Periodic Reporting for period 4 - ClusterWeb (Unravelling the physics of particle acceleration and feedback in galaxy clusters and the cosmic web)
Periodo di rendicontazione: 2024-03-01 al 2025-02-28
Galaxy clusters and cosmic web filaments are the largest structures in the Universe, forming vast networks that span hundreds of millions of light-years. These structures grow over time as smaller clusters and groups of galaxies merge, generating shock waves and turbulence that heat the hot plasma within them. In these magnetized plasmas, particles called cosmic rays are accelerated to extreme energies, creating diffuse radio emission that can be detected over immense scales.
However, how these cosmic rays are accelerated remains a mystery. Understanding this process is important for unraveling how energy is distributed across the Universe’s largest structures. It also provides insight into fundamental physical processes that could help us understand high-energy phenomena across the cosmos.
This project aims to systematically study these diffuse radio sources to learn how their properties depend on factors such as the mass of their host clusters. It also seeks to explore the lower-density regions outside clusters, where shocks are present and could potentially accelerate particles. By creating ultra-deep, low-frequency radio images, the project will attempt to detect this emission and uncover the mechanisms behind particle acceleration in these environments.
Additionally, supermassive black holes located at the centers of galaxy clusters play a crucial role in regulating the temperature of the surrounding plasma. By releasing powerful jets and outbursts, these black holes can heat the gas, preventing it from cooling too rapidly. Understanding how this process has evolved over the lifetime of clusters is essential for building accurate models of galaxy cluster formation and evolution.
The project uses state-of-the-art radio telescopes, particularly LOFAR, a cutting-edge, pan-European radio telescope designed to achieve exceptional sensitivity, survey speed, and resolution at low frequencies. LOFAR combines signals from thousands of small, low-cost antennas spread across Europe to emulate a giant telescope, allowing it to study clusters with unprecedented detail. By complementing LOFAR observations with data from space telescopes like Chandra, XMM, and Planck, the project aims to make significant progress in understanding the origins of cosmic rays, magnetic fields, and the impact of supermassive black holes on their environments.
However, how these cosmic rays are accelerated remains a mystery. Understanding this process is important for unraveling how energy is distributed across the Universe’s largest structures. It also provides insight into fundamental physical processes that could help us understand high-energy phenomena across the cosmos.
This project aims to systematically study these diffuse radio sources to learn how their properties depend on factors such as the mass of their host clusters. It also seeks to explore the lower-density regions outside clusters, where shocks are present and could potentially accelerate particles. By creating ultra-deep, low-frequency radio images, the project will attempt to detect this emission and uncover the mechanisms behind particle acceleration in these environments.
Additionally, supermassive black holes located at the centers of galaxy clusters play a crucial role in regulating the temperature of the surrounding plasma. By releasing powerful jets and outbursts, these black holes can heat the gas, preventing it from cooling too rapidly. Understanding how this process has evolved over the lifetime of clusters is essential for building accurate models of galaxy cluster formation and evolution.
The project uses state-of-the-art radio telescopes, particularly LOFAR, a cutting-edge, pan-European radio telescope designed to achieve exceptional sensitivity, survey speed, and resolution at low frequencies. LOFAR combines signals from thousands of small, low-cost antennas spread across Europe to emulate a giant telescope, allowing it to study clusters with unprecedented detail. By complementing LOFAR observations with data from space telescopes like Chandra, XMM, and Planck, the project aims to make significant progress in understanding the origins of cosmic rays, magnetic fields, and the impact of supermassive black holes on their environments.
The project addressed three specific research topics: (1) cosmic rays and acceleration mechanisms in galaxy clusters, (2) the influence of supermassive black holes on galaxy cluster centers, and (3) cosmic rays in the larger environment surrounding galaxy clusters.
1. Cosmic Rays and Acceleration in Galaxy Clusters
The research aimed to create large samples of galaxy clusters with deep LOFAR observations to characterize their cosmic ray content and magnetic field properties. This required significant technical advancements in low-frequency calibration techniques, leading to a major breakthrough: the development of a method that, for the first time, enabled the creation of high-quality images at ultra-low frequencies. These images allowed researchers to investigate the origin of low-energy cosmic rays, revealing that past outbursts from supermassive black holes may have supplied clusters with a reservoir of cosmic rays.
The creation of large cluster samples also led to important findings. The occurrence rate of diffuse radio sources in clusters was quantified for the first time. The results support a model where particles are re-accelerated by turbulence, consistent with the observed occurrence rates. Furthermore, diffuse radio emission was detected in a sample of very distant clusters, suggesting that magnetic fields are amplified early during cluster formation.
2. Influence of Supermassive Black Holes on Cluster Centers
This project focused on developing techniques to produce images by using LOFAR stations across Europe to achieve exceptionally high angular resolution. For the first time, the centers of galaxy clusters were imaged at high resolution at low frequencies. This provided valuable insights into older outbursts, as low-frequency radio emission can trace aged cosmic rays. Additionally, the project enabled the first detailed studies of how supermassive black holes influence distant clusters.
3. Cosmic Rays in the Environment Surrounding Clusters
Ultra-deep imaging was conducted to study emission beyond the central regions of galaxy clusters. This revealed that cosmic rays can be accelerated in these outer regions and that magnetic fields are present even in low-density environments. Moreover, the discovery of a giant radio galaxy showed that black holes have a far-reaching influence and might be important for seeding the universe with magnetic fields.
