THE REDISCOVERY OF THE DIFFUSE GALACTIC LIGHT; MAPPING THE ISM AT MILLI-PC SCALES OVER THOUSANDS OF SQUARE DEGREES

Marc-Antoine Miville-Deschenes –  AIM Paris

Interstellar dust grains absorb starlight, they get heated and shine in the infrared-submm range. For decades, the signatures of this process in the visible-NIR for absorption and infrared-submm for the emission, seen both in intensity and polarization, have been used to reveal the structure of the interstellar medium, its magnetic field orientation and the nature of dust itself.
Another interaction between starlight and dust grains have not be exploited as much : dust scattering. In the 1930s, an excess of emission in the optical, compared to the sum of all stars, was detected. It was later noticed that not all interstellar dust clouds are dark in the optical but actually some are bright. Since then, this « Diffuse Galactic Light – DGL », also known as Galactic cirrus, has been barely analysed. It even disappeared from optical observations of the high Galactic latitude sky due to image processing aiming at detecting galaxies.

In the past few years, with raising interests on the diffuse structures of galaxy halos and galaxy interactions, new processing of optical data revealed the Galactic cirrus again. In the context of upcoming cosmological experiments like Euclid, ground based efforts were made in order to provide complementary optical observations. Such datasets, obtained at the CFHT for example, cover several thousands of square degrees on the sky at sub-arcsec resolution, revealing the Galactic cirrus like never.

In this seminar I will present this saga and how these images might open a totally new exploratory space for our understanding of the interstellar medium gas and dust evolution.