Periodic Reporting for period 4 - Fornax (Galaxy evolution in dense environments)
Reporting period: 2021-04-01 to 2022-09-30
On a "small" scale (up to hundreds of millions of light years) the Universe is far from homogeneous. Galaxies are distributed on long sheets and filaments, and avoid the large and empty cosmic voids. At the crossing between filaments we find the most massive structures in the Universe: galaxy clusters, each hosting thousands of galaxies inside a small volume. To this day, clusters continue to pull more and more galaxies towards them thanks to their gravitational attraction. Galaxies falling into clusters undergo rapid evolution as they collide with one another and feel the pressure of the hot (up to hundreds of millions of degrees) ambient gas. Eventually, these interactions deprive galaxies of their own cold gas (from which new stars would form) and thus shut down their star formation. From that point on these galaxies evolves "passively", that is, they continue to age without forming new stars.
This ERC project, called FORNAX, investigates the exact physical mechanisms that determine the evolution of galaxies in clusters. In particular, as clusters come in different size and mass, we want to understand down to what cluster mass events such as galaxy collision and interaction with the cluster hot ambient gas are relevant. To do so we will study the nearest small cluster, called Fornax. We will do so using a brand new radio telescope, MeerKAT, located in South Africa. This telescope will allow us to observe the cold gas of galaxies in Fornax with unprecedented sensitivity and resolution, and answer the questions of whether, through what processes and how quickly this gas is being removed from them.
This ERC project, called FORNAX, investigates the exact physical mechanisms that determine the evolution of galaxies in clusters. In particular, as clusters come in different size and mass, we want to understand down to what cluster mass events such as galaxy collision and interaction with the cluster hot ambient gas are relevant. To do so we will study the nearest small cluster, called Fornax. We will do so using a brand new radio telescope, MeerKAT, located in South Africa. This telescope will allow us to observe the cold gas of galaxies in Fornax with unprecedented sensitivity and resolution, and answer the questions of whether, through what processes and how quickly this gas is being removed from them.
The first part of this project consisted in preparing the tools needed to process the data of the MeerKAT telescope. This is challenging because sensitive observations such as those we planned to perform require a detailed understanding of the instrument -- something that is never trivial especially with a new telescope. Furthermore, MeerKAT produces very large amounts of data, and efficient algorithms are necessary to process them in a reasonable amount of time. For this reason, initially the FORNAX team focused on the development of a new data processing pipeline and on its testing. We also worked on analysing the first data coming from the new MeerKAT telescope to help verify that it is working well. Those early data gave us exciting new insights in the nature of the Fornax cluster and in particular of one of its most famous galaxies, Fornax A, resulting in the publication of the first images ever taken with MeerKAT.
About 2/3 into the project our "real" MeerKAT observations to study Fornax started officially. Thanks to the preparatory work done earlier we were immediately able to process the large amount of data coming our way, and obtain beautiful images of the cold gas in Fornax. The images revealed that cold gas is removed from galaxies and scattered in the space between them throughout the entire galaxy cluster volume. We found for the first time clear evidence that some of this gas is removed from galaxies following their interaction with the hot ambient gas, immediately answering one of our key questions.
About 2/3 into the project our "real" MeerKAT observations to study Fornax started officially. Thanks to the preparatory work done earlier we were immediately able to process the large amount of data coming our way, and obtain beautiful images of the cold gas in Fornax. The images revealed that cold gas is removed from galaxies and scattered in the space between them throughout the entire galaxy cluster volume. We found for the first time clear evidence that some of this gas is removed from galaxies following their interaction with the hot ambient gas, immediately answering one of our key questions.
Our MeerKAT observations contribute to a radical change of our view of Fornax. Once thought to be a relatively old, settled system, Fornax is now turning out to be a very dynamic environment, where galaxies undergo significant interactions and transformation. Thanks to the high resolution and unprecedented sensitivity of our MeerKAT data, we have established that the interaction between galaxies and the ambient gas is a key driver of their evolution even in a small galaxy cluster like Fornax.