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Curated by RSF Research Staff

Discovery of unusual spindle-like galaxies

Galaxies can be really peculiar and astronomers create especially two classifications for these strange objects: the Messier catalog or the New General Catalog. These galaxies can host ultraluminous X-rays or present funny shape like the Whirlpool Galaxy or “cigar galaxy” also named prolate rotator. A prolate spheroid is a spheroid that is "pointy" instead of "squashed,". Like a spindle, these galaxies are shaped like a cigar and rotate along their longest axis.

Until recently this type of “cigar galaxy” was very rare and their formation was a mystery. However, a study describing new findings was published in the journal Astronomy and Astrophysics by a team from the Max Planck Institute for Astronomy in Germany. The researchers used data from the Calar Alto Legacy Integral Field Area (CALIFA) survey to reach their findings. This is a project to study the light from 600 galaxies with the Calar Alto Observatory in Spain. Care was taken to make sure these galaxies were picked at random so that they were representative of the universe as a whole.

M82, a previously known cigar galaxy, seen by Hubble. NASA/ESA/The Hubble Heritage Team (STScI / AURA)

Athanasia Tsatsi and his team presented for eight early-type galaxies appearing like “cigar galaxy”. They found that prolate rotation is more common among the most massive early-type galaxies. They investigated the implications of these findings with simulations and showed that the rotation around the major axis could be the result of a polar merger, with the amplitude of prolate rotation depending on the initial bulge-to-total stellar mass ratio of its progenitor galaxies.

Additionally, they investigated the origin of this prolate rotation in polar galaxy merger remnants. It appears that prolate rotation might be more common than previously expected, and can help towards a better understanding of their dynamical structure and formation origin.

“Until now astronomers thought that this type of galaxy is extremely rare. It was really surprising to see so many galaxies with such a feature, practically ten times more than expected!”

Athanasia Tsatsi, Max-Planck-Institut, Germany

This work, combined with future, higher quality observations of the sample of galaxies presented and orbit-based dynamical modeling, will give better insights into the dynamical nature of this special type of rotators. These results, combined with cosmological simulations, will help towards setting better constraints on the formation origin as well as the rate of occurrence of prolate rotation in massive early-type galaxies.

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