Overcoming the Dominant Foreground of Inflationary B-modes: Tomography of Galactic Magnetic Dust via Measurements of Starlight Polarization

Project Information

PASIPHAE

Grant agreement ID: 771282

DOI

10.3030/771282

Project closed

EC signature date 11 January 2018

Start date 1 June 2018

End date 31 May 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 887 500,00

EU contribution

€ 1 887 500,00

Coordinated by

IDRYMA TECHNOLOGIAS KAI EREVNAS
Greece

Periodic Reporting for period 4 - PASIPHAE (Overcoming the Dominant Foreground of Inflationary B-modes: Tomography of Galactic Magnetic Dust via Measurements of Starlight Polarization)

Reporting period: 2022-12-01 to 2024-05-31

Summary of the context and overall objectives of the project

The PASIPHAE ERC project supported the first phase of the PASIPHAE (Polar-Areas Stellar-Imaging in Polarization High-Accuracy Experiment) experiment - a unique Astrophysics experiment taking place at Skinakas Observatory in Crete, Greece, and at the South African Astronomical Observatory, located near the city of Sutherland in South Africa. The experiment is a collaborative effort of the Astrophysics Group in Crete (the joint Astrophysics group at the Foundation of Research and Technology-Hellas and the University of Crete) with the Inter-University Center for Astronomy and Astrophysics (IUCAA) in Pune, India, the California Institute of Technology in the USΑ, the South African Astronomical Observatory, and the Oslo University in Norway.

The PASIPHAE experiment will use unique, innovative polarimeters (the wide-area linear optical polarimeters, or WALOPs) that are designed specifically for this purpose, to map, with unprecedented accuracy, a property of starlight called polarization - the same property that polarized sunglasses take advantage of to reduce the glare from diffuse light from the sky. In starlight, polarization reveals the magnetic field permeating dust clouds that the light passed through on its way to reach us. PASIPHAE will measure 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 radiation that has been left behind by our Universe's dense and hot past, known as the cosmic microwave background, . 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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The PASIPHAE ERC project fully supported the first, most challenging, technique-development phase and first data-taking phase of this pioneering experiment.

During the PASIPHAE ERC project, we demonstrated for the first time in real data from ESA's Planck microwave mission the importance of the role that the complexity of the Galactic "veil" plays in contaminating our microwave view of the early Universe. We developed new, robust statistical techniques to go from polarimetric observations of starlight to tomographic measurements of the local magnetic fields (direction and strength) in intervening interstellar clouds.

In anticipation of the new polarimeters, we developed multiple new calibration techniques that will allow us to reach unprecedented levels of accuracy in polarimetric observations. These calibration techniques will be invaluable not only for PASIPHAE, but for all experiments using optical polarimetry, in astrophysics and beyond.

We took first data, mapping a region of the sky extending over more than 15 times the area of the full moon, and created the first 3-dimensional map of the Galactic magnetic field on such an extended scale. We made the software that takes us from polarimetric measurements to 3D maps, which we developed, freely available to the entire scientific community (see https://pasiphae.science/software).

We developed new, high-accuracy techniques for measuring the magnetic field of our Milky Way Galaxy once polarimetric data have been acquired. These techniques have been widely recognized by the astrophysics community, earned awards for the young researchers that spearheaded their development, and have ushered in a new era of precision Galactic magnetometry.

Almost 100 publications in high-impact refereed journals were produced, with results from the PASIPAHE ERC project.

Finally, we developed a multi-faceted outreach program to involve the general public in this exciting project and in modern cosmology. This included the development of visualization software that allows the user to fly through our mapped stars, the intervening clouds, and their magnetic fields, both on a computer screen and in a virtual-reality environment (see https://pasiphae.science/visualization and https://www.youtube.com/watch?v=dB_6J1zhmPI ). And it also included a diverse set of outreach activities, ranging from talks for the general public, to virtual-reality fly-through demos, to open nights at the Skinakas Observatory, to articles in the popular press, to free astrophysics and cosmology classes for schoolchildren and all interested citizens, to youtube and instagram content both on our own Institute of Astrophysics channel as well as on popular science channels, to events combining science and art (a musical retelling of our modern story of cosmogony in the style of ancient myths and epic troubadours) in collaboration with the local artist community of the Greek mountains.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our project has pushed forward the state of the art in using polarimetry to map the properties of dust and magnetic fields in the interstellar medium.

We have demonstrated that 3D magnetic tomography can work and does work, provided sensitive enough measurements of stellar polarizations and stellar distances are available.

We have made high-accuracy polarimetry possible thanks to the development of multiple new calibration techniques, of high value for the entire optopolarimetric community.

We have showed that, even in clouds where very little dust is present, this dust does have a polarization signature, and that this signature is measurable with an experiment such as PASIPAHE.

Thanks to original theoretical work on the properties of interstellar turbulence, and its relation to magnetic field strength and optopolarimetric signals, we have decreased the error in estimates of Galactic magnetic fields inside interstellar neutral hydrogen clouds by an order of magnitude.

And we have conducted the largest-area to-date deep, high-accuracy stellar optopolarimetric survey outside the Galactic plane.

Our future, wider-field data-taking with the PASIPHAE experiment, extending beyond the end of this project, will extend these measurements over large sections of the sky. We will measure, with unprecedented accuracy, the polarization of millions of stars. We will provide a wealth of polarimetric data with which to study the properties of dust and magnetic fields in interstellar clouds. And we will add an invaluable tool in our collective efforts, as astronomical community, to measure the polarization of the cosmic microwave background, including a potential signature from the beginning of the Universe. The breakthroughs of th ePASIPHAE ERC project have made all of these possible.

Magnetic field directions in the region of magnetic tomography demonstration (Panopoulou et al. 2019

A first glimpse at our Galaxy's magnetic field in 3D (from Pelgrims et al. 2024)

Optical polarizations in the region of magnetic tomography demonstration (Panopoulou et al. 2019)