{
  "id": "1402.7076",
  "version": "v2",
  "published": "2014-02-27T21:00:21.000Z",
  "updated": "2014-08-06T01:42:26.000Z",
  "title": "The Mass-Independence of Specific Star Formation Rates in Galactic Disks",
  "authors": [
    "Louis E. Abramson",
    "Daniel D. Kelson",
    "Alan Dressler",
    "Bianca M. Poggianti",
    "Michael D. Gladders",
    "Augustus Oemler",
    "Benedetta Vulcani"
  ],
  "comment": "6 pages, 2 figures; Accepted to ApJL March 2014. ArXiv version updated to reflect changes made during refereeing; results unchanged",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO"
  ],
  "abstract": "The slope of the star formation rate/stellar mass relation (the SFR \"Main Sequence\"; ${\\rm SFR}-M_*$) is not quite unity: specific star formation rates $({\\rm SFR}/M_*)$ are weakly-but-significantly anti-correlated with $M_*$. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions -- portions of a galaxy not forming stars -- with $M_*$. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass $({\\rm sSFR_{\\rm disk}\\equiv SFR}/M_{*,{\\rm disk}})$ reduces the $M_*$-dependence of SF efficiency by $\\sim0.25$ dex per dex, erasing it entirely in some subsamples. Quantitatively, we find $\\log {\\rm sSFR_{disk}}-\\log M_*$ to have a slope $\\beta_{\\rm disk}\\in[-0.20,0.00]\\pm0.02$ (depending on SFR estimator and Main Sequence definition) for star-forming galaxies with $M_*\\geq10^{10}M_{\\odot}$ and bulge mass-fractions $B/T\\lesssim0.6$, generally consistent with a pure-disk control sample ($\\beta_{\\rm control}=-0.05\\pm0.04$). That $\\langle{\\rm SFR}/M_{*,{\\rm disk}}\\rangle$ is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any ${\\rm SFR}-M_*$ relation, including: manifestations of \"mass quenching\" (bulge growth), factors shaping the star-forming stellar mass function (uniform $d\\log M_*/dt$ for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in ${\\rm SFR}(M_*,t)$). Our results emphasize the need to treat galaxies as composite systems -- not integrated masses -- in observational and theoretical work.",
  "revisions": [
    {
      "version": "v2",
      "updated": "2014-08-06T01:42:26.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "specific star formation rates",
      "galactic disks",
      "star formation rate/stellar mass relation",
      "sloan digital sky survey",
      "mass-independence"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/2041-8205/785/2/L36",
      "journal": "The Astrophysical Journal",
      "year": 2014,
      "month": "Apr",
      "volume": 785,
      "number": 2
    },
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1283150,
      "adsabs": "2014ApJ...785L..36A"
    }
  }
}