# Cosmology Seminar: Tone Ruud

Tone Ruud is a PhD student at ITA

### On polarized CMB foregrounds and the galactic magnetic field: A story of insufficient length about insufficient knowledge

In this student-friendly talk, I aim to give an overview of the problem of foregrounds for CMB polarization detection, what we know and what we don't, and its relation to the projects I've been working on recently. I will begin with a quick introduction of the CMB and its foregrounds, focusing on the problem of their separation. Moving quickly through the temperature case, I will mostly focus on polarization, including a cautionary tale of the consequences of underestimating the importance of foregrounds (we all love having a go at BICEP). In the main part of the talk, I will discuss the physics of the two important foreground contributors for polarized CMB; diffuse synchrotron and thermal dust emission. These are both intimately connected to the magnetic field of the Milky Way, which thus merits a section of its own.

The actual foregrounds are the result of a complex interplay between several different factors, few of which are sufficiently well understood. Using what information we do have, we can still build models of the expected foreground emission, and I will report on a project we have been working on to that effect. Finally, to bring the story back to where we started, I will devote the final section to the Spider experiment, a balloon-borne polarimeter aiming to constrain the tensor-to-scalar ratio $r$ to ~ 0.03 \pm xx, and thus, as its competitors, completely dependent on a well-constrained foreground model in order to achieve its goal. I will give a status report on our Spider mapmaking efforts, including some preliminary results.

## Organizer

Benjamin Racine and Bridget Falck
Published Dec. 5, 2016 8:03 PM - Last modified Dec. 5, 2016 10:12 PM