Evidence for dust evolution within the Taurus Complex from Spitzer images

摘要

We present Spitzer images of the Taurus Complex (TC) and take advantage ofthe sensitivity and spatial resolution of the observations to characterize thediffuse IR emission across the cloud. This work highlights evidence of dustevolution within the translucent sections of the archetype reference forstudies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100um observations to produce a dust temperature map and a far-IR dust opacity mapat 5' resolution. The average dust temperature is about 14.5K with a dispersionof +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger thanthe average value for the diffuse ISM. This opacity increase and theattenuation of the radiation field (RF) both contribute to account for thelower emission temperature of the large grains. The structure of the TCsignificantly changes in the mid-IR images that trace emission from PAHs andVSGs. We focus our analysis of the mid-IR emission to a range of eclipticlatitudes where the zodiacal light residuals are small. Within this cloud area,there are no 8 and 24 um counterparts to the brightest 160 um emissionfeatures. Conversely, the 8 and 24 um images reveal filamentary structure thatis strikingly inconspicuous in the 160 um and extinction maps. The IR colorsvary over sub-parsec distances across this filamentary structure. We comparethe observed colors with model calculations quantifying the impact of the RFintensity and the abundance of stochastically heated particles on the dust SED.To match the range of observed colors, we have to invoke variations by a factorof a few of both the interstellar RF and the abundance of PAHs and VSGs. Weconclude that within this filamentary structure a significant fraction of thedust mass cycles in and out the small size end of the dust size distribution.