Witnessing the fragmentation of a filament into prestellar cores in Orion B/NGC 2024
Witnessing the fragmentation of a filament into prestellar cores in Orion B/NGC 2024
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在猎户座 B/NGC 2024 中见证细丝碎裂成星际核心
DOI：
10.1051/0004-6361/202140857
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发表时间：
2023
影响因子：
6.5
通讯作者：
Konyves V.
中科院分区：
文献类型：
--
作者：
Shimajiri Y.;Andre Ph.;Peretto N.;Arzoumanian D.;Ntormousi E.;Konyves V.
赫歇尔最近对附近分子云的观测表明，丝状结构无处不在，而且大多数星际核心都是以致密的丝状形式形成的。因此，探测分子丝的详细密度和速度结构对于提高我们对恒星形成过程的观测理解至关重要。目的我们的目标是表征典型分子丝在分裂成核心的过程中的密度和速度场。方法我们用Nobeyama 45m望远镜绘制了猎户座B分子云中NGC 2024区域的一部分，在 12CO (J= 1–0)、13CO (J= 1–0)、 C18O (J= 1–0) 和 H13CO+(J= 1–0) 线，以及 NGC 2024 的西南部分，对应于 NGC 2024S 灯丝，在 H13CO+(J= 1–0) 中使用北方扩展毫米波阵列 (NOEMA) 干涉仪。结果 13CO、C18O 和 H13CO+ 发射图至少部分跟踪在 8 英寸分辨率的 ArTéMiS+Herscheldata 中看到的丝状结构。从 ArTéMiS+Herscheldust 发射数据得出的 NGC 2024S 灯丝的中值径向柱密度分布与半功率直径 DHPPlummer=0.081±0.014 pc 的 Plummer 分布很好地拟合，这与之前用 Herschel 对附近分子灯丝的研究结果相似。 另一方面，从 Nobeyama13CO 和 Nobeyama13CO 测量的 NGC 2024S 的半功率直径C18O 数据比用赫歇尔测量的细丝直径更宽，并且源自 H13CO+ 数据的半功率直径更窄。这些结果表明，13CO 和 C18O 数据仅追踪赫歇尔细丝的（低密度）外部部分，而 H13CO+ 数据仅追踪（致密）内部部分。我们在 NOEMA 覆盖的 Herschelmap 部分中识别出四个核心，并发现每个 Herschelcore 对应于在组合的 NOEMA+45m H13CO+数据立方体中检测到的单个核心。 Nobeyama H13CO+质心速度图揭示了NGC 2024S灯丝长轴和短轴上的速度梯度，以及沿长轴周期λ~0.2 pc的速度振荡。质心速度和柱密度分布之间的比较显示了 H13CO+ 或 C18O 中的暂定 λ/4 相移。在任何单个示踪剂中的所有核心中都没有同时观察到这种 λ/4 偏移，但在 H13CO+ 或 C18O 中的每个核心中暂时观察到了这种 λ/4 偏移。 H13CO+ 和 C18O 速度模式之间的差异可能源于 H13CO+ 和 C18O 探测的密度范围的差异。我们制作了一个玩具模型，该模型考虑了三个速度场分量：横向速度梯度、纵向速度梯度和由破碎引起的纵向振荡模式。综合数据的检查表明，纵向振荡分量在模型的速度结构函数中产生振荡模式。由于 Nobeyama H13CO+质心速度数据的速度结构函数确实显示出振荡模式，因此我们建议我们的观测部分追踪了核心形成运动以及 NGC 2024S 细丝分裂成核心的过程。我们还发现 NGC 2024S 中的平均核心质量对应于灯丝中的有效 Bonnor-Ebert 质量。这与在更高线质量的细丝中形成更高质量的核的情况是一致的。
ContextRecentHerschelobservations of nearby molecular clouds have shown that filamentary structures are ubiquitous and that most prestellar cores form in dense filaments. Probing the detailed density and velocity structure of molecular filaments is therefore crucial for improving our observational understanding of the star formation process.AimsWe aim to characterize both the density and the velocity field of a typical molecular filament in the process of fragmenting into cores.MethodsWe mapped a portion of the NGC 2024 region in the Orion B molecular cloud with the Nobeyama 45m telescope, in the12CO (J= 1–0),13CO (J= 1–0), C18O (J= 1–0), and H13CO+(J= 1–0) lines, and the southwestern part of NGC 2024, corresponding to the NGC 2024S filament, with the NOrthern Extended Millimeter Array (NOEMA) interferometer in H13CO+(J= 1–0).ResultsThe maps of13CO, C18O, and H13CO+emission trace at least part of the filamentary structure seen in the 8″ resolution ArTéMiS+Herscheldata. The median radial column density profile of the NGC 2024S filament as derived from ArTéMiS+Herscheldust emission data is well fitted by a Plummer profile with a half-power diameterDHPPlummer=0.081±0.014 pc, which is similar to the findings of previous studies of nearby molecular filaments withHerschel.On the other hand, the half-power diameters of NGC 2024S as measured from the Nobeyama13CO and C18O data are broader than, and the half-power diameter derived from the H13CO+data narrower than the filament diameter measured withHerschel.These results suggest that the13CO and C18O data trace only the (low-density) outer part of theHerschelfilament and the H13CO+data only the (dense) inner part. We identify four cores in the portion of theHerschelmap covered by NOEMA and find that eachHerschelcore corresponds to a single core detected in the combined NOEMA+45m H13CO+data cube. The Nobeyama H13CO+centroid velocity map reveals velocity gradients along both the major and the minor axis of the NGC 2024S filament, as well as velocity oscillations with a periodλ~0.2 pc along the major axis. Comparison between the centroid velocity and the column density distribution shows a tentativeλ/4 phase shift in H13CO+or C18O. Thisλ/4 shift is not simultaneously observed for all cores in any single tracer but is tentatively seen for each core in either H13CO+or C18O. The difference between the H13CO+and C18O velocity patterns may arise from differences in the range of densities probed by H13CO+and C18O. We produced a toy model that takes into account the three velocity-field components: a transverse velocity gradient, a longitudinal velocity gradient, and a longitudinal oscillation mode caused by fragmentation. Examination of synthetic data shows that the longitudinal oscillation component produces an oscillation pattern in the velocity structure function of the model. Since the velocity structure function of the Nobeyama H13CO+centroid velocity data does show an oscillation pattern, we suggest that our observations are partly tracing core-forming motions and the fragmentation of the NGC 2024S filament into cores. We also find that the mean core mass in NGC 2024S corresponds to the effective Bonnor-Ebert mass in the filament. This is consistent with a scenario in which higher-mass cores form in higher-line-mass filaments.
NGC 1068 中的恒星形成
DOI：
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发表时间：
1983
期刊：
影响因子：
--
作者：
D. Weedman
通讯作者：
D. Weedman