A KOSMA 7 deg$\mathsf{^{2}}$ $\mathsf{^{13}}$CO 2–1 and $\mathsf{^{12}}$CO 3–2 survey of the Perseus cloud

Abstract

Context. Characterizing the spatial and velocity structure of molecular clouds is a first step towards a better understanding of interstellar turbulence and its link to star formation. Aims. We present observations and structure analysis results for a large-scale (∼7.10 deg 2 ) 13 CO J = 2-1 and 12 CO J = 3-2 survey towards the nearby Perseus molecular cloud observed with the KOSMA 3 m telescope. Methods. We study the spatial structure of line-integrated and velocity channel maps, measuring the ∆-variance as a function of size scale. We determine the spectral index β of the corresponding power spectrum and study its variation across the cloud and across the lines. Results. We find that the spectra of all CO line-integrated maps of the whole complex show the same index, β ≈ 3.1, for scales between about 0.2 and 3 pc, independent of isotopomer and rotational transition. A complementary 2MASS map of optical extinction shows a noticeably smaller index of 2.6. In contrast to the overall region, the CO maps of individual subregions show a significant variation of β. The 12 CO 3-2 data provide e.g. a spread of indices between 2.9 in L 1455 and 3.5 in NGC 1333. In general, active star forming regions show a larger power-law exponent. We find that the ∆-variance spectra of individual velocity channel maps are very sensitive to optical depth effects clearly indicating self-absorption in the densest regions. When studying the dependence of the channel-map spectra as a function of the velocity channel width, the expected systematic increase of the spectral index with channel width is only detected in the blue line wings. This could be explained by a filamentary, pillar-like structure which is left at low velocities while the overall molecular gas is swept up by a supernova shock wave.

Submillimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined fromJ = 3–2 andJ = 1–0 Transitions of CO

“…Typical values are 7 pc, 7 km s À1 , and 6 ; 10 4 M , in size, line width, and virial mass, respectively. Their line widths are larger than those of the GMCs in our galaxy (e.g., Williams & Blitz 1998;Ikeda et al 1999;Sun et al 2006). We note a trend that the masses of these clumps are relatively large compared with those of high-mass cloud cores in the Milky Way, which are of the order of 10 3 M (e.g., Burton et al 2005;Yonekura et al 2005).…”

The link between molecular cloud structure and turbulence

“…Although the Δ-variance determined from extinction maps shows interesting particularities for different clouds, one has to note that there can be large differences in the value of β within each individual complex, as was shown by Sun et al (2006) for Perseus. We thus have to be careful in interpretating different values of β and the shape of the spectrum depending on the type of cloud and tracer.…”

TheHerschelview of the massive star-forming region NGC 6334

“…Fitting the slope β thus provides a measure for the amount of structure on various scales in a given image. See Ossenkopf et al (2008a,b) for a description of the method and, e.g., Sun et al (2006) and Schneider et al (2011) for its observational application.…”

“…This implies first that these regions are not fundamentally different in their spatial structure and second that small-scale structure dominates because the β-values are low. Interestingly, the "Filaments" sub-region has the lowest value, 1.7, which is indeed characteristic for filamentary structures (see Sun et al 2006, who compared Δ-variance results from molecular line maps with different tracers and A V -maps). Figure 9 shows the Δ-variance determined for the whole complex.…”