1. Interferometric 3D observations of LIRGs
Masa Imanishi
NAOJ (National Astronomical
Observatory of Japan)
NMA (Nobeyama Millimeter Array)

2. Luminous infrared galaxies（LIRGs）
L(IR) > 10^11 Lsun
(Normal spiral ~ 10^10 Lsun)
optical IR
M100（Sbc）
LIRGs IR
optical
Luminous energy source is hidden behind dust

3. AGNs in LIRGs are buried
NLR
AGNs obscured by
torus-shaped dust
Sy2
Detectable via optical spectroscopy
LIRGs have a large amount of
nuclear gas and dust
Buried AGNs are elusive
>80% LIRGs = non-Sy

4. buried AGN or compact SB ?
X-ray : AGN >> SB
Compton thick (NH>10^24 cm-^2)
buried AGN in LIRGs
Future X-ray satellite
sensitive at E > 10keV

5. Effects to the surrounding ISM
Maloney et al.1996
XDR around
an X-ray emitting
buried AGN

6. 0.5% * Mc2 SB
<< 1 pc
6-40% * Mc2
Hot dust
(several 100K)
Strong mid-IR
(10-20um) emission
AGN

7. Millimeter line ratio AGN and SB separated HCN/HCO+ J=1-0 HCN/CO
Starburst
pure AGN
J=1-0
(Kohno astro-ph/ )

8. Resolve multiple-nuclei
Our NMA interferometric HCN/HCO+ survey
Compared to single-dish obs.:
Extract only nuclear emission
Resolve multiple-nuclei
HCN/HCO+ taken simultaneously

9. NMA data Single nucleus LIRGs HCN > HCO+ HCN > HCO+
NGC4418
(Buried AGN)
UGC5101
（Buried AGN）
Mrk273
（Buried AGN）
HCN > HCO+
HCN > HCO+
HCN > HCO+
Imanishi et al. 2004 AJ
Imanishi et al AJ

10. NMA data (II) HCN > HCO+ HCN > HCO+ NMA Mrk 231 IR08572+3915
(Buried AGN)
Mrk 231
（type-1 AGN）
HCN > HCO+
HCN > HCO+
Imanishi et al AJ

11. Spatially resolve multiple components (1)
HCN < HCO+
Arp299
Imanishi & Nakanishi 2006
PASJ
HCN ~ HCO+

12. Spatially resolve multiple components (2)
HCN > HCO+
HCN < HCO+
Mrk 266
Imanishi et al.
2008 in prep

13. Spectrally resolve multiple components
W-nucleus
E-nucleus
Imanishi et al.
2007 AJ
Spatially-unresolved

14. NMA
HCN/HCO+
IR-buried
-AGNs
★:LIRGs
IR-Starburst
HCN/CO

15. Interpretation High HCN/HCO+ in AGN HCN abundance enhancement
Meijerink et al. 2006
2. IR-radiative pumping enhance HCN flux

16. Molecular gas high abundance ρ∝r^-1.5 low abundance abundance
tau=1 sphere
ρ∝r^-1.5
(Gierence et al. 1992)
abundance
surface area
flux

17. HCN/HCO+ abundance: model dependent
PDR
XDR
HCO+/HCN NH
high
low
density=10^5.5 cm^-3
Meijerink et al. 2006

18. Interpretation High HCN/HCO+ in AGN HCN abundance enhancement
2. IR-radiative pumping enhance HCN flux
HCN has a line at 14um
Aalto et al. 1995

19. IR radiative pumping HCN has a line at 14um 14um AGN is a strong
Aalto et al. 1995
HCN has a line
at 14um
HCN(1-0)
Cascade
AGN is a strong
IR 14um emitter
(hot dust)
3.5mm
14um

20. HCO+ line at 12um is weak !
Not detected !

21. high HCN(1-0)/HCO+(1-0) ratios in nuclei of buried AGN candidates
Summary
NMA 3D (spatial and velocity) data :
high HCN(1-0)/HCO+(1-0) ratios
in nuclei of buried AGN candidates
Imanishi et al AJ
Imanishi et al AJ
Imanishi et al in prep

22. End

23. High-CR PDR XDR HCN(1-0)/HCO+(1-0) intensity ratio = high
(in some parameter range)
High-CR PDR
XDR
10^4/cc
G0=
10^3
10^4
10^5
FX=1.6 16
160
HCN(1-0)/
HCO+(1-0)
0.36
0.34
0.32
21.7
22.6
Meijerink et al. 2006

24. ULIRGs Compact cores (<500pc) are energetically dominant optical
IR(12um)
Soifer et al. 2000
Very compact starburst
or AGN ?

