{
  "abstract": "We present deep, wide-field Magellan/Megacam imaging of the ultrafaint Milky Way (MW) satellites Grus II (Gru II) and Horologium II (Hor II), with the aim of deriving improved constraints on their distances, luminosities, and structural parameters, while also searching for possible signs of tidal disturbance. Our photometry reaches ∼3 mag deeper than the discovery data, enabling robust measurements of these quantities. Both systems exhibit color–magnitude diagrams consistent with old (∼12.5 Gyr), very metal-poor stellar populations. We find Gru II to be at a distance of 52.3 ± 1.9 kpc, with absolute magnitude M V = −4.07 ± 0.50 mag, while fitting an exponential profile to the stellar distribution yields a half-light radius of 6 . ′ ⁡ 8 ± 0 . ′ ⁡ 5 (103 ± 9 pc), and ellipticity ϵ = 0.25 ± 0.07. Hor II is further away at a distance of 72 . 4 − 5.5 + 5.9 kpc, with M V = −2.10 ± 0.44 mag, and is more compact with r h = 2 . ′ ⁡ 1 ± 0 . ′ ⁡ 2 ( 4 4 − 5 + 6 pc) and ϵ = 0.3 2 − 0.16 + 0.20 , adopting an exponential profile. Both galaxies lie within the typical size–luminosity locus of MW ultrafaint dwarfs. Gru II shows an asymmetric morphology including multidirectional clumpy features, some of which could be suggestive of tidal disturbance. We further identify and spectroscopically confirm a new distant member just outside 3 r h in Gru II, providing independent evidence for member stars at large projected radii. In contrast to Gru II, Hor II appears regular, with no significant extended structure detected to the surface-brightness limits of our data.",
  "abstract_shown": true,
  "affiliations": [
    "University of Arizona",
    "Stanford University",
    "Dartmouth College",
    "Rubin Observatory/AURA",
    "University of Chicago",
    "NSF-Simons AI Institute for the Sky (SkAI)",
    "NSF NOIRLab",
    "University of Virginia",
    "Lund University",
    "University of Tampa",
    "Queen’s University",
    "University of Surrey",
    "Space Telescope Science Institute",
    "Yale University",
    "University of Colorado Boulder",
    "Montana State University",
    "Universidad de Tarapacá",
    "University of Toronto",
    "ASTRAVEO LLC",
    "Applied Materials Inc."
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 34,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Deepthi S. Prabhu",
      "orcid": "0000-0002-8217-5626"
    },
    {
      "affs": [
        0
      ],
      "name": "David J. Sand",
      "orcid": "0000-0003-4102-380X"
    },
    {
      "affs": [
        1
      ],
      "name": "Anirudh Chiti",
      "orcid": "0000-0002-7155-679X"
    },
    {
      "affs": [
        2
      ],
      "name": "Burçin Mutlu-Pakdil",
      "orcid": "0000-0001-9649-4815"
    },
    {
      "affs": [
        2
      ],
      "name": "Sasha N. Campana",
      "orcid": "0009-0007-9488-7050"
    },
    {
      "affs": [
        3
      ],
      "name": "J. L. Carlin",
      "orcid": "0000-0002-3936-9628"
    },
    {
      "affs": [
        4,
        5
      ],
      "name": "A. P. Ji",
      "orcid": "0000-0002-4863-8842"
    },
    {
      "affs": [
        2
      ],
      "name": "Jaclyn Jensen",
      "orcid": "0000-0002-4350-7632"
    },
    {
      "affs": [
        6
      ],
      "name": "C. E. Martínez-Vázquez",
      "orcid": "0000-0002-9144-7726"
    },
    {
      "affs": [
        0
      ],
      "name": "Dennis Zaritsky",
      "orcid": "0000-0002-5177-727X"
    },
    {
      "affs": [
        7
      ],
      "name": "A. B. Pace",
      "orcid": "0000-0002-6021-8760"
    },
    {
      "affs": [
        8
      ],
      "name": "A. H. Riley",
      "orcid": "0000-0001-5805-5766"
    },
    {
      "affs": [
        9
      ],
      "name": "D. Crnojević",
