J/ApJ/876/53 Chandra X-ray point sources in the Fornax cluster (Jin+, 2019)
Chandra detection of intracluster X-ray sources in Fornax.
Jin X., Hou M., Zhu Z., Li Z.
<Astrophys. J., 876, 53 (2019)>
=2019ApJ...876...53J 2019ApJ...876...53J
ADC_Keywords: Clusters, galaxy; X-ray sources
Keywords: galaxies: clusters: individual (Fornax) ; X-rays: binaries ;
X-rays: galaxies: clusters
Abstract:
Based on archival Chandra observations with a total exposure of 1.3Ms,
we study X-ray point sources in the Fornax cluster of galaxies, with
the primary aim of searching for intracluster X-ray source
populations. We detect 1177 point sources out to a projected radius of
∼30' (∼180kpc) from the cluster center and down to a limiting 0.5-8keV
luminosity of ∼3x1037erg/s. We construct the source surface density
profile, after excluding sources associated with foreground stars,
known globular clusters, ultra-compact dwarfs, and galactic nuclei.
From this profile we statistically identify ∼183 excess sources that
are not associated with the bulk stellar content of the individual
member galaxies of Fornax, nor with the cosmic X-ray background.
Taking into account Poisson error and cosmic variance, the cumulative
significance of this excess is at the ≳2σ level (with a maximum
of 3.6σ) outside three effective radii of the central giant
elliptical, NGC 1399. The luminosity function of the excess sources is
found to be significantly steeper than that of the GC-hosting sources
(presumably low-mass X-ray binaries (LMXBs)), disfavoring the
possibility that unidentified GCs are primarily responsible for the
excess. We show that a large fraction of the excess can be related to
the extended stellar halo of NGC 1399 and/or the diffuse intracluster
light, thus providing strong evidence for the presence of intracluster
X-ray sources in Fornax, the second unambiguous case for a galaxy
cluster after Virgo. Other possible origins of the excess, including
supernova-kicked LMXBs and stripped nucleated dwarf galaxies are
discussed.
Description:
The Fornax cluster, particularly its core region, has been extensively
observed by Chandra, chiefly with its Advanced CCD Imaging
Spectrometer (ACIS). Initially, we acquired a total of 30 archival
Chandra observations, which include 12 ACIS-I and 18 ACIS-S
observations. We reprocessed the archival level-1 data and a log of
the final 29 observations --spanning 1999 Dec to 2015 Nov-- is given
in Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 54 29 Log of Chandra observations
table2.dat 123 1279 Catalog of detected X-ray sources
in the Fornax cluster
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
I/284 : The USNO-B1.0 Catalog (Monet+ 2003)
VII/180 : Galaxies in Fornax Cluster and five nearby groups (Ferguson+ 1990)
J/MNRAS/344/188 : BVI photometry in Fornax cluster galaxies (Karick+, 2003)
J/ApJS/153/223 : ACS Virgo Cluster Survey. I. (Cote+, 2004)
J/ApJS/169/213 : ACS Fornax Cluster Survey. I. (Jordan+, 2007)
J/ApJS/169/401 : ChaMP X-ray point source catalog (Kim+, 2007)
J/AJ/137/498 : UCD and bright GC in Fornax (Gregg+, 2009)
J/ApJ/706/223 : X-ray point sources near the Galactic Center (Hong+, 2009)
J/ApJ/721/1368 : X-ray emission from the Sombrero galaxy (Li+, 2010)
J/ApJ/736/90 : Chandra X-ray sources of NGC 1399 (Paolillo+, 2011)
J/A+A/533/A33 : LMXBs detected in nearby galaxies (Zhang+, 2011)
J/A+A/547/A65 : Extended stellar objects in galaxies (Bruens+, 2012)
J/ApJ/763/40 : UBVI photom. of GCs in the Fornax galaxy cluster (Kim+, 2013)
