A KOSMA 7 deg2 13CO 2-1 and 12CO 3-2 survey of the Perseus cloud I.: Structure analysis

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 (similar to 7.10 deg(2)) (CO)-C-13 J = 2-1 and (CO)-C-12 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 Delta-variance as a function of size scale. We determine the spectral index beta 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, beta approximate to 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 beta. The (CO)-C-12 3-2 data provide e. g. a spread of indices between 2.9 in L 1455 and 3.5 in NGC1333. In general, active star forming regions show a larger power-law exponent. We find that the Delta-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.