S255N中存在大质量原星系团的证据
Evidence for a Massive Protocluster in S255N
摘要：
S255 N是一个明亮的远红外源，包含许多活跃恒星形成的迹象，但缺乏一个突出的近红外星团。我们目前通过无线电观测中红外线，旨在探索该地区的演化状态。我们的观测资料包括亚毫米阵列的1.3毫米连续谱和谱线数据、VLA的3.6厘米连续谱和1.3厘米水脉泽数据以及斯皮策空间望远镜的1.3厘米水脉泽图像。在我们的3.6厘米高分辨率多组态图像中，清晰地显示了先前已知的UCHII区域G192.584 - 0.041的彗星形态。1.3mm的连续辐射被分解为三个致密的核心，它们都是以尘埃辐射为主，半径<7000AU。这些核心的质量估计范围从6到35 Msun。最明亮的尘埃核心（SMA1）的质心偏离彗星UCHII区域的峰值1.1 "（2800 AU），并显示出该区域最强的HC3N，CN和DCN线发射。SMA1也表现出紧凑的CH3OH，SiO和H2CO排放，并可能包含一个年轻的热核。我们发现空间和运动学的证据表明，SMA1可能包含进一步的多重性，与一个新检测到的H2O脉泽的组件一致。没有中红外点源对应于任何尘埃核，进一步表明这些物体的早期演化阶段。主要的中红外辐射是一种漫反射的宽带成分，它跟踪彗星UCHII区域的表面，但被其南部边缘的前景物质所掩盖。另外一个4.5微米的线性特征从SMA1的东北方向发出，与一群甲醇脉泽对准，并可能追踪到SMA1内原恒星的外流。我们的观测提供了直接的证据，证明S255N正在形成一个由中等质量到高质量恒星组成的星团。
英文摘要：
S255N is a luminous far-infrared source that contains many indications of active star formation but lacks a prominent near-infrared stellar cluster. We present mid-infrared through radio observations aimed at exploring the evolutionary state of this region. Our observations include 1.3mm continuum and spectral line data from the Submillimeter Array, VLA 3.6cm continuum and 1.3cm water maser data, and multicolor IRAC images from the Spitzer Space Telescope. The cometary morphology of the previously-known UCHII region G192.584-0.041 is clearly revealed in our sensitive, multi-configuration 3.6cm images. The 1.3mm continuum emission has been resolved into three compact cores, all of which are dominated by dust emission and have radii < 7000AU. The mass estimates for these cores range from 6 to 35 Msun. The centroid of the brightest dust core (SMA1) is offset by 1.1'' (2800 AU) from the peak of the cometary UCHII region and exhibits the strongest HC3N, CN, and DCN line emission in the region. SMA1 also exhibits compact CH3OH, SiO, and H2CO emission and likely contains a young hot core. We find spatial and kinematic evidence that SMA1 may contain further multiplicity, with one of the components coincident with a newly-detected H2O maser. There are no mid-infrared point source counterparts to any of the dust cores, further suggesting an early evolutionary phase for these objects. The dominant mid-infrared emission is a diffuse, broadband component that traces the surface of the cometary UCHII region but is obscured by foreground material on its southern edge. An additional 4.5 micron linear feature emanating to the northeast of SMA1 is aligned with a cluster of methanol masers and likely traces a outflow from a protostar within SMA1. Our observations provide direct evidence that S255N is forming a cluster of intermediate to high-mass stars.
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