Additionally, the deep radio images obtained for the project uncovered galaxies with radio-emitting tails trailing behind them. These tails trace cosmic rays stripped from galaxies as they fall into clusters, illustrating how the dense environments of large-scale structures can influence galaxies. This stripping process likely plays a significant role in suppressing star formation in cluster galaxies by depleting their gas reservoirs needed for star formation.
The technical breakthroughs achieved during this project, including the creation of high-quality images in the decameter band and high-resolution imaging using LOFAR’s European baselines, have paved the way for numerous other scientific studies that are now benefiting from these newly developed techniques.
1. Cosmic Rays and Acceleration in Galaxy Clusters
The research aimed to create large samples of galaxy clusters with deep LOFAR observations to characterize their cosmic ray content and magnetic field properties. This required significant technical advancements in low-frequency calibration techniques, leading to a major breakthrough: the development of a method that, for the first time, enabled the creation of high-quality images at ultra-low frequencies. These images allowed researchers to investigate the origin of low-energy cosmic rays, revealing that past outbursts from supermassive black holes may have supplied clusters with a reservoir of cosmic rays.
The creation of large cluster samples also led to important findings. The occurrence rate of diffuse radio sources in clusters was quantified for the first time. The results support a model where particles are re-accelerated by turbulence, consistent with the observed occurrence rates. Furthermore, diffuse radio emission was detected in a sample of very distant clusters, suggesting that magnetic fields are amplified early during cluster formation.
2. Influence of Supermassive Black Holes on Cluster Centers
This project focused on developing techniques to produce images by using LOFAR stations across Europe to achieve exceptionally high angular resolution. For the first time, the centers of galaxy clusters were imaged at high resolution at low frequencies. This provided valuable insights into older outbursts, as low-frequency radio emission can trace aged cosmic rays. Additionally, the project enabled the first detailed studies of how supermassive black holes influence distant clusters.
3. Cosmic Rays in the Environment Surrounding Clusters
Ultra-deep imaging was conducted to study emission beyond the central regions of galaxy clusters. This revealed that cosmic rays can be accelerated in these outer regions and that magnetic fields are present even in low-density environments. Moreover, the discovery of a giant radio galaxy showed that black holes have a far-reaching influence and might be important for seeding the universe with magnetic fields.
Additionally, the deep radio images obtained for the project uncovered galaxies with radio-emitting tails trailing behind them. These tails trace cosmic rays stripped from galaxies as they fall into clusters, illustrating how the dense environments of large-scale structures can influence galaxies. This stripping process likely plays a significant role in suppressing star formation in cluster galaxies by depleting their gas reservoirs needed for star formation.
The technical breakthroughs achieved during this project, including the creation of high-quality images in the decameter band and high-resolution imaging using LOFAR’s European baselines, have paved the way for numerous other scientific studies that are now benefiting from these newly developed techniques.
This project achieved significant advancements, developing new techniques, producing groundbreaking discoveries, and expanding beyond the current state-of-the-art.
We conducted the largest low-frequency survey of galaxy clusters to date, determining that extended populations of cosmic rays are present in approximately 30% of clusters. The properties of the observed radio emission align well with predictions from the turbulent re-acceleration model, suggesting that these cosmic rays likely originate from turbulence in the cluster gas induced by merger events. These findings represent a major step forward compared to previous studies, which relied on smaller cluster samples observed at higher frequencies with limited sensitivity.
A key breakthrough of this project was the discovery of cosmic rays in some of the most distant clusters known. Detecting radio emission in distant clusters was unexpected, as it implies that magnetic fields in these young clusters were already amplified to levels comparable to those in the present-day universe. The project also produced the first high-resolution, low-frequency studies of feedback from supermassive black holes in galaxy clusters.
Ultra-deep imaging revealed radio emission between galaxy clusters, demonstrating that particle acceleration mechanisms operate efficiently even in these low-density environments. Furthermore, the project uncovered numerous galaxies affected by cluster gas stripping, a process that depletes their reservoirs of star-forming material.
Finally, two breakthrough techniques were developed: (1) a method for creating high-quality images of the radio sky at decameter frequencies, overcoming the extreme effects of Earth's ionosphere, and (2) a novel calibration and imaging algorithms enabling wide-field imaging of the sky at sub-arcsecond resolution, leveraging supercomputers to accelerate data processing.
We conducted the largest low-frequency survey of galaxy clusters to date, determining that extended populations of cosmic rays are present in approximately 30% of clusters. The properties of the observed radio emission align well with predictions from the turbulent re-acceleration model, suggesting that these cosmic rays likely originate from turbulence in the cluster gas induced by merger events. These findings represent a major step forward compared to previous studies, which relied on smaller cluster samples observed at higher frequencies with limited sensitivity.
A key breakthrough of this project was the discovery of cosmic rays in some of the most distant clusters known. Detecting radio emission in distant clusters was unexpected, as it implies that magnetic fields in these young clusters were already amplified to levels comparable to those in the present-day universe. The project also produced the first high-resolution, low-frequency studies of feedback from supermassive black holes in galaxy clusters.
Ultra-deep imaging revealed radio emission between galaxy clusters, demonstrating that particle acceleration mechanisms operate efficiently even in these low-density environments. Furthermore, the project uncovered numerous galaxies affected by cluster gas stripping, a process that depletes their reservoirs of star-forming material.
Finally, two breakthrough techniques were developed: (1) a method for creating high-quality images of the radio sky at decameter frequencies, overcoming the extreme effects of Earth's ionosphere, and (2) a novel calibration and imaging algorithms enabling wide-field imaging of the sky at sub-arcsecond resolution, leveraging supercomputers to accelerate data processing.