25. Outline 1. IR spectroscopy 2. Mm interferometric HCN(1-0) and
Select buried AGN candidate
2. Mm interferometric HCN(1-0) and
HCO+(1-0) follow-up observation
HCN(1-0)/HCO+(1-0) ratio

26. 3-4 um Subaru Buried AGN SB AGN+SB PAH strong (SB): Dust abs. weak
Ice
3.1um
Bare
3.4um
PAH
3.3um
PAH strong (SB):
Dust abs. weak
PAH weak (AGN):
Dust abs. strong

27. 5-35 um Spitzer GO1 SB Buried AGN AGN+SB PAH PAH PAH PAH PAH strong :
Silicate Abs. weak
PAH weak:
Silicate Abs. strong

28. Remaining ambiguity ★ SB AGN Exceptionally centrally-concentrated SB
Very high surface brightness
>>10^13Lsun/kpc^2 (SB max)
Extreme SB?
AGN

29. Interpretation High HCN/HCO+ in AGN HCN abundance enhancement
2. IR-radiative pumping enhance HCN flux
3. Turbulence decreases HCO+
Papadopoulos 2007
Regardless of AGN or SB ?
4. High gas density

30. Interpretation High HCN/HCO+ in AGN HCN abundance enhancement
2. IR-radiative pumping enhance HCN flux
3. Turbulence decreases HCO+
4. High gas density
N(crit): HCN ~ 5 * HCO+

31. ★:(U)LIRGs High gas density ULIRG : low HCN/CO scenario: unlikely ?
PDR
XDR
HCN/CO
HCN/HCO+
★:(U)LIRGs

32. NMA/RAINBOW data （III）
Buried AGN
AGN
SB or AGN ?
Imanishi et al.
2007
ArXiv/

33. 1. Infrared spectral shape
PAH
PAHs are excited in starburst PDRs
but destroyed near an AGN
Buried AGN
EW(PAH)<<100nm
composite
Starburst(SB)
3.3um PAH
featureless
EW(PAH)~100nm
3.4um/3.1um

34. 2. Dust absorption feature strength
starburst
Buried AGN
ULIRG core
<500pc
Foreground screen
dust　model
strong
exp(-Tau)
(Imanishi & Maloney 2003 ApJ )
Mixed dust model
Dust absorption
feature: weak
Tau(3.1) < 0.3
Tau(3.4) < 0.2
1-exp(-Tau)
Tau
Tau(9.7) < 1.7

35. 3. Dust temperature gradient
Av(3um) > Av(10um)
> Av(20um)
Buried AGN
Av(3um) =< Av(10um)
　　　=< Av(20um)
Starburst
dust in
edge-on
host

36. How to detect T-gradient ?
Spitzer
Subaru
Av(20um)
~20mag
Av(3um)
~110mag
Av(10um)
~40mag
Optical depth
9.7um
18um
Dust temperature
gradient

37. Strong T-gradient (II)
Spitzer
Subaru
Strong abs ULIRGs -> often show T-gradient

38. Opical non-Seyfert ULIRGs
Results
nearby(z<0.15)
Opical non-Seyfert ULIRGs
Luminous buried AGNs = 30-50%
30% ULIRGs = optical Sy (AGN + torus)
>50% ULIRGs = luminous AGN
NLR

39. L(dereddened AGN) ～L(IR)
Our line-of-sight obscuration: Non-Sy >> Sy2
NLR
Sy2:
Abs
weak
Non-Sy:
strong
L(dereddened AGN) ～L(IR)
Amount of nuclear dust: Non-Sy >> Sy2

40. Interpretation High HCN/HCO+ in AGN HCN abundance enhancement
2. IR-radiative pumping enhance HCN flux
3. Turbulence decreases HCO+
4. High gas density
5. CR-controlled chemistry
Papadopoulos 2007
HCN/HCO+ < 1

41. ★:(U)LIRGs XDR IR-buried -AGNs IR-Starburst PDR
NMA
(RAINBOW)
HCN/HCO+
★:(U)LIRGs
XDR
IR-buried
-AGNs
IR-Starburst
PDR
HCN/CO
Imanishi et al AJ ; 2007 in prep

42. Summary Imanishi et al. 2006 ApJ 637 114
1. Buried AGNs : 30-50% non-Sy ULIRGs
warm & cool
2. Nuclear dust amount:
non-Sy ULIRGs > Sy2 ULIRGs
Optical Sy (non-)detectability
depends on the amount of
nuclear dust
Imanishi et al ApJ
Imanishi et al ApJS astro-ph/

43. cool == starburst Buried AGNs: both warm/cool FIR colors NLR warm
pure buried AGN
NLR
warm
larger dust
column
cool FIR color
F25/F60=0.16(cool)
cool == starburst