QUIJOTE scientific results – V. The microwave intensity and polarization spectra of the Galactic regions W49, W51 and IC443

Abstract

We present new intensity and polarization maps obtained with the QUIJOTE experiment towards the Galactic regions W49, W51 and IC443, covering the frequency range from 10 to 20 GHz at $\sim 1\, \text{deg}$ angular resolution, with a sensitivity in the range 35–79 $\mu \text{K}\, \text{beam}^{-1}$ for total intensity and 13–23 $\mu \text{K}\, \text{beam}^{-1}$ for polarization. For each region, we combine QUIJOTE maps with ancillary data at frequencies ranging from 0.4 to 3000 GHz, reconstruct the spectral energy distribution and model it with a combination of known foregrounds. We detect anomalous microwave emission (AME) in total intensity towards W49 at 4.7σ and W51 at 4.0σ with peak frequencies $\nu _{\rm AME}=(20.0\pm 1.4)\, \text{GHz}$ and $\nu _{\rm AME}=(17.7\pm 3.6)\, \text{GHz}$, respectively; this is the first detection of AME towards W51. The contamination from ultracompact H ii regions to the residual AME flux density is estimated at 10 per cent in W49 and 5 per cent in W51, and does not rule out the AME detection. The polarized SEDs reveal a synchrotron contribution with spectral indices αs = −0.67 ± 0.10 in W49 and αs = −0.51 ± 0.07 in W51, ascribed to the diffuse Galactic emission and to the local supernova remnant, respectively. Towards IC443 in total intensity we measure a broken power-law synchrotron spectrum with cut-off frequency $\nu _{\rm 0,s}=(114\pm 73)\, \text{GHz}$, in agreement with previous studies; our analysis, however, rules out any AME contribution which had been previously claimed towards IC443. No evidence of polarized AME emission is detected in this study.

LSPE-Strip on-sky calibration strategy using bright celestial sources

“…W49 and W51 are two Galactic regions first discovered in a 22 cm survey by [42]. Using QUIJOTE-MFI information at 10-20 GHz in combination with other datasets, [43] have recently performed a detailed study of the microwave emission in intensity and polarisation of these two regions. A detailed discussion of their physical properties is presented in section 2 of that paper and references therein.…”

“…The angular extent of this source has been measured at 3.4 arcmin [44] so it may be considered a point source in both the Q-and W-bands. Being an HII region its emission is expected to be dominated by free-free emission, although [43] have discussed the possibility of the presence of anomalous microwave emission (AME). However, given the angular resolution (1 • ) of that analysis, the emission of the source gets diluted and it is difficult to tell whether the AME originates in the source or the surrounding background.…”

“…In any case, the level of AME detected in that study is low and does not cause a strong distortion of the free-free spectrum. In our analysis, then, we take as reference the flux densities reported in the PCCS2 (see table 2) at 44 and 100 GHz, and scale them to the Strip central frequencies with a free-free spectrum with spectral index 𝛼 = −0.13 to get the reference flux densities shown in table 4.1 QUIJOTE-MFI, WMAP and Planck maps show no clear indication of polarised emission in this region (see [43]), although the 100 GHz Stokes 𝑄 map shows some emission with a cloverleaf spatial structure with a maximum polarisation fraction of ∼ 1% that could be an indication of intensity to polarisation leakage. Based on this observational evidence, and on the fact that zero net polarisation is expected for free-free emission, we assume that this source has no polarisation at Strip frequencies and, together with Cas A , we use it as a control region for the intensity to polarisation leakage.…”

QUIJOTE scientific results – X. Spatial variations of Anomalous Microwave Emission along the Galactic plane

“…The physical processes responsible for AME are not clear yet. Even though limits on polarization (L ópez-Caraballo et al 2011 ;G énova-Santos et al 2015 ;Tramonte et al 2023 ) partly discard the possibility of a magnetic origin, it is still not clear whether they are linked to PAHs or not (Hensley et al 2016 ;Dickinson et al 2018 ;Ysard et al 2022 ). Theoretical models for the electric dipole emission from spinning dust depend on a large number of parameters (Ali-Ha ïmoud et al 2009 ;Silsbee, Ali-Ha ïmoud & Hirata 2011 ), so we chose instead to use a simpler, phenomenological model.…”

“…In the magnetic field scenario, these are the current upper limits on polarization for AME emission. According to recent data (L ópez-Caraballo et al 2011 ;Rubi ˜ no-Mart ín et al 2012 ;G énova-Santos et al 2015 ;Poidevin et al 2019 ;Tramonte et al 2023 ), the AME polarized emission fraction is ≤5 per cent, with the strongest constrains being ≤0.5 per cent (G énova-Santos et al 2017 ). A higher value is predicted in most magnetic models (Draine & Lazarian 1999 ;Draine & Hensley 2013 ;Hoang & Lazarian 2016 ).…”