Most of the information we have about the Milky Way stellar halo comes from its inner region, which we can observe close to the solar neighbourhood. However, for the first time the chemical properties of the external regions of the halo of our galaxy were explored with high resolution spectroscopy in the optical of a sample of 28 red giant stars at large distances from the Sun. The method that was used, i.e. a spectroscopic analysis, consists in separating the light of the stars in its different frequencies in order to obtain information on the star's chemical composition. The analysis of the chemical properties of the stars can provide information on the characteristics of the environment in which they were born.
Distant Milky Way halo giants marked on a Pan-STARRS1 map. Location of our targets overlaid on a RGB rendering of the distribution of Milky Way halo stars [Credit: Giuseppina Battaglia] |
Stellar haloes are a common component of galaxies like the Milky Way. "The theory explaining the formation of structure and galaxies in the Universe predicts that stellar haloes, and in particular their outer regions, consist mainly of the stellar component of destroyed, smaller galaxies." G.Battaglia comments "Qualitatively this is in agreement with the observational findings of this study, where we found remnants of cannibalized dwarf galaxies around the Milky Way."
For this study data from about 100 hours of telescope observing time were used, obtained on facilities in both the Northern and Southern hemisphere. Specifically, the team used the Very Large Telescope "Kueyen" (UT2) of the European Southern Observatory in Paranal and the Magellan telescope Clay in Las Campanas, both in Chile, as well as the Hobby Eberly Telescope, in Texas.
The findings are published in Astronomy & Astrophysics.
Source: Instituto De Astrofisica De Canarias (IAC) [January 31, 2018]