Study Links UV Brightness in Early-Type Galaxies to Stars from Dissolved Globular Clusters
A new study using Hubble Space Telescope data finds that the mysterious far-ultraviolet brightening seen in massive early-type galaxies is likely caused by second-generation stars originally formed in globular clusters that later dissolved into their host galaxies. The research identifies a specific combination of four photometric passbands that serves as a 'colour-colour fingerprint' sensitive to correlated enhancements in helium abundance and nitrogen-to-iron ratios. The findings support a unified explanation for two previously puzzling mass-dependent properties of early-type galaxies — their UV upturn and their anomalous nitrogen and sodium abundances.
Astronomers have used new Hubble Space Telescope WFC3 observations of two early-type galaxies — one UV-bright and one UV-weak — to test whether the so-called 'UV upturn' phenomenon and anomalous elemental abundance ratios share a common origin. The study, accepted for publication as a Monthly Notices of the Royal Astronomical Society Letter, finds that passbands F275W and F390W, combined with archival F475W and F850LP data, are uniquely sensitive to simultaneous enhancements in helium abundance (Y) and nitrogen-to-iron ratio ([N/Fe]). Radial profile analysis shows that while the optical colour F475W–F850LP decreases outward in both galaxies — consistent with known metallicity gradients — the UV colour F275W–F390W increases outward, as predicted if the UV upturn is driven by helium- and nitrogen-enriched second-generation stars from dissolved metal-rich globular clusters. The UV-bright galaxy displays a significantly steeper radial gradient in F275W–F390W and a higher implied fraction of chemically enriched stars than the UV-weak galaxy, consistent with the 'multiple populations' (MP) scenario proposed by the study's lead author. The results suggest that dissolved globular clusters are a key driver of the chemical and photometric diversity observed among massive early-type galaxies.
What's missing
The study is based on only two galaxies (one FUV-bright, one FUV-weak), limiting the statistical generalisability of the results.
What different sources said
- arXiv astro-phCenter
A Colour-colour Fingerprint Links the UV Upturn in Early-type Galaxies to Second-generation Stars from Dissolved Globular Clusters
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