A KOSMA 7 deg CO 2–1 and CO 3–2 survey of the Perseus cloud

I. Structure analysis

¹ KOSMA I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany e-mail: kefeng@ph1.uni-koeln.de
² SRON National Institut for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
³ Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

Received: 26 September 2005
Accepted: 25 January 2006

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 deg²) ¹³CO –1 and ¹²CO –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 Δ-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, , 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 ¹²CO 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 Δ-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.