This paper presents for the first time deep images obtained at 6 different wavelengths, from the UV of the GUViCS project to the optical and near-infrared obtained in the context of the Next Generation Virgo Survey with MegaCam on CFHT. Originally, these large observational campaigns were planned to study the Virgo cluster, but they also allow us to study background objects like Malin 1. The images offer us a new view of this spectacular galaxy, the largest galactic disk known, with a diameter above 250 kilo-parsec (in comparison, our Milky Way is only about 30 kpc wide).
The team of researchers extracted from these data the variation of the luminosity with the distance to the center of the galaxy, as well as the variation of the colors (corresponding to the ratios between the luminosity at various wavelengths). These colors strongly depends on the star formation history. The comparison of the observations with predictions of various numerical models allowed the team to estimate for the first time what must have been the history of star formation in the giant disk of Malin 1. It suggests that the giant disk has been in place for several Gyr, and that star formation proceed at a regular long-term rhythm despite the very low density.
This result is important as it clearly contradicts a scenario proposed a few years ago predicting that these giant galaxies are formed during violent interactions. Moreover, in the context of the cosmological formation of galaxies, numerous fusions and interaction should have perturbed the disk of Malin 1. The formation of such a structure and its survival for very long time offers then a challenge for cosmological simulations of the formation of galaxies.
What is the future of Malin 1? The giant disk contains a large quantity of gas in which star formation will keep proceeding at a low rate for billions of years, increasing progressively the stellar mass of the galaxy. Unless another galaxy comes in the picture to interact with Malin 1 and totally change its destiny. Few galaxies, however, may play this role as Malin 1 is a relatively isolated galaxy.
Dr. Samuel Boissier
Laboratoire d'Astrophysique de Marseille (AMU, CNRS).
Phone number: +33 4 91 05 59 37