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Structure of AGN Tori in Merging Galaxies
ルが多量にRevealed by Mid-infrared and X-ray Observations
唆Yamada+19, ApJへの期待

Satoshi Yamada (Kyoto Univ.)
状でなくY. Ueda, A. Tanimoto, Y. Toba (Kyoto Univ.)
M. Imanishi, T. Kawamuro (NAOJ)

長の解明

Galaxy Evolution Workshop 2019 @ Kavli IPMU

Major merger scenariolTight correlations between BH massand bulge mass => Coevolution?

l

Mass accretion onto a SMBH isobservable as an AGN.
AGN Unified Model
Urry & Padovani 1995

lThe gas and dust need to lose ~99% of their angular momentum.
=> A merger of gas-rich galaxies is a key mechanism!!

Galaxy merger

Ultra-/luminous infraredgalaxies (U/LIRGs)

Elliptical galaxies@ Hopkins+08

Obscured AGNs in U/LIRGsl

U/LIRG (Ultra-/Luminous Infrared Galaxy)Large IR luminosity (LIR > 1012/1011 L⦿ )(AGN+SB)

・Many of them are interacting galaxies.
l

During the final phase of a merger, rapid accretion onto theSMBHs takes place when nucleus is deeply enshrouded by gasand dust (= “buried” AGN; e.g., Hopkins+06).

lHowever, it is difficult to test the scenarioof merger-driven SMBH growth, becauseof thick obscuration.
=> X-rays and Mid-IR are useful!!

“Buried” AGN
https://www.subarutelescope.org/Pressrelease/
2006/02/15/j_index.html#fig1

lBroadband X-ray spectra enable

us to identify buried AGNs.
e.g.) Intensity of X-rays scatteredby the NLR gas relative to thatof the direct component.
(Scattering fraction: fscat)lIntensity [keV2 cm-2 s-1 keV-1]

Identification of buried AGNs ① : X-ray

To apply this method, however, we need
X-ray spectra with sufficiently high quality.
Such objects are very limited.
Upperhttp://www.asj.or.jp/geppou/archive_open/
2015_108_12/108_822.pdf

DirectComponent
ScatteredComponent

X-ray Energy [keV]

fscat < 0.5%
X-ray

Identification of buried AGNs ② : Mid-IR
l

Mid-IR luminosity should be proportional to thebolometric AGN luminosity times the torus covering fraction.

lTo make the contamination from thestar formation as small as possible, weadopt the nuclear (subarcsecond scale)
12 μm luminosity. (Asmus+14, 15)lWe propose new diagnostics thatuse the [O IV] 26 μm (Inami+13)
and nuclear 12 μm luminosity ratio
for identifying “buried” AGNs!!

[arcsec]

(nuc)L[O IV]/L12 μm ratio as diagnostics of buried AGNsl(nuc)To justify that the L[O IV]/L12 μm ratio is a good indicator for the buried AGNs,(nuc)we first investigate the correlation between L[O IV]/L12 μm and fscat.

We use 16 Compton-thin AGNs observed by Suzaku (e.g., Kawamuro+16).

(a) 42
fscat =1-2%
fscat =0.5-1%

log (L[O IV] / erg s-1)

lSy2

fscat <0.5%4140“Buried” AGN
43(nuc)-1log (L12 µm / erg s )44

(nuc)L[O IV]/L12 μm vs. fscat(nuc)

The L[O IV]/L12 μm ratio as a function of fscat, together with
their (a)average and standard error in three fscat bins.
42-1

fscat =1-2%

Sy2

fscat =0.5-1%-1.5(nuc)log (L[O IV] / L12 µm)-1log (L[O IV] / erg s )lfscat <0.5%-241-2.5-3

40-3.542-1

43(nuc)-1

log log(L12f µm /(%)
erg s )
scat044(nuc)=> Buried AGNs tend to have lower L[O IV]/L12 μm ratios.

Application to U/LIRGs
Next, we apply this(nuc)

L[O IV]/L12 μm method
to 23 local U/LIRGs
hosting AGNs
(Armus+09).
l42
log (L[O IV] / erg s-1)

lNon-Merger
Pre-Merger
Early Stage
Mid-Stage
Late Stage

Sy2

HST
UGC 510108572

ESO 286-19

41
Seyfert 1
Seyfert 2

We only use the AGNs
whose contribution to×3(SB)

AGN/SB Comp.

42

the Mid-IR luminosity greater

4344(nuc)log (L12 µm / erg s-1)

45
Yamada+19

than 1/3 (filled symbols), and exclude starburst-dominant ones.
lAGNs in most of mid- to late-stage mergers are buried,
while those in earlier stage ones and non-mergers are not.

