Lya i blått. Här kan man se hur galaxen badar i ett blått och diffust moln av Lyman alfa. Foto: M. H
Lya in blue: The galaxy bathed in a blue and diffuse cloud of Lyman alpha. Photo: M. Hayes.

These are the first results of the LARS project (Lyman Alpha Reference Sample), where the Hubble Space Telescope (HST) has been used to study 14 nearby galaxies in detail to find out how the so-called Lyα light travels through the galaxies.

“We found that Lyα light has a hard time finding its way out of the galaxies. In cases when it manages to get out, it is often so that the light bounces off clouds of neutral hydrogen. This bouncing makes the light travel farther and farther out, and in that way the galaxies appear larger in Lyα light than in ordinary visible light,” says Lucia Guaita, postdoctoral researcher at the Department of Astronomy, Stockholm University, who is working in the project.

The ultraviolet light used in the study comes from the hydrogen emitting radiation in the spectral line Lyman alpha (Lyα). Understanding how Lyα light is transported through and finds its way out of the galaxies is a very important piece of the puzzle when astronomers study how galaxies form and evolve. A large proportion of research on the early (and remote) Universe during the past 15 years uses Lyα observations to determine the properties of galaxies that are faint and difficult to detect. By studying more nearby galaxies of the same type in detail, it becomes easier to interpret observations of galaxies in the Universe's infancy.

“In the LARS project, we have selected galaxies that have the same characteristics as young galaxies in the distant Universe. When studied them more closely, they are found to have irregular shapes, due to collisions with other galaxies. These galaxy collisions were common earlier in the history of the Universe and they start the process of star formation in the galaxies,” says Matthew Hayes, a postdoctoral researcher at the IRAP, Toulouse, France, who is first author of the LARS team's first article.

Using the Hubble telescope's unique resolving power, researchers in the LARS project can study very accurately how ultraviolet radiation travels through galaxies and how it is affected by gas and dust. This is the first time that such a detailed and comprehensive study has been carried out.

LARS is the largest Swedish-led project carried out at the HST so far. The project is led by Professor Göran Östlin at the Department of Astronomy, Stockholm University. A picture of one of the galaxies observed in the project has been selected as this week's image on the Hubble telescope website.

“The first results of LARS are exciting, but we have a lot more data collected by Hubble on LARS’ behalf. We will publish a number of highly interesting results later this year,” says Göran Östlin.

Link to article.

For more information
Göran Östlin, Professor at the Department of Astronomy at Stockholm University, Tel +46 (0)8 5537 8513, email