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Polarimetry of Anomalous Microwave Emission: Implication for B-mode Polarization Detection and Galactic Science

Periodic Reporting for period 1 - PolAME (Polarimetry of Anomalous Microwave Emission: Implication for B-mode Polarization Detection and Galactic Science)

Reporting period: 2016-01-01 to 2017-12-31

The main goal of the PolAME project is to characterise the level of polarisation (i.e. the geometrical orientation of the oscillations of the radiation) of the Anomalous Microwave Emission (AME) observed at radio frequencies in the frequency range [10-100] Gigahertz (GHz). The AME is an emission that has been discovered about 20 years ago which is very likely produced by very small dust grain particles pervading the interstellar medium. The polarisation properties of the AME have to be characterised and understood completely for one willing to remove Galactic foregrounds in order to analyse the polarisation of the CMB for cosmology. This project is therefore important for the Galactic community as well as for the Cosmology community. The PolAME project uses the QUIJOTE-CMB experiment and its Multi-Frequency Instrument (MFI) for measuring the degree of polarisation of the AME in the domain range [10- 30] GHz toward a series of Molecular cloud regions. Molecular clouds are regions denser than the diffuse interstellar medium and they are regions where most of the star formation occurs in our Galaxy. They cover a large fraction of the full sky therefore it is important to understand the properties of the AME in these regions and not only in the diffuse interstellar medium of our Galaxy. The main objective of PolAME is to combine the QUIJOTE data with the data from the WMAP and Planck satellites that are publicly available, as well as with other publicly available data to isolate the AME components and study their properties in intensity and in polarisation. During the project we produced intensity and polarisation maps of the sample of 8 molecular clouds initially identified for the project. We added two more regions of interest to the sample. The analysis of this two more regions has been a test bed for the analysis method and allowed us to test the modelling of the various Galactic components that has to be done to isolate the AME components. Once this was done we put constraints on the level of polarisation of the AME component in these two regions. The initial sample of molecular clouds take advantage of this work and is presently under study. The new constraints put on the level of polarisation of AME in the molecular clouds studied until now enlarge the statistics available in the literature from similar studies on other regions. Our results also show the importance of the QUIJOTE-MFI which, currently, is the only experiment probing the sky in intensity and polarisation in the frequency range [10-20] GHz, for getting accurate measurements of the AME components in this frequency range.
With the QUIJOTE team we acquired new data with the MFI observing in the frequency range [10–20] GHz toward the sample of molecular clouds mentioned above. The regions observed with dedicated observations are the Taurus Molecular Cloud (TMC) complex, the LDN1527, LDN1608 and LDN1358 dark nebulae regions but additional observations of interest for the project have been observed within the MFI wide-survey which maps the fraction of the full sky observable from Tenerife, Spain. Our final sample covers a total of 10 molecular cloud regions. During the project the TMC and LDN1527 maps were produced and their quality assessed for science exploitation then the procedure used to detect AME and characterise its polarisation level has been tested and validated. This has been done in collaboration with the IAC team, including Prof. Rafael Rebolo, Dr. José Alberto Rubiño Martín and Dr. Ricardo Genova-Santos, and in collaboration with Prof. Clive Dickinson and his team over 4 secondments at the University of Manchester. The measurements of the AME in the frequency range [10–20] GHz clearly demonstrate the relevance and importance of the QUIJOTE-MFI data for sampling the electromagnetic spectrum at radio-frequencies lower than 20 GHz. Without the QUIJOTE-MFI information the previous studies making estimates of the AME at these frequencies from the analysis of data in the frequency range [28-100] GHz clearly underestimated the intensity of the AME at frequencies lower than 28 GHz. With the QUIJOTE-MFI data the location of the AME peaks, and the width of the AME features can be characterised more accurately. The other main result of our study is that the level of polarisation of the AME should be lower than about 5.3% in the LDN1527 region and lower than 4.2% in the TMC. This work has been submitted to the MNRAS journal for publication. Results about the TMC and L1527 have been presented at two conferences, at two workshops and during one seminar. The other molecular cloud regions are currently under analysis and a publication is in preparation. Our preliminary results show clear detection of AME in almost all of the molecular clouds from the sample. During the project some articles directly related to the PolAME project have been published. A proceeding showing preliminary results has been published (Poidevin et al. 2017). A full review about our current knowledge of the AME has been published (Dickinson et al. 2018). Additionally, the second paper of the QUIJOTE consortium presenting MFI data and analysis toward three galactic regions including two molecular cloud structures has been published (Genova-Santos et al. 2017). Additional publications from ongoing other collaborations also acknowledge the support of the MSCA.
One step beyond the state of the art has been to observe the sky, and specifically the molecular clouds sample identified for the PolAME project, in the frequency range [10-20] GHz with the QUIJOTE-MFI. This instrument provides new and unique astrophysical information, in intensity and in polarisation, that was not available before. Another step beyond the state-of-the-art comes from the study of the TMC itself. Previous studies in the literature are generally done on what is called point-like sources which means are focused on a small area on the sky of about a few square degrees. Here the study on the TMC is applied over an area of about sixteen square degrees on the sky. Such a large area makes the analysis challenging but despite the difficulty it has been possible to show a clear detection of AME over this area. The limit on the fraction of polarisation of this component is found to be lower than 4.2 % in the TMC and the total intensity of the AME in this region is found to be higher than expected from previous studies. The article presenting the study of the TMC and LDN1527 was revised internally within the QUIJOTE consortium and has been submitted to the MNRAS for publication. Additional analysis on the sample of 8 other molecular clouds also show detection of AME in these regions. This study therefore increases the statistics of detection of AME over Galactic sources and confirms the low level of polarisation expected from this component. All the results obtained so far are important for further cosmology studies since they show that the level of polarisation from the Galactic foregrounds in the frequencies range [10 - 40] GHz are expected to be quite low, if at all polarised, making this window a strategic one for further cosmology studies.
Polarimetry of AME in the Taurus Molecular Cloud