QUIJOTE Scientific Results. II. Polarisation Measurements of the
  Microwave Emission in the Galactic molecular complexes W43 and W47 and
  supernova remnant W44
  We present Q-U-I JOint TEnerife (QUIJOTE) intensity and polarisation maps at
10-20 GHz covering a region along the Galactic plane 24<l<45 deg, |b|<8 deg.
These maps result from 210 h of data, have a sensitivity in polarisation of ~40
muK/beam and an angular resolution of ~1 deg. Our intensity data are crucial to
confirm the presence of anomalous microwave emission (AME) towards the two
molecular complexes W43 (22 sigma) and W47 (8 sigma). We also detect at high
significance (6 sigma) AME associated with W44, the first clear detection of
this emission towards a SNR. The new QUIJOTE polarisation data, in combination
with WMAP, are essential to: i) Determine the spectral index of the synchrotron
emission in W44, beta_sync =-0.62 +/-0.03, in good agreement with the value
inferred from the intensity spectrum once a free-free component is included in
the fit. ii) Trace the change in the polarisation angle associated with Faraday
rotation in the direction of W44 with rotation measure -404 +/- 49 rad/m2. And
iii) set upper limits on the polarisation of W43 of Pi_AME <0.39 per cent (95
per cent C.L.) from QUIJOTE 17~GHz, and <0.22 per cent from WMAP 41 GHz data,
which are the most stringent constraints ever obtained on the polarisation
fraction of the AME. For typical physical conditions (grain temperature and
magnetic field strengths), and in the case of perfect alignment between the
grains and the magnetic field, the models of electric or magnetic dipole
emissions predict higher polarisation fractions.
