The bound fraction of young star clusters
The bound fraction of young star clusters
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DOI：
10.1051/0004-6361/201629312
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发表时间：
2016-11
影响因子：
6.5
通讯作者：
Nina Brinkmann;S. Banerjee;Bhawna Motwani;P. Kroupa
中科院分区：
文献类型：
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作者：
Nina Brinkmann;S. Banerjee;Bhawna Motwani;P. Kroupa
语境。新形成的星团内的残余气体通过时间尺度≲ 1 Myr 的恒星反馈被排出。随后星团的扩张导致部分恒星解绑，然后剩余的星团成员才能重新病毒化并形成幸存的星团。目标。我们研究了气体排出后的束缚分数作为恒星初始星团质量 M_(ecl) 的函数，并测量了原始质量偏聚、恒星演化和太阳距离潮汐场的影响。我们还评估了恒星形成效率 e_(SFE) 和气体排出速度 v_g 的影响。方法。我们使用 Sverre Aarseth 的 NBODY7 代码进行 N 体模拟，从嵌入相的致密团簇开始，并通过指数耗尽的外部引力场来近似气体排出。我们通过详细监测几个 Myr 上的不同拉格朗日半径，检查 0.1 pc、0.3 pc 和 0.5 pc 的初始半质量半径以及通常范围从 5 × 10^3 M_⊙ 到 5 × 10^4 M_⊙ 的 M_(ecl) 来跟踪重新病毒化的过程。结果。气体排出时间尺度和穿越时间之间关系的强烈影响意味着具有相同初始核心密度的团簇可以具有非常不同的结合分数。团簇体积中采用的 e_(SFE) = 0.33 导致在较宽的质量范围内对 v_g 具有明显的敏感性，而 e_(SFE) 的变化可以使团簇对快速下降的外部电势具有鲁棒性。我们证实，原始质量偏析导致更小的束缚分数，其影响可能随着质量的增加而减小。恒星演化对较低质量的星团有更大的影响，但通过动态摩擦加热可以使星团膨胀到类似的程度。所检查的星团在其潮汐半径内膨胀得很好，即使在强烈的潮汐场中也能幸免于气体排出。
Context. The residual gas within newly formed star clusters is expelled through stellar feedback on timescales ≲ 1 Myr. The subsequent expansion of the cluster results in an unbinding of a fraction of stars, before the remaining cluster members can re-virialize and form a surviving cluster. Aims. We investigate the bound fraction after gas expulsion as a function of initial cluster mass in stars M_(ecl) and gauge the influence of primordial mass segregation, stellar evolution and the tidal field at solar distance. We also assess the impact of the star-formation efficiency e_(SFE) and gas expulsion velocity v_g. Methods. We perform N-body simulations using Sverre Aarseth’s NBODY7 code, starting with compact clusters in their embedded phase and approximate the gas expulsion by means of an exponentially depleting external gravitational field. We follow the process of re-virialization through detailed monitoring of different Lagrange radii over several Myr, examining initial half-mass radii of 0.1 pc, 0.3 pc and 0.5 pc and M_(ecl) usually ranging from 5 × 10^3 M_⊙ to 5 × 10^4 M_⊙. Results. The strong impact of the relation between the gas expulsion timescale and the crossing time means that clusters with the same initial core density can have very different bound fractions. The adopted e_(SFE) = 0.33 in the cluster volume results in a distinct sensitivity to v_g over a wide mass range, while a variation of e_(SFE) can make the cluster robust to the rapidly decreasing external potential. We confirm that primordial mass segregation leads to a smaller bound fraction, its influence possibly decreasing with mass. Stellar evolution has a higher impact on lower mass clusters, but heating through dynamical friction could expand the cluster to a similar extent. The examined clusters expand well within their tidal radii and would survive gas expulsion even in a strong tidal field.