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The nature of the dust and gas in the nucleus of NGC 1068

The nature of the dust and gas in the nucleus of NGC 1068 . The nature of the dust and gas in the nucleus of NGC 1068 – . comparison to the Galactic center’s “Central Molecular Zone”. T. R. Geballe & R. E. Mason - Gemini Observatory T. Oka – University of Chicago. NGC 1068:

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The nature of the dust and gas in the nucleus of NGC 1068

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  1. The nature of the dust and gas in the nucleus of NGC 1068

  2. The nature of the dust and gas in the nucleus of NGC 1068 – comparison to the Galactic center’s “Central Molecular Zone” T. R. Geballe & R. E. Mason - Gemini Observatory T. Oka – University of Chicago

  3. NGC 1068: the prototypical Seyfert II galaxy UNIFIED MODEL OF AGN Appearance of AGN depends on orientation of nuclear region w.r.t. our line of sight Type II view Type I view Type II : View to the central engine is obscured by a torus of dusty molecular material. Can only see BLR in scattered light. Type I: torus does not block line of sight to the central region. BLR is directly observed.

  4. Extends outward to r ~ 100pc • Extends inward to r < 1 pc Structure and composition of obscuring material 100 pc NNGC 1068 NGC 1068: H2 2.12μm on CO 2-1 contours (Muller-Sanchez et al. 2009) H2O - VLBA Greenhill & Gwinn (1997) • Must contain dust to obscure AGN • If dust is present, then molecules too. • Generally thought to be sufficiently high • density and cool to be ~fully molecular. If it is molecular then one might expect that in a Type II AGN with bright central IR continuum source it would be possible to detect molecular gas absorbing (IR) radiation along the line of sight to the source + gas (molecules)

  5. Unsuccessful searches for CO fundamental band absorption lines UKIRT 2006 R=2,000 (150 km/s); 0.2”x1.0” NS slit slit Capetti et al. (1997) CO fundamental band Geballe et al. (2009) similar to Lutz et al. (2004) UKIRT 1998 R=15,000 (20 km/s) CO should be easiest interstellar molecule to detect via IR absorption spectroscopy; either as a broad band or as individual lines. Mason et al. (2006)

  6. Where is the CO not being detected? (i.e., how close into the center are we looking?) AO at L’ (Gratadour et al 2004) shows a bright central core of diameter ~11 pc (0.16”) and complex of sources oriented NS. For UKIRT R~2000 spectrum, the deconvolved FWHM at 3-5μm along slit was 0.3” (d~20 pc). undeconvolved PSF • Average 3-5μm continuum • “surface” is at r ~5-10 pc. • Our absorption data do not address the nature of the torus • inside of that radius. No CO τ= 1 at 3-5μm

  7. 3.4μm hydrocarbon Detected absorption features NGC 1068 0.4” x 0.4” Gemini N / MICHELLE Mason et al. (2006) 9.7μm Silicate Silicate (9.7μm) / hydrocarbon (3.4μm) absorptions occur at longer / shorter wavelength than CO (4.7μm). Silicate feature is found in dense and diffuse Galactic clouds. Hydrocarbon feature has only been found in diffuse Galactic clouds. Is the explanation for no CO that all of the cool ISM outside of r~5-10 pc and in our sightline is diffuse in nature?

  8. Galactic dense (n ≥ 103 cm-3) vs. diffuse (n < 103 cm-3) clouds(✔ = consistent with NGC 1068 IR data) PROPERTY DENSE DIFFUSE fraction of H in H2: ~100% ✔ ~50% ✔ presence of silicate feature YES ✔ YES ✔ presence of 3.4μm feature NO YES ✔ percent of C in CO ~100% ~1% ✔* * consistent with upper limit on CO column density … suggests diffuse cloud environment in outer portion of torus (r > 5-10 pc)

  9. Supporting evidence that hydrocarbon and silicate features are formed close to the nucleus in the same location : Hydrocarbon: UKIRT/UIST – Geballe et al. (2009) Silicate: Gemini/MICHELLE – Mason et al. (2006) Variations of silicate and hydrocarbon features across the nucleus are similar.Variations across the small nuclear continuum source imply proximity to nucleus. (2) The carriers of the hydrocarbon and silicate features coexist in diffuse clouds.

  10. What does that have to do with the Galactic center? Lutz et al. (1997) SILICATE L(AGN)~1045 ergs/s CO HYDRO- CARBON A similar diffuse cloud environment appears to make up a significant fraction of the Galaxy’s Central Molecular Zone. Lutz et al. (1996) L(Sgr A*)~1037 ergs/s

  11. Sightlines NGC 1068 Expanding Molecular Ring Central Molecular Zone GCS 3-2 Foreground spiral arms Milky Way - COBE Oka et al. (2005)

  12. Significance? GC has no BLR, no coronal lines (i.e., no strong far UV source). NGC 1068 has all of these and its AGN is 108 times more luminous. Yet both appear to have similar diffuse interstellar environments filling significant fractions of their central ~100 pc. - a result of the obscuration of N1068’s AGN Are the outer portions of AGN toroids typically diffuse cloud environments? Some type II AGNs show the silicate feature and some are known to have the hydrocarbon feature; don’t know iffeaturesare co-located CO has not been detected toward several other Type II AGN (Lutz et al. 2004), but upper limits are weak. MORE OBSERVATIONS NEEDED

  13. B. (1,1): Note similarity to CO, except for the broad absorption trough, on which narrow absorption lines from (dense) clouds in external spiral arms are superimposed. ==> trough is formed in diffuse clouds. C. (3,3): Overall absorption profile crudely approximates the (1,1) trough. ==> same gas as R(1,1) trough ==> trough gas is warm (250 K) No narrow features==> trough gas is in rapid motion; gas is close to the GC. D. (2,2): No absorption ==> non-LTE population distribution / low density (confirms comparison with CO). A. CO R(1) (2.34μm): Only narrow absorption features – from known spiral arms.No broad absorption trough. H3+ and CO spectra of GCS3-2 TROUGH Spiral arms TROUGH Column length of H3+ producing trough (CMZ) absorption is 10-100 pc (dependent on assumed c-r ionization rate)

  14. All eight observed stars within 30 pc of Sgr A* show the H3+ absorption due to warm and diffuse gas (2,2) (1,1) (3,3) (2,2) (1,1) (3,3) Goto et al. (2008) This gaseous environment appears to pervade the CMZ, but we need to observe on more sightlines. We are currently engaged in a program to find suitable probe stars.

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