J/ApJ/748/124 AGN X-ray variability in the 4Ms catalog (Young+, 2012)
Variability-selected low-luminosity active galactic nuclei in the 4Ms
Chandra Deep Field-South.
Young M., Brandt W.N., Xue Y.Q., Paolillo M., Alexander D.M., Bauer F.E.,
Lehmer B.D., Luo B., Shemmer O., Schneider D.P., Vignali C.
<Astrophys. J., 748, 124 (2012)>
=2012ApJ...748..124Y 2012ApJ...748..124Y
ADC_Keywords: X-ray sources ; Redshifts ; Active gal. nuclei
Keywords: galaxies: active - X-rays: galaxies
Abstract:
The 4 Ms Chandra Deep Field-South (CDF-S) and other deep X-ray surveys
have been highly effective at selecting active galactic nuclei (AGNs).
However, cosmologically distant low-luminosity AGNs (LLAGNs) have
remained a challenge to identify due to significant contribution from
the host galaxy. We identify long-term X-ray variability
(∼month-years, observed frame) in 20 of 92 CDF-S galaxies spanning
redshifts z~0.08-1.02 that do not meet other AGN selection
criteria. We show that the observed variability cannot be explained by
X-ray binary populations or ultraluminous X-ray sources, so the
variability is most likely caused by accretion onto a supermassive
black hole (SMBH). The variable galaxies are not heavily obscured in
general, with a stacked effective power-law photon index of
Γstack~1.93±0.13, and are therefore likely LLAGNs.
The LLAGNs tend to lie a factor of ~6-80 below the extrapolated
linear variability-luminosity relation measured for luminous AGNs.
Description:
The details of the 4Ms CDF-S source catalog are available in Xue et
al. (2011, Cat. J/ApJS/195/10). The 4Ms CDF-S, constructed from 54
Chandra observations over 10.8 years, covers an area of 464.5 arcmin2.
Of 716 X-ray sources with multi-wavelength identifications, 419
(58.5%) have spectroscopic redshift measurements and 92 CDF-S galaxies
have "good-quality" observations (see Section 3).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 176 92 X-ray properties of CDF-S galaxies
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2013)
II/253 : Chandra Deep Field South: multi-colour data (Wolf+, 2008)
J/A+A/555/A42 : The XMM-CDFS catalogues (Ranalli+, 2013)
J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)
J/ApJ/720/368 : Color-magnitude relations of galaxies in CDFs (Xue+, 2010)
J/A+A/507/1277 : Multiwavelength phot. of CDFS X-ray sources (Brusa+, 2009)
J/ApJS/179/19 : CDFS survey: 2 Ms source catalogs (Luo+, 2008)
J/ApJ/640/167 : AGNs and ULIRGs in the CDF-South (Alonso-Herrero+, 2006)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- XID [66/679] Sequence number (1)
5 A1 --- f_XID [V] V = long-term X-ray variable source (20
sources); blank = non-variable CDF-S galaxy
7- 24 A18 --- Name CDF-S name (HHMMSS.ss+DDMMSS.s; J2000;
in Simbad)
26- 29 F4.2 --- z [0.04/2.01] Redshift from litterature (see
section 2)
31 A1 --- f_z [ps] Redshift measurement: s=spectro, p=photo
33 I1 --- l_NCts [0/1]? Upper 3σ limit flag on NCts (2)
35- 39 F5.1 ct NCts [19/608.9] Total net 0.5-8.0 keV counts
41- 45 F5.2 [10-7W] Lx [38.9/42.4] Log 0.5-8 keV, rest frame
X-ray luminosity; in erg/s
47- 49 F3.1 --- Geff [0.5/3] Effective photon index Γeff (3)
51- 53 F3.1 --- E_Geff [0/3.5] Upper confidence interval on Geff
55- 57 F3.1 --- e_Geff [0/2.6] Lower confidence interval on Geff
59- 62 F4.1 --- chi2 [0/11.2] Variability statistic
64- 69 F6.4 --- Pchi2 [0/1] Probability variability is due to chance
71- 73 F3.1 --- R [1.2/9.3] Maximum-to-minimum flux ratio
75- 79 F5.2 --- nxs [-0.3/0.7] Excess variance
81- 84 F4.2 --- e_nxs [0.01/0.5] Error in nxs
86- 90 F5.2 --- nxsc [-0.4/2] Excess variance corrected for
sampling bias
92- 95 F4.2 --- e_nxsc [0.01/1.5] Error in nxsc
97-102 F6.2 Msun/yr SFR [0.01/541] Xue et al. 2010,
Cat. J/ApJ/720/368, Star Formation Rate
104-109 F6.3 10+10Msun Mstar [0.002/62] Stellar mass, from Xue et al. 2010,
Cat. J/ApJ/720/368
111-115 F5.2 --- (H/L)XB [0.01/76] High/Low-mass luminosity ratio (4)
117-122 F6.4 --- nxsxb [0.0001/0.05] Excess variance expected due
to X-ray binary population
124-135 A12 --- Mvis Visual classification of galaxy morphology (5)
137-142 F6.2 mag VMag [-23.77/-15.77] Absolute V-band magnitude
144-148 F5.2 mag U-V [-0.91/1.55] The (U-V) color index
150-153 A4 --- color Color classification of galaxy morphology
(blue or red)
155-165 A11 --- Mclass Final classification of galaxy morphology (5)
167-170 F4.2 [Msun] MBH [4.8/8.6] Logarithm of black hole mass
172-176 F5.2 [-] Edd [-5.7/-1.2] Eddington ratio (6)
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Note (1): In CDF-S catalog (Xue et al. 2011, Cat. J/ApJS/195/10;
<[XLB2011] NNN> in Simbad).
Note (2): Flag is:
0 = net counts;
1 = 3σ upper limit.
Note (3): The effective photon index is calculated from the band ratio.
For sources detected in the soft band but not the hard band,
Γeff is a lower limit. When the counts are too low to
determine reliably the photon index from the band ratio,
Γeff is set to 1.4.
Note (4): Expected from HMXB and LMXB populations.
Note (5): Classification with: "early-type", "late-type", "merger",
"irregular", "off-nuclear" or "undetermined" indications
Note (6): Eddington ratio:
Lbol/LEdd=[κ2-10keVL2-10keV]/[1.25x1038(MBH/M☉)]
See section 6.2 for further explanations.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 18-Oct-2013