Abstract
High resolution submm observations are important in probing the morphology, column density and dynamics of obscured active galactic nuclei (AGNs). With high resolution (0.06 x 0.05) ALMA 690 GHz observations we have found bright (TB >80 K) and compact (FWHM 10x7 pc) CO 6-5 line emission in the nucleus of the extremely radio-quiet galaxy NGC1377. The integrated CO 6-5 intensity is aligned with the previously discovered jet/outflow of NGC1377 and is tracing the dense (n>1e4 cm-3), hot gas at the base of the outflow. The velocity structure is complex and shifts across the jet/outflow are discussed in terms of jet-rotation or separate, overlapping kinematical components. High velocity gas (deltaV +-145 km/s) is detected inside r<2-3 pc and we suggest that it is emerging from an inclined rotating disk or torus of position angle PA=140+-20 deg with a dynamical mass of approx 3e6 Msun. This mass is consistent with that of a supermassive black hole (SMBH), as inferred from the M-sigma relation. The gas mass of the proposed disk/torus constitutes <3% of the nuclear dynamical mass. In contrast to the intense CO 6-5 line emission, we do not detect dust continuum with an upper limit of S(690GHz)<2mJy. The corresponding, 5 pc, H2 column density is estimated to N(H2)<3e23 cm-2, which is inconsistent with a Compton Thick (CT) source. We discuss the possibility that CT obscuration may be occuring on small (subparsec) or larger scales. From SED fitting we suggest that half of the IR emission of NGC1377 is nuclear and the rest (mostly the far-infrared (FIR)) is more extended. The extreme radio quietness, and the lack of emission from other star formation tracers, raise questions on the origin of the FIR emission. We discuss the possibility that it is arising from the dissipation of shocks in the molecular jet/outflow or from irradiation by the nuclear source along the poles.
Highlights
NGC 1377 is a nearby (21 Mpc (1 = 102 pc)) lenticular galaxy with a far-infrared (FIR) luminosity of LFIR = 4.3 × 109 L (Roussel et al 2003)
NGC 1377 is the most radio-quiet, FIRexcess galaxy known to date; its radio emission is weaker by a factor ≈37 compared to normal galaxies (Roussel et al 2003, 2006)
If all the mid-IR luminosity (1 × 109 L to 4 × 109 L ) is due to an accreting supermassive black hole (SMBH), we find it is growing at a rate of 1–10% Eddington, which would place it in the quasar mode of accretion5
Summary
14), high surface brightness source (Imanishi et al 2011) in the nucleus of NGC 1377 It is not clear whether this structure is part of an obscuring torus or disk, and whether it is opaque enough to absorb X-rays emerging from an accreting supermassive black hole. Direct detection on pc-scales of the dust torus around an AGN have remained elusive until recently when Atacama Large Millimeter/submillimeter Array (ALMA) band 9 (690 GHz) observations of the Seyfert galaxy NGC 1068 revealed the presence of the obscuring torus and its turbulent dynamics (García-Burillo et al 2016; Gallimore et al 2016). 5 we examine the possible source of the CO 6−5 high-velocity gas, the dynamics of the nuclear disk, and the acceleration region of the jet/outflow. Peak flux densityb Fluxc (central beam) (whole map) α: 03:36:39.075 (±0. 01) δ: –20:54:07.06 (±0. 01) 90 ± 10 mJy beam−1
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