According to the modern estimations, about 3% of all galaxies can not be categorized as having some distinct ‘standard’ shape, and thus are called the irregular galaxies. Most of these stellar systems are typically formed via impact of strong gravitational pull. For example, that type of event might happen when some larger neighbor galaxy strips its smaller companion of matter and distorts its structure. However, an opposite process – when an irregular galaxy regains its ordered shape – can also happen. But in a bit different way, although it seems to look similar.

This kind of transformation has been recently described in a scientific paper published at arXiv.org. Here a team of scientists from the United States, Czech Republic, South Korea and France studied an irregular dwarf galaxy, which is currently undergoing a metamorphosis of becoming a regular elliptical dwarf galaxy.

The authors say that this study is an important waypoint for researching the origins and evolution of dwarf elliptical galaxies, since they are the dominant galaxy type (by the number) in galaxy clusters. They had chosen the Virgo Cluster galaxy IC 3418 for their studies. This object is probably a unique example of so-called ram pressure stripping effect – when the gaseous intra-cluster medium creates a pressure on the moving galaxy and this pressure is strong enough to overcome the gravitational potential of particular galaxy, and thus removes part of the gas contained in it.

IC 3418 is famous for an unusual one-sided tail of tidal nature, which formed after its collision with the Virgo Supercluster at some point in the past, according to the previous studies. The team noted the processes taking place in this irregular galaxy several months ago. In the current study the astronomers analyzed those processes more precisely by performing kinematic and morphological analysis of the IC 3418 tail features based on the optical spectroscopy data obtained with the LRIS spectrograph on the Keck I telescope on 26-27 February 2009 and DEIMOS spectrograph on the Keck II telescope on February 14, 2010.

According to the results of the current study, the authors strongly argue that ram pressure stripping is a crucial phase required to convert dwarf irregulars into dwarf elliptical galaxies, and that IC 3418 is a clear example of such transformation. The images of the main body and tail of IC 3418 revealed central star formation region with indications of recently formed stars and a clear evidence of emerging spiral arms. There is no apparent evidence of galactic bar, although the spiral structure points to a prospective disk system.

The age distribution analysis also indicates that the tail of IC 3418 consists mostly of young stars mainly, unlike the regular tidal tails. This fact contradicts the previous studies, as the team also concludes that the tail has been likely produced not by gravitational impact of tidal stripping, but via ram pressure stripping of gas, happening as IC 3418 moves towards us through the cluster at a speed of 900 km/s.

The authors predict that these regions will leave the galaxy by joining the intracluster space, as most of the outer tail features have velocities exceeding the escape velocity. Meanwhile, some of the inner tail features will most certainly remain bound to IC 3418 and eventually will fall back into its source – the galaxy itself.

This will complete the transformation cycle: the tail should disappear as IC 3418 becomes a true dwarf elliptical galaxy.

By Alius Noreika, Source: www.technology.org