Molecular line emission in NGC 1068 imaged with ALMA II. The chemistry of the dense molecular gas
Artikel i vetenskaplig tidskrift, 2014

Aims. We present a detailed analysis of Atacama Large Millimeter/submillimeter Array (ALMA) Bands 7 and 9 data of CO, HCO+, HCN, and CS, augmented with Plateau de Bure Interferometer (PdBI) data of the ~200 pc circumnuclear disc (CND) and the ~1.3 kpc starburst ring (SB ring) of NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy. We aim to determine the physical characteristics of the dense gas present in the CND, and to establish whether the different line intensity ratios we find within the CND, as well as between the CND and the SB ring, are due to excitation effects (gas density and temperature differences) or to a different chemistry. Methods. We estimate the column densities of each species in local thermodynamic equilibrium (LTE). We then compute large one-dimensional, non-LTE radiative transfer grids (using RADEX) by using only the CO transitions first, and then all the available molecules to constrain the densities, temperatures, and column densities within the CND. We finally present a preliminary set of chemical models to determine the origin of the gas. Results. We find that, in general, the gas in the CND is very dense (>105 cm-3) and hot (T> 150 K), with differences especially in the temperature across the CND. The AGN position has the lowest CO/HCO+, CO/HCN, and CO/CS column density ratios. The RADEX analyses seem to indicate that there is chemical differentiation across the CND. We also find differences between the chemistry of the SB ring and some regions of the CND; the SB ring is also much colder and less dense than the CND. Chemical modelling does not succeed in reproducing all the molecular ratios with one model per region, suggesting the presence of multi-gas phase components. Conclusions. The LTE, RADEX, and chemical analyses all indicate that more than one gas-phase component is necessary to uniquely fit all the available molecular ratios within the CND. A higher number of molecular transitions at the ALMA resolution is necessary to determine quantitatively the physical and chemical characteristics of these components.

galaxies: active / galaxies: individual: NGC 1068 / galaxies: ISM / galaxies: nuclei / molecular processes / radio lines: galaxies

Författare

S. Viti

University College London (UCL)

S. G. Burillo

A. Fuente

L. K. Hunt

Osservatorio Astrofisico di Arcetri

A. Usero

C. Henkel

King Abdulaziz University

Max Planck-institutet

A. Eckart

Universität zu Köln

Max Planck-institutet

S. Martin

Université Grenoble Alpes

M. Spaans

University of Groningen, Kapteyn Astronomical Institute

Sebastien Muller

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

F. Combes

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

M. Krips

Université Grenoble Alpes

E. Schinnerer

Max Planck-institutet

V. Casasola

INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Bologna

Francesco Costagliola

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

I. Marquez

CSIC - Instituto de Astrofísica de Andalucía (IAA)

P. Planesas

P.P. van der Werf

Leiden University

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

A. J. Baker

Rutgers, The State University of New Jersey

F. Boone

Universite de Toulouse

L. J. Tacconi

Max Planck-institutet

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 570 28- A28

Ämneskategorier

Astronomi, astrofysik och kosmologi

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201424116