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arXiv 0902.0796astro-ph.CO
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探测低金属量恒星形成：SBS0335-052中超级星团的射电辐射

Probing Star Formation at Low Metallicity: The Radio Emission of Super Star Clusters in SBS0335-052

K. E. Johnson, L. K. Hunt, A. E. Reines

备注：
accepted AJ, 14 pages, 5 figures
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摘要：

我们提出了高分辨率的无线电连续观测的新生恒星在贫金属星系SBS 0335-052。这些无线电数据是用甚大天线阵拍摄的，包括0.7厘米、1.3厘米、2厘米、3.6厘米和6厘米的观测。这些观测使我们能够探测与该星系中极其年轻的恒星形成区域相关的热射电星云。在星系的南部发现了两个离散而明亮的恒星形成区域，这些区域似乎与以前在光学波长下发现的大质量星团有关。然而，剩下的大质量星团与无线电辐射（无论是热辐射还是非热辐射）的关系并不明显，这一点已经达到了这些无线电数据的敏感极限。这两个射电探测到的星团的光谱能量分布与纯粹的热辐射一致，整个区域的电离通量约为1.2 x 10^ 53 s^-1，相当于约12，000颗“典型的”O型星（O型7.5 V）。这里提出的观测结果已经解决了以前检测到的弥散非热发射的重要贡献，这意味着以前的重大恒星形成事件。目前仅这一南部区域的恒星形成率（SFR）就约为1.3 M_sun yr^-1，或约为23 M_sun yr^-1 kpc^-2。这个来自热射电发射的SFR也表明，以前的光学复合线研究没有检测到SBS 0335-052中当前恒星形成的重要部分。根据模型对射电光谱能量分布的拟合，我们推断出两个最年轻的星团的全球平均密度n_e > 10^3-10^4 cm^-3。此外，致密和弥散射电辐射之间的比较表明，高达~50%的电离通量可能泄漏出致密的HII区域。

英文摘要：

We present high-resolution radio continuum observations of the nascent starburst in the metal-poor galaxy SBS 0335-052. These radio data were taken with the Very Large Array and include observations at 0.7cm, 1.3cm, 2cm, 3.6cm, and 6cm. These observations enable us to probe the thermal radio nebulae associated with the extremely young star-forming regions in this galaxy. Two discrete and luminous star-forming regions are detected in the south of the galaxy that appear to be associated with massive star clusters previously identified at optical wavelengths. However, the remaining optically-identified massive star clusters are not clearly associated with radio emission (either thermal or non-thermal) down to the sensitivity limits of these radio data. The spectral energy distributions of the two radio-detected clusters are consistent with being purely thermal, and the entire region has an inferred ionizing flux of ~1.2 x 10^ 53 s^-1, which is equivalent to ~12,000 "typical" O-type stars (type O7.5 V). The observations presented here have resolved out a significant contribution from diffuse non-thermal emission detected previously, implying a previous episode of significant star formation. The current star formation rate (SFR) for this southern region alone is ~1.3 M_sun yr^-1, or ~ 23M_sun yr^-1 kpc^-2. This SFR derived from thermal radio emission also suggests that previous optical recombination line studies are not detecting a significant fraction of the current star formation in SBS 0335-052. From model fits to the radio spectral energy distribution, we infer a global mean density in the two youngest clusters of n_e > 10^3-10^4 cm^-3. In addition, a comparison between the compact and diffuse radio emission indicates that up to ~50% of the ionizing flux could be leaking out of the compact HII regions.

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