Forming Super Star Clusters in the Central Starburst of NGC 253
Forming Super Star Clusters in the Central Starburst of NGC 253
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DOI：
10.3847/1538-4357/aaecd1
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发表时间：
2018-04
期刊：
影响因子：
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通讯作者：
A. Leroy;A. Bolatto;E. Ostriker;F. Walter;M. Gorski;A. Ginsburg;N. Krieger;R. C. Levy;D. Meier
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文献类型：
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作者：
A. Leroy;A. Bolatto;E. Ostriker;F. Walter;M. Gorski;A. Ginsburg;N. Krieger;R. C. Levy;D. Meier
NGC 253 拥有最近的核星暴。先前的观测显示该区域富含分子气体，并且有与最近恒星形成相关的稠密云层。我们使用阿塔卡马大型亚毫米/毫米阵列 (ALMA) 以 2 pc 分辨率对该区域的 350 GHz 灰尘连续谱和分子线发射进行成像。我们的观察揭示了〜14个明亮、紧凑（〜2-3 pc FWHM）的灰尘排放结。这些源中的大多数很可能正在形成超级星团 (SSC)，这是基于其推断的动力学和气体质量、与 36 GHz 无线电连续谱发射的关联以及与追踪致密激发气体的线发射的一致性。其中一个源与已知的 SSC 重合，但其余源在哈勃近红外 (IR) 成像中仍然不可见。我们的观察表明，气体仍然占这些来源总质量的很大一部分。它们在 350 GHz 的高亮度温度也意味着在红外光谱能量分布峰值附近有很大的光学深度。因此，这些光源可能具有较大的红外光球层，并且红外辐射力可能超过 L/c。尽管如此，观察到的中等速度色散表明，来自辐射、风和超新星的反馈尚未扰乱大多数来源。这种恒星形成模式似乎在爆发中产生了很大一部分恒星。我们主张这样一种情况：这个阶段持续~1 Myr，之后星团脱落它们的诞生茧，但继续产生电离光子。驱动观察到的冷气体和 X 射线流出的强烈反馈可能发生在星团从这个早期阶段出现之后。
NGC 253 hosts the nearest nuclear starburst. Previous observations show a region rich in molecular gas, with dense clouds associated with recent star formation. We used the Atacama Large Submillimeter/Millimeter Array (ALMA) to image the 350 GHz dust continuum and molecular line emission from this region at 2 pc resolution. Our observations reveal ∼14 bright, compact (∼2–3 pc FWHM) knots of dust emission. Most of these sources are likely to be forming super star clusters (SSCs) based on their inferred dynamical and gas masses, association with 36 GHz radio continuum emission, and coincidence with line emission tracing dense, excited gas. One source coincides with a known SSC, but the rest remain invisible in Hubble near-infrared (IR) imaging. Our observations imply that gas still constitutes a large fraction of the overall mass in these sources. Their high brightness temperature at 350 GHz also implies a large optical depth near the peak of the IR spectral energy distribution. As a result, these sources may have large IR photospheres, and the IR radiation force likely exceeds L/c. Still, their moderate observed velocity dispersions suggest that feedback from radiation, winds, and supernovae are not yet disrupting most sources. This mode of star formation appears to produce a large fraction of stars in the burst. We argue for a scenario in which this phase lasts ∼1 Myr, after which the clusters shed their natal cocoons but continue to produce ionizing photons. The strong feedback that drives the observed cold gas and X-ray outflows likely occurs after the clusters emerge from this early phase.