HII区与M33的绝对散射：金属丰度方位角变化的证据吗？
The Abundance Scatter in M33 from HII Regions: Is There Any Evidence for Azimuthal Metallicity Variations?
摘要：
用Gemini North望远镜的GMOS摄谱仪获得了M33盘内2kpc的25个H Ⅱ区的光谱。从[O III]4363极光线的探测中测得的氧丰度梯度显示了大约0.06 dex的散射，比Rosolowsky和Simon最近报道的这个星系的值要小得多。对来自R23强线指示器的H II区域的大样本的丰度分析证实，在M33的整个盘上，散射很小，与测量的不确定性一致，并且与在其他旋涡星系中观察到的情况相当。因此，没有证据表明该星系中星际介质的金属丰度在空间尺度上从100 pc到几kpc存在显著的方位角变化。相当一部分M33 H II区域的极光线探测显示出的光谱特征揭示了硬电离辐射源（如He II发射和大的[Ne III]，[O III]线通量）。由于R23在这种情况下严重低估了氧的丰度，因此在基于这一强线指标的河外H II区域的化学丰度研究中必须小心。
英文摘要：
Optical spectra of 25 H II regions in the inner two kpc of the M33 disk have been obtained with the GMOS spectrograph at the Gemini North telescope. The oxygen abundance gradient measured from the detection of the [O III]4363 auroral line displays a scatter of approximately 0.06 dex, a much smaller value than recently reported by Rosolowsky & Simon in this galaxy. The analysis of the abundances for a large sample of H II regions derived from the R23 strong-line indicator confirms that the scatter is small over the full disk of M33, consistent with the measuring uncertainties, and comparable to what is observed in other spiral galaxies. No evidence is therefore found for significant azimuthal variations in the present-day metallicity of the interstellar medium in this galaxy on spatial scales from ~100 pc to a few kpc. A considerable fraction of M33 H II regions with auroral line detections show spectral features revealing sources of hard ionizing radiation (such as He II emission and large [Ne III], [O III] line fluxes). Since R23 is shown to severely underestimate the oxygen abundances in such cases, care must be taken in chemical abundance studies of extragalactic H II regions based on this strong-line indicator.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
