J/ApJ/949/49 Opt. selected close galaxy pairs with Chandra obs. (He+, 2023)
A Chandra X-ray survey of optically selected close galaxy pairs: unexpectedly
low occupation of active galactic nuclei.
He L., Hou M., Li Z., Feng S., Liu X.
<Astrophys. J., 949, 49 (2023)>
=2023ApJ...949...49H 2023ApJ...949...49H
ADC_Keywords: Galaxies, interacting; Active gal. nuclei; Redshifts; Optical;
X-ray sources; Black holes
Keywords: Galaxy nuclei ; Interacting galaxies ; Galaxy mergers ;
X-ray active galactic nuclei
Abstract:
High-resolution X-ray observations offer a unique tool for probing the
still-elusive connection between galaxy mergers and active galactic
nuclei (AGNs). We present an analysis of nuclear X-ray emission in an
optically selected sample of 92 close galaxy pairs (with projected
separations ≲20kpc and line-of-sight velocity offsets <500km/s) at
low redshift ({bar}z∼0.07), based on archival Chandra observations.
The parent sample of galaxy pairs is constructed without imposing an
optical classification of nuclear activity, thus it is largely free of
selection effect for or against the presence of an AGN. Nor is this
sample biased for or against gas-rich mergers. An X-ray source is
detected in 70 of the 184 nuclei, giving a detection rate of
38%-5%+5%, down to a 0.5-8keV limiting luminosity of
≲1040erg/s. The detected and undetected nuclei show no systematic
difference in their host galaxy properties such as galaxy morphology,
stellar mass, and stellar velocity dispersion. When potential
contamination from star formation is avoided (i.e.,
L2-10keV>1041erg/s), the detection rate becomes 18%-3%+3%
(32/184), which shows no excess compared to the X-ray detection rate
of a comparison sample of optically classified single AGNs. The
fraction of pairs containing dual AGN is only 2%-2%+2%. Moreover,
most nuclei at the smallest projected separations probed by our sample
(a few kiloparsecs) have an unexpectedly low apparent X-ray luminosity
and Eddington ratio, which cannot be solely explained by circumnuclear
obscuration. These findings suggest that close galaxy interaction is
not a sufficient condition for triggering a high level of AGN activity.
Description:
Extending the study of Hou+ 2020 (J/ApJ/900/79), in this work we use
archival Chandra observations to survey the nuclear X-ray emission
from a new sample of close galaxies pairs.
In this work, we construct a new sample of close galaxy pairs based on
the parent sample of galaxy pairs recently presented by F19
(Feng+ 2019ApJ...880..114F 2019ApJ...880..114F). The F19 sample itself was extracted from
the SDSS DR7 (II/294).
We cross-matched the F19 sample with the Chandra X-ray data archive to
select pairs with observations taken with the Advanced CCD Imaging
Spectrometer (ACIS) and publicly available as of June 2022.
Our final sample consists of 92 optically and X-ray selected galaxy
pairs, which have rp ranging from 3.0 to 19.7kpc.
See Section 2.
To help constrain the presence of intrinsically luminous but heavily
obscured AGNs in the sample galaxies, we utilized archival NuSTAR
observations that are sensitive to the hard (≳10keV) X-rays from
obscured AGNs.
