Core fragmentation and Toomre stability analysis of W3(H2O): A case
  study of the IRAM NOEMA large program CORE
  The fragmentation mode of high-mass molecular clumps and the properties of
the central rotating structures surrounding the most luminous objects have yet
to be comprehensively characterised. Using the IRAM NOrthern Extended
Millimeter Array (NOEMA) and the IRAM 30-m telescope, the CORE survey has
obtained high-resolution observations of 20 well-known highly luminous
star-forming regions in the 1.37 mm wavelength regime in both line and dust
continuum emission. We present the spectral line setup of the CORE survey and a
case study for W3(H2O). At ~0.35" (700 AU at 2 kpc) resolution, the W3(H2O)
clump fragments into two cores (West and East), separated by ~2300 AU. Velocity
shifts of a few km/s are observed in the dense-gas tracer, CH3CN, across both
cores, consistent with rotation and perpendicular to the directions of two
bipolar outflows, one emanating from each core. The kinematics of the rotating
structure about W3(H2O) W shows signs of differential rotation of material,
possibly in a disk-like object. The observed rotational signature around
W3(H2O) E may be due to a disk-like object, an unresolved binary (or multiple)
system, or a combination of both. We fit the emission of CH3CN (12-11) K = 4-6
and derive a gas temperature map with a median temperature of ~165 K across
W3(H2O). We create a Toomre Q map to study the stability of the rotating
structures against gravitational instability. The rotating structures appear to
be Toomre unstable close to their outer boundaries, with a possibility of
further fragmentation in the differentially-rotating core W3(H2O) W. Rapid
cooling in the Toomre-unstable regions supports the fragmentation scenario.
Combining millimeter dust continuum and spectral line data toward the famous
high-mass star-forming region W3(H2O), we identify core fragmentation on large
scales, and indications for possible disk fragmentation on smaller spatial
scales.
