Malin 1 is one of the largest spiral galaxies ever observed in the cosmos. It has a diffuse disk and gigantic spiral arms, and although it has already been studied by contemporary astrophysics, it continues to present mysteries because, despite being a huge galaxy, the molecular gas, the essential ingredient for a galaxy that contains –basically– all kinds of stars.
The research, published in the latest issue of the journal Letters from the astrophysicist diary, confirms the absence of molecular gas at a limit twenty times lower than that previously observed, in the year 2000. Current evidence indicates that all spiral galaxies form stars and therefore possess dense clouds of cold molecular gas (hydrogen molecules) where stars are forming. Although molecular hydrogen does not emit radiation, other molecules do, such as carbon monoxide. It is the latter molecule, and other molecular hydrogen tracer molecules, that have yet to be detected in the Malin 1 galaxy.
“Surprisingly, although we know that Malin 1 has young stars, the emission of molecular gas has so far not been detected by tracers such as carbon monoxide (CO), which is typically used to identify the distribution of molecular gas in galaxies,” he explains. Gaspar Galaz, PhD in astrophysics at the University of Paris, who has been studying the Malin 1 galaxy for years.
Located more than a billion light-years from the Milky Way, Malin 1 is almost seven times larger than our host galaxy, with a diameter of about 650,000 light-years. Malin 1 was discovered in 1986 by a team of famous astronomers of the time, including David Malin, hence its name. It is the first of a class of galaxies that has been called a “low surface luminosity giant spiral galaxy”. “They are not very common and to date it is not known how many exist like them. However, computer simulations indicate that there should be many more, and we should detect several hundred more in the future,” says Galaz.
“We think the molecular gas is there. It has to be, because, as we know, Malin 1 also contains young stars,” explains Gaspar Galaz. The new research suggests that such gas may be in different physical conditions than most spiral galaxies.
“In particular, we think it is hotter and, therefore, the traditionally used CO molecular emission line, and even in this study, perhaps not the most suitable for tracking molecular gas in this type of galaxy. . Another possibility would be that the molecular gas is actually at such an extraordinarily low density that star formation has definitely ceased, except in very specific places in the galaxy where it is colder and denser,” adds UC- CATA.
To achieve these results, more than 17 hours of observation were required, carried out between 2018 and 2019, using the Byrd radio telescope, 100 meters in diameter, with the instrument that detects submillimeter radiation ARGUS. The Byrd Radio Telescope is located in Green Bank, West Virginia, United States.
It is hoped that we will be able to learn more about this galaxy in future studies, targeting specific locations in Malin 1 with the ALMA radio telescope and possibly also using other molecules to track the molecular gas.
“We also know from our recent observations with the VLT/MUSE (an optical instrument) that this galaxy has ionised atomic hydrogen emission in some places where stars formed recently,” concludes Galaz.