and find significant differences between the two populations in the soft band. Due to the unprecedented large exposure, the COSMOS-Legacy area is three times larger than surveys at similar depths and its depth is three times fainter than surveys covering similar areas. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.

The half-a-field shift tiling strategy was designed to uniformly cover the COSMOS Hubble area in depth and point-spread function (PSF) size by combining the old C-COSMOS (Elvis et al., 2009, ApJS, 184, 158) observations with the new Chandra ones (see Figure 1 in the reference paper). The main properties of the new ACIS-I Chandra COSMOS-Legacy observations are summarized in Table 1 therein. The observations took place in four blocks: 2012 November to 2013 January; 2013 March to July; 2013 October to 2014 January; and 2014 March. The mean net effective exposure time per field was 48.8 ks after all the cleaning and reduction operations.


Catalog Bibcode

2016ApJ...819...62C

References

The Chandra Cosmos Legacy Survey: overview and point source catalog.
    Civano F., Marchesi S., Comastri A., Urry M.C., Elvis M., Cappelluti N.,
    Puccetti S., Brusa M., Zamorani G., Hasinger G., Aldcroft T.,
    Alexander D.M., Allevato V., Brunner H., Capak P., Finoguenov A., Fiore F.,
    Fruscione A., Gilli R., Glotfelty K., Griffiths R.E., Hao H.,
    Harrison F.A., Jahnke K., Kartaltepe J., Karim A., Lamassa S.M.,
    Lanzuisi G., Miyaji T., Ranalli P., Salvato M., Sargent M., Scoville N.J.,
    Schawinski K., Schinnerer E., Silverman J., Smolcic V., Stern D., Toft S.,
    Trakhenbrot B., Treister E., Vignali C.
   <Astrophys. J., 819, 62 (2016)>
   =2016ApJ...819...62C    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in July 2016 based on CDS Catalog J/ApJ/819/62, file table5.dat.

Parameters

Source_ID
The Chandra Legacy Survey source designation, "cid NNNN", with numbers among 1-3811; or "lid NNNN", with numbers among 38-6208. The "lid" sources are the 2,273 new sources and the "cid" sources are the 1743 sources updated from the C-COSMOS Catalog (Elvis et al. 2009, ApJS, 184, 158: called the CCOSMOSCAT table in the HEASARC database systems). The HEASARC has removed the underscore character ("_") from these designations that was used in the original reference, e.g., changed "cid_1" to 'cid 1".

Name
The Chandra X-ray source J2000.0 position-based name using the 'CXOC' prefix for the original C-COSMOS sources (entries with source_id starting with "cid"), and the 'CXOL' prefix for the 2,273 new source (entries with source_id starting with "lid"), e.g., "CXOC J095833.4+0195927" and "CXOL J095915.8+015154". The HEASARC created these names following IAU recommendations based on their J2000.0 source positions. The use of the 'CXOC' prefix for the the original Elvis et al. 2009, ApJS, 184, 158 sources is in accordance with that catalog. Lacking guidance for the prefix for the 2,273 new sources, the HEASARC has adopted the unofficial "CXOL" prefix for the Chandra X-ray Observatory Legacy Survey source names.

RA
The Right Ascension of the centroid of the Chandra source in the selected equinox. The source detection and location procedure is discussed in Section 4 of the reference paper.

Dec
The Declination of the centroid of the Chandra source in the selected equinox. The source detection and location procedure is discussed in Section 4 of the reference paper.

LII
The Galactic Longitude of the Chandra source centroid.

BII
The Galactic Latitude of the Chandra source centroid.

Error_Radius
The positional error of the Chandra source position, in arcseconds, calculated as specified in Section 4.1.2 of the reference paper.

FB_Detect_Likelihood
The best-fit maximum likelihood parameter value in CMLDetect of the Chandra source in the "full" 0.5-7 keV band, DET_ML. This is related to the Poisson probability that a source candidate is a random fluctuation of the background (Prandom), by DET_ML - -ln(Prandom). As a consequence, sources with small values of DET_ML have high values of Prandom and are then likely to be background fluctuations. The authors chose a threshold significance value of 2 x 10-5 that corresponds to DET_ML = 10.8, i.e., a source needs to have DET_ML > 10.8 in at least one of the three bands to be included in the final catalog. This value is the same as was used in C-COSMOS. To improve the final completeness of the catalog, the authors also searched for less significant sources up to about 100 times higher P, which corresponds to a threshold DET_ML = 6. Similarly to what was done in C-COSMOS, sources with DET_ML in the range 6 - 10.8 were only considered in this catalog if these have DET_ML > 10.8 in another band. Sources with DET_ML < 6 are considered to be undetected.

