Hubble Space Telescope Observations of the Blue Compact Dwarf SBS 0335–052: A Probable Young Galaxy
Hubble Space Telescope Observations of the Blue Compact Dwarf SBS 0335–052: A Probable Young Galaxy
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哈勃太空望远镜观测蓝矮星 SBS 0335–052：一个可能的年轻星系
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
V. Lipovetsky
中科院分区：
文献类型：
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作者：
T. Thuan;Y. Izotov;V. Lipovetsky
我们给出了极缺金属（Z ~ Z☉/41）蓝致密矮星系（BCD） SBS 0335-052的HST WFPC2 V和I图像和GHRS紫外分光光度法在Lyα和O I λ1302周围的光谱区域。BCD中所有恒星的形成都发生在6个年龄≤25 Myr的超级星团（ssc）中，它们位于~2'或520pc大小的区域内。尘埃明显存在，并在空间上与ssc混合在一起。ssc大致沿东南-西北方向排列，离最亮的星团有系统的变红趋势。观测到的颜色对位置的依赖可能是由于尘埃的微分消光和由于顺序传播的恒星形成而引起的颜色随时间演变的综合影响。有一个半径约380pc的超壳层，描绘出一个巨大的超新星空洞。恒星的瞬时形成速率是~0.4 M☉y -1。没有观测到强的窄Lyα发射。相反，有低强度的宽（FWZI = 20 Å） Lyα发射叠加在更宽的Lyα被H I包络吸收上。这种宽的低强度发射是由Lyα光子的共振散射引起的。没有强烈的Lyα发射可能部分是由于尘埃的吸收，但主要是由于多次散射从小的HST孔径中去除了Lyα光子。由于氢离子云几乎是面朝上的，几何效应也可能起作用，因为光子在垂直于平面的方向上比沿着平面更容易逃逸。BCD似乎是一个年轻的星系，正在经历它最初的恒星形成爆发之一。这一结论是基于以下证据得出的：(1)下伏延伸的低表面亮度成分不规则且呈丝状，表明很大一部分发射来自电离气体。任何潜在的恒星群必须小于~108年。(2)潜在的成分具有非常蓝的颜色[-0.34≤(V-I)0≤0.16]，与气体发射的颜色一致。(3)在戈达德高分辨率光谱仪的吸收光谱中没有检测到O I λ1302谱线，使得BCD的H I包络中N(O)/N(H)的上限比猎户座的值小3000多倍。
We present HST WFPC2 V and I images and GHRS UV spectrophotometry of the spectral regions around Lyα and O I λ1302 of the extremely metal-deficient (Z ~ Z☉/41) blue compact dwarf galaxy (BCD) SBS 0335-052. All the star formation in the BCD occurs in six super-star clusters (SSCs) with ages ≤25 Myr, within a region of ~2' or 520 pc in size. Dust is clearly present and mixed spatially with the SSCs. The SSCs are roughly aligned in the southeast-northwest direction, and there is a systematic increase in reddening of the clusters away from the brightest one. The observed color dependence on position may be the combined effects of differential extinction by dust and color evolution with time due to sequential propagating star formation. There is a supershell of radius ~380 pc, delineating a large supernova cavity. The instantaneous star formation rate is ~0.4 M☉ yr-1. Strong narrow Lyα emission is not observed. Rather there is low-intensity broad (FWZI = 20 Å) Lyα emission superposed on even broader Lyα absorption by the H I envelope. This broad low-intensity emission is caused by resonant scattering of Lyα photons. The absence of strong Lyα emission may be due partly to dust absorption, but is due mainly to multiple scattering that removes Lyα photons from the small HST aperture. As the H I cloud is seen nearly edge-on, geometrical effects may also play a role as photons escape more easily in a direction perpendicular to the plane than along it. The BCD appears to be a young galaxy, undergoing one of its very first bursts of star formation. This conclusion is based on the following evidence: (1) The underlying extended low surface brightness component is irregular and filamentary, suggesting that a significant part of the emission comes from ionized gas. Any underlying stellar population must be younger than ~108 yr. (2) The underlying component has very blue colors [-0.34 ≤ (V-I)0 ≤ 0.16], consistent with gaseous emission colors. (3) The O I λ1302 line is not detected in absorption in the Goddard High Resolution Spectrograph spectrum, setting an upper limit for N(O)/N(H) in the H I envelope of the BCD of more than 3000 times smaller than the value in Orion.