Submitted by Pooja Pandey on Thu, 06/07/2023 - 13:58
There are many big questions about the universe we live in. One of the main interests for scientists is to understand how the first galaxies shine and how their light travels through the universe. To answer this question, they are applying many different approaches. Now with the incredible power that James Webb Space Telescope (JWST) has given they are following-up individual galaxies that are farther away than ever before to answer the questions related to how the first galaxies lit up the universe.
In this study we only used a small portion of the sky, in order to calibrate our methods and use the powerful combination of the MUSE and JEMS surveys. We are currently working on reproducing this study in a much larger and complete sample. This will allow us to draw statistically relevant conclusions, as well as to study all kind of galaxies (not just LAEs). Charlotte Simmonds
Recently, the researchers studied a sample of Lyman-alpha emitters, or LAEs to understand how the first stars and galaxies lit up the universe.
A LAE is a type of galaxy that shows evidence of producing significant amounts of ionising photons, produced by young massive stars. These photons are energetic enough to kick out an electron from hydrogen atoms, making them positively charged or ionised. Therefore, it is very important to understand these photons for finding out how the universe lit up during the Epoch of Reionisation, a cosmic period when stars and galaxies gradually started lighting up the universe.
In order to study these galaxies, the scientists combined observations taken from two different instruments. First, they used MUSE, an instrument on the very Large Telescope located in the North of Chile, to obtain accurate distances to the galaxies.This allowed them to build a sample of 30 LAEs chosen to be located at the tail end of the Epoch of Reionisation (called NIRCam). They then went on to study the ionising properties of this sample of galaxies. For this they used the JEMS survey, which consists of five different observations of the sky, made by an imager onboard of the JWST, in different bands or colours. This survey was designed to overlap with the MUSE coverage of the sky to give more detailed results.
The findings, published in Oxford Academic, revealed that these sample of galaxies is very efficient in producing ionising photons, supporting the idea that LAEs might be the main culprits for lighting up the universe. Promisingly, these findings agree with theories and simulations: that there is a delay between the production of ionising photons and them managing to escape the galaxy. Ionising photons get easily absorbed by the gas and dust in galaxies. Therefore, once they are produced, some time is needed so that channels free of gas and dust can be created (for example through supernova explosions) and these photons can escape and hence, produce light.
“Although this kind of study has been done several times in the past, before the JWST era, it was impossible to do this for individual galaxies at the Epoch of Reionisation,” said Charlotte Simmonds, postdoctoral researcher at Cambridge’s Cavendish Laboratory and first author of the study. “In this regard, this is one of the first times we are able to look at individual LAEs at this epoch.”
Another thing that has surprised the scientists is the discovery of at least one Active Galactic Nuclei (AGN). This means that the galaxy is hosting a supermassive black hole that is actively accumulating material. They discovered this due to the high amount of ionising photons production, much more than what stars within galaxies can produce.
“In this study we only used a small portion of the sky, in order to calibrate our methods and use the powerful combination of the MUSE and JEMS surveys. We are currently working on reproducing this study in a much larger and complete sample. This will allow us to draw statistically relevant conclusions, as well as to study all kind of galaxies (not just LAEs),” concluded Simmonds.
Reference:
Simmonds, C., Tacchella, S., Maseda, M., Willams, C.C., Baker, W.M., Witten, C.E.C, et.al 'The ionising photon production efficiency at z 6 for Lyman-alpha emitters using JEMS and MUSE', Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 4, August 2023, Pages 5468–5486, https://doi.org/10.1093/mnras/stad1749
Image:
Epoch of re-ionisation
Credit: NASA/ESA