SIMBAD references

The secular evolution of isolated barred galaxies is studied by means of fully self-consistent 3D numerical simulations with stars, gas, star formation, and radiative cooling. The formation of a strong bar in a typical Sc disc produces a starburst of intermediate power inside the bar and in the centre. Very young bars (≲500Myr) are characterised by intense star formation along their major axis (essentially observed in SBc) whereas star formation in older bars predominates either at the centre or along a nuclear ring and along an inner ring (mainly observed in SBb or SBa). Newly formed stars in the central regions are very easily swept out of the plane by vertical resonances which results in the formation of a small young bulge. These are clear evidences of an evolution from late-type to early-type galaxies. Our method to simulate star formation, based on Toomre's criterion, naturally reproduces in the disc the observations of (i) the threshold of star formation at low gas surface densities (≲7M_☉pc^–2), (ii) the mild power-law dependence of the star formation rate (SFR) with the gas surface density (SFR~{SIGMA}_g^∼1.3) at higher gas densities (>13M_☉ pc^–2), and, (iii) the highly non-linear behaviour in-between if energy release from supernovae is allowed. In the bar region, energy release leads to a significant alteration of the power-law relation between SFR and gas surface density, i.e. the ``Schmidt law'' shows a deep trough. The model parameters which mainly influence the rate of star formation are the gas mass fraction, the amount of mechanical energy released by supernovae and winds, the presence or absence of a bar, and the effectiveness of radiative cooling. The model parameters which mainly influence the space distribution of star formation are the star formation efficiency, the amount mechanical energy released, and the presence or absence of a bar. In general, the radiative cooling is so efficient that the mechanical energy injected is more important than the thermal part. Gaseous discs including star formation are supported by the turbulent pressure generated by mechanical energy release. Over most of the galaxy, the slopes of pre-existing abundance gradients in both gas and stars are considerably reduced over a few dynamical timescales by the formation of a bar. As observed, the stronger the bar, the shallower the chemical composition gradient. However, the intense central star formation steepens the abundance gradients in the corresponding region (≲1kpc). In some models, the furious star formation along the bar is able to steepen the abundance gradient inside the bar. At a fixed radius, scatter around the mean gaseous abundance comes from a large-scale variation between arm and interarm regions (about 0.6-0.8dex), and an intrinsic, small-scale scatter (about 0.3-0.4dex). The azimuthal variation is damped with time unless spiral density waves are regenerated.