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Subaru Seminars are usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you would like to give a seminar, please contact Subaru seminar organizers (Rusu Cristian Eduard, Tae-Soo Pyo, Nagayoshi Ohashi) by email : sseminar_at_subaru.naoj.org (please change"_at" to @).

April 30, Monday, 11am in 104A

" ALMA reveals a rotating dense molecular torus in the AGN NGC 1068"

Masatoshi Imanishi (NAOJ)


An AGN (active galactic nucleus) is an object which emits very strong radiation from the nuclear compact region of a galaxy. It is now widely believed that a mass-accreting supermassive black hole (SMBH) is the main energy generation mechanism of an AGN. According to the AGN unification paradigm, a dusty gaseous torus is thought to be present around a mass-accreting supermassive black hole (SMBH), because this model can naturally explain various observational results of AGNs. However, since the putative torus is spatially compact, say <10 pc or <0.15" at the distance of 15 Mpc, its observational understanding is still highly incomplete. ALMA high-spatial-resolution observations are expected to play a vital role to unravel the properties of the AGN torus. We present our results of ALMA 0.04" x 0.07" resolution observations of the nearby (~14 Mpc) well-studied type-2 AGN NGC 1068 in the HCN J=3-2 and HCO+ J=3-2 molecular lines. Previous observations of NGC 1068 have shown that the morphologies of the optical ionized gas emission and radio jet are extended along the N-S direction. Thus, it is expected that the putative torus is aligned roughly along the E-W direction. We have clearly demonstrated, for the first time, that both HCN J=3-2 and HCO+ J=3-2 emission lines (dense molecular tracers) are elongated along the E-W direction (PA = 105 deg east of north) both morphologically and dynamically, as expected for NGC 1068. The estimated molecular mass and size are comparable to those expected from the classical AGN torus model. However, we found that (1) torus molecular emission is highly asymmetric in that the western part is brighter and shows higher turbulence the eastern part, and (2) the torus dynamics is far from the Keplerian motion governed by the gravity of the central SMBH. We will discuss detailed physical/morphological/dynamical properties of the torus in NGC 1068 revealed from our ALMA high-spatial-resolution data.

April 30, Monday, 11:30am in 104A

" Study of X-ray Irradiated Inter Stellar Medium around Circinus Galaxy Nucleus with Chandra and ALMA 10 pc Resolution data"

Taiki Kawamuro (NAOJ)


We are interested in how the AGN affects its surrounding material, and consequently whether it has strong impacts on the galaxy evolution. In this seminar, I would like to talk on our recent study of inter stellar medium irradiated by AGN X-ray emission in Circinus galaxy using Chandra and ALMA 10 pc resolution data. We create maps of 6.4 keV iron-Kalpha line emitting regions based on ~300 ksec Chandra/ACIS data. The maps enable us to know gas distribution irrespective of its atomic/molecular phases. They are compared with those of molecular emission observed with ALMA. A noticeable finding is that the iron emission line is bright around the nucleus (< 60 pc) and therein the molecular line emission is suppressed. This suggests that the molecular gas close to the AGN tends to be dissociated into the atomic gas. We quantitatively discuss this in accordance with the X-ray Dominated Region (so called XDR) model. We estimate a key parameter of an effective ionization parameter (xi_eff = L_X/(R^2 n_H2 N_H^1.1)) at R = 60 pc, corresponding to an outer limb of the iron line bright region, given the X-ray luminosity (L_X) and the attenuating column density (N_H) for incident X-rays. The hydrogen density (n_H2) is constrained by fitting the observed molecular line ratios to those predicted from a non-LTE model. Then, we find that the estimated ionization parameter is consistent with an atomic-to-molecular hydrogen transition boundary predicted from an XDR model (Maloney 1996). Thus, we suggest that the X-ray radiation likely dissociates molecules within the Circinus galaxy nucleus. Given a correlation between the molecular gas surface density and the starformation rate, the result implies the suppression of the star formation therein.


Seminars are also held at JAC, CFHT, and IfA.



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