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 T _ { d } \sim 35 K and a global molecular gas-to-dust ratio M ( H _ { 2 } ) / M _ { d } \sim 600 .
Including the atomic gas component yields a total gas-to-dust ratio of \sim 830 .
Such high values are typical for IR-bright spirals and in order to reconcile them with the significantly lower ratio of \sim 100 obtained for the Milky Way a cold dust reservoir , inconspicuous at FIR wavelengths , is usually postulated .
However , while there is good evidence for the presence of cold gas/dust in NGC 7469 beyond its central region , our 450 \mu m map and available interferometric ^ { 12 } CO J=1–0 maps show the bright sub-mm/CO emission confined in the inner \sim 2.5 kpc , where a high ^ { 12 } CO ( J=3–2 ) / ( J=1–0 ) ratio ( \sim 0.85 - 1.0 ) is measured .
This is consistent with molecular gas at T _ { kin } \ga 30 K , suggesting that the bulk of the ISM in the starburst center of NGC 7469 is warm .
Nevertheless the corresponding total gas-to-dust ratio there remains high , of the order of \sim 500 .
We argue that , rather than unaccounted cold dust mass , this high ratio suggests an overestimate of M ( H _ { 2 } ) from its associated ^ { 12 } CO J=1–0 line luminosity by a factor of \sim 5 when a Milky Way value for this conversion is used .
Finally the diffuse cold gas and dust that is the likely source of the observed faint extended 450 \mu m and ^ { 12 } CO J=1–0 emission has an estimated total gas-to-dust ratio of \sim 50 - 160 , closer to the Galactic value .