Multi-phase Turbulence Density Power Spectra in the Perseus Molecular Cloud

Abstract

We derive two-dimensional spatial power spectra of four distinct interstellar medium tracers, H i , 12 CO( J  = 1–0), 13 CO( J  = 1–0), and dust, in the Perseus molecular cloud, covering linear scales ranging from ∼0.1 pc to ∼90 pc. Among the four tracers, we find the steepest slopes of −3.23 ± 0.05 and −3.22 ± 0.05 for the uncorrected and opacity-corrected H i column density images. This result suggests that the H i in and around Perseus traces a non-gravitating, transonic medium on average, with a negligible effect from opacity. On the other hand, we measure the shallowest slope of −2.72 ± 0.12 for the 2MASS dust extinction data and interpret this as the signature of a self-gravitating, supersonic medium. Possible variations in the dust-to-gas ratio likely do not alter our conclusion. Finally, we derive slopes of −3.08 ± 0.08 and −2.88 ± 0.07 for the 12 CO(1–0) and 13 CO(1–0) integrated intensity images. Based on theoretical predictions for an optically thick medium, we interpret these slopes of roughly −3 as implying that both CO lines are susceptible to the opacity effect. While simple tests for the impact of CO formation and depletion indicate that the measured slopes of 12 CO(1–0) and 13 CO(1–0) are not likely affected by these chemical effects, our results generally suggest that chemically more complex and/or fully optically thick media may not be a reliable observational tracer for characterizing turbulence.