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

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.