Speaker
Description
In this talk, I will present our work with the data from the Long-Term 10 program of the newly commissionned NenuFAR telescope in Nançay. This program aimed at observing radio recombination lines (RRLs) between 10 and 85 MHz in absorption in various Galactic lines of sight. I will present the results we obtained observing towards Cassiopeia A, Cygnus A, and Tau A. For each of these lines of sight, we used the beam-forming mode, and we integrated several tens of hours. The nominal spectral resolution was 95.4~Hz, and the frequency range was 10-85 MHz. We built and applied a reduction pipeline, mostly to remove RFI contamination and correct the baselines. We also fitted the Carbon RRLs (CRRLs) associated to various line-of-sight clouds. Indeed, the line variation with the electronic quantum number provides constraints on the physical properties of the clouds: the electron temperature Te, the electron density ne, as well as the temperature of the radiation field T0, the mean turbulent velocity and the typical size of the cloud. Cas A and Cyg A are the brightest sources in the sky at these frequencies, and were already observed by LOFAR, so we used them to benchmark our methodology. In these sources, we improved the signal-to-noise ratio (SNR) and spectral resolution compared to LOFAR observations. We detected 398 Calpha lines (out of 443 theoretically comprised in this frequency range) towards Cas A. Globally, our final constraints slightly differ from those inferred from LOFAR results, which we could relate to the large beam-size of NenuFAR. I will then present the first detection of CRRLs towards Taurus A. In order to identify line-of-sight clouds, we used complementary tracers: CO, HI and dust. Our analysis revealed several spatially separated velocity components in the line-of-sight, shedding light on the organisation of the multiphase ISM. Finally, I will finally present numerous perspectives opened up by our studies: detections of higher order transitions (beta, gamma, etc.), of other species (H, He, etc.) and of other Galactic environments.
