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arXiv · 2608.25671

Stellar mass growth in COSMOS-Web: a mass-complete main sequence to z ~ 8 and its consistency with GSMF evolution

M. P. Koprowski·K. Lisiecki·P. Sawant·J. V. Wijesekera
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Abstract

The star-forming main sequence (MS) links the instantaneous star-formation rate of galaxies to their stellar-mass growth and therefore to the evolution of the galaxy stellar mass function (GSMF). We determine a mass-complete MS in COSMOS-Web out to z=8 and test whether its mass and redshift dependence is consistent with the observed evolution of the GSMF. We stacked 251,462 star-forming galaxies in Herschel and JCMT maps and corrected the far-infrared fluxes for blending using forward-modeled maps. We combined the resulting infrared luminosities with the unobscured ultraviolet emission to derive total star-formation rates and fitted a redshift-dependent MS. We independently measured the quiescent fraction and evolved the observed z=8 COSMOS-Web GSMF forward within a continuity-equation framework including stellar-mass return, suppression of in-situ growth by the quiescent fraction, and mergers. The MS is well described by a power law at low masses with a redshift-dependent turnover toward high masses. We measure a low-mass slope of gamma=1.215+/-0.028, implying a mildly increasing specific star-formation rate with stellar mass. The GSMF evolved using this relation follows the observed progressive flattening of the low-mass end substantially better than the literature MS prescriptions considered here. Mergers change the low-mass number densities by <=0.2 dex by z~0.65 and have little effect on the slope. Small differences in MS normalization also accumulate strongly, producing large differences in the evolved GSMF after several Gyr. The observed GSMF evolution provides an independent integral test of the MS. Our results favor a mildly super-linear low-mass MS and show that both its slope and normalization must be measured accurately to reproduce the buildup of the galaxy stellar-mass distribution.

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M. P. Koprowski, K. Lisiecki, P. Sawant, J. V. Wijesekera. 2026-08-26. Stellar mass growth in COSMOS-Web: a mass-complete main sequence to z ~ 8 and its consistency with GSMF evolution. https://arxiv.org/abs/2608.25671

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