Euclid Q1 Data Shows Disc Breaks Track Galaxy Structural Evolution Over Cosmic Time
Euclid Q1 observations demonstrate that disc breaks trace the structural maturation of galaxies, increasing in frequency and prominence toward the present epoch. The findings support inside-out disc growth scenarios and highlight the value of wide-field high-resolution imaging for evolutionary studies. Larger samples and multi-wavelength follow-up are required to confirm causality.
The team examined 1,200 galaxies with stellar masses above 10^9.5 solar masses across 0<z<1 using Euclid's high-resolution VIS imaging and NISP photometry. They fitted broken exponential profiles to radial light distributions and cross-matched with photometric redshifts and stellar population parameters derived from ground-based surveys. Breaks appear in 35% of discs at z0.2 versus 18% at z0.8, with outer disc scale lengths increasing by 0.4 dex on average since z=1.
This pattern aligns with hydrodynamical simulations where secular processes and minor mergers redistribute stars outward after z~1, producing the observed up-bending profiles. It contradicts earlier claims from smaller HST samples that breaks are largely primordial. The result supplies the first statistically robust observational timeline for when disc outskirts assemble.
Future Euclid data releases will extend the sample to 10^5 galaxies and add spectroscopic redshifts, allowing separation of environmental and mass-driven effects. Ground-based IFU follow-up on the same targets can test whether breaks coincide with age or metallicity gradients predicted by inside-out growth models.
Euclid DR1: Disc break fraction at z<0.1 will exceed 40% in mass-selected samples above 10^10 solar masses within 18 months of release.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2609.26877)
- [2]Supporting Source(https://arxiv.org/abs/2305.06367)