Institute of Astrophysics and Space Sciences | 2017 Feb 15
[img3="Mosaic with the infrared images of the six massive elliptical galaxies at halfway the life time of the Universe found in the Hubble Ultra Deep Field. The images reveal the stellar envelopes, as well as potential satellite galaxies.The most detailed study of the outskirts of massive elliptical galaxies at half the age of the Universe was carried out by an international team ... and contributes to the understanding of how the largest galaxies of the Universe evolved over time.
Credits: Ignacio Trujillo, HUDF 2012"]http://www.iastro.pt/img/news/2017Fev15_2.jpg[/img3][hr][/hr]
Galaxies have dramatically grown in size since the early Universe, and elliptical galaxies, in particular, are the largest galaxies in both size and mass. What is the main driver behind the late growth of their outer parts was the question that motivated this study.
With disc galaxies, like our Milky Way, it is fairly easy to identify their distinct parts: the central bulge, the disc with its spiral arms, and a halo of stars enveloping the whole. Astronomers can tell, for instance, that the stellar halo is formed mostly by stars from satellite galaxies that merged into them.
For elliptical galaxies, however, this is much harder because these galaxies look much like a smooth, featureless cloud of stars. Fernando Buitrago (IA and FCUL) says: “With elliptical galaxies, there is direct evidence of merging of satellite galaxies going on, but it is hard to ascertain that the processes that have been happening for these galaxies to grow their outer envelopes are the same that we see occurring in disc galaxies like our own.” ...
The Cosmic Assembly of Stellar Haloes in Massive Early-Type Galaxies - Fernando Buitrago et al
- Monthly Notices of the RAS 466(4):4888 (May 2017) DOI: 10.1093/mnras/stw3382
arXiv.org > astro-ph > arXiv:1602.01846 > 04 Feb 2016 (v1), 13 Jan 2017 (v3)