National Autonomous University of Mexico (UNAM) | 2019 May 02
Institute of Radio Astronomy (IRyA) and Astrophysics
An international scientific team led by a Mexican researcher discovered globular clusters rotating at the same speed as the gas in the disk of the spiral galaxy Messier 106 (also known as M106 or NGC 4258) to which they belong. Because of their disk-like arrangement and speed, these distant objects could be relics of cosmic high noon. ...False color image of M106. The image combines neutral hydrogen data (blue) from
the WSRT with optical data (red and green) from the CFHT. Yellow circles highlight
the observed globular clusters, which are distributed in a rotating disk whose
velocity is the same as that of the neutral gas (Credit: Divakara Mayya, INAOE)
Dr. González-Lópezlira explains that globular clusters are groups of between one hundred thousand and one million stars. They are common objects, especially in large galaxies. “The Milky Way, our galaxy, has 160 of these clusters, but very large galaxies can have tens of thousands. Usually, these clusters are distributed as in a sphere. All the stars of a globular cluster are approximately of the same age and have more or less the same chemical composition. We do not know exactly how these clusters were formed, and there are several hypotheses that try to explain it: one says that they precede the formation of galaxies, another one that clusters formed along with them, yet another postulates that some appear when gas collides during a galaxy merger,” she says. In the Milky Way, for example, most of the globular clusters seemed to have formed together with the galaxy; a few were formed or acquired later, when one or several smaller galaxies merged with it.
Globular clusters are very old objects that formed about 11.5 billion years ago, 2.3 billion years after the Big Bang and shortly before the rate of cosmic star formation reached its peak, 10 billion years ago. “This period is known as cosmic high noon. The clusters are very bright and can be seen at very large distances, which means that they can give us clues as to how the galaxies were assembled during this period of maximum star formation,” says the astrophysicist.
The article that was published in the May 1st issue of the ApJ is part of a larger project to study the globular cluster systems of nine spiral galaxies within a radius of 52 million light-years. “We are particularly interested in the relationship between the number of globular clusters and the mass of the central black hole in spiral galaxies,” says the researcher. The relationship is very tight for elliptical galaxies, but it is not as clear in spiral galaxies. The Milky Way, for example, does not fulfill it. Dr. González-Lópezlira adds: “The nine spiral galaxies that we are going to study have good estimates of the masses of their black holes and are at distances where the globular clusters can be seen well with the Canada-France-Hawaii Telescope (CFHT), with which we made the initial observations.” ...
Spectroscopy of NGC 4258 Globular Cluster Candidates:
Membership Confirmation and Kinematics ~ Rosa A. Gonzaléz-Lópezlira et al