UV Slopes At All Redshifts Are Consistent with H=1 Stochastic Star Formation Histories

TL;DR

This study demonstrates that UV-slope distributions across all redshifts align with models assuming stochastic galaxy growth with a Hurst parameter of 1, challenging the need for exotic stellar populations in early galaxies.

Contribution

It shows that UV-slope data at all redshifts are consistent with H=1 stochastic star formation histories, providing a unified explanation for galaxy growth without exotic assumptions.

Findings

UV-slope distributions match H=1 stochastic models at all redshifts.

Median UV-slope at z=0 agrees with local starburst measurements.

Early galaxies' UV slopes can be explained without exotic stellar populations.

Abstract

Multiple investigations support describing galaxy growth as a stochastic process with correlations over a range of timescales governed by a parameter, $H$, empirically and theoretically constrained to be near unity. Here, we show that the distribution of UV-slopes, $\beta$, derived from an ensemble of theoretical $H=1$ star formation histories (SFHs) is consistent with data at all redshifts $z\le 16$. At $z=0$, the median value $\langle\beta_{H=1}\rangle=-2.27$ agrees well with the canonical $\beta_0=-2.23$ for local starbursts \citep{meurer1999}. At $4\lesssim z\lesssim16$, JWST data span the model distribution's 2nd to 98th percentiles. Values of $-2.8\le \beta \le -2.5$ should be common in early galaxies without reference to exotic stellar populations -- arising solely from a null hypothesis of $H=1$ for the underlying diversity of galaxy growth histories. Future data should be interpreted with this fact in mind.