A Multi-Transition Study of Molecules toward NGC 1068 based on High-Resolution Imaging Observations with ALMA

Abstract

We present 0.8-mm band molecular images and spectra obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068. Distributions of CO isotopic species (${}^{13}$CO and C${}^{18}$O) $J$ = 3--2, CN $N$ = 3--2 and CS $J$ = 7--6 are observed toward the circumnuclear disk (CND) and a part of the starburst ring with an angular resolution of $\sim$1.${}^{\prime \prime }$3 $\times$ 1.${}^{\prime \prime }$2. The physical properties of these molecules and shock-related molecules such as HNCO, CH${}_3$CN, SO, and CH${}_3$OH detected in the 3-mm band were estimated using rotation diagrams under the assumption of local thermodynamic equilibrium. The rotational temperatures of the CO isotopic species and the shock-related molecules in the CND are, respectively, 14--22 K and upper limits of 20--40 K. Although the column densities of the CO isotopic species in the CND are only from one-fifth to one-third of that in the starburst ring, those of the shock-related molecules are enhanced by a factor of 3--10 in the CND. We also discuss the chemistry of each species, and compare the fractional abundances in the CND and starburst ring with those of Galactic sources such as cold cores, hot cores, and shocked molecular clouds in order to study the overall characteristics. We find that the abundances of shock-related molecules are more similar to abundances in hot cores and/or shocked clouds than to cold cores. The CND hosts relatively complex molecules, which are often associated with shocked molecular clouds or hot cores. Because a high X-ray flux can dissociate these molecules, they must also reside in regions shielded from X-rays.

26 pages, 3 figures, Accepted for publication in PASJ

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• ALMA imaging of C2H emission in the disk of NGC1068
• ALMA view of the ${}^{12}$C/${}^{13}$C isotopic ratio in starburst galaxies
• ALMA Astrochemical Observations of the Infrared-Luminous Merger NGC 3256
• Molecular-Cloud-Scale Chemical Composition I: Mapping Spectral Line Survey toward W51 in the 3 mm Band
• A statistical study of giant molecular clouds traced by ${}^{13}$CO, C${}^{18}$O, CS, and CH${}_3$OH in the disk of NGC 1068 based on ALMA observations
• Starburst Energy Feedback Seen Through HCO${}^{+}$/HOC${}^{+}$ Emission in NGC 253 from ALCHEMI
• Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images
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• ALMA polarimetry measures magnetically aligned dust grains in the torus of NGC 1068
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• Merger-induced Shocks in the Nearby LIRG VV 114 through Methanol Observations with ALMA
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• ALMA [CI] observations toward the central region of a Seyfert galaxy NGC 613
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• ALMA observations of CS in NGC 1068: chemistry and excitation
• Molecular Distribution in the Spiral Arm of M51
• Impact of an Active Sgr A* on the Synthesis of Water and Organic Molecules Throughout the Milky Way
• High-Temperature Chemistry in External Galaxies
• A Spectral Analysis of the Centimeter Regime of Nearby Galaxies: RRLs, Excited OH, and NH${}_3$
• High resolution ALMA observations of dense molecular medium in the central regions of active galaxies