A high pitch angle structure in the Sagittarius Arm
A high pitch angle structure in the Sagittarius Arm
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DOI：
10.1051/0004-6361/202141198
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发表时间：
2021-07
影响因子：
6.5
通讯作者：
M. Kuhn;R. Benjamin;C. Zucker;A. Krone-Martins;R. D. de Souza;A. Castro-Ginard;E. Ishida;M. Pov
中科院分区：
文献类型：
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作者：
M. Kuhn;R. Benjamin;C. Zucker;A. Krone-Martins;R. D. de Souza;A. Castro-Ginard;E. Ishida;M. Pov
语境。在螺旋星系中，恒星的形成往往会遵循螺旋图案的特征，包括旋臂、支刺、羽毛和分支。然而，在我们自己的银河系中，由于我们从盘内的角度来看，将单个恒星形成区域与其更大的银河系环境连接起来一直是一项挑战。几乎所有现代银河系模型的一个特征是人马座臂，它位于太阳内部，俯仰角约为 12°。目标。我们使用 Spitzer/IRAC 候选 YSO (SPICY) 目录中的年轻恒星物体 (YSO) 绘制了人马臂一段中恒星形成区域的 3D 位置和速度，以将其分布与人马臂模型进行比较。方法。这些物体的距离和速度来自 Gaia EDR3 天体测量和分子线勘测。我们推断了空间聚集的 YSO 群的视差和自行，并根据空间相关分子云的速度估计了它们的径向速度。结果。我们在银河经度范围 ℓ ∼ 4. ° 0–18. ° 5 中确定了 25 个恒星形成区域，这些区域排列在狭窄的、∼1 kpc 长的线性结构中，具有高俯仰角 ψ = 56° 和高纵横比 ∼7:1。该结构包括 M8、M16、M17 和 M20 等大质量恒星形成区域。结构中的运动非常一致，银河系自转方向的速度为|Vφ|≈240 ± 3 km s−1（略高于平均水平），并向内（VR ≈ -4.3 km s−1）和负Z方向（VZ ≈ -2.9 km s−1）轻微漂移。结构承受的旋转剪切为 ΔΩ = 4.6 km s−1 kpc−1。结论。对于人马臂的一段来说，观察到的 56° 俯仰角非常高。我们讨论将此特征作为较低桨距角人马座臂内的子结构、支线或孤立结构的可能解释。
Context. In spiral galaxies, star formation tends to trace features of the spiral pattern, including arms, spurs, feathers, and branches. However, in our own Milky Way, it has been challenging to connect individual star-forming regions to their larger Galactic environment owing to our perspective from within the disk. One feature in nearly all modern models of the Milky Way is the Sagittarius Arm, located inward of the Sun with a pitch angle of ∼12°. Aims. We map the 3D locations and velocities of star-forming regions in a segment of the Sagittarius Arm using young stellar objects (YSOs) from the Spitzer/IRAC Candidate YSO (SPICY) catalog to compare their distribution to models of the arm. Methods. Distances and velocities for these objects are derived from Gaia EDR3 astrometry and molecular line surveys. We infer parallaxes and proper motions for spatially clustered groups of YSOs and estimate their radial velocities from the velocities of spatially associated molecular clouds. Results. We identify 25 star-forming regions in the Galactic longitude range ℓ ∼ 4. ° 0–18. ° 5 arranged in a narrow, ∼1 kpc long linear structure with a high pitch angle of ψ = 56° and a high aspect ratio of ∼7:1. This structure includes massive star-forming regions such as M8, M16, M17, and M20. The motions in the structure are remarkably coherent, with velocities in the direction of Galactic rotation of |Vφ|≈240 ± 3 km s−1 (slightly higher than average) and slight drifts inward (VR ≈ −4.3 km s−1) and in the negative Z direction (VZ ≈ −2.9 km s−1). The rotational shear experienced by the structure is ΔΩ = 4.6 km s−1 kpc−1. Conclusions. The observed 56° pitch angle is remarkably high for a segment of the Sagittarius Arm. We discuss possible interpretations of this feature as a substructure within the lower pitch angle Sagittarius Arm, as a spur, or as an isolated structure.