Periodic Reporting for period 1 - GalaxyConnect (Unveiling the properties of the first galaxies through their connection with the intergalactic medium)
Reporting period: 2021-07-01 to 2023-06-30
Understanding how the first galaxies formed is one of the most important unanswered questions in astronomy. One way of studying the first galaxies is to directly observe the light emitted by the stars and gas they contain. This can be difficult though, as many of the galaxies are very faint. However, galaxies do not grow in isolation, but rather they are surrounded by a cosmic web of gas. Another way we can learn about the first galaxies is by studying this connection between the galaxies and the intergalactic gas.
Galaxies can interact with the gas surrounding them in different ways. After the Big Bang, the gas in the cosmic web was cold and neutral until the first galaxies in the Universe formed. Light from the stars formed in these galaxies ionized and heated the cosmic web, in a period known as the epoch of reionization. As well as this, outflows driven by supernovae in the galaxies enriched the cosmic web with elements such as carbon and oxygen. Carefully characterising the properties of the cosmic web in the early Universe can therefore provide insights into the nature of the first galaxies.
The cosmic web can be observed as a pattern of absorption features in light coming from distant, luminous sources. By making measurements of the statistics of these absorption features and comparing with statistics derived from cosmological simulations, the ionization state, temperature and chemical composition of the intergalactic gas can be unveiled. A key objective of the GalaxyConnect project was to combine theoretical models and observational data to understand how the cosmic web evolves.
As well as this, the light coming from the faintest galaxies can be measured using a technique called intensity mapping. This involves making a map across the sky of gas emission coming from certain elements or molecules. This process relates to another objective of the GalaxyConnect project, which was to understand the emission signature of galaxies into the reionization epoch.
Galaxies can interact with the gas surrounding them in different ways. After the Big Bang, the gas in the cosmic web was cold and neutral until the first galaxies in the Universe formed. Light from the stars formed in these galaxies ionized and heated the cosmic web, in a period known as the epoch of reionization. As well as this, outflows driven by supernovae in the galaxies enriched the cosmic web with elements such as carbon and oxygen. Carefully characterising the properties of the cosmic web in the early Universe can therefore provide insights into the nature of the first galaxies.
The cosmic web can be observed as a pattern of absorption features in light coming from distant, luminous sources. By making measurements of the statistics of these absorption features and comparing with statistics derived from cosmological simulations, the ionization state, temperature and chemical composition of the intergalactic gas can be unveiled. A key objective of the GalaxyConnect project was to combine theoretical models and observational data to understand how the cosmic web evolves.
As well as this, the light coming from the faintest galaxies can be measured using a technique called intensity mapping. This involves making a map across the sky of gas emission coming from certain elements or molecules. This process relates to another objective of the GalaxyConnect project, which was to understand the emission signature of galaxies into the reionization epoch.
To achieve the objectives of the GalaxyConnect project, observational data and cosmological simulations were carefully compared.
One of the key observational datasets used in the project was obtained as part of the XQR-30 survey. This was a 248-hour ESO large programme dedicated to observing quasars in the early Universe. Quasars are among the brightest objects in the Universe and are ideal “backlights” for studying absorption signatures from the cosmic web. This dataset was used to make some of the most precise measurements of the properties of intergalactic gas to date and the results were found to be in excellent agreement with cosmological simulations of the reionization of the cosmic web.
The observed quasars are powered by supermassive black holes in the early Universe. Since the quasar emits so much light, very little absorption occurs from the cosmic web close to the quasar. As part of the GalaxyConnect project, it was shown that reproducing the amount of absorption close to the quasar means that the supermassive black holes must grow in short bursts.
To further understand how light coming from galaxies influences the ionization state of intergalactic gas, detailed cosmological simulations were performed. From these simulations, different quantities could be measured, such as the amount of light that escapes from the galaxies. This helped to understand how the Universe transitioned from cold and neutral to hot and ionized.
The cosmic web is also an important probe of cosmological models and the nature of dark matter. Over the course of the GalaxyConnect project, new simulations explicitly designed to model the cosmic web in the early Universe were performed. From these simulations, the impact of inhomogeneous ionization and heating of intergalactic gas on these cosmological measurements was quantified.
Finally, work was carried out to prepare for future intensity mapping experiments observing emission from molecular gas contained within the first galaxies. This involved understanding existing data from galaxies observed at a more recent period in the history of the Universe, as well as understanding complementary observations that can be compared with the intensity mapping data.
The first results from the GalaxyConnect project have been already presented at international conferences and published in scientific journals. Future publications based on data gathered over the course of the project are being prepared for publication.
One of the key observational datasets used in the project was obtained as part of the XQR-30 survey. This was a 248-hour ESO large programme dedicated to observing quasars in the early Universe. Quasars are among the brightest objects in the Universe and are ideal “backlights” for studying absorption signatures from the cosmic web. This dataset was used to make some of the most precise measurements of the properties of intergalactic gas to date and the results were found to be in excellent agreement with cosmological simulations of the reionization of the cosmic web.
The observed quasars are powered by supermassive black holes in the early Universe. Since the quasar emits so much light, very little absorption occurs from the cosmic web close to the quasar. As part of the GalaxyConnect project, it was shown that reproducing the amount of absorption close to the quasar means that the supermassive black holes must grow in short bursts.
To further understand how light coming from galaxies influences the ionization state of intergalactic gas, detailed cosmological simulations were performed. From these simulations, different quantities could be measured, such as the amount of light that escapes from the galaxies. This helped to understand how the Universe transitioned from cold and neutral to hot and ionized.
The cosmic web is also an important probe of cosmological models and the nature of dark matter. Over the course of the GalaxyConnect project, new simulations explicitly designed to model the cosmic web in the early Universe were performed. From these simulations, the impact of inhomogeneous ionization and heating of intergalactic gas on these cosmological measurements was quantified.
Finally, work was carried out to prepare for future intensity mapping experiments observing emission from molecular gas contained within the first galaxies. This involved understanding existing data from galaxies observed at a more recent period in the history of the Universe, as well as understanding complementary observations that can be compared with the intensity mapping data.
The first results from the GalaxyConnect project have been already presented at international conferences and published in scientific journals. Future publications based on data gathered over the course of the project are being prepared for publication.
The GalaxyConnect project has already produced results that go beyond the state of the art. Of particular note is the new, extremely precise measurement of absorption from the cosmic web carried out as part of the XQR-30 survey. These results are vital for understanding when the light from the first galaxies finished heating up the intergalactic gas. As well as this, the new insights into the growth of the first supermassive black holes and the escape of light from the first galaxies that came from the GalaxyConnect will certainly form the basis for future research.
The data gathered from this project will be valuable for many research groups around the world. Interest in the first galaxies is currently extremely high, thanks to the new results from JWST. The indirect analysis of the first galaxies via their interactions with the cosmic web as carried out by the GalaxyConnect project is highly complementary to these new observations, and continuing both approaches will be critical to make progress in this field. Furthermore, the data gathered as part of the GalaxyConnect project will be important for preparing for the next generation of European telescopes, such as the 39-metre ELT.
The data gathered from this project will be valuable for many research groups around the world. Interest in the first galaxies is currently extremely high, thanks to the new results from JWST. The indirect analysis of the first galaxies via their interactions with the cosmic web as carried out by the GalaxyConnect project is highly complementary to these new observations, and continuing both approaches will be critical to make progress in this field. Furthermore, the data gathered as part of the GalaxyConnect project will be important for preparing for the next generation of European telescopes, such as the 39-metre ELT.