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Mid-IR emission from low-luminosity AGN

Mid-IR emission from low-luminosity AGN. R. Mason (Gemini), E. Lopez Rodriguez (U. Florida), C. Packham (U. Florida), J. Radomski (Gemini), N. Levenson (Gemini), A. Alonso Herrero (CSIC), I. Aretxaga (INAOUE), L. Colina (CSIC), M. Elitzur (U. Kentucky), P. Roche (Oxford University).

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Mid-IR emission from low-luminosity AGN

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  1. Mid-IR emission from low-luminosity AGN R. Mason (Gemini), E. Lopez Rodriguez (U. Florida), C. Packham (U. Florida), J. Radomski (Gemini), N. Levenson (Gemini), A. Alonso Herrero (CSIC), I. Aretxaga (INAOUE), L. Colina (CSIC), M. Elitzur (U. Kentucky), P. Roche (Oxford University)

  2. Towards the low-luminosity end of the AGN phenomenon • Large fraction of LINERs host accreting supermassive black holes • Hard X-ray point sources • Compact, flat-spectrum radio cores • Broad H • UV variability • Etc. • Link between relatively quiescent Galactic Centre SMBH and Seyferts, quasars etc.? • Also very numerous - for a complete understanding of the accretion phenomenon, need to understand LLAGN.

  3. MIR not well constrained LLAGN: not your standard AGN? (I) • LLAGN contain radiatively inefficient accretion flow, not (only) standard thin accretion disk • Appear to fit SEDs better than standard disks • Possess MIR “big red bump” instead of “big blue bump”? (Ho 2008) Ptak et al. 2004, model fits to NGC 3998 SED L: RIAF with/without truncated thin disk R: disk and synchrotron models; quasar templates • But see also e.g. Maoz (2007), Netzer (2009)

  4. M. Elvis LLAGN: not your standard AGN? (II) • AGN unification: orientation-dependent obscuration determines AGN classification • Torus (and/or BLR) missing in LLAGN? Disk wind model: the “torus” is just an optically thick region of a wind flowing off the accretion disk Low-luminosity AGN (Lbol< 1042 erg/sec) can’t produce these winds, so no torus and eventually no BLR (Elitzur & Shlosman 2006; Elitzur & Ho 2009)

  5. Torus? Obscuration/dust evidence • Spitzer spectroscopy --> MIR hot dust component in LINER 1s but not in LINER 2s (Sturm et al. 2006) • Analogous to Seyfert 1/2; AGN unification • Also inferred by Tang et al. (2009) from Spitzer IR spectral indices • Silicate emission in some LINERs • E.g. M87 (Perlman et al. 2007, Bressan et al. 2006) • BLR detected in polarised light in some LINERs (Barth et al. 1999)

  6. Torus? Obscuration/dust evidence • HST: UV cores usually detected when no obvious nuclear dust (Pogge et al. 2000) • Nucleus or jet? • Correlation between LX and NH: less obscuration at low LX Zhang et al. 2009 • Small Fe KEW in LINERs • Look for emission reprocessed by dust in the MIR

  7. Importance of spatial resolution • Faint central engines --> spatial resolution • Optical, UV, radio: HST, interferometry • MIR: observe from the ground • 8m telescope diffraction limit approx. 0.3” in N band • LLAGN almost completely unexplored at this resolution • M87 (Perlman et al. 2001, Whysong & Antonucci 2004); NGC 4258 (Chary et al. 2000); NGC 4579 (Horst et al. 2006); NGC 1097 (Mason et al. 2007); M81 (Grossan et al. 2001) M87 @ 10.8 m; Perlman et al. 2001

  8. LLAGN imaging sample • Exploratory N band imaging of 17 LLAGN w/ Michelle & T-ReCS (Gemini N/S) • plus 4 from literature w/ <0.5” resolution • Mostly LINERs, a few low-luminosity Seyferts • 38.8 < log L2-10 keV < 41.1 (erg/sec) • 3 Mpc < D < 36 Mpc • 0.3” = 6 - 60 pc • Photometry • Aperture photometry • Integrate under standard star PSF scaled to peak emission • PSF fitting? Faint! (few - few tens of mJy) • Many show extended emission

  9. Approx. 9” 24” NGC 1097 JHK (Prieto et al. 2005), 11.7 m (Mason et al. 2007) SDSS gri

  10. Updated LLAGN SEDs • New data points for poorly-constrained region of LLAGN SEDs (cf. Ho 1999, Maoz 2007) • LMIR significantly reduced cf. large-aperture data • Of use for constraining accretion models? • Compare aperture photometry to literature data • Only M81 appears variable (Willner et al. 2004, Grossan et al. 2002) Grey/black points from Ho 1999, Maoz 2007

  11. Do LLAGN host tori? • X-ray emission from Seyferts is correlated with MIR emission (reprocessing by torus dust) • Lutz, Krabbe, Horst, Ramos Almeida, Levenson, Gandhi • Do LLAGN lie on the extrapolation of the Seyfert fit? Some LLAGN close to Seyfert correlation, many have MIR excess! Perhaps indicates that some LLAGN do have tori? Need further analysis of host galaxy “contamination” MIR errors ~ 15%; X-ray TBD…

  12. Source of the extended emission? • Torus • Point source in single-dish MIR Seyfert images • Narrow-line region • Often subtle in Seyferts in MIR; expect weaker in LLAGN • Non-thermal emission from AGN + jets • Probably present (e.g. M87) • Morphology? • Old stars & circumstellar shells • Likely source of silicate emission in M87 (Buson et al. 2009) • Dust heated by circumnuclear star formation • Don’t LINERs have old stellar populations? E.g Kewley et al. (2006) • NGC1097 counterexample: 106Mo, 106 yr-old nuclear cluster

  13. Conclusions • Work in progress! • New MIR images of LLAGN reveal nucleus and surrounding emission at much higher resolution than previously • Some objects lie on extrapolation of Seyfert MIR/X-ray correlation, many have MIR “excess” • Need further work to assess non-nuclear contribution • Extended emission suggests star formation in LLAGN nuclei??

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