Buried AGNs fraction with merger stage(nuc)

L[O IV]/L12 μm ratios tend to decrease with merger stage.
=> The fraction of buried AGNs in U/LIRGs increases as theHST
galaxy-galaxy interaction becomes more significant.
(b) -1.5
Average
SF-corrected(Upper limit)(nuc)log (L[O IV] / L12 µm)l-2
Swift/BAT AGN

-2.5

-3

“Buried” AGN
Nonmerger

Pre + Early
Merger Stage

Mid + Late

Yamada+19

Buried AGNs fraction with merger stage(nuc)

L[O IV]/L12 μm ratios tend to decrease with merger stage.
=> The fraction of buried AGNs in U/LIRGs increases as theHST
galaxy-galaxy interaction becomes more significant.
(b) -1.5
Average
SF-corrected(Upper limit)(nuc)log (L[O IV] / L12 µm)l-2
Swift/BAT AGN

-2.5

-3

“Buried” AGN
Nonmerger

Pre + Early
Merger Stage

Mid + Late

Yamada+19

Buried AGNs fraction with merger stage(nuc)

L[O IV]/L12 μm ratios tend to decrease with merger stage.
=> The fraction of buried AGNs in U/LIRGs increases as theHST
galaxy-galaxy interaction becomes more significant.

To confirm such an evolutional
scenario,
Average
SF-corrected
it is important to investigate(Upperthelimit)
torus
properties and fscat(%) by using the-2
Swift/BAT AGN
broadband X-ray spectral analysis.
(b) -1.5(nuc)log (L[O IV] / L12 µm)

l-2.5

-3

“Buried” AGN
Nonmerger

Pre + EarlyMerger Stage

Mid + LateYamada+19

X-ray observations of U/LIRGsl

U/LIRG

AGNs (and SB) are hidden by gas and dust.
l(AGN+SB)

Hard X-rays (> 10 keV) are usefuldue to high penetrating power
against obscuration.
=> hydrogen column density (NH),torus structure, and fscat)l

NuSTAR (3-79 keV) observations
revealed the properties of obscured
AGNs (e.g., Ricci+17)

Hard X-ray

X-ray observations of Nonmerger LIRGsl

Are the buried AGNs triggered by mergers?
=> “Nonmerger” LIRGs are the best targets.
(NGC 5135, UGC 2608)l

We analyze broadband (0.4-70 keV)

NGC 5135 (DSS)

X-ray spectra using the data fromNuSTAR, Chandra, XMM-Newton, and Suzaku.

l

To investigate the torus properties, we adopt
the X-ray clumpy torus model (Tanimoto+19).

SB+AGNUGC 2608(Pan-STARRS)X-ray clumpy torus model : XCLUMPYl

XCLUMPY model (Tanimoto+19)

・geometry : the same clump distribution as that of theCLUMPY model in the infrared band (Nenkova+08).
・Radial distribution : Power law

lFree Parameter・column density : NH [cm-2]torus angular width : σ [°]・inclination :θ (=80°; fixed)

θσNH (eq)Broadband X-ray spectral analysis
E_FE

0.01
E_FE

NGC 5135

keV2 (Photons cm−2 s−1 keV−1)−1(data-model)/ error(data−model)/error
keV (Photons cm s keV )0.01

1010-31010-4

1010-410−5200
2-2−211

Energy (keV)

1010
Energy (keV)−3−410−5(data−model)/error−1−22−4(data-model) / error−31010-3

UGC 2608

2200-2−211

Energy (keV)

1010

Energy (keV)

NGC 5135

UGC 2608

Column density (N_H)

 5 x 10^24 [cm-2]

 5 x 10^24 [cm-2]

Torus angular width (σ)< 19 [degree]< 34 [degree]

Scattering fraction (f_scat)

0.9—3.7 [%]0.5—2.6 [%]l

We find that both of AGNs in these two Nonmerger LIRGs are
not deeply “buried” (σ < 30, fscat > 0.5%).

~-> consistent with the results from the L[O IV]/L12μm diagnostics.

Summaryl

In order to identify buried AGNs, we propose new diagnostics
that use the ratio between [O IV] 26 μm and nuclear 12 μm
luminosities.

l

By applying the criteria for 23 local U/LIRGs, we find thatthe fraction of buried AGNs in U/LIRGs increase withmerging stage. (Yamada+19, ApJ)l

Also, the broadband X-ray spectral analysis of two AGNs
in nonmerger LIRGs indicate that they are not deeply buried.