Periodic Reporting for period 3 - PASIPHAE (Overcoming the Dominant Foreground of Inflationary B-modes: Tomography of Galactic Magnetic Dust via Measurements of Starlight Polarization)
Período documentado: 2021-06-01 hasta 2022-11-30
PASIPHAE will use unique, innovative polarimeters that are designed specifically for this purpose, to map, with unprecedented accuracy, the polarization of millions of stars at areas of the sky away from the Galactic plane, in both the Northern and the Southern hemispheres. Combined with stellar distances provided by ESA’s Gaia mission, this data will allow us, for the very first time, to construct a tomographic map of the Galactic magnetic field, and the dust that resides in our own Galaxy. This magnetized dust produces polarized microwaves that obscure our view of the polarization of the cosmic microwave background, the radiation that has been left behind by our Universe's dense and hot past. The polarization of the microwave background is believed to contain evidence of a period of inflationary expansion that took place only moments after the Big Bang. By removing the "veil" of Galactic dust, our results will allow accurate estimates of the polarization of the radiation emitted during the Big Bang in order to probe the first instants of the Universe, as well as the, yet-unknown, physics of Gravity at unprecedentedly high densities and temperatures.
Our demonstration of the Galactic tomography technique (Panopoulou, Tassis, Skalidis et al. 2019, https://arxiv.org/abs/1809.09804) showed how the combination of measurements of the optical polarization of stars with measurements of stellar distances from ESA's Gaia mission can allow us to disentangle the polarization signal imparted by different clouds along the line of sight. In the same paper, we also demonstrated how the magnetic fields in clouds that reside one behind another can be severely misaligned - a situation which is particularly problematic for measurements of the polarization of the cosmic microwave background. Our work showed how such cases can be identified and, if necessary, removed from the processing of microwave data. Subsequent datataking by PASIPHAE will allow us to identify most such problematic cases, allowing for a much improved "dust cleaning" of the microwave polarization sky.
Our demonstration that an average direction of the magnetic field can be established even for clouds with very little dust emission (Skalidis et al. 2018 https://arxiv.org/abs/1802.04305) showed that PASIPHAE can help "clean" the dust contamination even in regions where the amount of dust does not allow a confident measurement of its effects in any other way. At the opposite end of starlight polarization strengths, Panopoulou, Hensley, Skalidis et al. (2019, https://arxiv.org/abs/1903.09684) showed that a region where the Planck mission had found puzzling strong polarized dust emission is also characterized by unusually high starlight polarization, further cementing the tight correlation between polarization of stars (measured by PASIPHAE) and polarized emission from dust (obscuring polarization measurements of cosmic microwaves). This connection is at the heart of PASIPHAE's power to clear the way towards detecting the signature of inflation.
The effect of the local bubble on the polarized microwave sky was shown to be significant, but possible to account for with a combination of polarization and Gaia data (Skalidis & Pelgrims 2019, Pelgrims et al. 2020).
Finally, our (yet unpublished) data taking to establish new optopolarimetric standards has shown that many of the standards currently in use are not stable enough to ensure the high level of accuracy needed for experiments such as PASIPHAE. However, the new standard stars we have been observing, verified for brightness and polarization stability over several years and with many measurements, will cover this need, not only for PASIPHAE, but also for any future polarimetric experiments.