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arXiv 0804.0828astro-ph
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Spitzer对M33和热星H II区域连接的观测

Spitzer Observations of M33 and the Hot Star, H II Region Connection

Robert H. Rubin, Janet P. Simpson, Sean W. J. Colgan, Reginald J. Dufour, Gregory Brunner, Ian A. McNabb, Adalbert W. A. Pauldrach, Edwin F. Erickson, Michael R… 展开作者

Robert H. Rubin, Janet P. Simpson, Sean W. J. Colgan, Reginald J. Dufour, Gregory Brunner, Ian A. McNabb, Adalbert W. A. Pauldrach, Edwin F. Erickson, Michael R. Haas, Robert I. Citron

摘要:

我们用斯皮策太空望远镜在河外的一些H Ⅱ区观测到了[S Ⅳ] 10.51,H(7-6)12.37,[Ne Ⅱ] 12.81,[Ne Ⅲ] 15.56和[S Ⅲ] 18.71 μ m的发射线。之前的一篇论文介绍了我们对基本上面对面的螺旋星系M83的数据和分析。在这里,我们报告我们的结果,本集团螺旋星系M33。所选星云覆盖了很宽的银河系中心半径(R_G)范围。观测是用红外光谱仪的短波长、高分辨率模块进行的。上面的五条线是同空间观测的,因此可以对通量进行可靠的比较。从测量的通量,我们确定了离子丰度比,包括Ne++/Ne+,S ~(3+)/S ~(++),S ~(++)/Ne ~(++),发现随着R_G的增大,电离度逐渐增大。通过对H Ⅱ区的Ne(Ne+,Ne++)和S(S++,S ~(3+))的主要电离态取样,我们可以估算Ne/H,S/H和Ne/S比值。由线性最小二乘拟合发现,金属丰度随R_G的增加而降低:dlog(Ne/H)/dR_G = -0.058 ± 0.014和dlog(S/H)/dR_G = -0.052 ± 0.021dex kpc ~(-1)。Ne/S比值随R_G的变化不明显。与我们之前对M83的类似研究不同,我们在研究中确认该比值是上限,而对于M33,导出的比值可能是Ne/S的可靠指标。这是因为H II区的金属丰度比M83低,电离度比M83高。Ne和S都是在恒星中C和O燃烧后的α-链式反应中产生的主要元素,使得它们的产量对恒星金属丰度的依赖性很小。因此,可以预期Ne/S在整个星系中保持相对恒定。M33中H II区的Ne/S比值中位数(平均值)为16.3(16.9),略高于

英文摘要:

We have observed emission lines of [S IV] 10.51, H(7-6) 12.37, [Ne II] 12.81, [Ne III] 15.56, and [S III] 18.71 um in a number of extragalactic H II regions with the Spitzer Space Telescope. A previous paper presented our data and analysis for the substantially face-on spiral galaxy M83. Here we report our results for the local group spiral galaxy M33. The nebulae selected cover a wide range of galactocentric radii (R_G). The observations were made with the Infrared Spectrograph with the short wavelength, high resolution module. The above set of five lines is observed cospatially, thus permitting a reliable comparison of the fluxes. From the measured fluxes, we determine the ionic abundance ratios including Ne++/Ne+, S3+/S++, and S++/Ne+ and find that there is a correlation of increasingly higher ionization with larger R_G. By sampling the dominant ionization states of Ne (Ne+, Ne++) and S (S++, S3+) for H II regions, we can estimate the Ne/H, S/H, and Ne/S ratios. We find from linear least-squares fits that there is a decrease in metallicity with increasing R_G: d log (Ne/H)/dR_G = -0.058+-0.014 and d log (S/H)/dR_G = -0.052+-0.021 dex kpc-1. There is no apparent variation in the Ne/S ratio with R_G. Unlike our previous similar study of M83, where we conjectured that this ratio was an upper limit, for M33 the derived ratios are likely a robust indication of Ne/S. This occurs because the H II regions have lower metallicity and higher ionization than those in M83. Both Ne and S are primary elements produced in alpha-chain reactions, following C and O burning in stars, making their yields depend very little on the stellar metallicity. Thus, it is expected that Ne/S remains relatively constant throughout a galaxy. The median (average) Ne/S ratio derived for H II regions in M33 is 16.3 (16.9), just slightly higher than

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