Astronomy Tea Talk

The Serkowski relation is the cornerstone of studies of starlight polarizations as a function of wavelength. Although empirical, its extensive use since its inception by Serkowski+1975 to describe polarization induced by interstellar dust has elevated the relation to the status of an indisputable "law". I will discuss the effects of the three - dimensional structure of the interstellar medium (ISM) on the wavelength dependence of interstellar polarization. I will present, for the first time, compelling observational evidence that the three - dimensional structure of the magnetized ISM often results to the violation of the Serkowski relation. I will show that three - dimensional effects impact interstellar cloud parameters derived from Serkowski fits as well. Finally, I will discuss how multiwavelength stellar polarization measurements offer an independent probe of the LOS variations of the magnetic field orientation, and thus constitute a potentially valuable new tool for the 3D cartography of the interstellar medium.

Foreground contamination is the biggest challenge for 21 cm cosmology. Traditional linear foreground filters can remove foregrounds only for ideal instruments, but calibration errors in real experiments spoil the effectiveness of filters and leave bright foreground residuals in the estimated signal. In this talk, I will present a new foreground subtraction algorithm, called HyFoReS, that can mitigate this challenge. HyFoReS separates signal from foregrounds by cross correlating the foreground-contaminated signal estimate made by traditional methods with an accurate measurement of foregrounds. The algorithm has shown great promise in both simulations and real data and has broad applicability to line intensity mapping experiments in general.