The SEDIGISM survey: Molecular cloud morphology. I. Classification and
  star formation
  We present one of the very first extensive classifications of a large sample
of molecular clouds based on their morphology. This is achieved using a
recently published catalogue of 10663 clouds obtained from the first data
release of the SEDIGISM survey. The clouds are classified into four different
morphologies by visual inspection and using an automated algorithm -- J plots.
The visual inspection also serves as a test for the J plots algorithm, as this
is the first time it has been used on molecular gas. Generally, it has been
found that the structure of molecular clouds is highly filamentary and our
observations indeed verify that most of our molecular clouds are elongated
structures. Based on our visual classification of the 10663 SEDIGISM clouds,
15% are ring-like, 57% are elongated, 15% are concentrated and 10% are clumpy
clouds. The remaining clouds do not belong to any of these morphology classes
and are termed unclassified. We compare the SEDIGISM molecular clouds with
structures identified through other surveys, i.e. ATLASGAL elongated structures
and the bubbles from Milky Way Project (MWP). We find that many of the ATLASGAL
and MWP structures are velocity coherent. ATLASGAL elongated structures overlap
with ~ 21% of the SEDIGISM elongated structures (elongated and clumpy clouds)
and MWP bubbles overlap with ~ 25% of the SEDIGISM ring-like clouds. We also
analyse the star-formation associated with different cloud morphologies using
two different techniques. The first technique examines star formation
efficiency (SFE) and the dense gas fraction (DGF), based on SEDIGISM clouds and
ATLASGAL clumps data. The second technique uses the high-mass star formation
(HMSF) threshold for molecular clouds. The results indicate that clouds with
ring-like and clumpy morphologies show a higher degree of star formation.
