No temperature fluctuations in the giant H II region H 1013
No temperature fluctuations in the giant H II region H 1013
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巨型 H II 区 H 1013 没有温度波动
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
B. Brandl
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作者：
G. Stasińska;C. Morisset;S. Simón;S. Simón;F. Bresolin;D. Schaerer;D. Schaerer;B. Brandl
虽然碰撞激发线在H II区域可以很容易地探测星系中星际介质的化学成分，重要的温度波动的可能存在投下了一些怀疑的衍生丰度。为了给这个问题提供新的见解，我们对位于星系M101中的巨大H II区H 1013进行了详细的研究，该区域有许多观测数据，并被认为存在t2 = 0.03− 0.06的温度波动。我们首先用斯皮策太空望远镜获得的中红外光谱补充了现有的光学观测数据集。结合光学数据，该光谱提供了关于这个巨大的H II区域的温度结构的前所未有的信息。基于经验温度诊断的初步分析表明，温度波动应该相当微弱。然而，只有详细的光电离分析，考虑到物体的几何形状和观测孔径，才能正确地利用所有的观测数据。我们使用基于光电离代码Cloudy的Cloudy 3D软件包进行了这样的研究。我们已经能够产生的光电离模型所观察到的Hsurface亮度分布和电离恒星人口的已知属性比可以占大多数的线比在其不确定性的约束。由于观测约束既强又多，这就反对H 1013存在显著的温度波动。我们的最佳模型的氧丰度为12 + log O/H = 8.57，而Esteban等人（2009）和Bresolin（2007）分别主张的值为8.73和8.93，这是基于他们得出的显著温度波动。然而，我们的模型无法重现Esteban等人（2009）观察到的氧复合线的强度，以及Bresolin（2007）推断的非常低的Balmer跳跃温度。我们认为，由于观测困难，后者可能是错误的。另一方面，模型和观测之间关于复合线的差异不能归因于观测的不确定性，需要温度波动以外的解释。
While collisionally excited lines in H II regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived abundan ces. To provide new insights into this question, we have carried out a detailed study of a giant H II region, H 1013, located in the galaxy M101, for which many observational data exist and which has been claimed to harbour temperature fluctuations at a level of t 2 = 0.03− 0.06. We have first complemented the already available optical observational datasets with a mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with optical data, this spectrum provides unprecedented information on the temperature structure of this giant H II region. A preliminary analysis based on empirical temperature diagnostics suggests that temperature fluctuations should be quite weak. However , only a detailed photoionization analysis taking into acco unt the geometry of the object and observing apertures can make a correct use of all the observational data. We have performed such a study using the Cloudy 3D package based on the photoionization code Cloudy. We have been able to produce photoionization models constrained by the observed Hsurface brightness distribution and by the known properties of the ionizing stellar population than can account for most of the line ratios within their uncertainties. Since the observational constraint s are both strong and numerous, this argues against the presence of significant temperature fluctuations in H 1013. The oxygen abund ance of our best model is 12 + log O/H = 8.57, as opposed to the values of 8.73 and 8.93 advocated by Esteban et al. (2009) and Bresolin (2007), respectively, based on the significant tem perature fluctuations they derived. However, our model is not able to reproduce the intensities of the oxygen recombination lines observed by Esteban et al. (2009), as well as the very low Balmer jump temperature inferred by Bresolin (2007). We have argued that the latter might be in error, due to observational difficulties. On the other h and, the discrepancy between model and observation as regards the recombination lines cannot be attributed to observational uncertainties and requires an explanation other than te mperature fluctuations.