Galaxy Evolution: Modeling the Role of Non-thermal Pressure in the Interstellar medium

Galaxy evolution depends strongly on the physics of the interstellar medium (ISM). Motivated by the need to incorporate the properties of the ISM in cosmological simulations, we construct a simple method to include the contribution of non-thermal components in the calculation of pressure of interstellar gas. In our method, we treat three non-thermal components turbulence, magnetic fields and cosmic rays and effectively parametrize their amplitude. We assume that the three components settle into a quasi-steady-state that is governed by the star formation rate, and calibrate their magnitude and density dependence by the observed radio-FIR correlation, relating synchrotron radiation to star formation rates of galaxies. We implement our model in single-cell numerical simulation of a parcel of gas with constant pressure boundary conditions and demonstrate its effect and potential. Then, the non-thermal pressure model is incorporated into RAMSES and hydrodynamic simulations of isolated galaxies with and without the non-thermal pressure model are presented and studied. Specifically, we demonstrate that the inclusion of realistic non-thermal pressure reduces the star formation rate by an order of magnitude and increases the gas depletion time by as much. We conclude that the non-thermal pressure can prolong the star formation epoch and achieve consistency with observations without invoking artificially strong stellar feedback. DOI: https://doi.org/10.1093/mnras/stu2717 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-121892 Accepted Version Originally published at: Birnboim, Yuval; Balberg, Shmuel; Teyssier, Romain (2015). Galaxy evolution: modelling the role of non-thermal pressure in the interstellar medium. Monthly Notices of the Royal Astronomical Society, 447(4):3678-3692. DOI: https://doi.org/10.1093/mnras/stu2717 ar X iv :1 31 1. 12 06 v3 [ as tr oph .C O ] 8 J un 2 01 5 Mon. Not. R. Astron. Soc. 000, 1–17 (2014) Printed 9 June 2015 (MN LTEX style file v2.2) Galaxy Evolution: Modeling the Role of Non-thermal Pressure in the Interstellar medium Yuval Birnboim, Shmuel Balberg, & Romain Teyssier Racah Institute of Physics, The Hebrew University, Jerusalem 91904 Israel Institute for Computational Science, University of Zrich, Winterthurerstrasse 190, CH-8057 Zrich, Switzerland Accepted —. Received —; in original — ABSTRACT Galaxy evolution depends strongly on the physics of the interstellar medium (ISM). Motivated by the need to incorporate the properties of the ISM in cosmological simulations we construct a simple method to include the contribution of non-thermal components in the calculation of pressure of interstellar gas. In our method we treat three non-thermal components turbulence, magnetic fields and cosmic rays and effectively parametrize their amplitude. We assume that the three components settle into a quasi-steady-state that is governed by the star formation rate, and calibrate their magnitude and density dependence by the observed Radio-FIR correlation, relating synchrotron radiation to star formation rates of galaxies. We implement our model in single cell numerical simulation of a parcel of gas with constant pressure boundary conditions and demonstrate its effect and potential. Then, the non-thermal pressure model is incorporated into RAMSES and hydrodynamic simulations of isolated galaxies with and without the non-thermal pressure model are presented and studied. Specifically, we demonstrate that the inclusion of realistic non-thermal pressure reduces the star formation rate by an order of magnitude and increases the gas depletion time by as much. We conclude that the non-thermal pressure can prolong the star formation epoch and achieve consistency with observations without invoking artificially strong stellar feedback.Galaxy evolution depends strongly on the physics of the interstellar medium (ISM). Motivated by the need to incorporate the properties of the ISM in cosmological simulations we construct a simple method to include the contribution of non-thermal components in the calculation of pressure of interstellar gas. In our method we treat three non-thermal components turbulence, magnetic fields and cosmic rays and effectively parametrize their amplitude. We assume that the three components settle into a quasi-steady-state that is governed by the star formation rate, and calibrate their magnitude and density dependence by the observed Radio-FIR correlation, relating synchrotron radiation to star formation rates of galaxies. We implement our model in single cell numerical simulation of a parcel of gas with constant pressure boundary conditions and demonstrate its effect and potential. Then, the non-thermal pressure model is incorporated into RAMSES and hydrodynamic simulations of isolated galaxies with and without the non-thermal pressure model are presented and studied. Specifically, we demonstrate that the inclusion of realistic non-thermal pressure reduces the star formation rate by an order of magnitude and increases the gas depletion time by as much. We conclude that the non-thermal pressure can prolong the star formation epoch and achieve consistency with observations without invoking artificially strong stellar feedback.