{
  "id": "2109.13526",
  "version": "v1",
  "published": "2021-09-28T07:01:34.000Z",
  "updated": "2021-09-28T07:01:34.000Z",
  "title": "The local environment of flat galaxies",
  "authors": [
    "Suman Sarkar",
    "Arunima Banerjee",
    "Dmitry Makarov"
  ],
  "comment": "11 pages, 4 figures, 3 tables",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "The existence of flat or bulgeless galaxies poses a challenge to the hierarchical structure formation scenario advocated by modern cosmology. We determine the geometrical environment of a sample of $315$ flat galaxies from the Revised Flat Galaxy Catalog (RFGC) using `local dimension' $D$, which, on a given length scale, quantifies the dimension of the cosmic structure in which a galaxy is embedded. For galaxies residing in filaments, nodes and sheets, $D \\sim 1$, $D \\sim 1.5$ and $D \\sim 2$ respectively; $D \\sim 3$ represents field galaxies. We also determine the local dimensions of a sample of 15,622 non-flat galaxies identified in the Galaxy Zoo project from the Sloan Digital Sky Survey (SDSS). We find that the median values of $D$ for the flat and the non-flat galaxies are $2.2$ and $1.8$ respectively, implying that flat galaxies are located in a relatively sparser environment compared to non-flat galaxies; a Kolmogorov-Smirnov (KS) test indicates that their geometrical environments are different at $>99$\\% confidence level. Further, using a group finding algorithm, we study the local environment of a subset of $779$ flat galaxies with major-to-minor axes ratio $a/b >10$ identified as superthin galaxies. We find that the median clusterization index $k_{\\rm{min}}$ for superthin flat galaxies $\\sim$ $2.3$ while $\\sim$ $1.7$ for other flat galaxies, confirming that the superthins reside in an under-dense environment compared to other flat galaxies at $> 98 \\%$ confidence level. Our results may therefore have important implications for the formation and evolution models of flat galaxies in the universe.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2021-09-28T07:01:34.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "local environment",
      "non-flat galaxies",
      "confidence level",
      "sloan digital sky survey",
      "local dimension"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 11,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}