Evidence for Dust Evolution Within the Taurus Complex from Spitzer Images

摘要

We present Spitzer images of the Taurus Complex (TC). We take advantage of the sensitivity and the spatial resolution of the observations to characterize the diffuse infrared (IR) emission across the cloud. This work highlights evidence of dust evolution within the translucent sections of the archetype reference for studies of quiescent molecular clouds. We combine the Spitzer 160 μm and IRAS 100 μm observations to produce a dust temperature map and a far-IR (FIR) dust opacity map at 5' resolution. The average dust temperature is about 14.5 K with a dispersion of ±1 K across the cloud. The FIR dust opacity is tightly correlated with the extinction derived from Two Micron All Sky Survey stellar colors and is a factor of 2 larger than the average value for the diffuse interstellar medium. This opacity increase and the attenuation of the radiation field both contribute to account for the lower emission temperature of the large grains. The structure of the TC significantly changes in the mid-IR (MIR) images that trace emission from polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs). We focus our analysis of the MIR emission to a range of ecliptic latitudes away from the zodiacal bands and where the zodiacal light residuals are small. Within this cloud area, there are no 8 and 24 μm counterparts to the brightest 160 μm emission features. Conversely, the 8 and 24 μm images reveal filamentary structure that is strikingly inconspicuous in the 160 μm and extinction maps. The IR colors vary over subparsec distances across this filamentary structure. We compare the observed colors with model calculations quantifying the impact of the radiation field intensity and the abundance of stochastically heated particles on the dust spectral energy distribution. To match the range of observed colors, we have to invoke variations by a factor of a few of both the interstellar radiation field and the abundance of PAHs and VSGs. We conclude that within this filamentary structure a significant fraction of the dust mass cycles in and out the small-size end of the dust size distribution.