See Section 3.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 86 184 Information of close galaxy pairs with Chandra
observation
table2.dat 148 70 X-ray properties of close galaxy pairs
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
V/156 : LAMOST DR7 catalogs (Luo+, 2019)
J/ApJ/705/L76 : AGNs with double-peaked [OIII] lines (Wang+, 2009)
J/ApJ/737/101 : AGN pairs from SDSS-DR7. I. (Liu+, 2011)
J/ApJ/746/L22 : Dual AGNs in the nearby Universe (Koss+, 2012)
J/MNRAS/419/2095 : HMXBs in nearby galaxies (Mineo+, 2012)
J/ApJ/764/41 : X-ray binary evolution across cosmic time (Fragos+, 2013)
J/ApJ/799/72 : Binary AGNs from the VLA Stripe 82 survey (Fu+, 2015)
J/other/RAA/16.C7 : LAMOST-SDSS galaxy pairs (Shen+, 2016)
J/ApJ/836/99 : NuSTAR serendipitous survey: 40-month cat (Lansbury+, 2017)
J/ApJ/869/171 : Chandra observations of NuSTAR sources (Tomsick+, 2018)
J/MNRAS/474/3875 : Galaxy And Mass Assembly (GAMA): DR3 (Baldry+, 2018)
J/ApJ/900/79 : Chandra obs. of SDSS AGN pairs at zmed∼0.1 (Hou+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- SDSS SDSS name (JHHMMSS.ss+DDMMSS.s)
21- 29 F9.5 deg RAdeg Right Ascension (J2000) (1)
31- 39 F9.5 deg DEdeg [-10.3/65.2] Declination (J2000) (1)
41- 46 F6.4 --- z [0.017/0.18] Spectroscopic redshift
48- 51 F4.1 kpc rp [3/19.7] Projected physical separation
of galaxy pairs
53- 56 F4.1 [Msun] logMs [7.1/11.8]? log stellar mass
58- 62 F5.2 Msun/yr SFR [0/50]? Star Formation Rate (2)
64- 68 F5.2 Msun/yr E_SFR [0/74.3]? Upper uncertainty in SFR
70- 74 F5.2 Msun/yr e_SFR [0/32]? Lower uncertainty in SFR
76- 78 F3.1 [Msun] logMBH [5.6/8.9]? log black hole mass (3)
80- 84 F5.2 [10-7W] logLX [39.2/42.9] log 0.5-8keV limiting
X-ray luminosity
86 I1 --- Flag [0/1] X-ray detection flag
(1=X-ray detection)
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Note (1): Optical position of the galaxy nucleus.
Note (2): Given by the MPA-JHU DR7 catalog;
Note (3): Estimate inferred from σ* assuming the MBH-σ*
relation of Gultekin+ 2009ApJ...706..404G 2009ApJ...706..404G
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- SDSS SDSS name (JHHMMSS.ss+DDMMSS.s)
21- 29 F9.5 deg RAdeg Right Ascension (J2000) (1)
31- 39 F9.5 deg DEdeg [-10.3/65.2] Declination (J2000) (1)
41- 46 F6.1 ct Cts [2/5274] Observed net counts in
0.5-8keV bands
48- 51 F4.1 ct E_Cts [2/77] Upper uncertainty in Cts
53- 56 F4.1 ct e_Cts [1.3/76] Lower uncertainty in Cts
58 A1 --- l_F0.5-2 Limit flag on F0.5-2
59- 64 F6.2 10-6ph/cm2/s F0.5-2 [0.26/786] Observed 0.5-2keV photon
flux
66- 70 F5.2 10-6ph/cm2/s E_F0.5-2 [0.1/35]? Upper uncertainty in F0.5-2
72- 76 F5.2 10-6ph/cm2/s e_F0.5-2 [0.1/28]? Lower uncertainty in F0.5-2
78 A1 --- l_F2-8 Limit flag on F2-8
79- 84 F6.2 10-6ph/cm2/s F2-8 [0.1/636] Observed 2-8keV photon flux
86- 90 F5.2 10-6ph/cm2/s E_F2-8 [0.05/37]? Upper uncertainty in F2-8
92- 96 F5.2 10-6ph/cm2/s e_F2-8 [0.05/28.4]? Lower uncertainty in
F2-8
98 A1 --- l_logL0.5-2 Limit flag on logL0.5-2
99- 104 F6.2 [10-7W] logL0.5-2 [38.9/42.8] Log 0.5-2keV unabsorbed
luminosity; erg/s
106- 109 F4.2 [10-7W] E_logL0.5-2 [0.01/0.5]? Upper uncertainty in
logL0.5-2
111- 114 F4.2 [10-7W] e_logL0.5-2 [0.01/0.9]? Lower uncertainty in
logL0.5-2
116 A1 --- l_logL2-10 Limit flag on logL2-10
117- 122 F6.2 [10-7W] logL2-10 [39.2/43.9] Log 2-10keV unabsorbed
luminosity; erg/s
124- 127 F4.2 [10-7W] E_logL2-10 [0.01/0.5]? Upper uncertainty in
logL2-10
129- 132 F4.2 [10-7W] e_logL2-10 [0.01/1.6]? Lower uncertainty in
logL2-10
134- 138 F5.2 --- HR [-0.95/0.97] Hardness ratio (2)
140- 143 F4.2 --- E_HR [0/0.8] Upper uncertainty in HR
145- 148 F4.2 --- e_HR [0.01/0.8] Lower uncertainty in HR
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Note (1): Centroid position of the X-ray counterpart.
Note (2): Where HR=(H-S)/(H+S) and S is the 0.5-2keV band and
H is the 2-8keV band.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Jul-2025