      "orcid": "0000-0002-1763-4128"
    },
    {
      "affs": [
        4
      ],
      "name": "G. Limberg",
      "orcid": "0000-0002-9269-8287"
    },
    {
      "affs": [
        2
      ],
      "name": "Laura Congreve Hunter",
      "orcid": "0000-0001-5368-3632"
    },
    {
      "affs": [
        10
      ],
      "name": "Kristine Spekkens",
      "orcid": "0000-0002-0956-7949"
    },
    {
      "affs": [
        0
      ],
      "name": "Michael G. Jones",
      "orcid": "0000-0002-5434-4904"
    },
    {
      "affs": [
        11
      ],
      "name": "Amandine Doliva-Dolinsky",
      "orcid": "0000-0001-9775-9029"
    },
    {
      "affs": [
        12
      ],
      "name": "Paul Bennet",
      "orcid": "0000-0001-8354-7279"
    },
    {
      "affs": [
        6
      ],
      "name": "V. M. Placco",
      "orcid": "0000-0003-4479-1265"
    },
    {
      "affs": [
        2
      ],
      "name": "Quinn O. Casey",
      "orcid": "0009-0005-9002-4800"
    },
    {
      "affs": [
        2
      ],
      "name": "Guinevere Herron",
      "orcid": "0000-0003-4394-7491"
    },
    {
      "affs": [
        13
      ],
      "name": "W. Cerny",
      "orcid": "0000-0003-1697-7062"
    },
    {
      "affs": [
        7
      ],
      "name": "Nitya Kallivayalil",
      "orcid": "0000-0002-3204-1742"
    },
    {
      "affs": [
        6
      ],
      "name": "Y. Choi",
      "orcid": "0000-0003-1680-1884"
    },
    {
      "affs": [
        14
      ],
      "name": "Guy S. Stringfellow",
      "orcid": "0000-0003-1479-3059"
    },
    {
      "affs": [
        15
      ],
      "name": "D. L. Nidever",
      "orcid": "0000-0002-1793-3689"
    },
    {
      "affs": [
        16
      ],
      "name": "J. A. Carballo-Bello",
      "orcid": "0000-0002-3690-105X"
    },
    {
      "affs": [
        11
      ],
      "name": "M. Navabi",
      "orcid": "0000-0001-9438-5228"
    },
    {
      "affs": [
        6
      ],
      "name": "P. Massana",
      "orcid": "0000-0002-8093-7471"
    },
    {
      "affs": [
        17
      ],
      "name": "G. E. Medina",
      "orcid": "0000-0003-0105-9576"
    },
    {
      "affs": [
        11
      ],
      "name": "N. E. D. Noël",
      "orcid": "0000-0002-8282-469X"
    },
    {
      "affs": [
        18,
        19
      ],
      "name": "D. J. James",
      "orcid": "0000-0001-5160-4486"
    },
    {
      "name": "(MAGIC & DELVE Collaborations)"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/0p22bh3hcevrn.bib",
  "cited_by": 0,
  "doi": "10.3847/1538-4357/aea977",
  "fulltext_url": null,
  "id": "0p22bh3hcevrn",
  "issns": [
    "0004-637X",
    "1538-4357"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea977",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7165859499",
  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea977/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-14",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/0p22bh3hcevrn.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:11Z",
      "native_id": "10.3847/1538-4357/aea977",
      "source": "crossref",
      "url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea977"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Galaxies: Formation, Evolution, Phenomena",
      "subfield": "galaxies"
    }
  ],
  "title": "Deep Imaging of Grus II and Horologium. II. Structure and Extent of Two Ultrafaint Milky Way Satellites*",
  "title_text": "Deep Imaging of Grus II and Horologium. II. Structure and Extent of Two Ultrafaint Milky Way Satellites*",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:18:11Z",
  "url": "https://research.draconitic.com/paper/0p22bh3hcevrn",
  "venue": "The Astrophysical Journal",
  "versions": []
}