The effects of a hot gaseous halo on disc thickening in galaxy minor mergers

Benjamin P. Moster, Andrea Maccio, Rachel S. Somerville, Thorsten Naab, T. J. Cox

    Research output: Contribution to journalArticle

    Abstract

    We employ hydrodynamical simulations to study the effects of dissipational gas physics on the vertical heating and thickening of disc galaxies during minor mergers. For the first time we present a suite of simulations that includes a diffuse, rotating, cooling, hot gaseous halo, as predicted by cosmological hydrodynamical simulations as well as models of galaxy formation. We study the effect of this new gaseous component on the vertical structure of a Milky Way-like stellar disc during 1:10 and 1:5 mergers. For 1:10 mergers, we find no increased final thin disc scale height compared to the isolated simulation, leading to the conclusion that thin discs can be present even after a 1:10 merger if a reasonable amount of hot gas is present. The reason for this is the accretion of new cold gas, leading to the formation of a massive new thin stellar disc that dominates the surface brightness profile. In a previous study, in which we included only cold gas in the disc, we showed that the presence of cold gas decreased the thickening by a minor merger relative to the no-gas case. Here, we show that the evolution of the scale height in the presence of a cooling hot halo is dominated by the formation of the new stellar disc. In this scenario, the thick disc is the old stellar disc that has been thickened in a minor merger at z≳ 1, while the thin disc is the new stellar disc that reforms after this merger. When galactic winds are also considered, the final scale height is larger due to two effects. First, the winds reduce the star formation rate, leading to a less massive new stellar disc, such that the thickened old disc still dominates. Secondly, the winds exert a pressure force on the gas in the disc, leading to a shallower gas profile and thus to a thicker new stellar disc. In addition, we study the evolution of the scale height during a 1:5 merger and find that a thin disc can be present even after this merger, provided enough hot gas is available. The final scale height in our simulations depends on the mass of the hot gaseous halo, the efficiency of the winds and the merger mass ratio. We find post-merger values in the range 0.5 ≲z 0≲ 1.0kpc in good agreement with observational constraints by local galaxies.

    Original languageEnglish (US)
    Pages (from-to)2045-2057
    Number of pages13
    JournalMonthly Notices of the Royal Astronomical Society
    Volume423
    Issue number3
    DOIs
    StatePublished - Jul 1 2012

    Fingerprint

    merger
    halos
    galaxies
    gas
    scale height
    cold gas
    simulation
    thickening
    effect
    high temperature gases
    gases
    cooling
    galactic winds
    disk galaxies
    galactic evolution
    physics
    star formation rate
    profiles
    accretion
    mass ratios

    Keywords

    • Galaxies: evolution
    • Galaxies: interactions
    • Galaxy: disc
    • Galaxy: evolution
    • Galaxy: structure
    • Methods: numerical

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

    Cite this

    The effects of a hot gaseous halo on disc thickening in galaxy minor mergers. / Moster, Benjamin P.; Maccio, Andrea; Somerville, Rachel S.; Naab, Thorsten; Cox, T. J.

    In: Monthly Notices of the Royal Astronomical Society, Vol. 423, No. 3, 01.07.2012, p. 2045-2057.

    Research output: Contribution to journalArticle

    Moster, Benjamin P. ; Maccio, Andrea ; Somerville, Rachel S. ; Naab, Thorsten ; Cox, T. J. / The effects of a hot gaseous halo on disc thickening in galaxy minor mergers. In: Monthly Notices of the Royal Astronomical Society. 2012 ; Vol. 423, No. 3. pp. 2045-2057.
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