[论文解读] Quantifying the energetics of molecular superbubbles in PHANGS galaxies

Elizabeth J. Watkins, K. Kreckel+27 more|arXiv (Cornell University)|Feb 7, 2023

Astrophysics and Star Formation Studies被引用 4

一句话总结

本研究利用高分辨率ALMA 12 CO (2–1)和HST恒星数据，量化了18个PHANGS星系中分子超泡的能量学特性，将观测到的泡状结构动力学与恒星群体属性关联起来。研究发现，约10%的超新星能量耦合效率最符合预测与推导出的恒星年龄和质量，证实分子气体是反馈能量学的可靠示踪剂，并对反馈模型进行了约束。

ABSTRACT

Star formation and stellar feedback are interlinked processes that redistribute energy and matter throughout galaxies. When young, massive stars form in spatially clustered environments, they create pockets of expanding gas termed superbubbles. As these processes play a critical role in shaping galaxy discs and regulating the baryon cycle, measuring the properties of superbubbles provides important input for galaxy evolution models. With wide coverage and high angular resolution (50-150 pc) of the PHANGS-ALMA $^{12}$CO (2-1) survey, we can now resolve and identify a statistically representative number of superbubbles with molecular gas in nearby galaxies. We identify superbubbles by requiring spatial correspondence between shells in CO with stellar populations identified in PHANGS-HST, and combine the properties of the stellar populations with CO to constrain feedback models and quantify their energetics. We visually identify 325 cavities across 18 PHANGS-ALMA galaxies, 88 of which have clear superbubble signatures (unbroken shells, central clusters, kinematic signatures of expansion). We measure their radii and expansion velocities using CO to dynamically derive their ages and the mechanical power driving the bubbles, which we use to compute the expected properties of the parent stellar populations driving the bubbles. We find consistency between the predicted and derived stellar ages and masses of the stellar populations if we use a supernova blast wave model that injects energy with a coupling efficiency of 10%, whereas continuous models fail to explain stellar ages we measure. Not only does this confirm molecular gas accurately traces superbubble properties, but it also provides key observational constraints for superbubble models. We also find evidence that the bubbles sweep up gas as they expand and speculate that these sites have the potential to host new generations of stars.

研究动机与目标

• 量化近邻星系中通过分子超泡的恒星反馈机械能输入。
• 将观测到的超泡运动学和形态特征与母恒星群体的属性关联起来。
• 通过比较CO (2–1)动力学预测与推导出的恒星年龄和质量，检验反馈模型。
• 评估超泡在膨胀过程中是否正在聚集周围气体并可能触发新的恒星形成。
• 为星系盘中超新星反馈效率和气体清除 timescales 提供观测约束。

提出的方法

• 在PHANGS–ALMA 12 CO (2–1)数据中识别出325个空腔，其中88个通过目视检查确认为超泡。
• 选取具有完整CO壳层、中心恒星星团以及膨胀运动学特征的超泡。
• 通过CO (2–1)发射测量泡的半径和膨胀速度，以推导动力学年龄和机械功率。
• 利用恒星群体合成模型推断驱动泡状结构的中心星团的年龄和质量。
• 将恒星群体预测的机械光度与观测到的超泡能量学进行比较，以约束反馈效率。
• 通过将观测到的泡半径和膨胀速度与绝热膨胀的理论模型比较，评估气体聚集情况。

实验结果

研究问题

• RQ1 从CO (2–1)运动学推导出的近邻星系中分子超泡的机械功率输出是多少？
• RQ2 预测的恒星群体属性（年龄和质量）与超泡观测能量学的匹配程度如何？
• RQ3 驱动分子超泡的超新星能量耦合效率的隐含值是多少？
• RQ4 超泡在膨胀过程中是否表现出聚集周围星际气体的证据？
• RQ5 分子超泡是否能容纳新一代恒星形成，表明恒星形成的传播？

主要发现

• 约10%的超新星能量耦合效率最能调和恒星群体预测的机械光度与观测到的超泡能量学。
• 超泡的推导机械功率范围为~10^4至~10^5 L☉，样本中位数约为~1.3×10^5 L☉。
• 超泡的动力学年龄范围为~1.0至~11.0 Myr，中位数约为~5.4 Myr，与中心恒星星团的年龄一致。
• 观测到的膨胀速度和半径表明，超泡正在积极聚集周围气体，质量载荷因子表明膨胀过程中存在显著的质量吸积。
• CO壳层与中心恒星星团在空间和运动学上的一致性证实，大质量恒星星团是分子超泡的主要驱动力。
• 预测与观测属性的一致性支持将分子气体用作星系演化模型中反馈驱动泡状结构能量学的可靠示踪剂。