J/A+A/618/A66 Redshifts of obscured AGN (Simmonds+, 2018)
XZ: Deriving redshifts from X-ray spectra of obscured AGN.
Simmonds C., Buchner J., Salvato M., Hsu L.T., Bauer F.E.
<Astron. Astrophys. 618, A66 (2018)>
=2018A&A...618A..66S 2018A&A...618A..66S (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; X-ray sources ; Redshifts; Spectroscopy ;
Photometry
Keywords: galaxies: active - X-rays: galaxies -
galaxies: distances and redshifts
Abstract:
Redshifts are fundamental for our understanding of extragalactic X-ray
sources. Ambiguous counterpart associations, expensive optical
spectroscopy and/or multimission multiwavelength coverage to resolve
degeneracies make estimation often difficult in practice.
We attempt to constrain redshifts of obscured Active Galactic Nuclei
(AGN) using only low-resolution X-ray spectra.
Our XZ method fits AGN X-ray spectra with a moderately complex
spectral model incorporating a corona, torus obscurer and warm mirror.
Using the Bayesian X-ray Astronomy (BXA) package, we constrain
redshift, column density, photon index and luminosity simultaneously.
The redshift information primarily comes from absorption edges in
Compton-thin AGN, and from the Fe Kα fluorescent line in heavily
obscured AGN. A new generic background fitting method allows us to
extract more information from limited numbers of source counts.
We derive redshift constraints for 74/321 hard-band detected sources
in the Chandra deep field South. Comparing with spectroscopic
redshifts, we find an outlier fraction of 8%, indicating that our
model assumptions are valid. For three Chandra deep fields, we release
our XZ redshift estimates.
The independent XZ estimate is easy to apply and effective for a large
fraction of obscured AGN in todays deep surveys without the need for
any additional data. Comparing to different redshift estimation
methods, XZ can resolve degeneracies in photometric redshifts, help to
detect potential association problems and confirm uncertain
single-line spectroscopic redshifts. With high spectral resolution and
large collecting area, this technique will be highly effective for
Athena/WFI observations.
Description:
XZ, redshift estimates from X-ray spectra alone, are presented for
three Chandra survey fields: CDF-S, AEGIS-XD and COSMOS. The spectra
are described in Buchner et al. (2015, Cat. J/ApJ/802/89 ); sources
are all 2-10keV detected. Only sources where redshift information was
gained (IG>1) are included. For comparison, redshift information from
photo-z and spec-z is included from existing catalogues (CDF-S: Hsu et
al. (2014, J/ApJ/796/60), AEGIS-XD: Nandra et al. (2015, Cat.
J/ApJS/220/10), COSMOS: Salvato et al. (2009ApJ...690.1250S 2009ApJ...690.1250S)). In some
cases, XZ uncertainties are small and the method provides an
independent measurement of the redshift of the AGN obscurer. Beyond
that, when photo-z, spec-z and/or XZ disagree, problematic redshift
measurements can be identified. For examples of use, see our paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cosmos.dat 95 86 Redshift information in COSMOS AGN
cdfs.dat 107 138 Redshift information in CDF-S AGN
aegis.dat 95 140 Redshift information in AEGIS-XD AGN
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See also:
II/284 : COSMOS Multi-Wavelength Photometry Catalog (Capak+, 2007)
VII/265 : COSMOS Morphological Catalog (V1.1) (Tasca+ 2009)
J/ApJ/796/60 : ECDFS galaxies photometric redshifts + counterparts (Hsu+ 2014)
J/ApJ/802/89 : Luminosity function of X-ray-selected AGNs (Buchner+, 2015)
J/ApJS/220/10 : AEGIS-X Deep survey of EGS (AEGIS-XD) (Nandra+, 2015)
Byte-by-byte Description of file: cosmos.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- XID Identification (cosmos_NNNN)
13- 16 I4 ct Counts Amount of detected source counts
18- 26 F9.5 deg RAdeg Right ascension (J2000)
28- 34 F7.5 deg DEdeg Declination (J2000)
36- 39 F4.2 --- XZ 50% quantile of the posterior of XZ
41- 44 F4.2 --- b_XZ 10% quantile of the posterior of XZ
46- 49 F4.2 --- B_XZ 90% quantile of the posterior of XZ
51- 54 F4.2 --- photoz 50% quantile of the posterior of photoz
56- 59 F4.2 --- b_photoz 10% quantile of the posterior of photoz
61- 64 F4.2 --- B_photoz 90% quantile of the posterior of photoz
66- 70 F5.2 [cm-2] logNH 50% quantile of the posterior of NH (1)
72- 76 F5.2 [cm-2] b_logNH 10% quantile of the posterior of NH (1)
78- 82 F5.2 [cm-2] B_logNH 90% quantile of the posterior of NH (1)
84- 90 F7.4 --- specz ?=-9.999 Spectroscopic redshift
92- 95 F4.2 --- IG [1/4.32] Information gained
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Note (1): In logarithmic units.
