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arXiv 1302.1009astro-ph.CO
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NGC6946盘上58个HII区域的填充因子与半径的关系

The filling factor - radius relation for 58 HII regions across the disk of NGC6946

B. Cedrés, J. E. Beckman, A. Bongiovanni, J. Cepa, A. Asensio Ramos, C. Giammanco, A. Cabrera-Lavers, E. Alfaro

备注：
10 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters
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摘要：

利用10.4 m GTC（La Palma）上的OSIRIS可调谐窄带成像仪，我们在7.3 × 7.5平方角分的视场上，在[SII]λλ、6717、6731的双重谱线和Hα中，对SAB（rs）cd星系NGC 6946进行了成像。从这些图中，我们已经产生了星盘上557个HII区的Hα光度和有效半径的星表，并导出了其中370个HII区的[SII]发射线比率。Hα观测被用来推导出样品区域的平均亮度加权电子密度，而[SII]线比率使我们能够推导出这些线中大部分辐射的密集区中的原位电子密度值，对于58个区域。这是迄今为止单个星系同类数据中最大的数据集。一个经典的两相模型被用来推导区域的填充因子。我们发现，虽然平均电子密度的区域的半径的平方根减少，在原位密度基本上是独立的这个半径。因此，随着区域半径和亮度的增加，填充因子系统地下降，填充因子和半径之间的幂律指数为-2.23。这些测量应提高更精细的物理模型的HII地区的前景。

英文摘要：

Using the OSIRIS tunable narrow band imager on the 10.4m GTC (La Palma) we have mapped the SAB(rs)cd galaxy NGC 6946 over a 7.3x7.5 square arcminutes field in the emission lines of the [SII]λλ, 6717, 6731 doublet, and in Hα. From these maps we have produced catalogs of the Hαluminosities and effective radii of 557 HII regions across the disk, and derived the [SII] emission line ratios of 370 of these. The Hαobservations were used to derive the mean luminosity-weighted electron densities for the regions of the sample, while the [SII] line ratios allowed us to derive values of the in situ electron densities in the denser zones from which the major fraction of the radiation in these lines is emitted, for 58 of the regions. This is by far the largest data set of its kind for a single galaxy. A classical two phase model is used to derive the filling factors of the regions. We find that although the mean electron density decreases with the square root of the radius of the regions, the in situ density is essentially independent of this radius. Thus the filling factor falls systematically, as the radius and the luminosity of the regions increases, with a power law of exponent -2.23 between filling factor and radius. These measurements should enhance the perspectives for more refined physical models of HII regions.

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