Saral G, Hora J L, Audard M, Koenig X P, Martínez-Galarza J R, Motte F, Nguyen-Luong Q, Saygac A T, Smith H A
Department of Astronomy, University of Geneva, Ch. d'Ecogia 16, 1290 Versoix, Switzerland.
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
Astrophys J. 2017 Apr 20;839(2). doi: 10.3847/1538-4357/aa6575. Epub 2017 Apr 21.
We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH II regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H II regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.
我们展示了对恒星形成复合体W51和W43的研究结果，这是第一象限中最亮的两个复合体。为了确定W51和W43中的年轻恒星天体（YSO）种群，我们使用了基于中红外和2MASS/UKIDSS近红外数据的颜色-星等关系。我们在W51中识别出302个I类YSO和1178个II类/过渡盘候选体，在W43中识别出917个I类YSO和5187个II类/过渡盘候选体。我们还使用最小生成树（MST）方法在这两个区域识别出了数十组YSO。我们发现这两个区域的星团密度相似，尽管斯皮策太空望远镜无法探测到W43最密集的部分。通过使用II/I类比率，我们追踪了区域内的相对年龄，并根据星团的形态，我们认为几个恒星形成地点在年龄和物理条件方面是相互独立的。我们使用光谱能量分布拟合来识别大质量YSO（MYSO）候选体，因为它们在恒星形成过程中起着至关重要的作用，然后检查它们是否与任何大质量恒星形成示踪剂有关，如UCH II区、脉泽或致密碎片。我们在W51中分别识别出17个MYSO候选体，在W43中识别出14个，并且发现承载MYSO候选体的YSO组在位置上与W51中的H II区相关，尽管我们在W43中没有看到任何与先前识别出的大质量致密碎片相关的MYSO候选体。
