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arXiv 2108.07684astro-ph.GAastro-ph.HE
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从XMM-XXL场看宽线活动星系的极尘遮蔽

Polar dust obscuration in broad-line active galaxies from the XMM-XXL field

V. Buat, G. Mountrichas, G. Yang, M. Boquien, Y. Roehlly, D. Burgarella, M. Stalevski, L. Ciesla, P. Theulé

摘要:

在活动星系核附近的极地地区观测到尘埃,已知尘埃对活动星系核的中红外辐射和对紫外光辐射的遮蔽有很大贡献。我们在XMM-XXL视场中选择了1275 BLAGN的样本,并提供了光学到红外光度数据。这些活动星系核是沿着它们的极地方向观察到的,我们预计当它存在时,位于极地周围的尘埃的影响最大。我们使用了X-CIGALE,它引入了一个尘埃成分来解释沿极地方向的遮蔽,模拟为前景屏幕,以及一个消光曲线,因为它在短波长处显着陡峭或更灰色。通过比较不同拟合的结果,我们能够定义源的子样本,这些子样本具有支持或反对极地遮蔽的积极统计证据,并使用灰色或陡峭的消光曲线来描述。我们发现了类似的一部分来源,有积极的证据支持和反对极地尘埃。应用统计校正,我们估计,我们的样本中有一半可能含有极地尘埃,其中,60%表现出陡峭的消光曲线和40%平坦的消光曲线,虽然后者的百分比被发现取决于所采用的消光曲线。在V波段的遮蔽与X射线柱密度无关,而A_V/N_H比值的范围很大,并且在平坦的消光曲线上尘埃温度较高,而在陡峭的消光曲线上尘埃温度较低。在拟合这些复合系统的光谱能量分布时忽略这一极地尘埃成分会导致对恒星贡献的高估。一个单一的拟合与极尘组件描述的SMC消光曲线有效地克服了这个问题,但它无法识别所有的活动星系核与极尘模糊。

英文摘要:

Dust is observed in the polar regions of nearby AGN and it is known to contribute substantially to their mid-IR emission and to the obscuration of their UV to optical emission. We selected a sample of 1275 BLAGN in the XMM-XXL field, with optical to infrared photometric data. These AGN are seen along their polar direction and we expect a maximal impact of dust located around the poles when it is present. We used X-CIGALE, which introduces a dust component to account for obscuration along the polar directions, modeled as a foreground screen, and an extinction curve that is chosen as it steepens significantly at short wavelengths or is much grayer. By comparing the results of different fits, we are able to define subsamples of sources with positive statistical evidence in favor of or against polar obscuration and described using the gray or steep extinction curve. We find a similar fraction of sources with positive evidence for and against polar dust. Applying statistical corrections, we estimate that half of our sample could contain polar dust and among them, 60% exhibit a steep extinction curve and 40% a flat extinction curve; although these latter percentages are found to depend on the adopted extinction curves. The obscuration in the V-band is not found to correlate with the X-ray column density, while A_V/N_H ratios span a large range of values and higher dust temperatures are found with the flat, rather than with the steep extinction curve. Ignoring this polar dust component in the fit of the spectral energy distribution of these composite systems leads to an overestimation of the stellar contribution. A single fit with a polar dust component described with an SMC extinction curve efficiently overcomes this issue but it fails at identifying all the AGN with polar dust obscuration.

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