Decoding the Star-Forming Main Sequence or: How I Learned to Stop Worrying and Love the Central Limit Theorem

Understand

Star-formation rates (SFR) of disk galaxies strongly correlate with stellar mass, with a small dispersion in SSFR at fixed mass, sigma~0.3 dex.

• With such small scatter this star-formation main sequence (SFMS) has been interpreted as deterministic and fundamental.
• Here we demonstrate that it is a simple consequence of the central limit theorem.
• Our derivation begins by approximating in situ stellar mass growth as a stochastic process, much like a random walk (where the expectation of SFR at any time is equal to the SFR at the previous time).