1. ALMA observations of CS in NGC 1068: chemistry and excitation
- Author
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Carsten Henkel, Serena Viti, A. Fuente, Nanase Harada, M. Scourfield, Francoise Combes, Amélie Saintonge, Susanne Aalto, A. Alonso-Herrero, Sergio Martín, Shuro Takano, Kotaro Kohno, M. Krips, A. Usero, Santiago García-Burillo, Taku Nakajima, P. van der Werf, Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737, Alonso Herrero, A. [0000-0001-6794-2519], Agencia Estatal de Investigación (AEI), MCIU/AEI/FEDER, and Unidad de Excelencia María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC
- Subjects
Physics ,Active galactic nucleus ,010308 nuclear & particles physics ,Thermodynamic equilibrium ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Ring (chemistry) ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Submillimeter Array ,Galaxy ,Chemistry ,Barred spiral galaxy ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,NGC 1068 ,nuclei [Galaxies] ,0103 physical sciences ,Radiative transfer ,radio lines ,010303 astronomy & astrophysics ,individual [Galaxies] ,Alma observations ,Line (formation) - Abstract
We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 ($\sim14$ Mpc). This Seyfert 2 barred galaxy possesses a circumnuclear disc (CND, $r\sim200$ pc) and a starburst ring (SB ring, $r\sim1.3$ kpc). These high-resolution maps ($\sim0.5$", $\sim35$ pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by non-LTE analysis conducted using the radiative transfer code RADEX to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code UCLCHEM is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be $\geq10^5$ cm$^{-2}$, although exact values vary, reaching $10^6$ cm$^{-2}$ at the AGN. The conditions in the two arms of the SB ring appear similar to one another, though the density found ($\sim10^4$ cm$^{-2}$) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multi-phase gas components in order to fit the observed emission over the galaxy. A larger number of high resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring., 32 pages, 19 figures, 6 tables, accepted for publication in MNRAS
- Published
- 2020