Stochastic modelling of star-formation histories I: the scatter of the star-forming main sequence
Abstract
We present a framework for modelling the star-formation histories of galaxies as a stochastic process. We define this stochastic process through a power spectrum density with a functional form of a broken power law. Star-formation histories are correlated on short time-scales, the strength of this correlation described by a power-law slope, α, and they decorrelate to resemble white noise over a time-scale that is proportional to the time-scale of the break in the power spectrum density, τbreak. We use this framework to explore the properties of the stochastic process that, we assume, gives rise to the log-normal scatter about the relationship between star-formation rate and stellar mass, the so-called galaxy star-forming main sequence. Specifically, we show how the measurements of the normalization and width (σMS) of the main sequence, measured in several passbands that probe different time-scales, give a constraint on the parameters of the underlying power spectrum density. We first derive these results analytically for a simplified case where we model observations by averaging over the recent star-formation history. We then run numerical simulations to find results for more realistic observational cases. As a proof of concept, we use observational estimates of the main sequence scatter at z ∼ 0 and M⋆ ≈ 1010 M⊙ measured in H α, UV+IR, and the u-band. The result is degenerate in the τbreak-α space, but if we assume α = 2, we measure \tau _break=170^{+169}_{-85} Myr. This implies that star-formation histories of galaxies lose `memory' of their previous activity on a time-scale of ∼200 Myr.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2019
- DOI:
- 10.1093/mnras/stz1449
- arXiv:
- arXiv:1901.07556
- Bibcode:
- 2019MNRAS.487.3845C
- Keywords:
-
- galaxies: evolution;
- galaxies: star formation;
- galaxies: statistics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 24 pages, 15 figures, submitted to MNRAS, comments welcome