Kelly, G;
Viti, S;
Garcia-Burillo, S;
Fuente, A;
Usero, A;
Krips, M;
Neri, R;
(2017)
Molecular shock tracers in NGC1068: SiO and HNCO.
Astronomy & Astrophysics
, 597
, Article A11. 10.1051/0004-6361/201628946.
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Abstract
Aims. We present and compare the distribution of two shock tracers, SiO and HNCO, in the circumnuclear disk (CND) of NGC 1068. We aim to determine the causes of the variation in emission across the CND. Methods. SiO(3−2) and HNCO(6−5) emission has been imaged in NGC 1068 with the Plateau de Bure Interferometer (PdBI). We perform an LTE and RADEX analysis to determine the column densities and physical characteristics of the gas emitting these two lines. We then use a chemical model to determine the origin of the emission. Results. There is a strong SiO peak to the east of the AGN, with weak detections to the west. This distribution contrasts that of HNCO, which is detected more strongly to the west. The SiO emission peak in the east is similar to the peak of the molecular gas mass traced by CO. HNCO emission is offset from this peak by as much as ~80 pc (1′′). We compare velocity integrated line ratios in the east and west. We confirm that SiO emission strongly dominates in the east, while the reverse is true in the west. We use RADEX to analyse the possible gas conditions that could produce such emission. We find that, in both east and west, we cannot constrain a single temperature for the gas. We run a grid of chemical models of potential shock processes in the CND and find that SiO is significantly enhanced during a fast (60 km s-1) shock but not during a slow (20 km s-1) shock, nor in a gas not subjected to shocks at all. We find the inverse for HNCO, whose abundance increases during slow shocks and in warm non-shocked gas. Conclusions. High SiO and low HNCO indicated a fast shock, while high HNCO and low SiO indicates either a slow shock or warm, dense, non-shocked gas. The East Knot is therefore likely to contain gas that is heavily shocked. From chemical modelling, gas in the West Knot may be non-shocked, or maybe undergoing a much milder shock event. When taking into account RADEX results, the milder shock event is the more likely of the two scenarios.
| Type: | Article |
|---|---|
| Title: | Molecular shock tracers in NGC1068: SiO and HNCO |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1051/0004-6361/201628946 |
| Publisher version: | http://doi.org/10.1051/0004-6361/201628946 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | galaxies: ISM, galaxies: individual: NGC 1068, galaxies: nuclei, ISM: molecules |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1550425 |
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