The properties of SCUBA cores in the Perseus molecular cloud: the bias
  of clump-finding algorithms
  We present a new analysis of the properties of star-forming cores in the
Perseus molecular cloud, identified in SCUBA 850 micron data. Our goal is to
determine which core properties can be robustly identified and which depend on
the extraction technique. Four regions in the cloud are examined: NGC1333,
IC348/HH211, L1448 and L1455. We identify clumps of dust emission using two
popular automated algorithms, CLFIND and GAUSSCLUMPS, finding 85 and 122 clumps
in total respectively. Some trends are true for both populations: clumps become
increasingly elongated over time and are consistent with constant surface
brightness objects, with an average brightness ~4 to 10 times larger than the
surrounding molecular cloud; the clump mass distribution (CMD) resembles the
stellar intial mass function, with a slope alpha = -2.0+/-0.1 for CLFIND and
alpha = -3.15+/-0.08 for GAUSSCLUMPS, which straddle the Salpeter value. The
mass at which the slope shallows (similar for both algorithms at M~6 Msun)
implies a star-forming efficiency of between 10 and 20 per cent. Other trends
reported elsewhere depend on the clump-finding technique: we find protostellar
clumps are both smaller (for GAUSSCLUMPS) and larger (for CLFIND) than their
starless counterparts; the functional form, best-fitting to the CMD, is
different for the two algorithms. The GAUSSCLUMPS CMD is best-fitted with a
log-normal distribution, whereas a broken power law is best for CLFIND; the
reported lack of massive starless cores in previous studies can be seen in the
CLFIND but not the GAUSSCLUMPS data. Our approach highlights similarities and
differences between the clump populations, illustrating the caution that must
be exercised when comparing results from different studies and interpreting the
properties of continuum cores.
