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

摘要

Sensitive observations with ALMA allow astronomers to observe the detaileddistributions of molecules with relatively weak intensity in nearby galaxies.In particular, we report distributions of several molecular transitionsincluding 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 Seyfert2 galaxy NGC 1068 observed with the ALMA early science program. The central$\sim$1 arcmin ($\sim$4.3 kpc) of this galaxy was observed in the 100 GHzregion covering $\sim$96--100 GHz and $\sim$108--111 GHz with an angularresolution of $\sim4"\times2"$ (290 pc$\times$140 pc) to study the effects ofan active galactic nucleus and its surrounding starburst ring on molecularabundances. Here, we present images and report a classification of moleculardistributions into three main categories: (1) Molecules concentrated in thecircumnuclear 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 inthe 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 moleculessuch as HC$_3$N observed in the CND are easily dissociated by UV photons andX-rays, our results indicate that these molecules must be effectively shielded.In the starburst ring, the relative intensity of methanol at each clumpy regionis not consistent with those of $^{13}$CO, C$^{18}$O, and CS. This differenceis probably caused by the unique formation and destruction mechanisms ofCH$_3$OH.