Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA
Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA
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DOI：
10.3847/1538-4357/ac8d93
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发表时间：
2022-08
期刊：
影响因子：
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通讯作者：
T. O’Neill;R. Indebetouw;K. Sandstrom;A. Bolatto;K. Jameson;L. Carlson;Molly K. Finn;M. Meixner;E. Sabbi;M. Sewiło
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作者：
T. O’Neill;R. Indebetouw;K. Sandstrom;A. Bolatto;K. Jameson;L. Carlson;Molly K. Finn;M. Meixner;E. Sabbi;M. Sewiło
NGC 602是小麦哲伦星云中“翅膀”区域的一个年轻且贫金属的星团。我们通过对相关的H II区N90中分子气体的高分辨率（约0.4秒差距）阿塔卡马大型毫米波/亚毫米波阵列观测结果进行分析，揭示了该星团近期的演化历史。我们识别出了110个由一氧化碳发射所追踪的分子团块（半径<0.8秒差距），并研究了这些团块与相关的年轻恒星天体（YSOs）和主序前（PMS）恒星之间的关系。这些团块具有较高的位力参数（典型的α位力 = 4 - 11），并且可能保留着相邻的超巨壳SMC - SGS 1的中性氢成分在过去约800万年之内发生碰撞的痕迹。我们得到了一个一氧化碳亮区到氢气的转换因子，即X_CO,B = (3.4 ± 0.2)×10²⁰ 平方厘米⁻²（开尔文·千米·秒⁻¹）⁻¹，并对一氧化碳暗氢气体的观测团块特性进行校正，从而得出N90中的总分子气体质量为16600 ± 2400倍太阳质量。通过将年轻恒星天体的总质量与总分子气体质量进行比较，我们得出近期（约100万年）的恒星形成率为130 ± 30倍太阳质量每百万年，效率为8% ± 3%。在团块特性或主序前恒星年龄与距NGC 602的距离之间几乎不存在明显的径向趋势。在最年轻（约200万年）的恒星代中，我们没有发现触发恒星形成情景的证据，相反，我们得出结论，NGC 602并未直接导致该区域近期恒星形成的顺序恒星形成过程是有可能的。
NGC 602 is a young, low-metallicity star cluster in the “Wing” of the Small Magellanic Cloud. We reveal the recent evolutionary past of the cluster through analysis of high-resolution (∼0.4 pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated H ii region N90. We identify 110 molecular clumps (R < 0.8 pc) traced by CO emission, and study the relationship between the clumps and associated young stellar objects (YSOs) and pre-main-sequence (PMS) stars. The clumps have high virial parameters (typical α vir = 4–11) and may retain signatures of a collision in the last ≲8 Myr between H i components of the adjacent supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H2 gas conversion factor of X CO,B = (3.4 ± 0.2) × 1020 cm−2 (K km s−1)−1, and correct observed clump properties for CO-dark H2 gas to derive a total molecular gas mass in N90 of 16,600 ± 2400 M ⊙. We derive a recent (≲1 Myr) star formation rate of 130 ± 30 M ⊙ Myr−1 with an efficiency of 8% ± 3% assessed through comparing total YSO mass to total molecular gas mass. Very few significant radial trends exist between clump properties or PMS star ages and distance from NGC 602. We do not find evidence for a triggered star formation scenario among the youngest (≲2 Myr) stellar generations, and instead conclude that a sequential star formation process in which NGC 602 did not directly cause recent star formation in the region is likely.