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Byte-by-byte Description of file: cdfs.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- XID Identification (cdfs4Ms_NNN)
13- 16 I4 ct Counts Amount of detected source counts
18- 26 F9.6 deg RAdeg Rigth ascension (J2000)
28- 37 F10.6 deg DEdeg Declination (J2000)
39- 42 F4.2 --- XZ 50% quantile of the posterior of XZ
44- 47 F4.2 --- b_XZ 10% quantile of the posterior of XZ
49- 52 F4.2 --- B_XZ 90% quantile of the posterior of XZ
54- 58 F5.2 --- photoz ?=-9.99, 50% quantile of the posterior
of photoz
60- 64 F5.2 --- b_photoz ?=-9.99, 10% quantile of the posterior
of photoz
66- 70 F5.2 --- B_photoz ?=-9.99, 90% quantile of the posterior
of photoz
72- 76 F5.2 [cm-2] logNH 50% quantile of the posterior of NH (1)
78- 82 F5.2 [cm-2] b_logNH 10% quantile of the posterior of NH (1)
84- 88 F5.2 [cm-2] B_logNH 90% quantile of the posterior of NH (1)
90- 96 F7.4 --- specz ?=-9.999 Spectroscopic redshift
98-100 I3 --- quality [0/3]?=-99 Quality of specz, 0 is reliable
102-105 F4.2 --- IG [1/4.32] Information gained
107 I1 --- Sample [1/3] Subsample identification
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Note (1): In logarithmic units.
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Byte-by-byte Description of file: aegis.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- XID Identification (aegis_NNN)
11- 14 I4 --- Counts Amount of detected source counts
16- 23 F8.4 deg RAdeg Right ascension (J2000)
25- 32 F8.5 deg DEdeg Declination (J2000)
34- 37 F4.2 --- XZ 50% quantile of the posterior of XZ
39- 42 F4.2 --- b_XZ 10% quantile of the posterior of XZ
44- 47 F4.2 --- B_XZ 90% quantile of the posterior of XZ
49- 52 F4.2 --- photoz 50% quantile of the posterior of photoz
54- 57 F4.2 --- b_photoz 10% quantile of the posterior of photoz
59- 62 F4.2 --- B_photoz 90% quantile of the posterior of photoz
64- 68 F5.2 [cm-2] logNH 50% quantile of the posterior of NH (1)
70- 74 F5.2 [cm-2] b_logNH 10% quantile of the posterior of NH (1)
76- 80 F5.2 [cm-2] B_logNH 90% quantile of the posterior of NH (1)
82- 90 F9.6 --- specz ?=-9.999 Spectroscopic redshift
92- 95 F4.2 --- IG [1/4.32] Information gained
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Note (1): In logarithmic units.
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Acknowledgements:
Charlotte Simmonds, cpsimmonds(at)uc.cl
(End) Patricia Vannier [CDS] 12-Jul-2018