The first objective was to improve the multi-scale analysis of star-forming regions in order to bring a better understanding of the link between the filaments/cores and the turbulent environment. This objective has been fulfilled from several angles. The multi-scale segmentation method, based on the work initiated during my PhD, as been reviewed and substantially improved. This work as been published in Open Access in the Astronomy & Astrophysics journal (Robitaille et al. 2019) and made the cover of the August issue.
In this work, the now called Multi-scale non-Gaussian Segmentation (MnGSeg; open source code and software at :
https://github.com/jfrob27/pywavan(s’ouvre dans une nouvelle fenêtre)) technique was applied on the Herschel space observatory observations of the thermal dust emission at 250 m of the Polaris molecular complex and its derived gas density map. This particular region has been chosen by other recent studies, for its close location in our Galaxy (~150 pc) and as an early stage star-forming region, most probably dominated by turbulent processes. The major progress and result in this project, in addition to the improvement of the segmentation method itself, is that the study of the Polaris region allowed me to reveal new theoretical implications on the characterisation of the non-Gaussian processes in the interstellar medium (ISM).
The MnSeg technique allowed us to extract dense gaz structures in the ISM with specific statistical properties which corresponds well to the description of intermittent processes occurring in turbulence decay. I showed, with a wavelet formalism, that the non-Gaussian extraction perform with MnGSeg is in agreement with the anomalous scaling previously measured with more limited techniques like the structure function (Hily-Blant & Falgarone 2009; Federrath et al. 2010). In a submitted paper, we recently proved that the non-Gaussian part extracted using my multiscale analysis technique is associated with the multifractal topology of the gas. The upcoming effort of our research will be to link these local variations of density scaling with the IMF/CMF of star-forming regions.
Based on these new results, the following objectives have been explored, published or are part of an ongoing work:
- Constraining the origin of the IMF/CMF through multi-scale analysis techniques : new promising strategies are explored in order to join the concept of the multifractality of the ISM to the variation of core mass reservoirs in star forming regions
- Do massive star-formation regions have a distinct statistical signature? : The method has been applied on the nearby molecular complex Polaris Flare, which is the main subject of the publication by Robitaille et al. 2019. It is also currently applied on the massive star-formation region NGC2264, as well as on Cygnus X. Massive star-formation regions indeed show a different behaviour in terms of power distribution as a function of the spatial scales.
- Quantifying the influence of magnetic fields through the formation process of filaments and cold cores : The multi-scale aspect of the magnetic field fluctuations in the ISM is rarely investigated mainly because of the difficulty imposed by the vectorial values of polarisation maps. My previous works on the subject explored the multi-scale analysis of the amplitude of the gradient of the polarisation vector. During my Marie Curie project, I explored the linear property of wavelet transforms, where the continuous wavelet transform of a vector function is a vector whose components are the continuous wavelet transform of the different components.
