Andromeda galaxy中弥漫星际带的观测：M31 OB星的光谱学
A survey of diffuse interstellar bands in the Andromeda galaxy: optical spectroscopy of M31 OB stars
摘要：
我们提出了迄今为止最大的样本的中分辨率蓝到红光谱的B型超巨星在M31，并进行了第一次调查的弥漫星际带（DIBs）在这个星系。本文给出了M31三个区域34颗恒星的光谱分类、视向速度和星际红化。给出了5780和6283 DIB对11颗恒星的径向速度和等效宽度。在M31的三条视线中检测到的以下DIB的等效宽度也被呈现：4428、5705、5780、5797、6203、6269、6283、6379、6613、6660和6993。所有这些M31 DIB载体都以与星际Na I和/或H I相匹配的径向速度驻留在云中。DIB等效宽度与红化（E（B-V））之间的关系与在银河系局部ISM中观察到的一致。许多观测到的视线显示DIB强度（每单位红化）位于银河值范围的上端。DIB强度每单位变红（68%的置信度），与星际紫外辐射场强度。在星际紫外线通量最低的地方观察到最强的DIB。在我们的三个领域的平均斯皮策8/24微米的发射比略低于在银河系中测量，但我们确定这个比例和DIB的强度在M31之间没有相关性。从其中一个区域的三个M31 H II区的光谱中得出的星际氧丰度表明，该区域ISM的平均金属丰度为12 + log[O/H] = 8.54 +- 0.18，这大约等于太阳附近的值。
英文摘要：
We present the largest sample to-date of intermediate-resolution blue-to-red optical spectra of B-type supergiants in M31 and undertake the first survey of diffuse interstellar bands (DIBs) in this galaxy. Spectral classifications, radial velocities and interstellar reddenings are presented for 34 stars in three regions of M31. Radial velocities and equivalent widths are given for the 5780 and 6283 DIBs towards 11 stars. Equivalent widths are also presented for the following DIBs detected in three sightlines in M31: 4428, 5705, 5780, 5797, 6203, 6269, 6283, 6379, 6613, 6660, and 6993. All of these M31 DIB carriers reside in clouds at radial velocities matching those of interstellar Na I and/or H I. The relationships between DIB equivalent widths and reddening (E(B-V)) are consistent with those observed in the local ISM of the Milky Way. Many of the observed sightlines show DIB strengths (per unit reddening) which lie at the upper end of the range of Galactic values. DIB strengths per unit reddening are found (with 68% confidence), to correlate with the interstellar UV radiation field strength. The strongest DIBs are observed where the interstellar UV flux is lowest. The mean Spitzer 8/24 micron emission ratio in our three fields is slightly lower than that measured in the Milky Way, but we identify no correlation between this ratio and the DIB strengths in M31. Interstellar oxygen abundances derived from the spectra of three M31 H II regions in one of the fields indicate that the average metallicity of the ISM in that region is 12 + log[O/H] = 8.54 +- 0.18, which is approximately equal to the value in the solar neighbourhood.
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