摘要
星系棒的图案速度(或转动角速度)是棒旋星系的一个最重要的动力学参量。棒的图案速度?_(bar)的测量并不容易。目前直接测量?_(bar)的唯一方法是Tremaine和Weinberg (TW)在1984年提出来的。他们假设星系中示踪源的表面亮度满足连续性方程,即可利用示踪源的测光学和运动学参量推导出?_(bar)。详细介绍了TW方法,整理了文献中?_(bar)的测量结果,并讨论了测量过程中的误差来源。目前学术界利用老年恒星、中性氢气体H I、分子氢气体H_2,以及离化氢气体Hα作为示踪源,测量了大约50个星系的图案速度,并结合?_(bar)和星系自转曲线得到共转半径RCR。通过比较RCR和棒长a_(bar)发现,大部分星系棒都是快速旋转的(1≦RCR/a_(bar)≦1.4)。极少部分星系棒慢速旋转,并且这些棒似乎都位于由暗物质主导的星系中。同时也有研究声称发现了一些超快旋转的棒,但目前理论上无法解释它们,也无法确定它们的?_(bar)是否可靠,或是否由于违反了TW方法的某些条件而导致测量结果不准确。由于已有的测量样本太小,并偏向于早型星系,人们暂未发现图案速度与星系类型及星系棒性质之间的关系,但人们认为,星系棒的图案速度有可能与星系中暗物质的分布有关。积分视场光谱仪(integral field unit, IFU)巡天数据在测量?_(bar)上有着独特的优势。随着IFU数据的普及,未来将有更多的TW测量结果来检验这些结论。
The bar pattern speed,or angular speed,is one of the most important dynamical parameters in barred galaxies.Unfortunately,the measurement of bar pattern speed(Ωbar)is somewhat elusive.The only direct method for measuring the bar pattern speed was proposed by Tremaine&Weinberg(TW)in1984.Assuming that a trace population satisfies the continuity equation,the TW method derives the bar pattern speed by using the photometric and kinematic information of the tracer population.We present a detailed description of the TW method and additionally compile together a list of the current measured values ofΩbar found in the literature.We discuss the sources of error in the measurements.Previous studies have successfully applied the TW method to around50galaxies by using old stars,neutral hydrogen(H I),molecular hydrogen(H2)or ionized hydrogen(Hα)as the tracer population.The corotation radius(RCR)of a galaxy can be derived by combining its bar pattern speed and circular velocity curve.By comparing the RCR and bar length(αbar),previous studies have shown that most of the bars are rotating fast(1≤RCR/αbar≤1.4).A few bars rotate slowly,and all of their host galaxies seem to be dominated by dark matter.Some ultra-fast bars are also reported,which is difficult to explain by current theories.Either theirΩbar measurements are poor,or their tracer population violates the assumptions of the TW method.So far only a small sample of galaxies haveΩbar measurements,and the sample is biased towards early-type galaxies.No correlation is found betweenΩbar and galaxy morphology,or bar properties.However,Ωbar may be related to the distribution of dark matter in the galaxy center.Integral field unit(IFU)surveys have unique advantages on the measurement ofΩbar.More measurements of bar pattern speed from IFU data are necessary to investigate the relationship betweenΩbar and galaxy properties.
作者
邹燕飞
沈俊太
ZOU Yan-fei;SHEN Jun-tai(Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory,Chinese Academy of Sciences, Shanghai 200030, China;University of Chinese Academy of Sciences,Beijing 100049, China)
出处
《天文学进展》
CSCD
北大核心
2018年第4期366-383,共18页
Progress In Astronomy
基金
国家自然科学基金(11773052
11333003
11761131016)
973项目(2014CB845700)
