Subaru AO high-spatial-resolution IR K- and L-band search for buried dual

AGNs in merging galaxies

Masatoshi Imanishi ( 今西昌俊 )

NAOJ/Subaru Telescope

Imanishi+14 ApJ 780 106

Gas-rich galaxy mergers common in the universe

Simulation(Kazantzidis)

HST image

CDM galaxy formation:

Multiple SMBHs common in mergers

SM

BH

mass

bulge massNASA

bulge massS

MB

H m

ass

Gultekin+09

Supermassive blackhole （ SMBH ） ubiquitous at galaxy center

Many dual AGNs expected, if SMBHs are active

Wang+09 ApJ 705 L76

Double-peaked optical emission lines

~1% (87 / 6780 z<0.15 type-2 AGN)

Hβ

[OIII]4959

[OIII]5007

Dual AGN

outflow

jet interaction

Two discrete line emitting clouds

See also Liu+10,11, Smith+10, Pilyugin+12, Ge+12,Barrows+13

Fu+11b ApJ 733 103

Follow-up of double-peaked lines objects

~30% （ 16/50 ） double nuclei

Dual AGNs not required in the majority (~70%)（ Jet-cloud interaction etc ）

10”

Keck II/OSIRIS+LGS-AOH-band

Very small (<1%) dual AGN fraction in double-peaked lines dual AGN search

• miss face-on SMBHs

Edge-on:OK Face-on:undetectable

• Buried AGNs undetectable

Need observations at wavelengths oflow dust extinction

High-spatial-resolution imaging

Sensitive to face-on multiple SMBH with small separation

• radio (VLBI)

• X-ray 2-10 keV (Chandra; 0.5”)

Miss the majority of radio-quiet AGN

Miss Compton-thick (NH > 1024 cm-2) AGNs

Burke-Spolaor11

Teng+05,09,12,Iwasawa+11a,11b, Koss+12,Liu+13

Our method: Subaru AO infrared imaging

• Infrared K (2.2um) and L’(3.8um)

• Subaru-AO (0.1-0.15”)

Sensitive to buried AGNs, including radio-quiet ones

Sensitive to small separation (face-on) dual AGNs at late merging stage

AKARI 2.5-5um spectroscopy

Normal starbust

Buried AGN

PAH

Imanishi+10 ApJ 721 1233

Starburst: K-L blue(~0.5 mag)

Buried AGN: K-L red (~2 mag)

(AGN heated hot dust emission)

AGN (red K-L nucleus)

28/29 (U)LIRGs show at least one AGN

10”Imanishi+14 ApJ 780 106

Dual AGNs (two red K-L nuclei)

10”Imanishi+14 ApJ 780 106

4/29 (U)LIRGs

Subaru AO L’(3.8um) (0.1-0.2”)

Spitzer IRAC3.6um (1”/pix)

WISE3.4um >5”

Small fraction (15%) of IR buried dual AGN

1. Dust obscuration ?

2. Orbiting geometry ?

3. Non-simultaneous SMBH activation

SMBH mass ratio between two nuclei

AG

N lu

min

osi

ty r

atio

b

etw

een

tw

o n

ucl

ei

Less massive SMBHhas high Eddington ratio

More massive SMBH is more actively mass accreting (=high Eddington ratio)

Imanishi+14 ApJ 780 106

More massive SMBH has higher Eddington ratio

Non-simultaneous SMBH activation throughout the merging phase

Imanishi+14ApJ 780 106

Our Infrared K- and L-band AO imaging revealed non-simultaneous SMBH activation

Even if two SMBHs are present, only one SMBH can become sufficiently luminous to be detectable as an AGN

Can explain the observed small dual AGN fraction in merging galaxies

Summary

More massive SMBHs have higher Eddington ratio

Summary 2

SMBH activation is dominated by local conditions, rather than global galaxy properties

Difficult to predict by simulation

Need observational constraints

Imanishi+14 ApJ 780 106

End

Buried AGN

Lν(3-4μm) (intrinsic) = L(AGN)ν