In an article recently published in Astronomy and Astrophysics an international team, involving researchers from the Astrophysics Laboratory of Marseille study Malin 1 a nearby galaxy known only since the 80s and showing a very large disk of gas and stars. The observations of Malin 1, a perfect prototype of the giant galaxies with low brightness area have allowed scientists to make an unexpected discovery that challenges the assumptions about galaxy formation process of this type.

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Because of diffuse their appearance and their very low gloss, yet these massive galaxies are difficult to observe and remain unknown today. They could be a significant fraction of the galaxies in the universe especially as similar objects in Malin 1 may have escaped our vigilance. It is therefore essential to study them and understand their formation and evolution. It now becomes possible with telescopes and modern detectors are more sensitive to low surface brightness.

Malin 1 obtained six lengths wave different from the ultraviolet through the project the ‘ optical and near infrared through NGVS project with the camera Mega Cam Canada France Hawaii Telescope, CFHT. Originally planned to study the Virgo cluster, these great campaigns of observations also allow us to work on other objects in the background of this cluster, as is the case in this study.

The researchers extracted these data the variation in brightness with distance from the center of the galaxy, and the variation of the “colors” of the galaxy (ie brightness reports to different wavelengths). They depend heavily on the history of the galaxy. Comparison of these observational results with the predictions of various numerical models has allowed the team to estimate for the first time how to be the story of the formation of stellar. It suggests that the Evil one giant disk is in place for several billion years, and that stars are formed there in a modest but steady rate over the long-term.

The curve with error bars showing the variation with the radius of the color between the two bands GALEX FUV and NUV. This difference is sensitive to young stellar populations. The blue curve and red shows the model used in the article is consistent with these observations. Instead, the orange line shows the color of stars that may have formed during an interaction there are 1.4 billion years, or a formation of stars that would be moved from the center outward from this period (stars). These scenarios are clearly contradicted by new observations.

This result is important and surprising because it contradicts a proposed scenario in the last few years that these giant galaxies are formed during violent interactions. It now seems excluded by the new data. In the context cosmological galaxy formation, we expect many interactions and mergers that would disrupt the disk Malin 1. The formation of such a structure, and its survival in this context, therefore offers a new challenge for cosmological simulations of galaxy formation.

The red curve shows the history of the star formation rate (SFR) in the evil giant disk 1 from the model discussed in the article that correctly reproduces the star surface densities and colors of the galaxy. This story suggests a spread formation over several billion years. The error bar indicates an estimate of current star formation rate, estimated in an earlier study.