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Buried AGNs in nearby ULIRGs

Buried AGNs in nearby ULIRGs. Masa Imanishi. (National Astronomical Observatory of Japan). Compact cores (<500pc) are dominant. optical. IR(12um). Soifer et al. 2000. Very compact starburst or AGN ?. Ultraluminous Infrared Galaxies （ ULIRGs ）. Powerful energy source

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Buried AGNs in nearby ULIRGs

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  1. Buried AGNs in nearby ULIRGs Masa Imanishi (National Astronomical Observatory of Japan)

  2. Compact cores (<500pc) are dominant optical IR(12um) Soifer et al. 2000 Very compact starburst or AGN ? Ultraluminous Infrared Galaxies（ULIRGs） Powerful energy source is hidden behind dust L(IR)>10^12Lsun

  3. NLR ULIRGs have a large amount of nuclear gas and dust Buried AGNs are elusive AGNs in ULIRGs are buried AGNs obscured by torus-shaped dust Sy2 Detectable via optical spectroscopy

  4. Methods: 1. Spectral shape (PAH vs dust absorption) 2. Geometry of energy sources and dust Infrared 3-4 um spectroscopy IRCS on Subaru 8.2m telescope Optically non-Seyfert ULIRGs

  5. Buried AGN composite starburst featureless 3.3um PAH EW(PAH)<<100nm EW(PAH)~100nm 3.4um/3.1um 1. 3-4 um spectral shape PAH PAHs are excited in starburst PDRs but destroyed near an AGN

  6. Buried AGN AGN/SB composite Bare 3.4um Ice 3.1um Bare 3.4um Abs. feature Low EW(PAH) Subaru 3-4 um starburst Strong PAH

  7. starburst Buried AGN Foreground screen dustmodel Mixed dust model 1-exp(-τλ) exp(-τλ) τλ Dust absorption feature: weak strong Tau(3.1) < 0.3 Tau(3.4) < 0.2 2. dust/energy-source geometry (Imanishi & Maloney 2003 ApJ 588 165)

  8. 3-4 um Buried AGN composite Starburst PAH strong (starburst): Dust absorption weak PAH weak (AGN): Dust absorption strong

  9. Spitzer 5-35 um Buried AGN Starburst Composite PAH strong : Silicate abs. weak PAH weak: Silicate abs. strong

  10. Av(3um) =120 mag Av(10um) =50 mag Av(20um) <20 mag Strong dust temperature gradient Av(3um) > Av(10um) > Av(20um)

  11. Powerful buried AGNs fraction: LINER > HII (see also Nagar et al. 2003) Results Buried AGN signatures: 17/27 (63%) LINER ULIRGs (statistically complete) Pure buried AGNs show LINER spectra 3/13 (23%) HII-region ULIRGs (complete at RA=10-22hr)

  12. NLR Amount of nuclear dust: Non-Sy >> Sy2 Our line-of-sight obscuration: Non-Sy >> Sy2 Sy2: Abs weak Non-Sy: strong

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

  14. Optical Sy (non-)detectability depends on the amount of nuclear dust It is important to understand optically-elusive buried AGNs in ULIRGs. ( Imanishi et al. 2005, submitted ) Summary 1. Buried AGNs fraction: LINER > HII-region warm & cool 2. Nuclear dust amount: non-Sy ULIRGs > Sy2 ULIRGs

  15. Just for reference After this slide

  16. Ice : inside dense molecular gas HCN (= dense gas tracer) is concentrated to nuclei Strong ice absorption is nuclear core origin (not ISM in an edge-on host galaxy)

  17. Buried AGN starburst Strong dust temperature gradient Av(3um) > Av(10um) > Av(20um) Centrally-concentrated energy source

  18. Av(3um) =120 mag Av(10um) =50 mag Av(20um) <20 mag Strong dust temperature gradient Av(3um) > Av(10um) > Av(20um) Weak PAH ULIRGs: Dust temperature gradient

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