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Hans Publishers, Astronomy & Astrophysics, (575), p. A17

DOI: 10.1051/0004-6361/201424732

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Insights into gas heating and cooling in the disc of NGC 891 fromHerschelfar-infrared spectroscopy

Journal article published in 2015 by T. M. Hughes, K. Foyle, M. R. P. Schirm, T. J. Parkin, I. De Looze, C. D. Wilson, G. J. Bendo, M. Baes ORCID, J. Fritz, A. Boselli, A. Cooray, D. Cormier, O. Ł. Karczewski, V. Lebouteiller, N. Lu and other authors.
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby edge-on spiral galaxy, NGC 891: [CII] 158 $μ$m, [NII] 122, 205 $μ$m, [OI] 63, 145 $μ$m, and [OIII] 88 $μ$m. We find that the photoelectric heating efficiency of the gas, traced via the ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ ratio, varies from a mean of 3.5$\times$10$^{-3}$ in the centre up to 8$\times$10$^{-3}$ at increasing radial and vertical distances in the disc. A decrease in ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ but constant ([CII]+[OI]63)/$F_{\mathrm{PAH}}$ with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891's disc have hydrogen densities of 1