J/MNRAS/498/4790 Ultraluminous X-ray sources in local Universe (Kovlakas+, 2020)
A census of ultraluminous X-ray sources in the local Universe.
Kovlakas K., Zezas A., Andrews J.J., Basu-Zych A., Fragos T.,
Hornschemeier A., Lehmer B., Ptak A.
<Mon. Not. R. Astron. Soc., 498, 4790-4810 (2020)>
=2020MNRAS.498.4790K 2020MNRAS.498.4790K (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Galaxies, nearby ; Galaxy catalogs ;
Positional data
Keywords: methods: statistical - catalogues - X-rays: binaries -
X-rays: galaxies
Abstract:
Using the Chandra Source Catalog 2.0 and a newly compiled catalogue of
galaxies in the local Universe, we deliver a census of ultraluminous
X-ray source (ULX) populations in nearby galaxies. We find 629 ULX
candidates in 309 galaxies with distance smaller than 40Mpc. The
foreground/background contamination is ∼20 per cent. The ULX populations
in bona fide star-forming galaxies scale on average with star formation
rate and stellar mass (M*) such that the number of ULXs per galaxy is
0.45+0.06-0.09xSFR/(M☉/yr)+3.3+3.8-3.2xM*/M☉.
The scaling depends strongly on the morphological type. This analysis
shows that early spiral galaxies contain an additional population of
ULXs that scales with M*. We also confirm the strong
anticorrelation of the ULX rate with the host galaxy's metallicity. In
the case of early-type galaxies, we find that there is a non-linear
dependence of the number of ULXs with M*, which is interpreted as
the result of star formation history differences. Taking into account
age and metallicity effects, we find that the predictions from X-ray
binary population synthesis models are consistent with the observed
ULX rates in early-type galaxies, as well as spiral/irregular
galaxies.
Description:
We use the Heraklion Extragalactic Catalogue (HECATE), a compilation
of all galaxies within 200Mpc, from the HyperLEDA (Makarov et al.
2014A&A...570A..13M 2014A&A...570A..13M), arguably the most complete compilation of
galaxies with homogenized parameters. The HECATE adopts positions,
sizes, morphological classifications, and redshifts from the
HyperLEDA. These are complemented with size and redshift information
from other catalogues when not available in the HyperLEDA. It also
provides robust estimates of distances, along with SFRs, stellar
masses, metallicities and nuclear activity classifications.
To identify ULX candidates, we use the CSC 2.0
(https://cxc.harvard.edu/csc2/), which is a publicly available
catalogue of all the sources detected in Chandra observations
performed up to the end of 2014. It contains 317167 X-ray sources, an
improvement of more than a factor of 3 compared to the previous
version.
An X-ray source is associated with a HECATE galaxy if it is located
within its D25 region. The positional uncertainties of the sources
are not considered, since they are negligible with respect to the
dimensions of the galaxies. Out of the 317167 sources in the CSC 2.0,
we associate 23043 sources to 2218 galaxies within a distance of
200Mpc. The parameters of the host galaxies are listed in Table 1,
while the properties of the selected X-ray sources are given in Table 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 182 2218 Parameters of the 2218 host galaxies
table2.dat 220 23043 Properties of the 23043 X-ray sources
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See also:
IX/57 : The Chandra Source Catalog (CSC), Release 2.0 (Evans+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- ID [92/6740437] Source identifier from
HyperLEDA and HECATE (1)
9- 36 A28 --- Name Galaxy name (1)
38- 48 F11.7 deg RAdeg Right ascension (J2000) (1)
50- 60 F11.7 deg DEdeg Declination (J2000) (1)
62- 72 F11.7 arcmin R1 Semimajor axis (1)
74- 84 F11.7 arcmin R2 ? Semiminor axis (1)
86- 95 F10.6 deg PA []? North-to-East position angle (1)
97- 105 F9.6 --- T ? Morphological code
(see Table 3 of the article) (1)
107- 114 F8.4 --- e_T Error on T (1)
116- 123 F8.5 Mpc Dist ? Distance (1)
125- 132 F8.5 [Msun/yr] logSFR ? Logarithm of the star formation rate (1)
134- 140 F7.5 [-] logOH ? Metallicity 12+log(O/H) (1)
142 A1 --- AGN [Y/N/ ] Indicates if the galaxy hosts an
AGN (1)
144- 151 F8.6 --- f25 ? Fraction of the D25 region covered by
the CSC 2.0 stacks
153 I1 --- used [0/1] Indicates if the galaxy is used in
the analysis in this paper
(see Section 3.2 of the article)
155- 156 I2 --- Nobs Number of observed sources with
LX>1039erg/s excluding nuclear sources
if the host is classified as an AGN
158- 164 F7.5 --- Nf/b ? Number of expected foreground/background
source contamination in the ULX regime
166- 170 F5.2 --- Nulx ? Number of ULXs by subtracting interlopers
172- 176 F5.2 --- E_Nulx ? Upper error on Nulx
178- 182 F5.2 --- e_Nulx ? Lower error on Nulx
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Note (1): Values taken from the Heraklion Extragalactic Catalogue (HECATE)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- ID [92/6740437] Host galaxy identifier from
HyperLEDA and HECATE
9- 30 A22 --- Name X-ray source name
32- 52 F21.17 deg RAdeg Right ascension (J2000)
54- 74 F21.17 deg DEdeg Declination (J2000)
76- 94 E19.14 mW/m2 Flux ? Full-band (0.5-8.0keV) flux (1)
96- 114 E19.14 mW/m2 b_Flux ? Lower bound on Flux
116- 134 E19.14 mW/m2 B_Flux ? Upper bound on Flux
136 I1 --- Flagp [0/1] Flag indicating if the source is a pile-up
source (2)
138 I1 --- Flagu [0/1] Flag indicating if the source is
unreliable (0:reliable, 1:unreliable) (3)
140 I1 --- Flagn [0/1] Flag indicating if the source is
nuclear (4)
142- 160 F19.17 --- c Galactocentric scale parameter (5)
162- 180 E19.14 10-7W LX ? X-ray luminosity converted from Flux adopting
the distance of the host galaxy in the HECATE
182- 200 E19.14 10-7W b_LX ? Lower bound on LX
202- 220 E19.14 10-7W B_LX ? Upper bound on LX
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Note (1): Aperture-corrected net energy flux inferred from the PSF 90 per cent
enclosed count fraction aperture as provided by the CSC 2.0
Note (2): The fluxes and luminosities of pile-up sources are considered as
lower limits
Note (3): We characterize sources as 'reliable' or 'unreliable' based on their
attributes in the CSC 2.0. A source is marked as 'unreliable' if any
of the following conditions are met:
i - the flux is zero (i.e. upper limit) or no confidence interval
is provided;
ii - the 'ditherwarningflag' is on: indicating that the highest
peak of the power spectrum of the source occurs at the dither
frequency (or its beat frequency) in all observations;
iii - the 'streaksrcflag' is on: the source is found on an ACIS
readout streak in all observations;
iV - the 'satsrcflag' is on: saturated in all observations
Note (4): We consider sources as nuclear if they are located in the central
3arcsec region (i.e. three times the quadratic sum of the typical
positional uncertainty in the HECATE and the CSC 2.0 (1arcsec)). The
positional uncertainties of the sources are considered negligible
since 98 per cent of the circum-nuclear sources have positional
uncertainties of <3arcsec.
Note (5): We define the galactocentric scale parameter, c, as the deprojected
distance of a source from the centre of its host galaxy, normalized
by the galaxy's semimajor axis. See Appendix A of the article for a
full description of the calculation of c.
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 08-Aug-2023