arXiv 1504.021402015-04-08astro-ph.SR

湍流会聚流中星前核的形成、演化和重力碎裂的吸积

Prestellar Core Formation, Evolution, and Accretion from Gravitational Fragmentation in Turbulent Converging Flows

Munan Gong, Eve C. Ostriker

发表信息：: ApJ (2015) 806 31
DOI：: 10.1088/0004-637X/806/1/31

摘要：

我们研究星前核的形成和吸积的三维流体动力学模拟的基础上。我们的模拟代表本地$\sim 1$ PC地区内的巨大分子云的超音速湍流收敛，触发恒星形成的后激波层。我们包括紊流和自重，应用下沉粒子技术，并探讨了入流马赫数${\cal M}=2-16$的范围。两组核心的识别和比较：$t_1$ -核心识别的时间快照，在每个模拟，代表在一个单一的云图密集的结构; $t_\mathrm{coll}$ -核心识别在其各自的崩溃时间，代表最初的质量水库吸积。我们发现，核心和细丝的形成和演变是同时进行的。在核心崩溃的阶段，有一个定义明确的，收敛的特征质量的等温碎裂，是在冲击后压力的临界邦纳-埃伯特质量相媲美。与观测到的恒星初始质量函数（IMF）相比，$t_\mathrm{coll}$ -核心的核心质量函数（CMFs）显示出高质量核心（$\gtrsim 7M_\odot$）的不足。然而，$t_1$核心的CMF与观测到的CMF相似，并且包括许多重力稳定的低质量核心。$t_1$ -核心和$t_\mathrm{coll}$ -核心之间的差异表明，从观测到的CMF的完整样本可能不会演变成原恒星。在整个模拟过程中，单个汇粒子以大致恒定的速率吸积，即使在初始质量库吸积之后，每个自由落体时间也会获得一个$t_\mathrm{coll}$核心质量。高质量的汇在后期比低质量的汇按比例获得更多的质量。由于团块密度结构落入汇中，导致吸积速率的爆发。

英文摘要：

We investigate prestellar core formation and accretion based on three-dimensional hydrodynamic simulations. Our simulations represent local $\sim 1$pc regions within giant molecular clouds where a supersonic turbulent flow converges, triggering star formation in the post-shock layer. We include turbulence and self-gravity, applying sink particle techniques, and explore a range of inflow Mach number ${\cal M}=2-16$. Two sets of cores are identified and compared: $t_1$-cores are identified of a time snapshot in each simulation, representing dense structures in a single cloud map; $t_\mathrm{coll}$-cores are identified at their individual time of collapse, representing the initial mass reservoir for accretion. We find that cores and filaments form and evolve at the same time. At the stage of core collapse, there is a well-defined, converged characteristic mass for isothermal fragmentation that is comparable to the critical Bonner-Ebert mass at the post-shock pressure. The core mass functions (CMFs) of $t_\mathrm{coll}$-cores show a deficit of high-mass cores ($\gtrsim 7M_\odot$) compared to the observed stellar initial mass function (IMF). However, the CMFs of $t_1$-cores are similar to the observed CMFs and include many low-mass cores that are gravitationally stable. The difference between $t_1$-cores and $t_\mathrm{coll}$-cores suggests that the full sample from observed CMFs may not evolve into protostars. Individual sink particles accrete at a roughly constant rate throughout the simulations, gaining one $t_\mathrm{coll}$-core mass per free-fall time even after the initial mass reservoir is accreted. High-mass sinks gain proportionally more mass at late times than low-mass sinks. There are outbursts in accretion rates, resulting from clumpy density structures falling into the sinks.

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