Ground-based observations of galaxies are plagued by many variables that reduce the performance of the instruments, but thanks to technological advances we are now getting sharper and sharper images.
One of these, taken by the Gran Telescopio CANARIAS (GTC), is not only 10 times greater detail than any previous ground-based observation, but also shows the ability to explore the very faint stellar halo of a faraway galaxy.
The most widely accept model of galaxy evolution predicts the presence of stars inhabiting the halo, the "outskirts" of large galaxies. This stellar halo population tends to be very faint as there are a small number of stars compared to the inner galaxy over a significantly larger volume.
In the Milky Way, for example, only one percent of stars resides in the halo but the volume of this region is several times the disk of the Milky Way. Halo stars can form in globular clusters already further out or can end up there after a merger with a smaller galaxy.
In a paper, published in the Astrophysical Journal, the team used the GTC to observe the stellar halo of UGC0180, a spiral galaxy 500 million light-years away. The astronomers observed the galaxy for 8.1 hours of exposure and discovered a population of 4 billion stars, which is expected to be a few percent of the total number of stars in UGC0180.
“After showing that the technique works, the object of future research is to extend the study to other types of galaxies, to see whether this way of understanding their formation, predicted by the standard model, is correct or not,” said Ignacio Trujillo, the first author of the study, in a statement.
Most large surveys of galaxies can’t reach the depth and precision of GTC, so the information we can gather from those objects is somewhat truncated. The team is starting a pilot project in which they will be investigating the stellar halos of several hundred galaxies.
