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CLSCAT - Chandra Legacy Survey (CLS) Catalog |
HEASARC Archive |
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...62CReferences
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. Some of the values for the name parameter in the HEASARC's implementation of this table were corrected in April 2018.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 Help Desk.Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:26:04 EDT
- HEASARC Director: Dr. Andy Ptak
- NASA Official: Dr. Andy Ptak
- Web Curator: J.D. Myers
- Last Modified: 16-Sep-2024