Journal Article

Metallicity in the merger Seyfert galaxy NGC 6240

M. Contini

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 426, issue 1, pages 719-731
Published in print October 2012 | ISSN: 0035-8711
Published online October 2012 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-2966.2012.21764.x
Metallicity in the merger Seyfert galaxy NGC 6240

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Abstract

We have calculated the physical conditions throughout the merger Seyfert galaxy NGC 6240 by modelling the observed optical and infrared line ratios. We have found that the optical spectra are emitted by clouds photoionized by the power-law radiation flux from the active galactic nucleus/nuclei (AGN/AGNs), and heated mainly by the shock accompanying the propagation of the clouds outwards. The infrared line ratios are emitted from clouds ejected from a starburst which photoionizes the gas by the blackbody radiation flux corresponding to a stellar colour temperature of about 5 × 104 K. Both the flux from the AGN and the ionization parameters are low. The most characteristic physical parameters are the relatively high shock velocities (≥500 km s−1) and low pre-shock densities (∼40–60 cm−3) of the gas. The C/H, N/H, O/H relative abundances are higher than solar by a factor ≤1.5. We suggest that those relative abundances indicate trapping of H into H2 molecules rather than high metallicities. Adopting an initial grain radius of 1 μm, the dust temperatures calculated in the clouds reached by the power-law radiation and by the blackbody radiation are 81 and 68 K, respectively.

Keywords: radiation mechanisms: general; shock waves; ISM: abundances; galaxies: individual: NGC 6240; galaxies: Seyfert

Journal Article.  10333 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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