Galaxy mergers in the epoch of reionization – I. A JWST study of pair fractions, merger rates, and stellar mass accretion rates at <i>z</i> = 4.5–11.5
ABSTRACT We present a full analysis of galaxy major merger pair fractions, merger rates, and mass accretion rates, thus uncovering the role of mergers in galaxy formation at the earliest previously unexplored epoch of $4.5&lt; z&lt; 11.5$. We target galaxies with masses $\log _{10}(\mathrm{\it M}_*/\mathrm{M}_\odot) = 8.0 {\!-\!} 10.0$, utilizing data from eight JWST Cycle-1 fields [CEERS (Cosmic Evolution Early Release Science Survey), JADES (JWST Advanced Deep Extragalactic Survey) GOODS-S, NEP-TDF (North Ecliptic Pole Time-Domain Field), NGDEEP (Next-Generation Deep Extragalactic Exploratory Public Survey), GLASS (Grism Lens Amplified Survey from Space), El-Gordo, SMACS-0723, MACS-0416], covering an unmasked area of 189.36 $\mathrm{arcmin}^2$. We develop a new probabilistic pair-counting methodology that integrates full photometric redshift posteriors and corrects for detection incompleteness to quantify close pairs with physical projected separations between 20 and 50 kpc. Our analysis reveals an increase in pair fractions up to $z = 8$, reaching $0.211 \pm 0.065$, followed by a statistically flat evolution to $z = 11.5$. We find that the galaxy merger rate increases from the local Universe up to $z = 6$ and then stabilizes at a value of $\sim 6$ Gyr$^{-1}$ up to $z = 11.5$. The redshift evolution of both pair fractions and merger rates is well described by a power-law plus exponential model. In addition, we measure that the average galaxy increases its stellar mass due to mergers by a factor of $2.77 \pm 0.99$ from redshift $z = 10.5$ to $z = 5.0$. Lastly, we investigate the impact of mergers on galaxy stellar mass growth, revealing that mergers contribute as much as $71 \pm 25~{{\ \rm per\ cent}}$ to galaxy stellar mass growth. This indicates that mergers drive about half of galaxy assembly at high redshift.
Authors
- Jake Summers (ORCID: https://orcid.org/0000-0002-7265-7920)
- Rogier A. Windhorst (ORCID: https://orcid.org/0000-0001-8156-6281)
- Rolf A. Jansen (ORCID: https://orcid.org/0000-0003-1268-5230)
- Norman A. Grogin (ORCID: https://orcid.org/0000-0001-9440-8872)
- Nimish P. Hathi (ORCID: https://orcid.org/0000-0001-6145-5090)
- K. J. Duncan (ORCID: https://orcid.org/0000-0001-6889-8388)
- Nathan Adams (ORCID: https://orcid.org/0000-0003-4875-6272)
- Russell E. Ryan (ORCID: https://orcid.org/0000-0003-0894-1588)
- Madeline A. Marshall (ORCID: https://orcid.org/0000-0001-6434-7845)
- Christopher J. Conselice (ORCID: https://orcid.org/0000-0003-1949-7638)
- Seth H. Cohen (ORCID: https://orcid.org/0000-0003-3329-1337)
- Anton M. Koekemoer (ORCID: https://orcid.org/0000-0002-6610-2048)
- Dan Coe (ORCID: https://orcid.org/0000-0001-7410-7669)
- Jordan C. J. D’Silva (ORCID: https://orcid.org/0000-0002-9816-1931)
- Simon P. Driver (ORCID: https://orcid.org/0000-0001-9491-7327)
- Benne W. Holwerda (ORCID: https://orcid.org/0000-0002-4884-6756)
- Haojing Yan (ORCID: https://orcid.org/0000-0001-7592-7714)
- Brenda Frye (ORCID: https://orcid.org/0000-0003-1625-8009)
- Xiaojing Du (ORCID: https://orcid.org/0000-0002-5199-7192)
- James Trussler (ORCID: https://orcid.org/0000-0002-9081-2111)
- Nor Pirzkal (ORCID: https://orcid.org/0000-0003-3382-5941)
- Thomas Harvey (ORCID: https://orcid.org/0000-0002-8649-2936)
- Duncan Austin (ORCID: https://orcid.org/0000-0003-0519-9445)
- Christopher N. A. Willmer (ORCID: https://orcid.org/0000-0001-9262-9997)
- M. Nonino (ORCID: https://orcid.org/0000-0001-6342-9662)
- A. S. G. Robotham (ORCID: https://orcid.org/0000-0003-0429-3579)
- Lewi Westcott (ORCID: https://orcid.org/0009-0008-8642-5275)
- Qiong Li (ORCID: https://orcid.org/0000-0002-3119-9003)
- Leonardo Ferreira (ORCID: https://orcid.org/0000-0002-8919-079X)
- Rafael Ortiz (ORCID: https://orcid.org/0000-0002-6150-833X)
- Qiao Duan (ORCID: https://orcid.org/0009-0009-8105-4564)
- Honor Harris (ORCID: https://orcid.org/0009-0005-0817-6419)
- Thomas J. Broadhurst (ORCID: https://orcid.org/0000-0002-5807-4411)
Institutions
- Ikerbasque (ES)
- Herzberg Institute of Astrophysics (CA)
- Space Telescope Science Institute (US)
- University of Arizona (US)
- University of Louisville (US)
- Johns Hopkins University (US)
- University of the Basque Country (ES)
- The University of Western Australia (AU)
- University of Victoria (CA)
- Trieste Astronomical Observatory (IT)
- University of Manchester (GB)
- Kentucky Science Center (US)
- Royal Observatory (GB)
- Université Bourgogne Franche-Comté (FR)
- ARC Centre of Excellence for All-sky Astrophysics (AU)
- International Centre for Radio Astronomy Research (AU)
- Wake Forest University (US)
- Arizona State University (US)
- University of Baltimore (US)
- University of Missouri (US)
- University of Edinburgh (GB)
Publication Details
- Journal
- Monthly Notices of the Royal Astronomical Society
- Published
- 2025-04-17
- DOI
- https://doi.org/10.1093/mnras/staf638
- Citations
- 34
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 39.26