Letter to the Editor

Evolution of the star formation rate surface density main sequence

Insights from a semi-analytic simulation since z = 12

¹ Astronomical Observatory Institute, Faculty of Physics and Astronomy, Adam Mickiewicz University, ul. Słoneczna 36, 60-286 Poznań, Poland
² Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38205 La Laguna, Tenerife, Spain
⁴ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁵ INAF, Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste, Italy
⁶ SISSA, Via Bonomea 265, I-34136 Trieste, Italy
⁷ IFPU, Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy

^⋆ Corresponding author; jakub.nadolny@amu.edu.pl, quba.nadolny@gmail.com

Received: 29 October 2024
Accepted: 28 November 2024

Abstract

Context. Recent high-redshift (z >  4) spatially resolved observations with the James Webb Space Telescope have shown the evolution of the star formation rate (SFR) surface density (Σ_SFR) and its main sequence in the Σ_SFR − M_* diagram (Σ_SFRMS). The Σ_SFRMS is already observed at cosmic morning (z ∼ 7.5). The use of Σ_SFR is physically motivated because it is normalized by the area in which the star formation occurs, and this indirectly considers the gas density. The Σ_SFR − M_* diagram has been shown to complement the widely used (specific) SFR-M_*, particularly when selecting passive galaxies.

Aims. We establish the Σ_SFR evolution since z = 12 in the framework of the L-GALAXIES2020 semi-analytical model (SAM), and we interpret recent observations.

Methods. We estimated Σ_SFR(–M_*) and the cosmic star formation rate density (CSFRD) for the simulated galaxy population and for the subsamples, which were divided into stellar mass bins in the given redshift.

Results. The simulated Σ_SFR decreases by ∼3.5 dex from z = 12 to z = 0. We show that galaxies with different stellar masses have different paths of Σ_SFR evolution. We find that Σ_SFRMS is already observed at z ∼ 11. The simulated Σ_SFRMS agrees with the observed one at z = 0, 1, 2, 5, and 7.5 and with individual galaxies at z >  10. We show that the highest Σ_SFRMS slope of 0.709 ± 0.005 is at z ∼ 3 and decreases to ∼0.085 ± 0.003 at z = 0. This is mostly driven by a rapid decrease in SFR with an additional size increase for the most massive galaxies in this redshift range. This coincides with the dominance of the most massive galaxies in the CSFRD from the SAM. Observations show the same picture, in which the Σ_SFR evolutionary path depends on the stellar mass, that is, more massive galaxies have higher Σ_SFR at all redshifts. Finally, using the slope and normalization evolution, we derived the simulated Σ_SFRMS as a function of stellar mass and redshift.