Winston Elaine, Hora Joseph L, Tolls Volker
Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge MA 02138, USA.
Astron J. 2020 Aug;160(2). doi: 10.3847/1538-3881/ab99c8. Epub 2020 Jul 16.
We have conducted a study of star formation in the outer Galaxy from 65°< < 265°in the region observed by the GLIMPSE360 program. This Spitzer warm mission program mapped the plane of the outer Milky Way with IRAC at 3.6 and 4.5 m. We combine the IRAC, Wide-field Infrared Survey Explorer (WISE), and Two Micron All Sky Survey catalogs and our previous results from another outer Galaxy survey and identify a total of 47,338 young stellar objects (YSOs) across the field spanning >180° in Galactic longitude. Using the DBSCAN method on the combined catalog, we identify 618 clusters or aggregations of YSOs having five or more members. We identify 10,476 class I, 29,604 class II, and 7325 anemic class II/class III YSOs. The ratio of YSOs identified as members of clusters was 25,528/47,338, or 54%. We found that 100 of the clusters identified have previously measured distances in the WISE H II survey. We used these distances in our spectral energy distribution (SED) fitting of the YSOs in these clusters, of which 96 had YSOs with <3 fits. We used the derived masses from the SED model fits to estimate the initial mass function (IMF) in the inner and outer Galaxy clusters; dividing the clusters by galactocentric distances, the slopes were Γ = 1.87 ± 0.31 above 3 for < 11.5 kpc and Γ = 1.15 ± 0.24 above 3 for > 11.5 kpc. The slope of the combined IMF was found to be Γ = 1.92 ± 0.42 above 3 . These values are consistent with each other within the uncertainties and with literature values in the inner Galaxy high-mass star formation regions. The slopes are likely also consistent with a universal Salpeter IMF.
我们对银盘外的恒星形成进行了一项研究，研究范围为在GLIMPSE360计划观测区域内，银经65°< < 265°的区域。这个斯皮策空间望远镜的热任务计划用IRAC在3.6微米和4.5微米波段绘制了银盘外的平面图像。我们将IRAC、广域红外巡天探测器（WISE）和两微米全天巡天目录以及我们之前在另一次银盘外观测中的结果相结合，在跨越银经>180°的整个区域内总共识别出47338个年轻恒星天体（YSO）。使用DBSCAN方法对合并后的目录进行分析，我们识别出618个由五个或更多成员组成的YSO星团或聚集区。我们识别出10476个I类、29604个II类以及7325个贫血II类/III类YSO。被识别为星团成员的YSO的比例为25528/47338，即54%。我们发现，在WISE H II巡天中，之前已经测量过其中100个已识别星团的距离。我们在对这些星团中的YSO进行光谱能量分布（SED）拟合时使用了这些距离，其中96个星团中的YSO有<3次拟合。我们使用从SED模型拟合中得出的质量来估计银盘内和银盘外星团的初始质量函数（IMF）；按照到银心的距离对星团进行划分，对于<11.5千秒差距，在3微米以上的斜率为Γ = 1.87 ± 0.31，对于>11.5千秒差距，在3微米以上的斜率为Γ = 1.15 ± 0.24。发现合并后的IMF在3微米以上的斜率为Γ = 1.92 ± 0.42。在不确定性范围内，这些值相互一致，并且与银盘内高质量恒星形成区域的文献值一致。这些斜率可能也与通用的萨尔皮特IMF一致。
