The polarization and ultraviolet spectrum of Markarian 231
The polarization and ultraviolet spectrum of Markarian 231
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Markarian 231 的偏振和紫外光谱
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
J. Angel
中科院分区：
文献类型：
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作者：
Paul S. Smith;G. Schmidt;R. Allen;J. Angel
利用哈勃太空望远镜对特殊的塞弗特星系MERK 231进行的紫外光谱偏振测量与新的高质量地面测量相结合，提供了第一个几乎完整的1575到7900A之间的线偏振记录。伴随的紫外线光谱描绘了活动核的严重熄灭的发射线光谱，以及出现了大约2400A的蓝色连续谱。此外，由于He I lambda 3188，mg I lambda 2853，mg II lambda 2798，特别是几个Fe II的共振多重态的吸收特征被确定为一个众所周知的光学吸收系统，相对于发射线蓝移了约4600公里/S。这个连续体被认为是由大约10颗(实验5)围绕着原子核的年轻热恒星造成的。这一成分稀释了偏振的核光，意味着活动星系核(AGN)光谱的本征偏振度在2800A时接近20%。偏振度的迅速下降可以用尘埃颗粒强烈的频率相关散射截面和适度的星光稀释来解释。通过Hα和其他主要发射线的偏振度和位置角的奇特的S形状的反转被解释为两个速度偏移数百公里/S的区域的散射效应。需要第三个(弱)极化通量源来解释在3200到1800A之间近40度的位置角旋转。MRK231的位移吸收特征、偏振测量和光学/红外特性都表明它被归类为低电离或镁II宽吸收线类星体，其中大多数(如果不是全部的话)活动核的视线被尘埃和低电离气体云严重遮挡。
Ultraviolet spectropolarimetry acquired with the Hubble Space Telescope (HST) of the peculiar Seyfert galaxy Mrk 231 is combined with new high-quality ground-based measurements to provide the first, nearly complete, record of its linear polarization from 1575 to 7900 A. The accompanying ultraviolet spectrum portrays the heavily extinguished emission-line spectrum of the active nucleus plus the emergence of a blue continuum shortward of approximately 2400 A. In addition, absorption features due to He I lambda 3188, Mg I lambda 2853, Mg II lambda 2798, and especially several resonance multiplets of Fe II are identified with a well-known optical absorption system blueshifted approximately 4600 km/s with respect to emission lines. The continuum is attributed to approximately 10(exp 5) hot, young stars surrounding the nucleus. This component dilutes the polarized nuclear light, implying that the intrinsic polarization of the active galactic nucleus (AGN) spectrum approaches 20% at 2800 A. The rapid decline in degree of polarization toward longer wavelengths is best explained by the strongly frequency-dependent scattering cross section of dust grains coupled with modest starlight dilution. Peculiar S-shaped inflections in both the degree and position angle of polarization through H alpha and other major emission lines are interpreted as effects of scattering from two regions offset in velocity by several hundred km/s. A third source of (weakly) polarized flux is required to explain a nearly 40 deg rotation in position angle between 3200 and 1800 A. The displaced absorption features, polarimetry, and optical/infrared properties of Mrk 231 all point to its classification as a low-ionization, or Mg II broad absorption line quasar, in which most, if not all, lines of sight to the active nucleus are heavily obscured by dust and low-ionization gas clouds.