J/MNRAS/521/1620 The X-ray ExSeSS source sample from 2SXPS (Delaney+, 2023)
The Extragalactic Serendipitous Swift Survey (ExSeSS).
I. Survey definition and measurements of the X-ray number counts.
Delaney J.N., Aird J., Evans P.A., Barlow-Hall C., Osborne J.P.,
Watson M.G.
<Mon. Not. R. Astron. Soc. 521, 1620-1632 (2023)>
=2023MNRAS.521.1620D 2023MNRAS.521.1620D (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Spectroscopy ; Photometry ; Active gal. nuclei ;
Galaxies ; Positional data
Keywords: galaxies: active - X-rays: galaxies
Abstract:
We present the Extragalactic Serendipitous Swift Survey (ExSeSS),
providing a new well-defined sample constructed from the observations
performed using the Swift X-ray Telescope. The ExSeSS sample consists
of 79342 sources detected in the medium (1-2 keV), hard (2-10 keV),
or total (0.3-10 keV) energy bands, covering 2086.6 deg2 of sky across
a flux range of f_0.3-10 keV_ ∼ 10-15 - 10-10 erg/s/cm2.
Using the new ExSeSS sample we present measurements of the
differential number counts of X-ray sources as a function of 2-10 keV
flux that trace the population of Active Galactic Nuclei (AGNs) in a
previously unexplored regime. We find that taking the line-of-sight
absorption column density into account has an effect on the
differential number count measurements and is vital to obtain
agreement with previous results. In the hard band, we obtain a good
agreement between the ExSeSS measurements and previous, higher energy
data from NuSTAR and Swift/BAT when taking into account the varying
column density of the ExSeSS sample as well as the X-ray spectral
parameters of each of the samples we are comparing to. We also find
discrepancies between the ExSeSS measurements and AGN population
synthesis models, indicating a change in the properties of the AGN
population over this flux range that is not fully described by current
models at these energies, hinting at a larger, moderately obscured
population at low redshifts (z ≲ 0.2) that the models are not
currently taking into account.
Description:
Active Galactic Nuclei (AGNs) occur when the supermassive black hole
(SMBH) at the centre of a galaxy is rapidly accreting dust and gas,
emitting large amounts of energy across the electromagnetic spectrum.
Identifying AGN at X-ray wavelengths is particularly effective as the
X-ray emission is able to penetrate surrounding material, allowing
obscured sources that would not be found at other wavelengths to be
identified. In this paper, we present the Extragalactic Serendipitous
Swift Survey (ExSeSS), a new sample of truly serendipitous sources at
high Galactic latitudes and covering an area of 2086.6 deg2 which is
constructed from observations carried out with the Swift X-ray
telescope (XRT). Our sample is extracted from the 2SXPS which contains
all sources detected in the 0.3-1, 1-2, 2-10, and 0.3-10 keV range,
which we reduce to be primarily extragalactic and serendipitous to
provide an unbiased sample of X-ray sources to study the AGN
population.
As decribed in section 2, we removed areas covered by the Galactic
plane or large nearby galaxies so that the sample is dominated by
background extragalactic sources, and removing any X-ray sources
associated with the targets from the resulting catalogues so that only
truly serendipitous detections are retained. We only selected fields
dominated by extragalactic X-ray sources. Next, to create a truly
serendipitous sample of sources requires that we identify the targets
of the Swift/XRT observations corresponding to each of our data sets
and subsequently remove any X-ray sources associated with these
targets. We also defined a diagram flow to define ExSeSS targets.
Finally, we limited our sample to sources detected in the medium
(1-2 keV), hard (2-10 keV), or total (0.3-10 keV) bands from 2SXPS
leaving us with a total of 79342 sources in the ExSeSS sample as in
table.dat. We converted the rates in the individual bands into fluxes
assuming a simple power-law X-ray spectrum and correcting for Galactic
absorption which corresponds to the average over the ExSeSS area. The
section 3 explains integrations of number counts and rates, column
density analysis.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table.dat 511 79342 The final source catalogue of the ExSeSS sample
in soft, medium, hard X ray bands
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See also:
J/MNRAS/484/3785 : Relative specific Type Ia supernovae rate (Brown+, 2019)
J/MNRAS/459/1602 : AGN sample in the northern XMM-XXL field (Liu+, 2016)
J/A+A/661/A1 : The eFEDS X-ray catalogs (V7.4) (Brunner+, 2022)
J/A+A/588/A103 : Second ROSAT all-sky survey (2RXS) source catalog
(Boller+, 2016)
J/A+A/493/339 : XMM-Newton serendipitous Survey. V. (Watson+, 2009)
J/ApJ/836/99 : NuSTAR serendipitous survey: the 40-month catalog
(Lansbury+, 2017)
J/ApJ/819/62 : The COSMOS-Legacy Survey (CLS) catalog (Civano+, 2016)
J/ApJ/808/184 : NuSTAR surveys: ECDF-S catalog (Mullaney+, 2015)
J/ApJ/808/185 : NuSTAR surveys: COSMOS catalog (Civano+, 2015)
J/ApJ/749/21 : AGNs detected by 60 month Swift/BAT survey (Ajello+, 2012)
J/ApJS/251/2 : CDWFS: Chandra survey in Bootes. I. X-ray cat.
