RUI: Star Formation and Interstellar Gas in Extragalactic Tails and Bridges

星系之间的碰撞和近距离接触会引起星系的重大变化，极大地改变了星系的形态和恒星的形成速度。这种相互作用的一个常见后果是产生延伸的尾和桥，其中通常包含大质量的年轻恒星。这些结构可能会破碎和/或分散，形成新的矮星系和/或丰富星系间介质。目前，关于这些特征中的星际气体和恒星形成的性质仍有许多悬而未决的问题。在这些特征中，恒星形成的速率和效率是多少？它们是如何依赖于相互作用参数和时间尺度的？这些结构中的星际气体有什么特性？这些特征的性质是否与它们是矮星系的前身相一致？这些特征中的恒星形成是否受到“阈值”效应的影响，只发生在“临界”气体表面密度以上？为了解决这些问题，东田纳西州立大学（East Tennessee State University）的贝弗利·史密斯（Beverly Smith）博士将对24个尾星系和桥星系样本以及一个类似大小的矮星系样本进行全面的多波长研究。利用多波长数据，史密斯博士将测量原子与分子的氢比、金属丰度、恒星形成率以及这些尾和桥的效率，并将确定这些如何依赖于相互作用的参数。她将确定这些尾巴和桥的特性与矮星系的特性进行比较。这些观测将与样品中系统的流体动力学建模一起进行，这将更好地定义相互作用参数，并帮助确定触发尾和桥中恒星形成所需的条件。利用这些结果，史密斯博士将在彗尾和桥中寻找恒星形成的“阈值”，类似于在星系盘中发现的情况，并将调查潮汐特征下的恒星形成效率是否比理论模型所预测的由撞击压力剥离引起的特征更高。该奖项是在美国国家科学基金会本科院校研究项目的支持下颁发的

AST-0205761SmithCollisions and close encounters between galaxies can cause major changes in the galaxies, dramatically altering both the morphology and star formation rate. A frequent consequenceof such an interaction is the production of extended tails and bridges, which often contain massive young stars. These structures may fragment and/or disperse, forming new dwarf galaxies and/or enriching the intergalactic medium. At present, there are still many outstanding questions about the properties of the interstellar gas and star formation in these features. What are the rates and efficiencies of star formation in these features, and how do these depend on the interaction parameters and timescales? What are the properties of the interstellar gas in these structures? Are the properties of these features consistent with them being the precursors of dwarf galaxies? Is star formation in these features subject to a `threshold' effect, only occurring above a `critical' gas surface density?To address these questions, Dr. Beverly Smith, at East Tennessee State University, will carry out a comprehensive multi-wavelength study of a sample of two dozen tails and bridges and a similar size comparison sample of dwarf galaxies. Using multi-wavelength data, Dr. Smith will measure the atomic to molecular hydrogen ratios, metallicities, star formation rates, and efficiencies in these tails and bridges, and will determine how these depend upon the parameters of the interaction. She will determine how the properties of these tails and bridges compare with those of dwarf galaxies. These observations will be done in conjunction with hydrodynamical modeling of the systems in the sample, which will better define the interaction parameters and help determine the conditions needed to trigger star formation in tails and bridges. Using these results, Dr. Smith will search for a star formation `threshold' in tails and bridges analogous to that found for galactic disks, and will investigate whether the efficiency of star formation is higher in tidal features than in features caused by ram pressure stripping, as predicted by theoretical models. This award is made under the auspices of the Research in Undergraduate Institutions program at NSF.***