Abstract
We have updated our radially resolved semi-analytic models (SAMs) of
galaxy formation, which track both the atomic and molecular gas phases
of the interstellar medium. The models are adapted from those of Guo et
al. using similar methodology as by Fu et al. and are run on halo merger
trees from the Millennium and Millennium-II simulations with the
following main changes. (1) We adopt a simple star formation law
ΣSFR ∝ ΣH2. (2) We
inject the heavy elements produced by supernovae directly into the halo
hot gas, instead of first mixing them with the cold gas in the disc. (3)
We include radial gas inflows in discs using a model of the form
vinflow = αr. The models are used to study the radial
profiles of star formation rate and gas-phase metallicity in present-day
galaxies. The surface density profiles of molecular gas in L*
galaxies place strong constraints on inflow velocities, favouring models
where vinflow ˜ 7 km s-1 at a galactocentric
radius of 10 kpc. Radial gas inflow has little influence on gas-phase
and stellar metallicity gradients, which are affected much more strongly
by the fraction of metals that are directly injected into the halo gas,
rather than mixed with the cold gas. Metals ejected out of the galaxy in
early epochs result in late infall of pre-enriched gas and flatter
present-day gas-phase metallicity gradients. A prescription in which 80
per cent of the metals are injected into the halo gas results in good
fits to the flat observed metallicity gradients in galaxies with stellar
masses greater than 1010 M⊙, as well as the
relations between gas-phase metallicity and specific star formation rate
in the outer parts of galactic discs. We examine the correlation between
the gas-phase metallicity gradient and global galaxy properties, finding
that it is most strongly correlated with the bulge-to-total ratio of the
galaxy. This is because gas is consumed when the bulge forms during
galaxy mergers, and the gas-phase metallicity gradient is then set by
newly accreted gas.
Original language | English |
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Pages (from-to) | 1531-1548 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 434 |
Issue number | 2 |
DOIs | |
Publication status | Published - 12 Jul 2013 |
Keywords
- stars: formation
- ISM: atoms
- ISM: molecules
- galaxies: evolution
- galaxies: formation
- galaxies: ISM