Determining the physical processes that control galactic-scale star formation rates is essential for an improved understanding of galaxy evolution. The role of orbital shear is currently unclear, with some models expecting reduced star formation rates and efficiencies with increasing shear, e.g., if shear stabilizes gas against gravitational collapse, while others predicting enhanced rates, e.g., if shear-driven collisions between giant molecular clouds trigger star formation. Expanding on the analysis of 16 galaxies by C. Suwannajak et al., we assess the shear dependence of star formation efficiency (SFE) per orbital time (ϵorb) in 49 galaxies selected from the PHANGS-ALMA survey. In particular, we test a prediction of the shear-driven giant molecular cloud (GMC) collision model that ϵorb ∝ (1–0.7β), where , i.e., SFE per orbital time declines with decreasing shear. We fit the function ϵorb = ϵorb,0(1 − αCCβ) finding αCC ≃ 0.76 ± 0.16; an alternative fit with ϵorb normalized by the median value in each galaxy yields . These results are in good agreement with the prediction of the shear-driven GMC collision theory. We also examine the impact of a galactic bar on ϵorb finding a modest decrease in SFE in the presence of a bar, which can be attributed to lower rates of shear in these regions. We discuss the implications of our results for the GMC life cycle and environmental dependence of star formation activity.

中文翻译：

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剪切对圆盘星系形成速率的影响


确定控制银河系尺度恒星形成速率的物理过程对于更好地理解星系演化至关重要。轨道剪切的作用目前尚不清楚，一些模型预计恒星形成速率和效率会随着剪切力的增加而降低，例如，如果剪切稳定气体免受引力坍缩，而另一些模型则预测速率会提高，例如，如果巨型分子云之间的剪切驱动碰撞触发恒星形成。在 C. Suwannajak 等人对 16 个星系的分析的基础上，我们评估了从 PHANGS-ALMA 调查中选择的 49 个星系中恒星形成效率 （SFE） 每轨道时间 （εorb） 的剪切依赖性。特别是，我们测试了 εorb ∝ （1–0.7β） 的剪切驱动巨分子云 （GMC） 碰撞模型的预测，其中 ，即每个轨道时间的 SFE 随着剪切力的降低而下降。我们拟合函数 εorb = εorb，0（1 − αCCβ），得到 αCC ≃ 0.76 ± 0.16;由每个星系中的中值归一化的 εOrb 的替代拟合得到 。这些结果与剪切驱动 GMC 碰撞理论的预测非常吻合。我们还研究了银河棒对 εorb 的影响，发现在存在棒的情况下 SFE 适度降低，这可以归因于这些区域的剪切速率较低。我们讨论了我们的结果对 GMC 生命周期和恒星形成活动的环境依赖性的影响。