We present an integrated photometric spectral energy distribution ( SED ) of the Magellanic-type galaxy NGC 4449 from the far-ultraviolet to the submillimetre , including new observations acquired by the Herschel Space Observatory .
We include integrated UV photometry from the Swift Ultraviolet and Optical Telescope using a measurement technique which is appropriate for extended sources with coincidence loss .

In this paper , we examine the available multiwavelength data to infer a range of ages , metallicities and star formation rates for the underlying stellar populations , as well as the composition and the total mass of dust in NGC 4449 .
Our analysis of the global optical spectrum of NGC 4449 fitted using the spectral fitting code STARLIGHT suggests that the majority of stellar mass resides in old ( \gtrsim 1 Gyr old ) and metal-poor ( Z / \textrm { Z } _ { \odot } \sim 0.2 ) populations , with the first onset of star formation activity deduced to have taken place at an early epoch , approximately 12 Gyr ago .
A simple chemical evolution model , suitable for a galaxy continuously forming stars , suggests a ratio of carbon to silicate dust mass comparable to that of the Large Magellanic Cloud over the inferred time-scales .

We present an iterative scheme , which allows us to build an in-depth and multicomponent representation of NGC 4449 ‘ bottom-up ’ , taking advantage of the broad capabilities of the photoionization and radiative transfer code MOCASSIN ( MOnte CArlo SimulationS of Ionized Nebulae ) .
We fit the observed SED , the global ionization structure and the emission line intensities , and infer a recent star formation rate of 0.4 \textrm { M } _ { \odot } yr ^ { -1 } and a total stellar mass of \approx 1 \times 10 ^ { 9 } \textrm { M } _ { \odot } emitting with a bolometric luminosity of 5.7 \times 10 ^ { 9 } \textrm { L } _ { \odot } .
Our fits yield a total dust mass of 2.9 \pm 0.5 \times 10 ^ { 6 } \textrm { M } _ { \odot } including 2 per cent attributed to polycyclic aromatic hydrocarbons .
We deduce a dust to gas mass ratio of 1/190 within the modelled region .
While we do not consider possible additional contributions from even colder dust , we note that including the extended H i envelope and the molecular gas is likely to bring the ratio down to as low as \sim 1/800 .