Probing the star formation main sequence down to $10^7 M_{\odot}$ at $1 < z < 9$

Mérida, Rosa M. (author), Bradač, Maruša (author), Martis, Nicholas S. (author), Rihtaršič, Gregor (author), Harshan, Anishya (author), Judež, Jon (author)

The main sequence of star-forming galaxies (SFGMS or MS) is a fundamental scaling relation that provides a global framework for studying galaxy formation and evolution, as well as an insight into the complex star formation histories (SFHs) of individual galaxies. In this work, we combine large-area pre-JWST surveys (COSMOS2020, CANDELS), which probe high-$M_\star$ sources ($>10^9\,M_\odot$), with SHARDS/CANDELS FAINT and JWST data from CANUCS, CEERS, JADES, and UNCOVER, to obtain a high-$z$, star formation rate (SFR) and stellar mass ($M_\star$) complete sample spanning both high- and low-$M_\star$ regimes. Completeness in both $M_\star$ and the SFR is key to avoiding biases introduced by low-mass, highly star-forming objects. Our combined dataset is 80% complete down to $10^{7.6}\,M_\odot$ at $z\sim1$ ($10^{8.8}\,M_\odot$ at $z\sim9$). The overall intrinsic MS slope (based on the SFR$_{100}$ and $M_\star$ derived with \texttt{Dense Basis} and nonparametric SFHs) shows little evolution up to $z\sim5$, with values $\sim0.7 - 0.8$. The slope in the low-$M_\star$ regime becomes steeper than that in the high-$M_\star$ end at least up to $z\sim5$, but the strength of this change is highly dependent on the assumptions made on the symmetry of the uncertainties in $M_\star$ and SFR. If real, the steepening suggests reduced star formation efficiency or declining gas content with decreasing $M_\star$. The transition between the low-$M_\star$ regime and the canonical MS occurs around $10^{9.5}\,M_\odot$, independent of $z$. This critical value may coincide with the assembly of galaxies' disks, which can provide a mechanism for self-regulation that stabilizes them against feedback. The intrinsic scatter is compatible with canonical estimates, also at low-$M_\star$, ranging from $0.2-0.3$ dex. This is indicative of rapid variations in star formation being averaged out over $\lesssim100$ Myr.

• Language: English
• Keywords: galaxies, galaxy formation, photometry, high-redshift
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FMF - Faculty of Mathematics and Physics
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 18 str.
• Numbering: Vol. 707, art. no. A5
• PID: 20.500.12556/RUL-180814
• UDC: 524.8
• ISSN on article: 1432-0746
• DOI: 10.1051/0004-6361/202557448
• COBISS.SI-ID: 265913603
• Publication date in RUL: 17.03.2026

Record is a part of a journal

• Title: Astronomy & astrophysics
• Shortened title: Astron. astrophys.
• Publisher: EDP Sciences
• ISSN: 1432-0746
• COBISS.SI-ID: 392577

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: galaksije, nastanek galaksij, fotometrija, rdeči premik