{
  "id": "1407.5633",
  "version": "v2",
  "published": "2014-07-21T20:00:25.000Z",
  "updated": "2014-10-07T09:33:55.000Z",
  "title": "The stellar initial mass function of early type galaxies from low to high stellar velocity dispersion: homogeneous analysis of ATLAS$^{\\rm 3D}$ and Sloan Lens ACS galaxies",
  "authors": [
    "Silvia Posacki",
    "Michele Cappellari",
    "Tommaso Treu",
    "Silvia Pellegrini",
    "Luca Ciotti"
  ],
  "comment": "18 pages, 8 figures. Accepted for publication in MNRAS",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We present an investigation about the shape of the initial mass function (IMF) of early-type galaxies (ETGs), based on a joint lensing and dynamical analysis, and on stellar population synthesis models, for a sample of 55 lens ETGs identified by the Sloan Lens ACS (SLACS) Survey. We construct axisymmetric dynamical models based on the Jeans equations which allow for orbital anisotropy and include a dark matter halo. The models reproduce in detail the observed \\textit{HST} photometry and are constrained by the total projected mass within the Einstein radius and the stellar velocity dispersion ($\\sigma$) within the SDSS fibers. Comparing the dynamically-derived stellar mass-to-light ratios $(M_*/L)_{\\rm dyn}$, obtained for an assumed halo slope $\\rho_{\\rm h}\\propto r^{-1}$, to the stellar population ones $(M_*/L)_{\\rm pop}$, derived from full-spectrum fitting and assuming a Salpeter IMF, we infer the mass normalization of the IMF. Our results confirm the previous analysis by the SLACS team that the mass normalization of the IMF of high $\\sigma$ galaxies is consistent on average with a Salpeter slope. Our study allows for a fully consistent study of the trend between IMF and $\\sigma$ for both the SLACS and \\ATLAS samples, which explore quite different $\\sigma$ ranges. The two samples are highly complementary, the first being essentially $\\sigma$ selected, and the latter volume-limited and nearly mass selected. We find that the two samples merge smoothly into a single trend of the form $\\log\\alpha =(0.38\\pm0.04)\\times\\log(\\sigma_{\\rm e}/200\\,\\mathrm{km~s}^{-1})+(-0.06\\pm0.01)$, where $\\alpha=(M_*/L)_{\\rm dyn}/(M_*/L)_{\\rm pop}$ and $\\sigma_{\\rm e}$ is the luminosity averaged $\\sigma$ within one effective radius $R_{\\rm e}$. This is consistent with a systematic variation of the IMF normalization from Kroupa to Salpeter in the interval $\\sigma_{\\rm e}\\approx90-270\\,\\mathrm{km~s}^{-1}$.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-07-21T20:00:25.000Z",
      "abstract": "We present an investigation about the shape of the initial mass function (IMF) of early-type galaxies (ETGs), based on a joint lensing and dynamical analysis, and on stellar population synthesis models, for a sample of 55 lens ETGs identified by the Sloan Lens ACS (SLACS) Survey. We construct axisymmetric dynamical models based on the Jeans equations which allow for orbital anisotropy and include a dark matter halo. The models reproduce in detail the observed HST photometry and are constrained by the total projected mass within the Einstein radius and the stellar velocity dispersion ($\\sigma$) within the SDSS fibers. Comparing the dynamically-derived stellar mass-to-light ratios $(M/L)_{\\rm dyn}$ to the stellar population ones $(M/L)_{\\rm pop}$, derived from full-spectrum fitting and assuming a Salpeter IMF, we infer the mass normalization of the IMF. Our results confirm the previous analysis by the SLACS team that the mass normalization of the IMF of high $\\sigma$ galaxies is consistent on average with a Salpeter slope. Our study allows for a fully consistent study of the trend between IMF and $\\sigma$ for both the SLACS and ATLAS$^{\\rm 3D}$ samples, which explore quite different $\\sigma$ ranges. The two samples are highly complementary, the first being essentially $\\sigma$ selected, and the latter volume-limited and nearly mass selected. We find that the two samples merge smoothly into a single trend of the form $\\log\\alpha =(0.38\\pm0.04)\\times\\log(\\sigma_e/200\\, km s^{-1})+(-0.06\\pm0.01)$, where $\\alpha=(M/L)_{\\rm dyn}/(M/L)_{\\rm pop}$ and $\\sigma_e$ is the luminosity averaged $\\sigma$ within one effective radius $R_e$. This is consistent with a systematic variation of the IMF normalization from Kroupa to Salpeter in the interval $\\sigma_e\\approx 90-270\\,km s^{-1}$.",
      "comment": "15 pages, 8 figures. Submitted to MNRAS. Comments are welcome",
      "journal": null,
      "doi": null
    },
    {
      "version": "v2",
      "updated": "2014-10-07T09:33:55.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "stellar initial mass function",
      "high stellar velocity dispersion",
      "sloan lens acs galaxies",
      "early type galaxies"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1093/mnras/stu2098",
      "journal": "Monthly Notices of the Royal Astronomical Society",
      "year": 2015,
      "month": "Jan",
      "volume": 446,
      "number": 1,
      "pages": 493
    },
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1307294,
      "adsabs": "2015MNRAS.446..493P"
    }
  }
}