{
  "abstract": "Mergers are a crucial channel of galaxy growth, but their role relative to star formation remains uncertain at high redshift. Here we investigate merger rates and merger-driven stellar mass assembly for galaxies with stellar mass $M_\\star \\gtrsim 10^8 \\, {\\rm M_{\\odot}}$ at $z\\simeq 5-11$, by combining complementary theoretical approaches within $Λ$CDM. These include the DECODE semi-empirical model, the TNG100 and EAGLE hydrodynamical simulations, and the \\textsc{L-Galaxies} semi-analytical model, together with the Millennium and TNG100-Dark simulations used to examine dark matter subhalo statistics and merger timescales. This compares models with different treatments of baryonic physics and galaxy-halo connections. We find that dark matter-only simulations predict merger timescales $\\sim 30\\%$ longer than those inferred from cosmological simulations including baryons. Galaxy major merger ($M_{\\rm \\star,sat} / M_{\\rm \\star,cen} > 0.25$) rates are high at cosmic dawn and increase towards earlier epochs, reaching $\\sim 1/{\\rm Gyr}$ at $z\\sim 5$ and peaking at $\\sim 3/{\\rm Gyr}$ at $z\\sim 8$. Despite these high rates, mergers contribute only $\\lesssim 10\\%$ of the total cosmic stellar mass density evolution. The ex-situ stellar mass fraction ranges from a few percent to $\\sim 20\\%$ for all galaxies at $z\\gtrsim 5$, across different models and simulations. Their broad agreement implies that stellar mass assembly at cosmic dawn is dominated by in-situ star formation rather than mergers. These findings suggest that the high pair fractions identified by JWST may not directly trace efficient ex-situ stellar mass growth, highlighting the need for physically motivated merger timescales to interpret galaxy assembly in the early Universe.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.17575",
  "author_total": 16,
  "authors": [
    {
      "name": "Hao Fu"
    },
    {
      "name": "Mohammadreza Ayromlou"
    },
    {
      "name": "Francesco Shankar"
    },
    {
      "name": "Lars Hernquist"
    },
    {
      "name": "Andrea Lapi"
    },
    {
      "name": "Daniel Roberts"
    },
    {
      "name": "Feng Yuan"
    },
    {
      "name": "Maulik Bhatt"
    },
    {
      "name": "Evgenii Chaikin"
    },
    {
      "name": "Simona Gallerani"
    },
    {
      "name": "Luca Graziani"
    },
    {
      "name": "Antonio La Marca"
    },
    {
      "name": "George Mountrichas"
    },
    {
      "name": "Yingjie Peng"
    },
    {
      "name": "Haocheng Wang"
    },
    {
      "name": "Kai Wang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/bk35gn7ecxynj.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.17575",
  "fulltext_url": null,
  "id": "bk35gn7ecxynj",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.17575",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7221804461",
  "pdf_url": "https://arxiv.org/pdf/2610.17575",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/bk35gn7ecxynj.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:11Z",
      "native_id": "2610.17575",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.17575"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "Mergers may not be the main channel for galaxy stellar mass growth at redshift $z\\gtrsim5$: Predictions from cosmological hierarchical models and simulations",
  "title_text": "Mergers may not be the main channel for galaxy stellar mass growth at redshift z≳5: Predictions from cosmological hierarchical models and simulations",
  "type": "preprint",
  "updated_at": "2026-10-30T12:29:11Z",
  "url": "https://research.draconitic.com/paper/bk35gn7ecxynj",
  "venue": "arXiv",
  "versions": []
}