{
  "abstract": "We report an interesting line of sight towards the blazar PKS 1158+007 (J1201+0028) ($z_{\\rm em}$ = 1.369), revealing the rare detection of two intervening HI 21-cm absorption systems within a narrow redshift interval ($Δz \\sim 0.04$) using the MeerKAT radio telescope. The stronger absorber at $z_{\\rm abs}$ $=0.5653$ ($\\intτdv = 1.31\\pm0.04$ \\kms) is associated with a strong MgII $\\lambda2796$ system seen in the Sloan Digital Sky Survey (SDSS) and Dark Energy Spectroscopic Instrument (DESI) spectra, with rest-frame equivalent widths of $W_{2796} = 1.40\\pm0.07$~Å and $1.21\\pm0.11$~Å, respectively. In stark contrast, the second detection at $z_{\\rm abs}$ $= 0.5305$ reveals a distinct HI 21-cm absorption feature ($\\intτdv = 0.31 \\pm 0.04$ \\kms) with no associated metal absorption detectable in the optical spectra. This system represents a prime example of a \"metal-poor'' HI 21-cm absorber. Using photometric redshifts from Hyper Suprime-Cam (HSC) PDR3 and DESI Legacy Surveys DR10, we identify a broad galaxy overdensity (at $z \\sim0.53\\pm0.06$) coincident with these absorbers, suggesting the sightline pierces a complex large-scale structure or filament, which would be interesting to confirm with follow-up observations. These results underscore the power of blind HI 21-cm surveys to uncover the \"invisible'' cold gas phase of the Universe that optical/UV metal-line selection may systematically miss.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.07273",
  "author_total": 3,
  "authors": [
    {
      "name": "Abhisek Mohapatra"
    },
    {
      "name": "R. Srianand"
    },
    {
      "name": "R. Dutta"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/5vs5y29a79zz2.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.07273",
  "fulltext_url": null,
  "id": "5vs5y29a79zz2",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.07273",
  "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": "W7221040547",
  "pdf_url": "https://arxiv.org/pdf/2610.07273",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-05",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/5vs5y29a79zz2.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:22Z",
      "native_id": "2610.07273",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.07273"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "Multiple H I 21-cm absorbers towards blazar PKS 1158+007",
  "title_text": "Multiple H I 21-cm absorbers towards blazar PKS 1158+007",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:22Z",
  "url": "https://research.draconitic.com/paper/5vs5y29a79zz2",
  "venue": "arXiv",
  "versions": []
}