[论文解读] High-resolution, 3D radiative transfer modelling III. The DustPedia barred galaxies

Angelos Nersesian, Sam Verstocken+18 more|arXiv (Cornell University)|Apr 7, 2020

Galaxies: Formation, Evolution, Phenomena参考文献 131被引用 11

一句话总结

本研究利用三维蒙特卡罗辐射转移建模，量化了四座邻近棒旋星系（NGC 1365、M 83、M 95、M 100）中恒星群对尘埃的加热作用，发现年轻恒星平均贡献了总尘埃加热的59%，在星系棒区（53%）和星系核球区（38%）显著降低，此时年老恒星占主导。研究结果证实年轻恒星比例与特定恒星形成率之间存在强关联，挑战了红外辐射作为纯粹恒星形成示踪剂的假设。

ABSTRACT

Context: Dust in late-type galaxies in the local Universe is responsible for absorbing approximately one third of the energy emitted by stars. It is often assumed that dust heating is mainly attributable to the absorption of UV and optical photons emitted by the youngest (<= 100 Myr) stars. Consequently, thermal re-emission by dust at FIR wavelengths is often linked to the star-formation activity of a galaxy. However, several studies argue that the contribution to dust heating by much older stars might be more significant. Advances in radiation transfer (RT) simulations finally allow us to actually quantify the heating mechanisms of diffuse dust by the stellar radiation field. Aims: As one of the main goals in the DustPedia project, we have constructed detailed 3D stellar and dust RT models for nearby galaxies. We analyse the contribution of the different stellar populations to the dust heating in four face-on barred galaxies: NGC1365, M83, M95, and M100. We aim to quantify the fraction directly related to young stars, both globally and on local scales, and to assess the influence of the bar on the heating fraction. Results: We derive global attenuation laws for each galaxy and confirm that galaxies of high sSFR have shallower attenuation curves and weaker UV bumps. On average, 36.5% of the bolometric luminosity is absorbed by dust. We report a clear effect of the bar structure on the radial profiles of the dust-heating fraction by the young stars, and the dust temperature. We find that the young stars are the main contributors to the dust heating, donating, on average ~59% of their luminosity to this purpose throughout the galaxy. This dust-heating fraction drops to ~53% in the bar region and ~38% in the bulge region where the old stars are the dominant contributors to the dust heating. We also find a strong link between the heating fraction by the young stars and the sSFR.

研究动机与目标

• 量化邻近棒旋星系中年轻与年老恒星群对尘埃加热的贡献。
• 评估星系棒结构对尘埃加热比例和尘埃温度径向分布的影响。
• 校准年老恒星群在尘埃加热中的作用，以用于全局SED建模。
• 通过考虑年老恒星不可忽视的加热作用，提高恒星形成率估算的准确性。

提出的方法

• 利用一致框架，从二维图像重建了恒星与尘埃的三维分布。
• 使用SKIRT三维蒙特卡罗辐射转移代码，模拟任意三维几何结构中尘埃对辐射的吸收、散射及热再辐射。
• 基于光谱能量分布拟合与空间分布，将恒星群划分为年轻（≤100 Myr）和年老（超过1 Gyr）两部分。
• 全局及径向分区内推导了总辐射功率与消光律，以评估加热比例。
• 将特定恒星形成率（sSFR）与来自年轻恒星的尘埃加热比例进行相关分析。
• 绘制尘埃温度分布图，并关联到星系各组成部分的恒星群贡献。

实验结果

研究问题

• RQ1 在棒旋星系中，尘埃加热的多少比例可归因于年轻恒星群，多少比例来自年老恒星群？
• RQ2 棒结构的存在如何影响尘埃加热比例与尘埃温度的径向分布？
• RQ3 特定恒星形成率与来自年轻恒星的尘埃加热比例之间存在多大程度的相关性？
• RQ4 在这些星系中，消光曲线与紫外突起如何随sSFR和形态结构变化？
• RQ5 年老恒星群对尘埃加热的贡献能否被可靠校准，以用于SED拟合？

主要发现

• 在星系样本中，平均有36.5%的总辐射功率被尘埃吸收，与Sb-Sc型星系的先前研究结果一致。
• 年轻恒星群平均贡献了总尘埃加热的59%，各星系的全局比例分别为：NGC 1365（68%）、M 83（64%）、M 95（47%）和M 100（57%）。
• 在星系棒区，年轻恒星的贡献降至53%；在核球区进一步下降至38%，此时年老恒星主导尘埃加热。
• 由于年轻恒星的存在，星系中心区域和旋臂的尘埃温度更暖；而盘面区域的低温则主要由年老恒星群驱动。
• 确认了来自年轻恒星的尘埃加热比例与特定恒星形成率之间存在强相关性，支持了在M 51、M 31和M 81中先前的研究发现。
• sSFR较高的星系中，消光曲线更平缓，紫外突起更弱，反映出恒星群混合与几何结构对尘埃再处理过程的影响。