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

星系之间的SmithCollision和近距离碰撞会导致星系的重大变化，极大地改变星系的形态和恒星形成速度。这种相互作用的一个常见结果是产生延长的尾巴和桥，其中通常包含大质量的年轻恒星。这些结构可能碎裂和/或分散，形成新的矮星系和/或丰富星际介质。目前，在这些特征中，星际气体的性质和恒星的形成仍然存在许多突出的问题。在这些特征中恒星形成的速率和效率是多少，这些又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的性质是什么？这些特征的性质是否与它们是矮小星系的前驱相一致？在这些特征中恒星的形成是否受到“阈值”效应的影响，只有在“临界”气体表面密度以上才会形成？为了解决这些问题，东田纳西州立大学的贝弗利·史密斯博士将对20多个尾巴和桥的样本以及一个类似大小的矮星系比较样本进行一项全面的多波长研究。使用多波长数据，史密斯博士将测量原子与分子氢的比率、金属含量、恒星形成率以及这些尾巴和桥中的效率，并将确定这些因素如何依赖于相互作用的参数。她将确定这些尾巴和桥梁的性质与矮小星系的性质相比如何。这些观测将结合对样本中系统的流体动力学建模进行，这将更好地定义相互作用参数，并有助于确定触发尾巴和桥梁中恒星形成所需的条件。利用这些结果，史密斯博士将在恒星形成的尾部和桥梁中寻找一个类似于星系盘的恒星形成“阈值”，并将研究是否像理论模型预测的那样，在潮汐特征下恒星形成的效率高于冲压剥离导致的恒星形成效率。该奖项是在美国国家科学基金会本科院校研究项目的赞助下颁发的。

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.***