Presentasjon av masteroppgave: Eirik Bratli
Tracing the Interstellar Medium using extinction and polarisation
Cosmologists are now searching for the elusive B-mode Cosmic Microwave Background (CMB) polarisation signature, which theory states should come from primordial gravitational waves during inflation. The CMB entanglement with the galactic foreground emission increases the complexity of finding primordial B-modes. The removal of polarised foreground emission is one of the critical factors to achieve B-mode detection from gravitational waves. The physical nature of the galactic dust emission is essential to understand for the component separation of different signals to be accurate. Thermal dust emission is relevant to other fields in astronomy by extracting information about the grain composition, alignment with the galactic magnetic field, shape of the dust grains and the strength of the interstellar radiation field. Both extinction and polarisation of starlight combined with polarised thermal dust emission provide vital insight into the properties of galactic emission.
In this thesis, we are investigating the 3D dust distribution in the Milky Way using extinction estimates from Gaia Data Release 2 and Green et al. (2019). We calculate ten cumulative differential extinction maps from 0 to 3000 pc. We combine visual starlight polarisation (pv, qv, uv) from RoboPol with submillimeter polarisation intensity (Ps,Qs,Us) from the 353 GHz band of Planck looking at correlation between submillimeter and visual polarisation. Further, we calculate the difference in polarisation angle, ∆ψs/v, and the ratio, RP/p, between submillimeter and visual polarisation. Then we use this knowledge to estimate the spectral index for thermal dust emission, βd.
The extinction maps show structural differences over distance at all sightlines. We show there is not a linear correlation between extinction and dust and CO line emission. We calculate RP/p = 4.47 ± 0.82 MJy/sr, and the joint Pearson correlation coefficient between Qs, Us and qv, uv: R = −0.963 giving a best fit slope of QsUs versus qvuv is −4.535 ± 0.444 MJy/sr. We found the spectral index to be 1.56 ± 0.01.
Medveileder: Professor Ingunn Kathrine Wehus, Institutt for teoretisk astrofysikk, UiO
Intern sensor: Professor David Fonseca Mota, Institutt for teoretisk astrofysikk, UiO
Ekstern sensor: Postdoktor Mathieu Remazeilles, Universitetet i Manchester