Infrared cirrus and high-latitude molecular clouds

It is established that a close correlation exists between far-infrared cirrus emission observed with IRAS and the CO emission from high-latitude molecular clouds (HCLs). In all cases, the HLCs correspond to the central portions of 100-micron infrared cirrus features. This association firmly establishes at least some of the cirrus as features of the local interstellar medium with typical distances of 100 pc. The infrared energy distribution of the cirrus displays an excess of 12-micron and 25-micron emission over that expected from dust at equilibrium temperature, consistent with emission from very small (less than 10 A) transiently heated grains.