Is the Andromeda II galaxy the result of a merger?

How scientists from Poland used High-Throughput Compute to find an explanation for the origins of a galaxy that fits astronomical observations

Galaxies are massive systems of millions of stars and their planets, stellar dust and dark matter bound together by gravity. Scientists have a good understanding of how galaxies evolve and there are several accepted theories to explain how they are formed, based on information collected by telescopes.

But sometimes astronomical observations can be puzzling and the origins of Andromeda II, a dwarf spheroidal galaxy orbiting the massive Andromeda galaxy, remained a mystery.

An international team led by Ewa Łokas from the Nicolaus Copernicus Astronomical Centre in Poland looked into the problem to find a way to explain the origins of Andromeda II.

The most common explanation for the origin of dwarf spheroidal galaxies suggests that they evolve from the accretion of earlier progenitors by a larger galaxy. This model does not fit the observations for Andromeda II, especially its strong rotation signal.

Ewa and her colleagues simulated how a merger between two galaxies would take place considering parameters such as the relative velocity of the merging dwarfs, their masses, the structure of their disks and dark matter haloes.

The team used High-Throughput Compute to run about 20 simulations, each taking on average 400 CPU hours (the equivalent of about 16 days) to complete. The HTC resources provided by PL-Grid, who represents Poland in EGI, were “essential to complete the project in a reasonable time,” she says.

They found that the simulations that best reproduced the observed data for Andromeda II are the ones that considered a merger between two disk-shaped galaxies. “The conclusion is that Andromeda II could indeed have formed via merger,” says Ewa.

This illustration shows the three stages of the evolution of the Andromeda II galaxy: the two disky dwarf galaxies (only their stellar components) before the merger, after the first fly-by and at the end (final merged product)

References

E.L. Lokas et al. (2014) Andromeda II as a merger remnant. MNRAS 445 (1): L6-L10. doi: 10.1093/mnrasl/slu128 (abstract)