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arXiv 1106.0618astro-ph.CO
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赫歇尔室女星系团巡天。IX。四个室女座旋涡星系中的尘气质量比和金属丰度梯度

The Herschel Virgo Cluster Survey. IX. Dust-to-gas mass ratio and metallicity gradients in four Virgo spiral galaxies

Laura Magrini, Simone Bianchi, Edvige Corbelli, Luca Cortese, Leslie Hunt, Matthew Smith, Catherine Vlahakis, Jonathan Davies, George J. Bendo, Maarten Baes, Al… 展开作者

Laura Magrini, Simone Bianchi, Edvige Corbelli, Luca Cortese, Leslie Hunt, Matthew Smith, Catherine Vlahakis, Jonathan Davies, George J. Bendo, Maarten Baes, Alessandro Boselli, Marcel Clemens, Viviana Casasola, Ilse De Looze, Jacopo Fritz, Carlo Giovanardi, Marco Grossi, Thomas Hughes, Suzanne Madden, Ciro Pappalardo, Michael Pohlen, Sperello di Serego Alighieri, Joris Verstappen

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13 pages, 8 figures, A&A accepted
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摘要：

使用赫歇尔数据从开放时间的关键项目的赫歇尔室女星系团调查（HeViCS），我们研究了金属丰度梯度表示的金属丰度在气相中的HII区域的化学成分跟踪，并在固相中，跟踪的灰尘与气体的质量比之间的关系。我们推导出的径向梯度的尘埃气体质量比的HeViCS观测到的所有星系的金属丰度梯度在文献中。它们都是晚型Sbc星系，分别是NGC 4254、NGC 4303、NGC 4321和NGC 4501。我们研究了不同的依赖于金属的CO到H $_2$转换因子（\xco），用于转换的$^{12}$ CO观测到的分子氢的量。我们发现，在这些星系的尘埃-气体质量比径向轮廓是非常敏感的选择的\xco \值，因为分子气体是在内部的主要组成部分。我们发现，对于我们的样本中的三个星系，即NGC 4254，NGC 4321和NGC 4501，氧气和尘埃-气体径向梯度的斜率一致达到$\sim$ 0.6- 0.7 R $_{25}$，使用\xco \值在1/3-1/2银河系\xco范围内。对于NGC 4303，需要较低的\xco $\sim0.1\times$ 10 $^{20}$值。我们认为，这样低的\xco \值可能是由于\xco的金属度依赖性（从接近线性的NGC 4254，NGC 4321和NGC 4501到超线性的NGC 4303），特别是在径向区域R $_G<$ 0.6- 0.7 R $_{25}$，其中分子气体占主导地位。另一方面，原子气体成分占主导地位的外部区域受\xco选择的影响较小，因此我们不能对其值进行限制。

英文摘要：

Using Herschel data from the Open Time Key Project the Herschel Virgo Cluster Survey (HeViCS), we investigated the relationship between the metallicity gradients expressed by metal abundances in the gas phase as traced by the chemical composition of HII regions, and in the solid phase, as traced by the dust-to-gas mass ratio. We derived the radial gradient of the dust-to-gas mass ratio for all galaxies observed by HeViCS whose metallicity gradients are available in the literature. They are all late type Sbc galaxies, namely NGC4254, NGC4303, NGC4321, and NGC4501. We examined different dependencies on metallicity of the CO-to-H$_2$ conversion factor (\xco), used to transform the $^{12}$CO observations into the amount of molecular hydrogen. We found that in these galaxies the dust-to-gas mass ratio radial profile is extremely sensitive to choice of the \xco\ value, since the molecular gas is the dominant component in the inner parts. We found that for three galaxies of our sample, namely NGC4254, NGC4321, and NGC4501, the slopes of the oxygen and of the dust-to-gas radial gradients agree up to $\sim$0.6-0.7R$_{25}$ using \xco\ values in the range 1/3-1/2 Galactic \xco. For NGC4303 a lower value of \xco$\sim0.1\times$ 10$^{20}$ is necessary. We suggest that such low \xco\ values might be due to a metallicity dependence of \xco (from close to linear for NGC4254, NGC4321, and NGC4501 to superlinear for NGC4303), especially in the radial regions R$_G<$0.6-0.7R$_{25}$ where the molecular gas dominates. On the other hand, the outer regions, where the atomic gas component is dominant, are less affected by the choice of \xco, and thus we cannot put constraints on its value.

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