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Revealing the Universe's Secrets: Local Galaxies Unlock Mysteries of Distant Galaxies


Two of the 45 galaxies in the sample of local galaxies, observed with the Hubble Space Telescope. The colors indicate infrared, visual, and ultraviolet light from the stars in the galaxies. Credit: Melinder et al. (2023)
Two of the 45 galaxies in the sample of local galaxies, observed with the Hubble Space Telescope. The colors indicate infrared, visual, and ultraviolet light from the stars in the galaxies. Credit: Melinder et al. (2023)

In a groundbreaking effort to gain deeper insights into the nature of distant galaxies, an international team of astronomers has constructed a comprehensive sample of local galaxies for detailed analysis. By examining the relationship between the amount of light that escapes from a galaxy and its physical properties, researchers have shed light on the interpretation of observations made on galaxies in the early universe. This study has profound implications for understanding the astrophysics of distant galaxies and their formation and evolution.


The Mysteries of Lyman Alpha Light


The study of galaxies in the early universe often relies on the examination of a specific type of ultraviolet light known as "Lyman alpha." This particular light is emitted by the gas surrounding the hottest stars, making it an ideal tool for studying highly star-forming galaxies. However, unlike other types of light, the wavelength and direction of Lyman alpha light are influenced by numerous complex processes both inside and outside galaxies. The path of this light is convoluted, as it traverses regions with different physical conditions, leading to changes in its wavelength and absorption of an indeterminate fraction of the light.


Challenges of Interpreting Lyman Alpha Light


Galaxies in the distant universe present significant challenges due to their faintness and small size, making their observation and analysis incredibly difficult. To overcome this hurdle, the international team of astronomers embarked on building a "reference" sample of galaxies within our local neighborhood. While these galaxies are still hundreds of millions of light-years away, their proximity enables detailed study using a multitude of telescopes worldwide, both ground-based and in space.


Introducing the Lyman Alpha Reference Sample (LARS)


The Lyman Alpha Reference Sample, or LARS, represents an invaluable collection of local galaxies that have provided crucial insights into the nature of distant galaxies. In the recently published study, led by Jens Melinder, Senior Researcher at the University of Stockholm, the astronomers investigated the correlation between the escape fraction of Lyman alpha light and various physical properties of the galaxies within the sample. Their findings shed light on the intricate relationship between Lyman alpha light and cosmic dust, as well as the total mass of stars in a galaxy.



Correlations Unveiled


The research team's observations unveiled a clear connection between the amount of Lyman alpha light that escapes a galaxy and the presence of cosmic dust within it. This correlation confirms the long-held expectation that dust absorbs light, providing a quantitative measure of its impact. Furthermore, the astronomers identified a less explicit correlation between the escaping light and the total mass of stars within a galaxy. Conversely, no significant correlation was found between the escape fraction of Lyman alpha light and the rate of star formation in the galaxy.


Size Discrepancy and Theoretical Understanding


One intriguing finding of the study was the observation that galaxies appear considerably larger when observed in Lyman alpha light compared to other wavelengths. This effect, previously noted in theoretical simulations, aligns with the team's understanding of the complex physics governing the propagation of Lyman alpha light through interstellar gaseous clouds. Recognizing and accounting for this effect is crucial when studying distant galaxies, as the faint light from their outskirts may go undetected or fall outside the range of detectors.


Implications for Future Observations


The quantification of the observed effects holds significant implications for future observations of the earliest and most distant galaxies using advanced telescopes such as the Hubble and James Webb Space Telescopes. The newfound understanding of the detailed astrophysics of these galaxies is instrumental in developing comprehensive theories regarding the formation and evolution of the first galaxies in the universe.


Journal Information: Jens Melinder et al, The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission, The Astrophysical Journal Supplement Series (2023). DOI: 10.3847/1538-4365/acc2b8



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