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arXiv 1209.3011astro-ph.GA
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合并矮星系UM 448:来自VLT积分场谱的电离气体的化学动力学

The merging dwarf galaxy UM 448: chemodynamics of the ionized gas from VLT integral field spectroscopy

B. L. James, Y. G. Tsamis, M. J. Barlow, J. R. Walsh, M. S. Westmoquette

摘要:

使用VLT/FLAMES光学IFU观察,我们提出了一个详细的研究UM 448,附近的蓝色紧凑星系(BCG)以前报告有一个令人不安的高N/O丰度比。NTT/SuSI 2图像揭示了一种形态,暗示了两种对比色系统的合并,而我们的H-α发射图将UM 448分解为三个独立的区域,这些区域与恒星连续峰不一致。UM 448具有复杂的发射线轮廓,其线由窄的中心分量、底层宽分量和第三窄的蓝移分量组成。径向速度图显示了横跨UM 448的固体旋转的迹象,投影旋转轴与星系的连续形态相关。空间分辨,化学动力学分析。虽然UM 448的东尾具有典型的BCG电子温度(Te),但我们在星系主体内发现了一个区域,其中窄和宽的[O III] 4363线分量的温度相差5000 K,氧丰度相差0.4 dex。我们测量空间分辨和集成的离子和元素丰度为O,N,S和Ne在整个UM 448,并发现他们不同意,可能是由于磁通量加权Te从集成的光谱。这对来自附近和遥远宇宙中恒星形成星系的长缝和综合光谱的丰度具有重要意义。我们确实发现了一个N/O比增强的区域,它在星系主体内延伸了约0.6 kpc ^2的区域。然而,与以前的研究相反,我们没有发现大量沃尔夫-拉叶人口的证据,并得出结论,WR星本身不能负责产生所观察到的N/O过剩。相反,富含N的区域的位置和扰动形态表明,相互作用引起的贫金属气体的流入可能是负责的。

英文摘要:

Using VLT/FLAMES optical IFU observations, we present a detailed study of UM 448, a nearby Blue Compact Galaxy (BCG) previously reported to have an anomalously high N/O abundance ratio. NTT/SuSI2 images reveal a morphology suggestive of a merger of two systems of contrasting colour, whilst our H-alpha emission maps resolve UM 448 into three separate regions that do not coincide with the stellar continuum peaks. UM 448 exhibits complex emission line profiles, with lines consisting of a narrow, central component, an underlying broad component and a third, narrow blue-shifted component. Radial velocity maps show signs of solid body rotation across UM 448, with a projected rotation axis that correlates with the continuum morphology of the galaxy. A spatially-resolved, chemodynamical analysis is presented. Whilst the eastern tail of UM 448 has electron temperatures (Te) that are typical of BCGs, we find a region within the main body of the galaxy where the narrow and broad [O III] 4363 line components trace temperatures differing by 5000K and oxygen abundances differing by 0.4 dex. We measure spatially resolved and integrated ionic and elemental abundances for O, N, S and Ne throughout UM 448, and find they do not agree, possibly due the flux-weighting of Te from the integrated spectrum. This has significant implications for abundances derived from long-slit and integrated spectra of star-forming galaxies in the nearby and distant universe. A region of enhanced N/O ratio is indeed found, extended over a ~0.6 kpc^2 region within the main body of the galaxy. Contrary to previous studies, however, we do not find evidence for a large Wolf-Rayet population, and conclude that WR stars alone cannot be responsible for producing the observed N/O excess. Instead, the location and disturbed morphology of the N-enriched region suggests that interaction-induced inflow of metal-poor gas may be responsible.

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