(Masini+, 2020)
J/ApJS/238/32 : 3rd MAXI/GSC X-ray cat at high Galactic latitude
(Kawamuro+, 2018)
J/ApJS/236/48 : The Chandra UDS survey (X-UDS) (Kocevski+, 2018)
J/ApJS/235/4 : The 105-month Swift-BAT all-sky hard X-ray survey (Oh+,2018)
J/ApJS/233/17 : Swift/BAT AGN spectroscopic survey. V. X-ray data
(Ricci+, 2017)
J/ApJS/228/2 : Chandra Deep Field-South survey: 7Ms sources (Luo+, 2017)
J/ApJS/220/10 : AEGIS-X Deep survey of EGS (AEGIS-XD) (Nandra+, 2015)
J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)
J/ApJS/180/102 : AEGIS-X: Chandra deep survey (Laird+, 2009)
J/ApJS/161/185 : GIS catalog project : source catalog II (Ueda+, 2005)
J/ApJS/148/275 : ASCA AGN optical identifications (Akiyama+, 2003)
J/ApJS/133/1 : GIS catalog project : source catalog (Ueda+, 2001)
J/AJ/126/539 : The Chandra Deep Fields North and South (Alexander+, 2003)
VII/292 : DESI Legacy Imaging Surveys DR8 photometric redshifts
(Duncan, 2022)
IX/59 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR9
(Webb+, 2020)
IX/58 : 2SXPS Swift X-ray telescope point source catalogue
(Evans+, 2020)
IX/49 : XXL Survey: First results (Pierre+, 2016)
IX/46 : XMM-Newton Serendipitous Source Catalogue 3XMM-DR5
(XMM-SSC+ 2016)
IX/45 : The Chandra Source Catalog, Release 1.1 (Evans+ 2012)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Field Data field ID from the original 2SXPS
catalogue (Field)
7- 11 I5 --- ExSeSS The ID of unique sources in the ExSeSS
sample (ExSeSS_ID)
13- 18 I6 --- 2SXPS Source ID from the 2SXPS catalogue
(2SXPS_ID)
20- 30 I11 --- Set Data set ID from the original 2SXPS
32- 40 F9.5 deg RAdeg The right ascension of the source position
(J2000) (RA)
42- 50 E9.7 deg E_RAdeg The positive error in right ascension of
the source position (RA_pos)
52- 61 E10.7 deg e_RAdeg [] The negative error in right ascension of
the source position (RA_neg)
63- 71 F9.5 deg DEdeg The declination of the source position
(J2000) (Decl)
73- 81 E9.7 deg E_DEdeg The positive error in declination of the
source position (Decl_pos)
83- 92 E10.7 deg e_DEdeg [] The negative error in declination of the
source position (Decl_neg)
94-102 E9.7 ct/s MRate ?=-999 The rate for the medium 1-2 keV band
(Medium_Rate)
104-112 E9.7 ct/s E_MRate ?=-999 The error in the rate for the medium
1-2 keV band (MediumRatepos)
114-123 E10.7 ct/s e_MRate []?=-999 The error in the rate for the
medium 1-2 keV band (MediumRateneg)
125-133 E9.7 ct/s HRate ?=-999 The rate for the hard 2-10 keV band
(Hard_Rate)
135-143 E9.7 ct/s E_HRate ?=-999 The error in the rate for the hard
2-10 keV band (HardRatepos)
145-154 E10.7 ct/s e_HRate []?=-999 The error in the rate for the hard
2-10 keV band (HardRateneg)
156-164 E9.7 ct/s TRate ?=-999 The rate for the total 0.3-10 keV
band (Total_Rate)
166-174 E9.7 ct/s E_TRate ?=-999 The error in the rate for the total
0.3-10 keV band (TotalRatepos)
176-185 E10.7 ct/s e_TRate []?=-999 The error in the rate for the
total 0.3-10 keV band (TotalRateneg)
187-209 E23.20 deg2 MArea ?=-999 The corresponding area coverage to
the source rate value in the medium band
(Medium_Area)
211-233 E23.20 deg2 HArea ?=-999 The corresponding area coverage to
the source rate value in the hard band
(Hard_Area)
235-257 E23.20 deg2 TArea ?=-999 The corresponding area coverage to
the source rate value in the total band
(Total_Area)
259-280 E22.17 mW/m2 SFlux ?=-999 The flux for the soft 0.5-2 keV band
estimated from the medium (1-2 keV) band
rate (Soft_Flux)
282-303 E22.17 mW/m2 E_SFlux ?=-999 The error in the flux for the soft
0.5-2 keV band estimated from the medium
(1-2 keV) band rate (SoftFluxpos)
305-327 E23.17 mW/m2 e_SFlux []?=-999 The error in the flux for the soft
0.5-2 keV band estimated from the medium
(1-2 keV) band rate (SoftFluxneg)
329-350 E22.17 mW/m2 HFlux ?=-999 The flux for the hard 2-10 keV band
(Hard_Flux)
352-373 E22.17 mW/m2 E_HFlux ?=-999 The error in the flux for the hard
2-10 keV band (HardFluxpos)
375-397 E23.17 mW/m2 e_HFlux []?=-999 The error in the flux for the hard
2-10 keV band (HardFluxneg)
399-420 E22.17 mW/m2 TFlux ?=-999 The flux for the total 0.3-10 keV
band (Total_Flux)
422-443 E22.17 mW/m2 E_TFlux ?=-999 The error in the flux for the total
0.3-10 keV band (TotalFluxpos)
445-467 E23.17 mW/m2 e_TFlux []?=-999 The error in the flux for the
total 0.3-10 keV band (TotalFluxneg)
469-488 F20.15 cm-2 NH ?=-999 Effective column density for the hard
band sample for sources with fluxes above
the 0.1 per cent area covereage cut
(Effective_NH)
490-511 E22.17 mW/m2 HFluxvarNH ?=-999 The flux values in the 2-10 keV band
calculated using variable and effective NH
as described in sect. 3.2 with same 0.1%
area cut off (HardFluxvariableNh)
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Luc Trabelsi [CDS] 28-May-2026