Gas and dust in NGC 7469: sub-mm imaging and CO J=3-2

Abstract

We present sensitive sub-mm imaging of the Seyfert 1 galaxy NGC 7469 at 850 $\mu$m and 450 $\mu$m with the Submillimetre Common User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT) and ^{12}CO J=3-2 line observations of its central starbursting region. The global dust spectrum, as constrained by the new set of sub-mm data and available 1.30 mm and IRAS 100 $\mu$m, 60 $\mu$m data reveals a dominant warm dust component with a temperature of ${\mathrm{T}}_{\mathrm{d}}\sim 35$ K and a global molecular gas-to-dust ratio $\mathrm{M}({\mathrm{H}}_2)/{\mathrm{M}}_{\mathrm{d}}\sim 600$. Such high values are typical for IR-bright spirals and in order to reconcile them with the significantly lower ratio of ~ 100 obtained for the Milky Way a cold dust reservoir, inconspicuous at FIR wavelengths, is usually postulated. We present evidence that, rather than unaccounted cold dust mass, this high ratio suggests an overestimate of $\mathrm{M}({\mathrm{H}}_2)$ from its associated ^{12}CO J=1-0 line luminosity by a factor of ~ 5 when a Milky Way value for this conversion is used in starburst nuclei environments.

25 pages, 3 figures Accepted for publication in the Astrophysical Journal