Exploring the interplay between star formation efficiency and dust in regulating the UV luminosity of early systems in the JWST and ALMA era

Abstract

James Webb Telescope (JWST) observations have unveiled numerous galaxy candidates between $z \sim 9 - 16.5$, hinting at an over-abundance of sources at the bright-end of the UV luminosity function (UV LF) at z $\gsim$ 11. Complementarily, the Atacama Large Millimetre Array (ALMA) has been yielding dust mass estimates at $z \sim 5 - 7$. In this work, we develop an analytic formalism baselined against ALMA results, jointly exploring the impact of bursty star formation and its associated dust enrichment, on the visibility of early galaxies, while also modelling sources scattered off the main sequence of star formation. We incorporate dust production in type II Supernovae, dust destruction, ejection, growth and sputtering. Our key results are: (i) explaining the UV LF at $z \sim 5 - 13$ requires an average star formation efficiency that evolves as $f_*(z) = 10^{0.13z-3.5}$, with a number of observations exceeding this main sequence by a factor of 10; (ii) The dust enrichment of early systems is driven by dust production in SNII ejecta, while growth and sputtering impact the dust mass by 60\% and 40\% respectively at $z \sim 7$; (iii) galaxies at $z \gsim 9$ can retain significant dust, reaching average dust-to-stellar mass ratios of 0.19\% (0.14\%) at $z \sim 9$ ($z \sim 11$). Dust attenuation decreases with redshift as dust becomes increasingly dispersed within halos; (iv) observations by ALMA at $z \sim 5$ and 7 are not representative of the average population that makes up the UV LF; (v) assuming all stars to have formed instantaneously results in a high light-to-mass ratio. This naturally results in our model yielding a lower limit on the stellar mass contained in a halo, also under-predicting the observed stellar mass function.