{
  "abstract": "In the conventional spherical overdensity definition of a dark matter halo, masses and radii, e.g. $M_{200{\\rm m}}$ and $r_{200{\\rm m}}$, are equivalent. However, halos do exhibit a physical boundary at the splashback radius $r_{\\rm sp}$, which manifests as a sharp drop in density. Splashback radii are now routinely measured in stacked weak lensing profiles, but the expected trend of decreasing $r_{\\rm sp}/r_{200{\\rm m}}$ with mass has not been verified in observed galaxy groups or clusters. In this work, we show that several observational effects conceal the predicted mass-size relation. In particular, we quantify the impact of systematics on the mean density and lensing profiles of mock-observed halo samples, which are created by applying a realistic cluster-finding procedure to dark matter-only simulations. We reproduce the known impact of projection: preferentially observing systems in overdense regions. But, differing from previous works, we show that the same projection effect, combined with scatter in observed luminosities, causes a significant Eddington bias in the derived mass-observable relation and a complex suppression in mean density profiles over all radial scales. The magnitude of this effect is mass-dependent and coupled to the cluster-finding procedure and survey properties, making it challenging to model simply and motivating full forward-modeling of observed group and cluster samples. However, we demonstrate that a simple mitigation approach, effectively a weak lensing mass calibration, does well in approximately recovering the true mass-size relation. Finally, we show that only severe miscentering can bias the measurement of the halo size, but any miscentering can increase the measurement uncertainty.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.36531",
  "author_total": 2,
  "authors": [
    {
      "name": "Charlie T. Mpetha"
    },
    {
      "name": "Benedikt Diemer"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fqg18r688j6dn.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.36531",
  "fulltext_url": null,
  "id": "fqg18r688j6dn",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.36531",
  "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.CO"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7224121061",
  "pdf_url": "https://arxiv.org/pdf/2610.36531",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-27",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fqg18r688j6dn.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:50Z",
      "native_id": "2610.36531",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.36531"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    }
  ],
  "title": "Towards Reliably Measuring the Mass-Size Relation of Dark Matter Halos: Impact of projection, miscentering and Eddington bias",
  "title_text": "Towards Reliably Measuring the Mass-Size Relation of Dark Matter Halos: Impact of projection, miscentering and Eddington bias",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:50Z",
  "url": "https://research.draconitic.com/paper/fqg18r688j6dn",
  "venue": "arXiv",
  "versions": []
}