Thesis Topic: In search of the green light in the remote outskirts of galaxies: the survey of Planetary Nebulae in the halo of Andromeda (M31)


Thesis Supervisor: Magda Arnaboldi





The Andromeda galaxy, M31, is the closest giant spiral disk to our Milky Way, and our first step in the stairway to the Universe. Studies of its stellar populations and motions are crucial in the development
of the "near field cosmology" topic of research, as a vivid example of the halo formation from the hierarchical mass assembly. We can gain information on Andromeda past history by studying the discrete tracers, that populate its halo. In particular we can discover stars that shine in the green light of an aquamarine hue, all moving in the most remote regions of the Andromeda's halo. This is important because the halo contains the fossil records of the galaxy's past.

These stars that shine in a green light are Planetary Nebulae and the mechanism which powers their emission and colour is the same as for the Northern lights on our Earth. Each of these stars is a beacon, shining in the darkest and furthest regions of Andromeda, and they tell us about the orbits and the history of the stars that came to form the complex structures -- the Giant Stellar Stream -G1 and NE clump - NE and W shelves-- identified in its halo. Because M31 is only ~780 kpc away from us, its luminous disk is twice as extended as the full moon and its halo covers four time the area, this project was not attempted before.

Thanks to the recent technological developments with the largest/most advanced wide imager telescopes on the Mauna Kea mountain, on the Big Island of Hawaii, this exciting thesis project can now be carried out. Come and learn about the Planetary Nebulae stars, their motions and origin, to unchain the past origin of Andromeda!