Molecular Absorption Lines in the Circumnuclear Region Satoko Sawada-Satoh - Kagoshima University
Background & Motivations AGN circumnuclear torus Fuel tank of mass accretion onto SMBH Invented by astronomers, to explain Seyfert 1 & The size : < 1pc How can we confirm it? Requirement of 1 milliarcsec (mas) resolution to image VLBI can acheive it Urry & Padovani 1995 <1pc
AGN torus/disk & VLBI 199s mid ~ : A pc-scale masering molecular disk surrounding a SMBH. A pc-scale dense absorbing gas torus. s ~ : A torus model with several physical-phase layers inside. Jones & Wehrle (1997) HST Ferranres+ (1996) VLBA Miyoshi+ 1995 3pc
Molecular lines & VLBI Molecular gas in AGN region Important clues to study AGN fueling Compact (pc scale) High column density (1 3 cm ) Advantages of VLBI for absorption Can display thermal absorption in silhouette against a background synchrtron emission. Not detect the thermail emission No contamination of emissions Sensitive to detect the compact and dense absorbing gas beam size smaller, filling factor larger Emitting gas Absorbing gas HI absorption with VLA NGC379 VLA-C VLA-B VLA-A Irwin & Seaquist 1991 higher resolution
The target NGC 15 (1) A nearby radio gal. AGN : LINER/Sy Two-sided radio jet AGN torus suggested Several layers Free-free absorption (FFA) due to plasma HO maser OH absorption Redshifted from Vsys Ongoing infall? Relative Declination [mas] Sawada-Satoh+ 8 V LSR (km s -1 ) 16 165 17 175 18-1 - (c) (a) (b) -1 approaching jet 6 - -6 Kameno+ 3 Past VLBI images of NGC 15.1pc.pc HO maser spots Radio Continuum receding jet Relative Right Ascension [mas] FFA opacity (d) Flux Density (Jy/beam) 1 8 6 - -6 Impellizzeri+ 9 Circumnuclear torus 13 1 15 16 17 Velocity (km/s) XDR NGC 15 (e) Sawada-Satoh+ 8 OH absorption NGC 15 VLBA cm Central engine.pc. pc B C3 Eastern approaching jet C Flux Density (Jy/beam) 8 6 - -6-8 -1 Flux Density (Jy/beam) Flux Density (Jy/beam) 5 3 1-1 -3-6 - -6-8 -1-1 -1-16 Blank field 13 1 15 16 17 Velocity (km/s) 13 1 15 16 17 Velocity (km/s) 13 1 15 16 17 Velocity (km/s) Vsys Lines of sight 1pc Plasma gas region Western receding jet
The target NGC 15 () Molecular absorption at mm band HCO+(1-), HCN(1-), CO(1-) Velocity: 1-18 km/s Redshifted with respect to Vsys Similar to OH and HO Infall from the torus? or, another motion? Location of the absorption is a key! Need a high resolution image Liszt & Lucas (PdBI) HO maser Vsys Kameno+ 8
HCN (1-) absorption The first VLBI map of HCN (1-) (Sawada-Satoh+ ApJ 83 L3, 16) Two redshifted features, detected. The features around Vsys, not detected. Localized on the receding jet side. A depth of >1%, deeper with PdBI line/continuum. -.5 -.1 PdBI Liszt & Lucas Vsys (I) (II) HCN 1- optical depth maps DEC Offset [mas] - Optical Depth.1..3 (a) I.pc 6 - -6 RA Offset [mas] DEC Offset [mas] - Optical Depth.1..3 163-1677 1656 km s -1 (b) II 1698-171 1719 km s -1 receding jet.pc receding jet 6 - -6 RA Offset [mas] Sawada-Satoh+ (16) Flux Density [mjy] - HCN spectral profile (c) Radial Velocity [km s -1 ] KVN HCN(1-) Vsys (I) (a) (II) (b) 1 15 16 17
A possible model Several layers + clumpy HCN clouds (Sawada-Satoh+ 16) High opacity localized on the receding jet => Inclined torus At least two narrow absorptions => Inhomogeneous, clumpy Redshifted velocity => Ongoing infall onto SMBH (a) (b).pc XDR (maser) Circumnuclear torus Plasma region Western receding jet Eastern approaching jet HCN clouds Sawada-Satoh+ ApJ 83 L3, 16 The line of sight
Physical properties Column density of HCN 1- absorption Sawada-Satoh+ ApJ 83 L3, 16 Label Vp Vp-Vsys Δv NHCN(T=1K) NHCN(T=3K) [km/s] [km/s] [km/s] [1 1 cm ] [1 1 cm ] I 1656 19 31.7 9.5 5 II 1719 1 5.9 11 N(H) : 1-1 5 cm (HCN-to-H ratio of 1 9 ; Smith & Wardle 1) 1 order higher than N(e) by FFA opacity (~1 3 ; Kameno+ 1) Infall rate : ~.5-.5 Msun/yr Ṁ = f v R in N H m H V in Comparable to the rate estimated from X-ray luminosities (~. ; Wu & Cao 6)
Summary Conducted KVN observations of the HCN(1-) & HCO+(1-) absorption in NGC 15. Our HCN results are naturally explained by an AGN tors Two HCN absorption features are identified at redshifted velocities. Reached a depth of >1%, deeper than that of PdBI. Found N(H) of 1 --1 5 cm (HCN-to-H ratio of 1 9 ), assuming a Tex of 1- K High opacity of HCN absorption localized on the receding jet HCN gas is clumpy, and traces ongoing infall onto SMBH. The first VLBI detection of HCO + (1-) absorption A broad absorption feature (~5km/s), unlike HCN Localised on the receding jet side. Torus?