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arXiv 0903.3015astro-ph.CO
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低表面密度下的恒星形成规律

The Star Formation Law at Low Surface Density

Ted K. Wyder, D. Christopher Martin, Tom A. Barlow, Karl Forster, Peter G. Friedman, Patrick Morrissey, Susan G. Neff, James D. Neill, David Schiminovich, Mark … 展开作者

Ted K. Wyder, D. Christopher Martin, Tom A. Barlow, Karl Forster, Peter G. Friedman, Patrick Morrissey, Susan G. Neff, James D. Neill, David Schiminovich, Mark Seibert, Luciana Bianchi, Jose Donas, Timothy M. Heckman, Young-Wook Lee, Barrry F. Madore, Bruno Milliard, R. Michael Rich, Alex S. Szalay, Sukyoung K. Yi

摘要:

我们调查的性质,在低气体表面密度的恒星形成法使用的样本19个低表面亮度(LSB)星系与现有的HI地图在文献中,从银河系演化探测器卫星的紫外成像,和光学图像从斯隆数字巡天。所有LSB星系的(NUV-r)颜色与表面亮度较高的恒星形成星系相似,表明它们的平均恒星形成历史并没有很大的不同。基于四个LSB星系的UV和FIR数据,我们发现FIR/UV比显着小于1,这意味着低数额的内部UV消光LSB星系。我们使用紫外图像和HI地图来测量所有星系在同一区域内的恒星形成率和氢气表面密度。LSB星系的恒星形成率表面密度低于外推的幂律拟合的恒星形成率表面密度作为总气体密度的函数,为更高的表面亮度星系。虽然有更多的散射,LSB星系也低于恒星形成定律的第二个版本,其中恒星形成率表面密度与气体密度除以轨道时间相关。在这两个恒星形成定律中看到的低迷与理论模型相一致,该模型预测LSB星系中的恒星形成效率较低,这是由于分子比例随着密度的降低而下降。

英文摘要:

We investigate the nature of the star formation law at low gas surface densities using a sample of 19 low surface brightness (LSB) galaxies with existing HI maps in the literature, UV imaging from the Galaxy Evolution Explorer satellite, and optical images from the Sloan Digital Sky Survey. All of the LSB galaxies have (NUV-r) colors similar to those for higher surface brightness star-forming galaxies of similar luminosity indicating that their average star formation histories are not very different. Based upon four LSB galaxies with both UV and FIR data, we find FIR/UV ratios significantly less than one, implying low amounts of internal UV extinction in LSB galaxies. We use the UV images and HI maps to measure the star formation rate and hydrogen gas surface densities within the same region for all of the galaxies. The LSB galaxy star formation rate surface densities lie below the extrapolation of the power law fit to the star formation rate surface density as a function of the total gas density for higher surface brightness galaxies. Although there is more scatter, the LSB galaxies also lie below a second version of the star formation law in which the star formation rate surface density is correlated with the gas density divided by the orbital time in the disk. The downturn seen in both star formation laws is consistent with theoretical models that predict lower star formation efficiencies in LSB galaxies due to the declining molecular fraction with decreasing density.

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