The dependence of the initial mass function on metallicity and the opacity limit for fragmentation
The dependence of the initial mass function on metallicity and the opacity limit for fragmentation
复制标题
初始质量函数对金属丰度和碎片不透明度限制的依赖性
DOI：
10.1111/j.1365-2966.2005.09476.x
复制
发表时间：
2005
影响因子：
4.8
通讯作者：
M. Bate
中科院分区：
文献类型：
--
作者：
M. Bate
我们调查的不透明度限制的分子云的金属丰度的碎片上的恒星属性的依赖。我们比较了两个大规模的流体动力学模拟的结果星星集群的形成，解决了破碎过程的不透明度限制，其中第一个是由Bate，Bonnell和Bromm报道。这两个计算的初始条件是相同的，但在新的模拟中，不透明度极限的开始发生在较低的气体密度下，预计这将使褐矮星的最小质量增加3倍[到1.29木星质量（M J）]。我们发现，最低质量的物体在低金属丰度计算中高出3倍，正如预期的那样。然而，除了低质量截止值的这种偏移之外，由两种计算产生的初始质量函数（IMF）是不可区分的。特别是，中位数（特征）质量不变。这些结果支持了Bate & Bonnell提出的吸积-喷射模型，该模型预测了初始质量函数（IMF）的起源，该模型预测特征质量应与云中的平均热金斯质量成比例变化。他们还表明，以上的低质量截止的IMF的形式不应该显示出很强的金属依赖性，假设冷却是由灰尘和分子云的整体平均热金斯质量不依赖于它的金属。然而，如果一个分子云的平均热金斯质量是由气体在云形成过程中的热行为决定的，这将导致IMF的特征质量对金属丰度的间接依赖，因为特征质量和云的平均热金斯质量之间存在联系。Ke yw ords：吸积，吸积盘-流体动力学-双星：一般恒星：形成恒星：低质量，褐矮星-恒星：光度函数，质量函数。
We investigate the dependence of stellar properties on the opacity limit for fragmentation that is set by the metallicity of a molecular cloud. We compare the results from two large-scale hydrodynamical simulations of star cluster formation, which resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell & Bromm. The initial conditions of the two calculations are identical, but in the new simulation the onset of the opacity limit occurs at a lower gas density, and this is expected to increase the minimum mass of a brown dwarf by a factor of 3 [to ≈ 9 Jupiter masses (M J)]. We find that the lowest mass object is a factor of 3 higher in the low-metallicity calculation, as expected. However, apart from this shift of the low-mass cut-off, the initial mass functions (IMFs) produced by the two calculations are indistinguishable. In particular, the median (characteristic) mass is unchanged. These results add support to the accretion‐ejection model proposed by Bate & Bonnell for the origin of the initial mass function (IMF), which predicts that the characteristic mass should vary in proportion to the mean thermal Jeans mass in the cloud. They also indicate that the form of the IMF above the low-mass cut-off should not display a strong metallicity dependence, assuming that the cooling is dominated by dust and that the overall mean thermal Jeans mass of a molecular cloud does not depend on its metallicity. However, if the mean thermal Jeans mass of a molecular cloud is set by the thermal behaviour of gas during the formation of the cloud, this should lead to an indirect dependence of the characteristic mass of the IMF on metallicity because of the link between the characteristic mass and the mean thermal Jeans mass of the cloud. Ke yw ords: accretion, accretion discs ‐ hydrodynamics ‐ binaries: general ‐ stars: formation ‐ stars: low-mass, brown dwarfs ‐ stars: luminosity function, mass function.