FB_Count_Rate_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

FB_Count_Rate
The count rate of the Chandra source in the "full" 0.5-7 keV band, in counts per seconds. The count rates in the three bands reported here were obtained with CMLDetect. Vignetting and quantum efficiency were taken into account when measuring the effective exposure time.

FB_Count_Rate_Error
The uncertainty in the count rate of the Chandra source (err_rate) in the "full" 0.5-7 keV band, in counts per seconds. The count rate error at the 68% confidence level was computed using the equation err_rate = sqrt [CS + (1+a) x B]/(0.9 x T), where CS is the source net counts estimated by aperture photometry using an extraction radius including 90% of the encircled energy fraction (EEF) for each observation in which the source was detected; B is the background counts estimated in the same aperture on the background maps used in CMLDetect and corrected with a factor a = 0.5 introduced to account for the uncertainties on the background estimation in a given position (see Puccetti et al. 2009, ApJS, 185, 586); and T is the vignetting-corrected exposure time.

FB_Flux_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

FB_Flux
The flux of the Chandra source, in erg s-1 cm-2, in the entire 0.5-10 keV band. (Note that this band range differs from that used for the full-band counts and count rates). The fluxes F were obtained from the count rates using the relation F = CR x (CF x 10-11), where CR is the count rate in each band and CF is the energy conversion factor computed using the CIAO tool srcflux, assuming a power-law spectrum with slope Gamma of 1.4 and a Galactic column density of NH = 2.6 x 1020 cm-2. Due to the fact that the observations were taken in two different Chandra cycles, i.e., Cycle 8 for C-COSMOS and Cycle 14 for the new data, the authors used as CFs a weighted mean of the factors in the different cycles, depending on the exposure time for each source accumulated in each cycle to account for its variation (~15% between the two cycles). The Cycle 14 (Cycle 8) CFs are 1.71 (1.57), 7.40 (6.34), and 3.06 (3.04) counts erg-1 cm-2 for 0.5-10, 0.5-2 and 2-10 keV bands, respectively. The conversion factors are sensitive to the assumed spectral shape: for Gamma = 2, there is a change of 40% in the full band CF, ~5% in the soft band and ~20% in the hard band.

FB_Flux_Error
The uncertainty in the flux in the corresponding band of the Chandra source, in erg s-1 cm-2.

FB_SNR
The signal-to-noise ratio of the Chandra source detection in the "full" 0.5-7 keV band.

FB_Exposure
The exposure time at the source location in the "full" 0.5-7 keV band, in seconds (converted by the HEASARC from the kiloseconds unit used in the original table).

FB_Counts
The aperture photometry net counts for the Chandra source in the "full" 0.5-7 keV band, from each observation where the source was detected, using the point-spread function (PSF) radius at EEF = 0.9. The authors also extracted the background counts from the same observations using an annulus with rmin = rPSF + 8 pixels and rmax = rPSF + 40 pixels, where rPSF is the PSF radius at EEF = 0.95 (in pixels). In the background extraction, they excluded contamination by other nearby detected sources using an exclusion radius equal to rPSF.

FB_Counts_Error
The uncertainty in the 0.5-7 keV aperture photometry net counts.

SB_Detect_Likelihood
The best-fit maximum likelihood parameter value in CMLDetect of the Chandra source in the "soft" 0.5-2 keV band, DET_ML. This is related to the Poisson probability that a source candidate is a random fluctuation of the background (Prandom), by DET_ML - -ln(Prandom). As a consequence, sources with small values of DET_ML have high values of Prandom and are then likely to be background fluctuations. The authors chose a threshold significance value of 2 x 10-5 that corresponds to DET_ML = 10.8, i.e., a source needs to have DET_ML > 10.8 in at least one of the three bands to be included in the final catalog. This value is the same as was used in C-COSMOS. To improve the final completeness of the catalog, the authors also searched for less significant sources up to about 100 times higher P, which corresponds to a threshold DET_ML = 6. Similar to what was done in C-COSMOS, sources with DET_ML in the range 6 - 10.8 were only considered in this catalog if these have DET_ML > 10.8 in another band. Sources with DET_ML < 6 are considered to be undetected.

