We combine new dust continuum observations of the edge-on spiral galaxy NGC 4565 in all Herschel /SPIRE ( 250 , 350 , 500 \mu m ) wavebands , obtained as part of the Herschel Reference Survey , and a large set of ancillary data ( Spitzer , SDSS , GALEX ) to analyze its dust energy balance .
We fit a radiative transfer model for the stars and dust to the optical maps with the fitting algorithm FitSKIRT .
To account for the observed UV and mid-infrared emission , this initial model was supplemented with both obscured and unobscured star-forming regions .
Even though these star-forming complexes provide an additional heating source for the dust , the far-infrared/submillimeter emission long wards of 100 \mu m is underestimated by a factor of 3-4 .
This inconsistency in the dust energy budget of NGC 4565 suggests that a sizable fraction ( two-thirds ) of the total dust reservoir ( M _ { d } \sim 2.9 \times 10 ^ { 8 } M _ { \odot } ) consists of a clumpy distribution with no associated young stellar sources .
The distribution of those dense dust clouds would be in such a way that they remain unresolved in current far-infrared/submillimeter observations and hardly contribute to the attenuation at optical wavelengths .
More than two-thirds of the dust heating in NGC 4565 is powered by the old stellar population , with localized embedded sources supplying the remaining dust heating in NGC 4565 .
The results from this detailed dust energy balance study in NGC 4565 is consistent with that of similar analyses of other edge-on spirals .