AI 中文总结
本文通过甚大望远镜的FORS2偏振观测证实另外三个蓝溢热尘埃遮蔽星系的蓝溢来自AGN散射光，且W0116-0505的偏振特性需用石墨主导的尘埃双锥外流解释。
AI 中文摘要
（背景）热尘埃遮蔽星系（Hot DOGs）是一类被尘埃和气体严重遮蔽的超亮类星体。尽管大多数热尘埃遮蔽星系的静止紫外/光学光谱能量分布（SED）由其宿主星系的发射主导，但有一小部分显示出超出恒星形成预期的蓝溢发射。对这些蓝溢热尘埃遮蔽星系（BHDs）从X射线到远红外的详细多波长研究得出结论，这种蓝溢最可能的起源是来自中心引擎的散射光。此前针对BHDs W0116-0505和W0204-0506的研究已证实了这一情景，这些研究发现了高度偏振的紫外发射，这是散射光的关键特征。（目标）本文中，我们对另外三个BHDs研究了这种散射光情景，并进一步限制了W0116-0505中散射物质的性质。（方法）我们分析了甚大望远镜（VLT）的FORS2在$R_{\rm Special}$波段对三个BHDs的成像偏振观测，以及在$v_{\rm High}$和$I_{Bessel}$波段对W0116-0505的额外观测。（结果）我们发现，在$R_{\rm Special}$波段观测的所有三个BHDs的空间积分偏振度范围约为6%至15%，这证实了它们的蓝溢发射是由活动星系核（AGN）的散射光导致的。我们还发现，W0116-0505中的偏振度与静止帧波长存在显著依赖关系，且无法用汤姆孙散射或AGN照射到平滑的星际介质（ISM）来解释。我们发现，作为散射体的尘埃双锥外流可以成功解释观测结果，只要尘埃以石墨为主，这可能是由于外流气体的高温以及石墨相比硅酸盐更高的升华温度。
英文摘要
(Context) Hot Dust-Obscured Galaxies (Hot DOGs) are a population of hyper-luminous quasars heavily obscured by dust and gas. While most have rest UV/optical SEDs dominated by their host galaxy emission, a small fraction shows blue emission in excess of what is expected for star-formation. Detailed multi-wavelength studies from X-rays to the far-IR of these Blue Excess Hot DOGs (BHDs) have concluded the most likely origin of this blue excess is scattered light from the central engine. This scenario was confirmed by previous studies for the BHDs W0116-0505 and W0204-0506 which found highly polarized UV emission, a key signature of scattered light. (Aims) In this article we investigate this scattered light scenario in three other BHDs and further constrain the properties of the scattering material in W0116-0505. (Methods) We analyze new VLT/FORS2 imaging polarimetry observations in the $R_{\rm Special}$-band of three BHDs and additional observations of W0116-0505 in the $v_{\rm High}$- and $I_{Bessel}$-bands. (Results) We find spatially integrated polarization fractions in all three BHDs observed in the $R_{\rm Special}$-band ranging from about 6% to 15%. This confirms that their blue excess emission is due to AGN scattered light. We also find that the polarization fraction has a significant dependence with rest-frame wavelength in W0116-0505 and that it cannot be explained by Thomson scattering or by an AGN shining onto a smooth ISM. We find that a dusty bi-conical outflow acting as the scatterer can successfully explain the observations as long as the dust is dominated by graphites. This may be due to the high temperatures of the outflowing gas and the higher sublimation temperature of graphites compared to silicates.
Comments17 pages, 18 figures, 5 tables. Submitted to Astronomy & Astrophysics
