Impact of galactic shear and stellar feedback on star formation

Cédric Colling,Sam Geen,Patrick Hennebelle,Frédéric Bournaud,Olivier Iffrig

doi:10.1051/0004-6361/201833161

Abstract

Context. Feedback processes and the galactic shear regulate star formation. Aims. We investigate the effects of differential galactic rotation and stellar feedback on the interstellar medium (ISM) and on the star formation rate (SFR). Methods. A numerical shearing box is used to perform three-dimensional simulations of a 1 kpc stratified cubic box of turbulent and self-gravitating interstellar medium (in a rotating frame) with supernovae and H II feedback. We vary the value of the velocity gradient induced by the shear and the initial value of the galactic magnetic field. Finally, the different star formation rates and the properties of the structures associated with this set of simulations are computed. Results. We first confirm that the feedback has a strong limiting effect on star formation. The galactic shear has also a great influence: the higher the shear, the lower the SFR. Taking the value of the velocity gradient in the solar neighbourhood, the SFR is too high compared to the observed Kennicutt law, by a factor approximately three to six. This discrepancy can be solved by arguing that the relevant value of the shear is not the one in the solar neighbourhood, and that in reality the star formation efficiency within clusters is not 100%. Taking into account the fact that star-forming clouds generally lie in spiral arms where the shear can be substantially higher (as probed by galaxy-scale simulations), the SFR is now close to the observed one. Different numerical recipes have been tested for the sink particles, giving a numerical incertitude of a factor of about two on the SFR. Finally, we have also estimated the velocity dispersions in our dense clouds and found that they lie below the observed Larson law by a factor of about two. Conclusions. In our simulations, magnetic field, shear, H II regions, and supernovae all contribute significantly to reduce the SFR. In this numerical setup with feedback from supernovae and H II regions and a relevant value of galactic shear, the SFRs are compatible with those observed, with a numerical incertitude factor of about two.

Highlights

Star formation, a key phenomenon in our universe, is still not completely understood
Our understanding of star formation is directly linked to our comprehension of the cycle and the dynamics of the interstellar medium (ISM)
We study the influence of stellar feedback and the galactic shear on the ISM and the star formation rate (SFR) by performing a series of simulations of a stratified shearing box, with various physical parameters such as the initial magnetic field or the velocity gradient in the box

Summary

Introduction

Star formation, a key phenomenon in our universe, is still not completely understood. Part of the reason for this is that many physical processes interact over a large range of temporal and spatial scales. Our understanding of star formation is directly linked to our comprehension of the cycle and the dynamics of the interstellar medium (ISM). Because of this large range of scales, it is not possible to simulate a galaxy One possible solution is to simulate a small part of a galaxy in order to have a better spatial resolution One possible solution is to simulate a small part of a galaxy in order to have a better spatial resolution (e.g. Korpi et al 1999; Slyz et al 2005; de Avillez & Breitschwerdt 2005; Joung & Mac Low 2006; Kim et al 2011, 2013; Hill et al 2012; Gent et al 2013; Hennebelle & Iffrig 2014; Gatto et al 2015) at the cost of not solving the large galactic scales

Methods

Results

Discussion

Conclusion