Using the new capabilities of the Spitzer Space Telescope and extensive multiwavelength data from the Spitzer Infrared Nearby Galaxies Survey ( SINGS ) , it is now possible to study the infrared properties of star formation in nearby galaxies down to scales equivalent to large H ii regions .
We are therefore able to determine what fraction of large , infrared-selected star-forming regions in normal galaxies are highly obscured and address how much of the star formation we miss by relying solely on the optical portion of the spectrum .
Employing a new empirical method for deriving attenuations of infrared-selected star-forming regions we investigate the statistics of obscured star formation on 500 pc scales in a sample of 38 nearby galaxies .
We find that the median attenuation is 1.4 magnitudes in H \alpha and that there is no evidence for a substantial sub-population of uniformly highly-obscured star-forming regions .
The regions in the highly-obscured tail of the attenuation distribution ( A _ { H \alpha } \gtrsim 3 ) make up only \sim 4 % of the sample of nearly 1800 regions , though very embedded infrared sources on the much smaller scales and lower luminosities of compact and ultracompact H ii regions are almost certainly present in greater numbers .
The highly-obscured cases in our sample are generally the bright , central regions of galaxies with high overall attenuation but are not otherwise remarkable .
We also find that a majority of the galaxies show decreasing radial trends in H \alpha attenuation .
The small fraction of highly-obscured regions seen in this sample of normal , star-forming galaxies suggests that on 500 pc scales the timescale for significant dispersal or break up of nearby , optically-thick dust clouds is short relative to the lifetime of a typical star-forming region .