Cold dust and its relation to molecular gas in the dwarf irregular galaxy NGC 4449

We present observations of the dwarf irregular galaxy NGC4449 at 850 mum and 450 mum obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and Halpha emission. To explain the integrated mm-through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39 K and 168 K, respectively. The dust mass is dominated by the cold dust component; we derive a total dust mass of similar to3.8 x 10(6) M-circle dot, and with the local gas-to-dust ratio of similar to130 a total gas mass of MHI+H2 similar to 4.9 x 10(8) M-circle dot. Comparison with the HI mass leads to a total molecular gas mass of similar to3.4 x 10(8) M-circle dot. We derive a conversion factor of the CO line intensity to molecular hydrogen column density X-CO = N-H2/I-CO which is at least 11 times larger than the Galactic value. These values are in accord with the lower metallicity of NGC4449.