SB_Count_Rate_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

SB_Count_Rate
The count rate of the Chandra source in the "soft" 0.5-2 keV band, in counts per seconds. The count rates in the three bands reported here were obtained with CMLDetect. Vignetting and quantum efficiency were taken into account when measuring the effective exposure time.

SB_Count_Rate_Error
The uncertainty in the count rate of the Chandra source (err_rate) in the "soft" 0.5-2 keV band, in counts per seconds. The count rate error at the 68% confidence level was computed using the equation err_rate = sqrt [CS + (1+a) x B]/(0.9 x T), where CS is the source net counts estimated by aperture photometry using an extraction radius including 90% of the encircled energy fraction (EEF) for each observation in which the source was detected; B is the background counts estimated in the same aperture on the background maps used in CMLDetect and corrected with a factor a = 0.5 introduced to account for the uncertainties on the background estimation in a given position (see Puccetti et al. 2009, ApJS, 185, 586); and T is the vignetting-corrected exposure time.

SB_Flux_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

SB_Flux
The flux of the Chandra source, in erg s-1 cm-2, in the "soft" 0.5- keV band. The fluxes F were obtained from the count rates using the relation F = CR x (CF x 10-11), where CR is the count rate in each band and CF is the energy conversion factor computed using the CIAO tool srcflux, assuming a power-law spectrum with slope Gamma of 1.4 and a Galactic column density of NH = 2.6 x 1020 cm-2. Due to the fact that the observations were taken in two different Chandra cycles, i.e., Cycle 8 for C-COSMOS and Cycle 14 for the new data, the authors used as CFs a weighted mean of the factors in the different cycles, depending on the exposure time for each source accumulated in each cycle to account for its variation (~15% between the two cycles). The Cycle 14 (Cycle 8) CFs are 1.71 (1.57), 7.40 (6.34), and 3.06 (3.04) counts erg-1 cm-2 for 0.5-10, 0.5-2 and 2-10 keV bands, respectively. The conversion factors are sensitive to the assumed spectral shape: for Gamma = 2, there is a change of 40% in the full band CF, ~5% in the soft band and ~20% in the hard band.

SB_Flux_Error
The uncertainty in the flux in the corresponding band of the Chandra source, in erg s-1 cm-2.

SB_SNR
The signal-to-noise ratio of the Chandra source detection in the "soft" 0.5-2 keV band.

SB_Exposure
The exposure time at the source location in the "soft" 0.5-2 keV band, in seconds (converted by the HEASARC from the kiloseconds unit used in the original table).

SB_Counts
The aperture photometry net counts for the Chandra source in the "soft" 0.5-2 keV band, from each observation where the source was detected, using the point-spread function (PSF) radius at EEF = 0.9. The authors also extracted the background counts from the same observations using an annulus with rmin = rPSF + 8 pixels and rmax = rPSF + 40 pixels, where rPSF is the PSF radius at EEF = 0.95 (in pixels). In the background extraction, they excluded contamination by other nearby detected sources using an exclusion radius equal to rPSF.

SB_Counts_Error
The uncertainty in the 0.5-2 keV aperture photometry net counts.

HB_Detect_Likelihood
The best-fit maximum likelihood parameter value in CMLDetect of the Chandra source in the "hard" 2-7 keV band, DET_ML. This is related to the Poisson probability that a source candidate is a random fluctuation of the background (Prandom), by DET_ML - -ln(Prandom). As a consequence, sources with small values of DET_ML have high values of Prandom and are then likely to be background fluctuations. The authors chose a threshold significance value of 2 x 10-5 that corresponds to DET_ML = 10.8, i.e., a source needs to have DET_ML > 10.8 in at least one of the three bands to be included in the final catalog. This value is the same as was used in C-COSMOS. To improve the final completeness of the catalog, the authors also searched for less significant sources up to about 100 times higher P, which corresponds to a threshold DET_ML = 6. Similar to what was done in C-COSMOS, sources with DET_ML in the range 6 - 10.8 were only considered in this catalog if these have DET_ML > 10.8 in another band. Sources with DET_ML < 6 are considered to be undetected.

