Distributions of molecules in the circumnuclear disk and surrounding starburst ring in the Seyfert galaxy NGC 1068 observed with ALMA

Abstract

Sensitive observations with the Atacama Large Millimeter/submillimeter Array (ALMA) allow astronomers to observe and discuss the detailed distributions of molecules with relatively weak intensity in nearby galaxies. In particular, we report distributions of several molecular transitions including shock and dust related species ( 13 CO J = 1-0, C 18 O J = 1-0, 13 CN N = 1-0, CS J = 2-1, SO J N = 3 2 -2 1 , HNCO J Ka,Kc = 5 0,5 -4 0,4 , HC 3 N J = 11-10, 12-11, CH 3 OH J K = 2 K -1 K , and CH 3 CN J K = 6 K -5 K ) in the nearby Seyfert 2 galaxy NGC 1068. This is the first paper reporting our study of molecular distributions in NGC 1068 with the ALMA early science program. The central ∼1 arcmin (∼4.3 kpc) of this galaxy was observed in the 100 GHz region (band 3) covering ∼96-100 GHz and ∼108-111 GHz with an angular resolution of ∼ 4 ′′ × 2 ′′ (290 pc×140 pc). These observations were motivated to study the effects of an active galactic nucleus and its surrounding starburst ring on molecular abundances. In this article, we present images and report a classification of 1 molecular distributions into three main categories, defined as follows: (1) Molecules concentrated in the circumnuclear disk (CND) (SO J N = 3 2 -2 1 , HC 3 N J = 11-10, 12-11, and CH 3 CN J K = 6 K -5 K ), (2) Molecules distributed both in the CND and the starburst ring (CS J = 2-1 and CH 3 OH J K = 2 K -1 K ), (3) Molecules distributed mainly in the starburst ring ( 13 CO J = 1-0 and C 18 O J = 1-0). Since most of the molecules such as HC 3 N observed in the CND are easily dissociated by UV photons and X-rays, our results indicate that these molecules must be effectively shielded. In the starburst ring, the distribution of CH 3 OH is similar to those of 13 CO, C 18 O, and CS on the whole, but the relative intensity of methanol at each clumpy region is not consistent with those of 13 CO, C 18 O, and CS. This difference is probably caused by the unique formation and destruction mechanisms of CH 3 OH in the environment of the starburst ring.

Multimolecule ALMA observations toward the Seyfert 1 galaxy NGC 1097

“…This is an indication of a significant asymmetrical distribution of the molecular gas in the CND (also seen in CO 2−1, Hsieh et al 2008), similar to what is observed at higher resolution in NGC 1068 . Also in NGC 1068, though at slightly lower resolution, the emission of HNCO is observed distributed in two lobes at both sides of the AGN (Takano et al 2014). Such double peak distribution is in agreement with the CND being observed from a more inclined direction consistent with its Seyfert 2 nucleus.…”

“…The densest gas: SiO, HNCO and HC 3 N These three species are the ones showing the clearest contrast between the central region and the SF ring with a significant enhancement toward the nuclear region. Toward NGC 1068, an enhancement of SiO and HC 3 N in the surroundings of the AGN was already been recently reported (García-Burillo et al 2010;Takano et al 2014).…”

“…3.2) would increase by a factor of 5−6 for excitation temperatures of ∼20 K. Figure 5 clearly suggests observable variations in the HCN/HCO + line ratios within the CND even though the central region is only resolved over a few synthesized beams. Molecular variations in the central few hundred parsec CND around the AGN in NGC 1068 have been reported both at very high spatial resolution (35 pc, García-Burillo et al 2014;Viti et al 2014) for HCN and HCO + and at a coarser spatial resolution of 300 × 170 for a wider sample of species (Takano et al 2014). Here we discuss the different morphologies of the observed species toward NGC 1097 and compare it to what is observed in NGC 1068.…”

“…In fact, within the past year and while still in the early science phase, ALMA is already providing extremely high quality data on the chemistry of some of the brightest nearby prototypical galaxies, both AGNs (NGC 1068, García-Burillo et al 2014;Takano et al 2014;Viti et al 2014;NGC 1097, Izumi et al 2013 and SBs (NGC 253, Meier et al 2014). The unprecedented capabilities of these instruments allow us to extend molecular studies to either farther or fainter objects, thus increasing the significance of chemical comparative studies, now limited to a very reduced number of sources .…”

“…The unprecedented sensitivity of ALMA allows us to carry out multimolecule imaging studies of NGC 1097 which can be directly compared to similar studies toward the much brighter NGC 1068 (Takano et al 2014).…”