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Ultimate modelling of Radio foregrounds: a key ingredient for cosmology

Periodic Reporting for period 2 - RADIOFOREGROUNDS (Ultimate modelling of Radio foregrounds: a key ingredient for cosmology)

Período documentado: 2017-01-01 hasta 2018-12-31

The aim of this project is to combine two unique datasets, the nine Planck all-sky (30-857 GHz) maps and the four QUIJOTE Northern sky (10-20 GHz) maps, to provide the best possible characterization of the physical properties of polarized emissions in the microwave domain, together with an unprecedentedly thorough description of the intensity signal. This legacy information will be essential for future sub-orbital or satellite experiments.

In particular, the combination of Planck and QUIJOTE allowed us to achieve the following objetives:

to provide state-of-the-art legacy maps of the synchrotron and AME emissions in the Northern sky;
to characterize the synchrotron spectral index with high accuracy, fitting for the curvature of the synchrotron spectrum to constrain cosmic-ray electron physics;
to study the large-scale properties of the Galactic magnetic field using the radio information;
to model and characterize the level of a possible contribution of polarized anomalous microwave emission (AME);
to characterize the population of radio sources measured by Planck by adding unique information in the frequency domain of 10-20GHz;
to provide “added-value” data products for the scientific community;
to provide specific (open source) software tools for data processing, data visualization and public information.
The QUIJOTE (Q-U-I JOint TEnerife) experiment is a polarimeter with the aim of characterising the polarisation of the Cosmic Microwave Background and other galactic or extragalactic physical processes that emit in microwaves in the frequency range 10-42GHz, and at large angular scales. The project consists of two telescopes and three instruments surveying a large sky area from the Teide Observatory to provide high sensitivity maps of the Stokes parameters I, Q and U. The first QUIJOTE instrument, known as Multi-Frequency Instrument (MFI), has been surveying the northern sky in four individual frequencies between 10 and 20 GHz since November 2012. At the end of RADIOFOREGROUNDS, we have accumulated more than 10,000h of observations with the MFI in the so-called wide survey mode, providing data with an average sensitivity of 50 microK/beam in Stokes Q and U in a region of 20,000 square-degrees.

The MFI wide survey maps are internally available within the project, as well as numerical simulations that are being used to test our numerical methods to separate astrophysical components. The maps have been presented in conferences, and the associated scientific papers are being finalised. Once these papers are accepted for publication, the maps will be publicly available for the community.

Using these maps, we have determined the average spectral index of the polarised synchrotron emission in the northern sky (-3.06±0.04) and the synchrotron-dust correlation (~0.20±0.06). Our maps show a significant variability on the sky of these average properties, thus suggesting a complexity higher than expected in the synchrotron foreground. This conclusion has been also verified using two dedicated component separation algorithms: Neural Networks and an adaptive parametric method. The component maps in intensity and polarization produced with these algorithms provide an improved description of the radio foregrounds with respect to the previous status at the beginning of the project.

The new QUIJOTE data, in combination with WMAP and PLANCK satellite data, are essential to provide 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.

Thanks to the new QUIJOTE data, a systematic study of the AME in 63 regions was possible. The analysis provided a clean separation of the AME, free-free and synchrotron components. The new results showed for the first time a clear correlation of the AME intensity signal (normalised to the thermal dust optical depth) with the radiation field in the ISM. These new maps were also used to carry out a detailed modelling of the emission in some regions of astrophysical interest, as the North Polar Spur or the Fan region.

We have also developed a code to model the synchrotron and thermal dust emission processes in intensity and polarisation. Various models of the relativistic electron and dust grains 3D density distributions have been implemented. These models are based on parametric representations of the halo and spiral arms of the Galaxy, as well as of possible singular structures (e.g. bubbles).

Concerning the modelling of the radio source emission, we have obtained a refined model of the radio emission in star forming galaxies, and we have obtained predictions for the expected QUIJOTE source catalogue. From the observational point of view, we have implemented, tested and released the tools for single and multi-frequency detection of sources in radio maps, and we have concluded a follow-up programme with the VLA of a complete sample of 51 radio sources located inside the QUIJOTE cosmological fields.

We have also carried out studies to forecast constraints on cosmological parameters for future B-mode CMB experiments, showing the importance of including low frequency channels as a monitor for the synchrotron emission. We have made publicly available different tools, which allow one to forecast the level of galactic foreground residuals for a given experimental configuration, to obtain constraints on the tensor-to-scalar ratio and to estimate the contribution of extragalactic radio sources in future CMB experiments. This will allow the community to explore further possibilities of interest.

Finally, we concluded the architecture of the RADIOFOREGROUNDS database and created the data centre platform (DCP), which includes specific software for visualization of the maps produced by QUIJOTE and all the models of the different astrophysical components.
Using the combination of QUIJOTE data with Planck and WMAP, we have provided an improved description of the radio foregrounds in intensity and polarization. The synchrotron component is found to be significantly more complex than originally expected, showing important spatial variations of its basic properties (spectral index and correlation with the dust component). We have set the most stringent constraints ever obtained on the polarisation fraction of the AME. These limits provide important information to disentangle the physical mechanisms producing this emission. In intensity, we also provided a clean separation of the AME component from the other two (specially the free-free component). These results allowed us to find, for the first time, a clear correlation of the AME intensity signal (normalised to the thermal dust optical depth) with the radiation field in the ISM. This observed relation might provide hints on the nature of the AME mechanism.

The QUIJOTE MFI wide survey maps will be publicly available once the corresponding papers are accepted for publication. These maps provide a unique tool to characterize the radio foregrounds in the northern sky. The public tools that have been produced by the project could become a very valuable instrument for the community.