Star formation in Perseus - Clusters, filaments and the conditions for star formation

We present a complete survey of current star formation in the Perseus molecular cloud, made at 850 and 450 µm with SCUBA at the JCMT. Covering 3 deg 2 , this submillimetre continuum survey for protostellar act ivity is second in size only to that ofOphiuchus (Johnstone et al. 2004). Complete above 0.4 M⊙ (5� detection in a 14 '' beam), we detect a total of 91 protostars and prestellar cores. Of these, 80% lie in cluste rs, representative of star formation across the Galaxy. Two of the groups of cores are associated with the young stellar clusters IC348 and NGC1333, and are consistent with a steady or reduced star formation rate in the last 0.5 Myr, but not an increasing one. In Perseus, 40-60% of cores are in small clusters (< 50 M⊙) and isolated objects, much more than the 10% suggested from infrared studies. Complementing the dust continuum, we present a C 18 O map of the whole cloud at 1 ' resolution. The gas and dust show filamentary structure of th e dense gas on large and small scales, with the high column density filaments breaking up in to clusters of cores. The filament mass per unit length is 5-11 M⊙ per 0.1 pc. Given these filament masses, there is no requireme nt for substantial large scale flows along or onto the filament s in order to gather suffi cient material for star formation. We find that the probabili ty of finding a submillimetre core is a strongly increasing function of column density, as measured by C 18 O integrated intensity, P(core)∝ I 3.0 . This power law relation holds down to low column density, suggesting that there is no Av threshold for star formation in Perseus, unless all the low- Av submm cores can be demonstrated to be older protostars which have begun to lose their natal molecular cloud.