Clusters of galaxies are the largest spaces in the universe, containing hundreds or even thousands of galaxies. In the dense and inhospitable environment of these clusters, galaxies actively interact, and this can end or slow down the formation of stars. Astronomers want to know why.
Galaxies are dying in the most extreme corners of the universe. Their star formation is stopping, and astronomers want to know why.
The participants in a large project led by the Canadians hope to do this. In their work, they will use one of the most modern telescopes. The new program is called VERTICO, and its goal is to study in detail how the environment is killing its galaxies.
As the scientific director of this program, I lead a team of 30 specialists who, using the Large Atacam Millimeter Complex (ALMA), record high-resolution molecular hydrogen in a gaseous state in 51 galaxies from the closest galaxy cluster called the Virgo Cluster.
The $ 1.4 billion Atacama complex was commissioned in 2013. It is an antenna array of several interconnected radio telescopes installed at an altitude of 5,000 meters in the Atacama Desert in northern Chile. It is the result of international partnerships between Europe, USA, Canada, Japan, South Korea, Taiwan and Chile. As the largest ground-based astronomical project currently in operation, ALMA is the most advanced millimeter wave telescope complex. It is ideal for studying clusters of dense, cold gas from which new stars form, because this gas cannot be seen in the visible part of the spectrum.
ALMA's ambitious research programs, such as VERTICO, are designed to address strategic scientific problems that lead to major advances and breakthroughs in the field.
Clusters of galaxies
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The way galaxies live in the universe, how they interact with their intergalactic environment and with each other, has a major impact on their ability to form stars. But the question of how exactly this intergalactic space predetermines the life and death of galaxies remains unanswered.
Clusters of galaxies are the most massive and largest spaces in the universe, containing hundreds or even thousands of galaxies. Where there is mass, there is gravity. And the colossal gravitational forces present in the clusters accelerate galaxies to tremendous speeds, often thousands of kilometers per second, and also heat the plasma in intergalactic space to such high temperatures that it begins to emit X-rays.
In the dense and inhospitable environment of these clusters, galaxies actively interact with their surroundings and with each other. This interaction could end or slow down star formation.
Understanding which cooling mechanisms stop the formation of stars and how they do it is the main task of the participants in the joint VERTICO program.
Life cycle of galaxies
When galaxies in their clusters collapse, intergalactic plasma can quickly remove their gas in a violent reaction called tidal stripping. When the star-forming fuel is removed, it essentially kills the galaxy and turns it into a dead object in which no more stars are formed.
In addition, the high temperature of the clusters can stop the cooling of hot gases and their thickening, on the basis of which galaxies arise. In this case, the gas in the galaxy is not actively removed by the environment, but is consumed as stars form. This process is leading to a slow but inexorable cessation of star formation. This termination has a rather strange and painful name: exhaustion or suffocation.
These processes can proceed in different ways, but each of them leaves a unique and identifiable trail in the gas that forms the stars of the galaxy. One of the main tasks of the VERTICO program is to piece these tracks together and form a picture of how clusters are causing changes in galaxies. Based on the results of many years of work on the study of galactic evolution and the influence of the intergalactic environment on it, we want to solve new, very important riddles.
Ideal subject of research
The Virgo Cluster is an ideal location for such a detailed exploration of outer space. This is the closest large galaxy cluster to us and is in the process of forming. This means that we can get a static view of galaxies at different stages of their life cycles. This will allow us to create a detailed picture of how star formation is interrupted in galaxies.
Galaxies in the Virgo Cluster are observed at almost all wavelengths of the electromagnetic spectrum (for example, radio waves, optical waves, ultraviolet light). But we cannot yet observe the star-forming gas (it is carried out in the millimeter range) with the required accuracy and resolution. VERTICO, as one of the largest ALMA galactic exploration programs, will produce high-resolution maps of molecular hydrogen gas (fuel for star formation) for 51 galaxies.
Having obtained data from this large sample of galaxies at the Atakam complex, we will be able to understand exactly which cooling mechanism - tidal stripping or exhaustion - is killing galaxies in extreme environments and how.
By mapping star-forming gas in galaxies that are irrefutable examples of environmental cooling, VERTICO members will expand our understanding of how galaxies form and develop in these most saturated regions of the universe.
Toby Brown