HB_Count_Rate_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

HB_Count_Rate
The count rate of the Chandra source in the "hard" 2-7 keV band, in counts per seconds. The count rates in the three bands reported here were obtained with CMLDetect. Vignetting and quantum efficiency were taken into account when measuring the effective exposure time.

HB_Count_Rate_Error
The uncertainty in the count rate of the Chandra source (err_rate) in the "hard" 2-7 keV band, in counts per seconds. The count rate error at the 68% confidence level was computed using the equation err_rate = sqrt [CS + (1+a) x B]/(0.9 x T), where CS is the source net counts estimated by aperture photometry using an extraction radius including 90% of the encircled energy fraction (EEF) for each observation in which the source was detected; B is the background counts estimated in the same aperture on the background maps used in CMLDetect and corrected with a factor a = 0.5 introduced to account for the uncertainties on the background estimation in a given position (see Puccetti et al. 2009, ApJS, 185, 586); and T is the vignetting-corrected exposure time.

HB_Flux_Limit
This limit parameter is set to '<' if the corresponding parameter is the 90% confidence upper limit rather than a detection.

HB_Flux
The flux of the Chandra source, in erg s-1 cm-2, in the extended 2-10 keV band. (Note that this band range differs from that used for the hard-band counts and count rates). The fluxes F were obtained from the count rates using the relation F = CR x (CF x 10-11), where CR is the count rate in each band and CF is the energy conversion factor computed using the CIAO tool srcflux, assuming a power-law spectrum with slope Gamma of 1.4 and a Galactic column density of NH = 2.6 x 1020 cm-2. Due to the fact that the observations were taken in two different Chandra cycles, i.e., Cycle 8 for C-COSMOS and Cycle 14 for the new data, the authors used as CFs a weighted mean of the factors in the different cycles, depending on the exposure time for each source accumulated in each cycle to account for its variation (~15% between the two cycles). The Cycle 14 (Cycle 8) CFs are 1.71 (1.57), 7.40 (6.34), and 3.06 (3.04) counts erg-1 cm-2 for 0.5-10, 0.5-2 and 2-10 keV bands, respectively. The conversion factors are sensitive to the assumed spectral shape: for Gamma = 2, there is a change of 40% in the full band CF, ~5% in the soft band and ~20% in the hard band.

HB_Flux_Error
The uncertainty in the flux in the corresponding band of the Chandra source, in erg s-1 cm-2.

HB_SNR
The signal-to-noise ratio of the Chandra source detection in the "hard" 2-7 keV band.

HB_Exposure
The exposure time at the source location in the "hard" 2-7 keV band, in seconds (converted by the HEASARC from the kiloseconds unit used in the original table).

HB_Counts
The aperture photometry net counts for the Chandra source in the "hard" 2-7 keV band, from each observation where the source was detected, using the point-spread function (PSF) radius at EEF = 0.9. The authors also extracted the background counts from the same observations using an annulus with rmin = rPSF + 8 pixels and rmax = rPSF + 40 pixels, where rPSF is the PSF radius at EEF = 0.95 (in pixels). In the background extraction, they excluded contamination by other nearby detected sources using an exclusion radius equal to rPSF.

HB_Counts_Error
The uncertainty in the 2-7 keV aperture photometry net counts.

Hardness_Ratio
The hardness ratio, HR = (H-S)/(H+S), of the Chandra source, where H is the net counts in the hard band and S is those obtained in the soft band. Given the low number of counts for most of the sources (see Figure 9 of the reference paper), the authors used BEHR (Bayesian Estimation of HRs, Park et al. 2006, ApJ, 652, 610) which is particularly effective in the low-count regime, and does not need a detection in both bands in order to work.

Hardness_Ratio_Min
The 90% confidence lower limit to the value of the hardness ratio, HR = (H-S)/(H+S), of the Chandra source.

Hardness_Ratio_Max
The 90% confidence upper limit to the value of the hardness ratio, HR = (H-S)/(H+S), of the Chandra source


Contact Person

Questions regarding the CLSCAT database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 12-Jul-2016 14:02:51 EDT