Abstract

Contributed Talk - Splinter LowMet

Thursday, 12 September 2024, 17:25   (S23)

The regulation of star formation by the variable far-UV radiation and cosmic-ray ionization rate in low-metallicity environments

Vittoria Brugaletta
Universität zu Köln, I. Physikalisches Institut

We present magneto-hydrodynamic simulations of the low-metallicity multi-phase interstellar medium (ISM) conducted within the SILCC framework. Our new study includes two new features compared to previous works. The first is the self-consistent modeling of non-ionizing far-ultraviolet radiation from stellar clusters. The interstellar radiation field strength in Habing units can vary locally to values much higher or lower than the solar neighborhood’s average (G0 = 1.7), significantly changing the local photoelectric heating (PE) rate. The second is the self-consistent calculation of the cosmic-ray (CR) ionization rate from the energy density of cosmic rays, already computed from our code. Supernovae are a source for cosmic rays, and the local CR energy density is computed locally using our advection+anisotropic diffusion solver for cosmic rays. We analyze the impact of these two new models in environments with a metallicity of 0.02 Z_sun, where the lower dust-to-gas ratio makes the PE less efficient and comparable to, or weaker than, the heating by low-energy cosmic rays. Low-metallicity environments are subject to inefficient cooling due to the lack of metals, therefore they are expected to be warmer than the solar-metallicity ISM, affecting star formation. To have a better understanding of the different impacts that these two heating mechanisms have on the metal-poor ISM we use alternatively a variable G0 and CR ionization rate, as well as the constant values already used in the previous works of the SILCC collaboration. Among our main results, we find that, in the vicinity of highly star forming regions (with high G0 and CR ionization rate) star formation at low metallicity is strongly suppressed. In regions which are further away, where the value of G0 has dropped but the CR ionization rate is still high, the star formation is again suppressed by cosmic–ray heating. In pristine regions, with a low G0 and CR ionization rate, the metal–poor gas is overall cooler and is able to form stars.