This light is emitted from the gas surrounding the hottest stars and is particularly useful for observing galaxies with a high potential for star formation.
To gain a deeper understanding of observations regarding the most distant galaxies, a group of international astronomers has constructed a sample of local galaxies that can be studied in much greater detail.
The Connection Between Light and the Physical Properties of Galaxies
In a newly published study, astronomers discovered how the amount of light escaping from a galaxy correlates with its physical characteristics. This finding is significant for how we interpret observations of galaxies in the early universe.
One of the most useful ways to study galaxies in the early universe is through a special type of ultraviolet light known as “Lyman alpha“. This light is emitted from the gas surrounding the hottest stars, making it particularly effective for observing galaxies with a high star formation potential.
However, unlike other types of light, the wavelength and direction of movement are influenced by various physical processes occurring both inside and outside of galaxies. Lyman alpha light does not travel directly toward our telescopes; instead, it follows a complex path out of the galaxy.
The universe has much left to explore – (Image: Internet).
Along its journey, Lyman alpha light passes through regions with varying physical conditions, which not only affects the path of each photon particle but also alters their wavelengths and even absorbs some unidentified light.
Lyman alpha light can pass through some hotter regions, some dustier areas, and some with strong flowing gas clouds… All these physical conditions make interpreting the Lyman alpha light we observe extremely challenging. However, if we can accurately interpret this light, we will be richly rewarded as it allows us to learn about the physical properties of galaxies.
Exploring Our Neighboring Galaxies
The galaxies in the distant universe are faint and small, making them particularly difficult to observe. Therefore, a group of international astronomers began constructing a “reference” galaxy sample from local galaxies in the vicinity of our Milky Way. Although still hundreds of millions of light-years away, they are close enough for more detailed study using various telescopes around the world and in space.
The reference galaxy sample, known as “Lyman Alpha Reference Sample” or LARS, has revealed many interesting characteristics of these galaxies that are extremely useful when observing more distant galaxies. In the latest study, led by Jens Melinder, a senior researcher at Stockholm University and published in the supplementary series of the Astrophysical Journal, astronomers inferred how much Lyman alpha light escapes from the galaxies and whether this amount correlates with various physical characteristics of the galaxies.
Melinder explained: “With the new observations, we have established a relationship between the amount of Lyman alpha escaping from galaxies and some physical properties of these galaxies. For instance, there is a clear correlation between the amount of cosmic dust a galaxy has and the amount of Lyman alpha light it emits. This was previously predicted, as dust absorbs light, but now we have quantified that effect.”
Astronomers also found a relationship between the escaping light and the total mass of all the stars in the galaxy, although this correlation is less clear. On the other hand, other properties, such as the number of new stars a galaxy forms, do not seem to correlate with the amount of Lyman alpha escaping from the galaxy.
Another interesting result is that galaxies observed in Lyman alpha light appear significantly larger than when viewed at other wavelengths. This effect has been observed before and aligns with theoretical expectations.
Peter Laursen from the Cosmic Dawn Center, who also participated in the research, explained: “We see a similar effect in computer simulations of galaxies with calculations on how Lyman alpha moves through gas clouds in the interstellar medium. This confirms that we have a quite good theoretical understanding of the physical processes involved.”
This effect is crucial to consider when observing distant galaxies where light from their outskirts is too weak for detectors to detect. Quantifying the effect will be useful for future observations of the most distant, ancient galaxies.
Melinder added: “These results will help explain observations of very distant galaxies observed with the Hubble Space Telescope and the James Webb Space Telescope. Understanding the detailed astrophysical properties of this type of galaxy is essential for developing theories about how the first galaxies formed and evolved.”
