J/A+A/466/823 Hard 2-10kev X-ray selected sources (Georgantopoulos+, 2007)
Chandra and Spitzer observations of CDFS X-ray obscured QSOs.
Georgantopoulos I., Georgakakis A., Akylas A.
<Astron. Astrophys., 466, 823-830 (2007)>
=2007A&A...466..823G 2007A&A...466..823G
ADC_Keywords: X-ray sources ; QSOs ; Active gal. nuclei ; Redshifts
Keywords: galaxies: active - galaxies: quasars: general - X-rays: galaxies -
X-rays: general
Abstract:
We present Chandra and Spitzer data for the 186, extragalactic, hard
2-10keV X-ray selected sources, which lie in the central part of the
Chandra Deep Field South (CDFS). For the vast majority of sources
(99.5%), there is a spectroscopic or photometric redshift available.
We classify 17 sources as X-ray obscured QSOs, strictly according to
X-ray criteria, i.e. defined as having large hydrogen column densities
(NH>1022cm-2^) and luminosities (LX>1044erg/s). The surface
density of X-ray obscured QSOs is ∼210°-2. We find 18 candidate
Compton-thick NH>1024cm-2 sources, of which three have QSO
luminosities (LX>1044erg/s). The X-ray obscured QSO comprise a mixed
bag of objects, covering the redshift range z=1.3-4.3. Eight of these
show narrow-line optical spectra, two show no obscuration in their
optical spectra that present broad lines, while for the other seven
there is only a photometric redshift available. About half of the
X-ray obscured QSOs show high X-ray to optical flux ratios, X/O>1, and
red colours, I-3.6µm>4. Combining the X-ray with the mid-IR 8µm
or 24µm flux can be used as an additional diagnostic to sift out
the heavily obscured AGN. All X-ray selected QSOs present red mid-IR
colours and can be easily separated among mid-IR sources,
demonstrating that mid-IR selection provides a powerful tool for
detecting obscured QSOs.
Description:
The 1Ms CDFS data consist of 11 individual Chandra (Advanced CCD
Imaging Spectrometer) ACIS-I pointings with the aim points separated
by a few arcseconds. The 247 sources were detected in the 2-10keV
band down to a flux limit of 2x10-16erg/cm2/s (Gamma=1.4).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 92 186 Spectral fits
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See also:
J/ApJ/610/128 : NIR colors of hard X-ray-selected AGN (Watanabe+, 2004)
J/ApJ/618/123 : Hard X-ray-emitting AGNs (Silverman+, 2005)
J/A+A/467/73 : 3σ hard sample of XMDS survey (Tajer+, 2007)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [GZW2002] Sequential number,
[GZW2002] XID NNN in Simbad
4 A1 --- n_[GZW2002] [*] *: Compton-thick sources
6- 21 A16 --- Name Source name from Giacconni et al. (2002, Cat.
J/ApJS/139/369) JHHMMSS.s+DDMMSS
23- 27 F5.2 --- Gamma Best fit model power-law photon index
29- 32 F4.2 --- E_Gamma ? Error on Gamma (upper limit)
34- 37 F4.2 --- e_Gamma ? Error on Gamma (lower limit)
39 A1 --- l_NH Limit flag on NH
40- 46 F7.2 10+22cm-2 NH Rest-frame column density
48 A1 --- f_NH [i] i when upper limit is infinity
49- 55 F7.2 10+22cm-2 E_NH ? Error on NH (upper limit)
57- 63 F7.2 10+22cm-2 e_NH ? Error on NH (lower limit)
65- 69 F5.2 10-7W logLX ?=- logarithm of 2-10keV intrinsic luminosity
71- 76 A6 --- Class Optical spectroscopic classification as given
in Szokoly et al. (2004, J/ApJS/155/271) (1)
78- 82 F5.3 --- z ?=- Redshift from either Szokoly et al. (2004
J/ApJS/155/271) (spectroscopic) or Zheng
et al. (2004, J/ApJS/155/73) (photometric)
84- 87 F4.2 10-17W/m2 Flux Observed 2-10keV X-ray flux
89- 92 F4.2 --- chi2/dof ?=- Reduced chi2
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Note (1): Types defined in Szokoly et al. (2004, J/ApJS/155/271) as follows:
BLAGN = Objects with emission lines broader than 2000km/s. This
classification implies an optical type 1 AGN or QSO.
HEX = Object with unresolved emission lines and exhibiting high
ionization lines or emission line ratios indicating AGN
activity. These objects are dominantly optical type 2 AGNs
or QSOs, but in a few cases the optical type 1/2
distinction is not possible based on the data.
LEX = Objects with unresolved emission lines consistent with an
H II region-type spectra. These objects would be classified
as normal galaxies based on the optical data alone as the
presence of the AGN cannot be established.
ABS = A typical galaxy spectrum showing only absorption lines
BLLAC? = May be a BL Lac object
M-star = M-type star
star = A stellar spectrum
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 12-Oct-2007