J/ApJ/865/43 X-ray stacking analysis of Chandra-COSMOS gal. (Fornasini+, 2018)
Low-luminosity AGN and X-ray binary populations in COSMOS star-forming galaxies.
Fornasini F.M., Civano F., Fabbiano G., Elvis M., Marchesi S., Miyaji T.,
Zezas A.
<Astrophys. J., 865, 43 (2018)>
=2018ApJ...865...43F 2018ApJ...865...43F
ADC_Keywords: Galaxies, photometry; X-ray sources; Redshifts; Binaries, X-ray;
Models, evolutionary; Active gal. nuclei
Keywords: galaxies: active; galaxies: starburst; X-rays: binaries;
X-rays: galaxies
Abstract:
We present an X-ray stacking analysis of ∼75000 star-forming galaxies
between 0.1<z<5.0 using the Chandra COSMOS-Legacy survey to study the
X-ray emission of low-luminosity active galactic nuclei (AGN) and its
connection to host galaxy properties. The stacks at z<0.9 have
luminosity limits as low as 1040-1041erg/s, a regime in which
X-ray binaries (XRBs) can dominate the X-ray emission. Comparing the
measured luminosities to established XRB scaling relations, we find
that the redshift evolution of the luminosity per star formation rate
(SFR) of XRBs depends sensitively on the assumed obscuration and may
be weaker than previously found. The XRB scaling relation based on
stacks from the Chandra Deep Field South overestimates the XRB
contribution to the COSMOS high specific SFR stacks, possibly due to a
bias affecting the CDF-S stacks because of their small galaxy samples.
After subtracting the estimated XRB contribution from the stacks, we
find that most stacks at z>1.3 exhibit a significant X-ray excess
indicating nuclear emission. The AGN emission is strongly correlated
with stellar mass but does not exhibit an additional correlation with
SFR. The hardness ratios of the high-redshift stacks indicate that the
AGN are substantially obscured (NH∼1023cm-2). These obscured AGN
are not identified by IRAC color selection and have
LX∼1041-1043erg/s, consistent with accretion at an Eddington
rate of ∼10-3 onto 107-108M☉ black holes. Combining our
results with other X-ray studies suggests that AGN obscuration depends
on stellar mass and an additional variable, possibly the Eddington rate.
Description:
We selected our sample of star-forming galaxies from the COSMOS2015
photometric catalog (Laigle+ 2016, J/ApJS/224/24). After applying the
selection criteria described in Section 2, our sample consists of
74904 galaxies.
We perform X-ray stacking analysis making use of the Chandra stacking
tool CSTACK v4.32 (Miyaji+ 2008HEAD...10.0401M 2008HEAD...10.0401M). For each target,
CSTACK provides the net (background-subtracted) count rate in the soft
(0.5-2keV) and hard (2-8keV) bands using all 117 observations from the
Chandra COSMOS-Legacy survey and associated exposure maps.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 95 92 Properties of star-forming galaxy stacks
table3.dat 123 92 Stacked photometry
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/eso : ESO Science Archive Catalog (ESO, 1991-2019)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
J/AJ/126/539 : The Chandra Deep Fields North and South (Alexander+, 2003)
J/ApJ/663/81 : SED of hard X-ray selected AGN in XMDS (Polletta+, 2007)
J/ApJS/184/158 : Chandra COSMOS survey I. (Elvis+, 2009)
J/ApJ/708/137 : Broad-line AGNs in zCOSMOS survey (Merloni+, 2010)
J/ApJ/742/3 : Photometric catalogs for ECDF-S and CDF-N (Rafferty+, 2011)
J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)
J/MNRAS/427/3103 : COSMOS field supermassive black holes (Bongiorno+, 2012)
J/A+A/544/A156 : UltraVISTA Catalogue Release DR1 (McCracken+, 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/ApJS/220/10 : AEGIS-X Deep survey of EGS (AEGIS-XD) (Nandra+, 2015)
J/ApJ/813/82 : z<0.06 broad-line AGN emission-line measures (Reines+, 2015)
J/ApJS/219/15 : Morphologies of z=0-10 gal. with HST data (Shibuya+, 2015)
J/ApJ/819/62 : The COSMOS-Legacy Survey (CLS) catalog (Civano+, 2016)
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/ApJ/825/7 : Evolution of ∼6Ms CDF-S galaxies (Lehmer+, 2016)
J/ApJ/817/34 : C-COSMOS Legacy multiwavelength catalog (Marchesi+, 2016)
J/A+A/602/A123 : AGN vs. host galaxy data in COSMOS field (Lanzuisi+, 2017)
J/ApJS/228/2 : Chandra Deep Field-South survey: 7Ms sources (Luo+, 2017)
