QUIJOTE Scientific results. III. Microwave spectrum of intensity and
  polarization in the Taurus molecular cloud Complex and L1527
  We present new intensity and polarization observations of the Taurus
molecular cloud (TMC) region in the frequency range 10-20 GHz with the
Multi-Frequency Instrument (MFI) mounted on the first telescope of the QUIJOTE
experiment. From the combination of the QUIJOTE data with the WMAP 9-yr data
release, the Planck second data release, the DIRBE maps and ancillary data, we
detect an anomalous microwave emission (AME) component with flux density
$S_{\rm AME, peak} = 43.0 \pm 7.9\,$Jy in the Taurus Molecular Cloud (TMC) and
$S_{\rm AME, peak} = 10.7 \pm 2.7\,$Jy in the dark cloud nebula L1527, which is
part of the TMC. In the TMC the diffuse AME emission peaks around a frequency
of 19 GHz, compared with an emission peak about a frequency of 25 GHz in L1527.
In the TMC, the best constraint on the level of AME polarisation is obtained at
the Planck channel of 28.4 GHz, with an upper limit $\pi_{\rm AME}<$4.2$\,\%$
(95$\,\%$ C. L.), which reduces to $\pi_{\rm AME} <$3.8$\,\%$ (95$\,\%$ C.L.)
if the intensity of all the free-free, synchrotron and thermal dust components
are negligible at this frequency. The same analysis in L1527 leads to $\pi_{\rm
AME}<$5.3$\%$ (95$\,\%$C.L.), or $\pi_{\rm AME}<$4.5$\,\%$ (95$\%$C.L.) under
the same assumption. We find that in the TMC and L1527 on average about $80\%$
of the HII gas should be mixed with thermal dust. Our analysis shows how the
QUIJOTE-MFI 10-20 GHz data provides key information to properly separate the
synchrotron, free-free and AME components.
