How Bursty is Star Formation at <i>z</i> &gt; 5?

Abstract Motivated by observational evidence from JWST and theoretical results from cosmological simulations, we use a simple parametric, phenomenological model to test to what extent bursty star formation (SF) with standard initial mass function, no continuous SF, no mergers, and no dust can account for the observed properties in the M UV versus M * plane of galaxies at redshifts z &gt; 5. We find that the simplest model that fits the data has a quiescence period between bursts Δ t ∼ 100 Myr, and the stellar mass in each galaxy grows linearly as a function of time from z = 12 to z = 5 (i.e., repeated bursts in each galaxy produce approximately equal mass in stars). The distribution of burst masses across different galaxies follows a power-law <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mi>N</mml:mi> <mml:mo>/</mml:mo> <mml:mi>d</mml:mi> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> with slope α ∼ −2. At z &gt; 9–10 the observed galaxy population typically had only one or two bursts of stars formation, hence the observed stellar masses at these redshifts (reaching M * ∼ 10 10 M ⊙ ) roughly represent the distribution of masses formed in one burst.