J/ApJ/841/102 : Type 2 AGN host galaxies in Chandra-COSMOS (Suh+, 2017)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/92] Stack number
4- 7 I4 --- Ngal [2/8473] Number of galaxies in stack
9- 12 F4.2 --- zphot [0.2/3.6] Mean photometric redshift of
galaxies in stack
14- 17 F4.2 --- b_zphot [0.1/3] Lower bound on zphot
19- 22 F4.2 --- B_zphot [0.3/5] Upper bound on zphot
24- 28 F5.2 [Msun] logMstar [9.6/11.5] Mean galaxy (stellar) mass
30- 34 F5.2 [Msun] E_logMstar [0/0.5] Upper Uncertainty (1σ)
in logMstar
36- 39 F4.2 [Msun] e_logMstar [0.01/0.4] Lower Uncertainty (1σ)
in logMstar
41- 45 F5.2 [Msun] b_logMstar [9.5/11.4] Lower bound on logMstar range
47- 51 F5.2 [Msun] B_logMstar [9.6/11.9] Upper bound on logMstar range
53- 57 F5.2 [Msun/yr] logSFRstar [-0.3/2.8] Mean star formation rate
59- 62 F4.2 [Msun/yr] E_logSFRstar [0.03/0.6] Upper Uncertainty (1σ)
in logSFRstar
64- 67 F4.2 [Msun/yr] e_logSFRstar [0.04/0.9] Lower Uncertainty (1σ)
in logSFRstar
69- 73 F5.2 [Msun/yr] b_logSFRstar [-1.5/2.7] Lower bound on logSFRstar range
75- 78 F4.2 [Msun/yr] B_logSFRstar [0.4/3.4] Upper bound on logSFRstar range
80- 85 F6.2 [yr-1] logsSFR [-10.5/-8.2] Mean specific star formation
rate
87- 90 F4.2 [yr-1] E_logsSFR [0/0.6] Upper Uncertainty (1σ)
in logsSFR
92- 95 F4.2 [yr-1] e_logsSFR [0/0.9] Lower Uncertainty (1σ)
in logsSFR
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/92] Stack number
4- 6 F3.1 --- Sig [0/7.7] Significance of the stack
in the 0.5-2keV band
8- 15 F8.1 ks Exp [134/659084] Exposure
17- 21 F5.1 ct NCts [-12/433] Background-subtracted Net Counts
23- 26 F4.1 ct E_NCts [2/67] Upper Uncertainty (1σ) in NCts
28- 31 F4.1 ct e_NCts [0.8/67] Lower Uncertainty (1σ) in NCts
33- 37 F5.2 [10-7W] logLXobs [39.8/43.1] Mean obs model X-ray Luminosity,
log, erg/s (1)
39- 44 F6.2 [10-7W] E_logLXobs [0.06/0.2]?=-99.99 Upper Uncertainty
(1σ) in logLXobs (1)
46- 51 F6.2 [10-7W] e_logLXobs [0.06/0.2]?=-99.99 Lower Uncertainty
(1σ) in logLXobs (1)
53- 57 F5.2 [10-7W] logLXtyp [39.3/43.1] Mean typical model X-ray
luminosity, log, erg/s (2)
59- 64 F6.2 [10-7W] E_logLXtyp [0.05/0.2]?=-99.99 Upper Uncertainty
(1σ) in logLXtyp (2)
66- 71 F6.2 [10-7W] e_logLXtyp [0.08/0.3]?=-99.99 Lower Uncertainty
(1σ) in logLXtyp (2)
73- 78 F6.2 [10-7W] logLXagn [39/43]?=-99.99 AGN luminosity,
log, erg/s (3)
80- 85 F6.2 [10-7W] E_logLXagn [0.07/0.3]?=-99.99 Upper Uncertainty
(1σ) in logLXagn (3)
87- 92 F6.2 [10-7W] e_logLXagn [0.1/1.9]?=-99.99 Lower Uncertainty
(1σ) in logLXagn (3)
94- 99 F6.2 [10-7W] b_logLXagn [39.8/42.3]?=-99.99 Range (min) of
logLXagn, erg/s (4)
101-105 F5.2 [10-7W] B_logLXagn [39.9/43] Range (max) of logLXagn, erg/s (4)
107-111 F5.2 [10-7W] logLxrb [39.9/42.3] Estimated XRB contribution,
this paper; Equation 2
113-117 F5.2 [10-7W] logLxrb2 [39/42] Estimated XRB contribution,
Lehmer+ (2010ApJ...724..559L 2010ApJ...724..559L) relation
119-123 F5.2 [10-7W] logLxrb3 [39.5/43] Estimated XRB contribution,
Aird+ (2017MNRAS.465.3390A 2017MNRAS.465.3390A) relation
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Note (1): Mean X-ray luminosity based on the observationally motivated
spectral model which varies with z and sSFR. For stacks with <3σ
significance, the 3σ upper limit is provided in the column
E_logLXobs.
Note (2): Mean X-ray luminosity based on the typical spectral model with
Γ=1.9 and only Galactic absorption. For stacks with <3σ
significance, the 3σ upper limit is provided in the column
logLXtyp.
Note (3): AGN luminosity calculated by subtracting the hot gas contribution
and XRB contribution based on our XRB scaling relation parametrized in
Equation 2 from <LX,obs> in column LXobs. For stacks with >3σ
significance, if the XRB and gas contributions exceed <LX,obs>,
1σ upper limit is given in logLXagn; if the XRB and gas
contributions exceed even the 1σ upper limit on <LX,obs> (or the
3σ upper limit for stacks with <3σ significance), the
column logLXagn is set to null (-99.99).
Note (4): Minimum and maximum limit on AGN emission based on statistical
errors and accounting for plausible range of XRB contribution based on
three values in columns logLxrb, logLxrb2, logLxrb3
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 21-Aug-2019