The statistical properties of protostellar discs and their dependence on metallicity

Abstract

We present the analysis of the properties of large samples of protostellar discs formed in four radiation hydrodynamical simulations of star cluster formation. The four calculations have metallicities of 0.01, 0.1, 1 and 3 times solar metallicity. The calculations treat dust and gas temperatures separately and include a thermochemical model of the diffuse interstellar medium. We find the radii of discs of bound protostellar systems tend to decrease with decreasing metallicity, with the median characteristic radius of discs in the 0.01 and 3 times solar metallicity calculations being ≈20 and ≈65 au, respectively. Disc masses and radii of isolated protostars also tend to decrease with decreasing metallicity. We find that the circumstellar discs and orbits of bound protostellar pairs, and the two spins of the two protostars are all less well aligned with each other with lower metallicity than with higher metallicity. These variations with metallicity are due to increased small scale fragmentation due to lower opacities and greater cooling rates with lower metallicity, which increase the stellar multiplicity and increase dynamical interactions. We compare the disc masses and radii of protostellar systems from the solar metallicity calculation with recent surveys of discs around Class 0 and I objects in the Orion and Perseus star-forming regions. The masses and radii of the simulated discs have similar distributions to the observed Class 0 and I discs.

Searching for Giant Exoplanets around M-dwarf Stars (GEMS) I: Survey Motivation

“…On the contrary, simulations suggest that lower-metallicity molecular clouds should favor gravitational fragmentation (Elsender & Bate 2021;Matsukoba et al 2022), while GI is largely agnostic of the disk metallicity (Boss 2002). Put simply, in the optically thick environment of the disk, higher stellar metallicity leads to higher opacities (due to more free electrons in the disk) that can slow down the cooling timescales.…”

The influence of metallicity on a combined stellar and disk evolution

“…Independent of the accretion history of the star, a lower stellar metallicity results in a shorter disk lifetime 3 . Observations of disk fractions in low-metallicity clusters (Yasui et al 2010a) and statistical studies (Elsender & Bate 2021) suggest that the disk lifetime is indeed shorter for lower stellar metallicities. Nakatani et al (2018) explain this behavior with a metallicity-dependent photo-evaporation rate.…”

“…It is worth noting that the observed disk lifetimes in low-metallicity clusters cannot be conclusively explained by one mechanism alone (e.g., Nakatani et al 2018) and results, more likely, from the combination of the aforementioned aspects. In a more recent study, Elsender & Bate (2021) propose that increased stellar multiplicity in low-metallicity environments and resulting increased dynamical interactions might cause accretion disks to be smaller and have shorter lifetimes compared to those with higher metallicities.…”

Probing initial distributions of orbital eccentricity and disc misalignment via polar discs

“…Such distributions, in turn, depend on which physical properties are more significant in the formation process of these objects. In addition to dynamical interactions between stars (Bate et al 2002;Bate 2018;Elsender et al 2023), the presence and the strength of magnetic fields (Price & Bate 2007;Wurster et al 2019;Zhao et al 2020;Lebreuilly et al 2021), different metallicities (Elsender & Bate 2021) and the level of turbulence in the cloud (Bate et al 2010;Walch et al 2012) may play a significant role in setting the initial properties of disc and star populations.…”