J/ApJS/221/13 : ACS Fornax Cluster Survey. XI. GC candidates (Jordan+, 2015)
J/ApJ/812/34 : UCD candidates in M87/M49/M60 regions (Liu+, 2015)
J/A+A/586/A102 : UCDs in the halo of NGC1399 (Voggel+, 2016)
J/A+A/608/A142 : Fornax Deep Survey with VST. III. LSB gal. (Venhola+, 2017)
J/ApJ/858/102 : Gemini/NIFS and HST obs. of the galaxy M59-UCD3 (Ahn+, 2018)
J/A+A/611/A93 : NGC3115 & NGC1399 VEGAS-SSS GCs (Cantiello+, 2018)
J/ApJ/862/73 : Deep Chandra obs. of X-ray point sources in M87 (Luan+, 2018)
J/ApJS/235/26 : Ultradeep cat. of X-ray point sources in the GC (Zhu+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- ObsID [239/17549] Chandra observation identifier
7-12 A6 --- Inst Instrument (ACIS-I or ACIS-S)
14-15 I2 h RAh Aim-point hour of right ascension (J2000)
17-18 I2 min RAm Aim-point minute of right ascension (J2000)
20-24 F5.2 s RAs Aim-point second of right ascension (J2000)
26 A1 --- DE- Aim-point sign of declination (J2000)
27-28 I2 deg DEd Aim-point degree of declination (J2000)
30-31 I2 arcmin DEm Aim-point arcminute of declination (J2000)
33-37 F5.2 arcsec DEs Aim-point arcsecond of declination (J2000)
39-42 F4.1 ks Exp [3.6/98.8] Cleaned exposure time
44-54 A11 "Y:M:D" Date Start date of observation (UT)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/1279] Internal index number (1)
6- 13 F8.5 deg RAdeg [54.07/55.21] Source centroid Right
Ascension (J2000)
15- 23 F9.5 deg DEdeg [-35.9/-35] Source centroid Declination
in decimal degrees (J2000)
25- 28 F4.2 arcsec PosErr [0.07/1.87] Position error
30 A1 --- l_S0.5-2 The 3σ upper limit flag on S0.5-2
32- 36 F5.1 10-7ph/cm2/s S0.5-2 [0.1/963.7] The 0.5-2 keV photon flux
38- 41 F4.1 10-7ph/cm2/s E_S0.5-2 [0.0/33.1]? Upper 1σ uncertainty
in S0.5-2
43- 46 F4.1 10-7ph/cm2/s e_S0.5-2 [0.2/40.7]? Lower 1σ uncertainty
in S2-8
48 A1 --- l_S2-8 The 3σ upper limit flag on S2-8
50- 54 F5.1 10-7ph/cm2/s S2-8 [0.2/361.2] The 2-8 keV photon flux
56- 59 F4.1 10-7ph/cm2/s E_S2-8 [0.0/22.9]? Upper 1σ uncertainty
in S2-8
61- 64 F4.1 10-7ph/cm2/s e_S2-8 [0.2/25.8]? Lower 1σ uncertainty
in S2-8
66 A1 --- l_S0.5-8 The 3σ upper limit flag on S0.5-8
67- 72 F6.1 10-7ph/cm2/s S0.5-8 [1.4/1383.4] The 0.5-8 keV photon flux
74- 77 F4.1 10-7ph/cm2/s E_S0.5-8 [0.4/43.6]? Upper 1σ uncertainty
in S0.5-8
79- 82 F4.1 10-7ph/cm2/s e_S0.5-8 [0.5/45.6]? Lower 1σ uncertainty
in S0.5-8
84 A1 --- l_F0.5-8 The 3σ upper limit flag on F0.5-8
86- 91 F6.1 10-16mW/m2 F0.5-8 [5.1/5036.6] The 0.5-8 keV energy flux
in units of 10-16erg/s/cm2 (2)
93- 97 F5.1 10-16mW/m2 E_F0.5-8 [1.6/158.8]? Upper 1σ uncertainty
in F0.5-8
99-103 F5.1 10-16mW/m2 e_F0.5-8 [2.0/165.9]? Lower 1σ uncertainty
in F0.5-8
105-109 F5.2 --- HR [-0.99/0.94] Hardness ratio (3)
111-114 F4.2 --- E_HR [0.0/0.81] Upper 1σ uncertainty
in HR
116-119 F4.2 --- e_HR [0.0/0.81] Lower 1σ uncertainty
in HR
121-123 A3 --- Note Additional note flag(s) (4)
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Note (1): In order of increasing R.A.
Note (2): Converted from 0.5-8keV photon flux by assuming an absorbed
power-law spectrum with photon-index of 1.7 and column density
1021/cm2.
Note (3): Where HR=(S2-8-S0.5-2)/(S2-8+S0.5-2).
Note (4): Flag as follows:
G = source spatially coincident with known globular cluster (GC;
269 occurrences).
N = nuclear source of a member galaxy (4 occurrences).
U = source spatially coincident with known ultra-compact dwarf galaxy
(UCD; 15 occurrences).
F = source spatially coincident with foreground star (18 occurrences).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 09-Oct-2020