{"paper":{"title":"Interpreting the strong clustering of ultra-diffuse galaxies by halo spin bias","license":"http://creativecommons.org/licenses/by/4.0/","headline":"Ultra-diffuse galaxies cluster strongly because they occupy high-spin dark matter halos.","cross_cats":[],"primary_cat":"astro-ph.GA","authors_text":"Cheng Li, Houjun Mo, Qinglin Ma, Yangyao Chen","submitted_at":"2025-12-19T16:19:31Z","abstract_excerpt":"We use the IllustrisTNG300-ODM simulation to investigate the spin bias of low-mass halos and its connection to the strong clustering of ultra-diffuse galaxies (UDGs) reported by Zhang et al. (2025). By comparing two halo spin definitions-one using only bound particles ($\\lambda_{\\rm b}$) and another including unbound particles ($\\lambda_{\\rm a}$)-we demonstrate that the spin bias of low-mass halos critically depends on the definition. While $\\lambda_{\\rm a}$ yields stronger clustering for higher-spin halos at all masses, $\\lambda_{\\rm b}$ produces an inverted trend below $M_{\\rm h}\\sim 10^{11}"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"Using an empirical model implemented in SDSS-like mocks, we link the stellar surface-mass-density (Σ_*) of a galaxy to λ_a of its host halo and find an anti-correlation that more diffuse dwarfs tend to reside in higher-spin halos. The model naturally reproduces the observed strong clustering of UDGs within the standard ΛCDM framework without invoking exotic assumptions such as self-interacting dark matter.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The empirical anti-correlation between stellar surface-mass-density Σ_* and halo spin λ_a (including unbound particles) is assumed to hold across the relevant mass range and environments; if this link is driven by the same selection effects that define the observed UDG sample, the reproduction of clustering becomes partly tautological.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Strong clustering of ultra-diffuse galaxies is reproduced in ΛCDM by linking lower stellar surface density to higher host-halo spin measured with unbound particles.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"Ultra-diffuse galaxies cluster strongly because they occupy high-spin dark matter halos.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"dcb469ca19a84c0dc29af562ecc5f429c0686911102811881209ad75d243fa6a"},"source":{"id":"2512.17742","kind":"arxiv","version":2},"verdict":{"id":"cecf208f-5039-4b23-9a85-5f2e15c97fe0","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-16T20:51:41.785133Z","strongest_claim":"Using an empirical model implemented in SDSS-like mocks, we link the stellar surface-mass-density (Σ_*) of a galaxy to λ_a of its host halo and find an anti-correlation that more diffuse dwarfs tend to reside in higher-spin halos. The model naturally reproduces the observed strong clustering of UDGs within the standard ΛCDM framework without invoking exotic assumptions such as self-interacting dark matter.","one_line_summary":"Strong clustering of ultra-diffuse galaxies is reproduced in ΛCDM by linking lower stellar surface density to higher host-halo spin measured with unbound particles.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The empirical anti-correlation between stellar surface-mass-density Σ_* and halo spin λ_a (including unbound particles) is assumed to hold across the relevant mass range and environments; if this link is driven by the same selection effects that define the observed UDG sample, the reproduction of clustering becomes partly tautological.","pith_extraction_headline":"Ultra-diffuse galaxies cluster strongly because they occupy high-spin dark matter halos."},"references":{"count":1,"sample":[{"doi":"10.48550/arxiv.2209.07691","year":2016,"title":"V., 2016, ApJ, 824, 79 Aghanim N., et al., 2020, A&A, 641, A6 Amorisco N","work_id":"43631aa3-2576-48db-b207-5e32593df8b3","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":1,"snapshot_sha256":"591af98d1d2da8575bedb9259a2c66d37c6f1cbdd88d80c680e3cedfdea0e6af","internal_anchors":0},"formal_canon":{"evidence_count":2,"snapshot_sha256":"ee347bf22c418377679111e2e4b13001fbc8bf87caceae3e12ffcd22fafb06ed"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}