Radio galaxies at z 2.5: Results from Keck spectropolarimetry
Radio galaxies at z 2.5: Results from Keck spectropolarimetry
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DOI：
10.1051/0004-6361:20000076
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发表时间：
2000-10
影响因子：
6.5
通讯作者：
J. Vernet;R. Fosbury;M. Villar-Martin;M. Cohen;A. Cimatti;S. Di;S. Alighieri;R. Goodrich
中科院分区：
文献类型：
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作者：
J. Vernet;R. Fosbury;M. Villar-Martin;M. Cohen;A. Cimatti;S. Di;S. Alighieri;R. Goodrich
在对强大的河外射电源群进行分类时，已经积累了大量证据，表明射电星系和类星体是同一母体的方向依赖表现：包含相应大质量黑洞的大质量球状星系。建立这种统一的关键因素之一是在一些射电星系中用偏振光检测到的隐藏类星体的特征。我们对活动核的直接观察通常（但不一定完全）被厚核盘或环面遮挡，可以方便地充当“天然日冕仪”，它可以使射电星系的主体比类星体更清晰地看到。在这项研究中，我们利用 Keck II 望远镜对红移约为 2.5 的射电星系样本进行灵敏的分光偏振测量来消除类星体眩光。这代表了类星体比现在常见许多倍的时代，并且很可能是它们的宿主星系被组装成当今宇宙中最大质量星系的时期。我们表明，尘埃反射的类星体光通常在这些光源的静止框架紫外连续谱中占主导地位，并且高度聚集的散射介质导致活跃星系核光子的几乎灰色散射。然而，这些观察结果并不排除在一个吉里的演化过程中平均存在相当大的恒星形成率。散射尘埃产生的亚毫米再辐射可能仅占远红外总光度的一小部分（~10%）。对硬类星体辐射场在宿主星系的星际介质中激发的发射线的分析揭示了这一时期球体内发生剧烈化学演化的证据。中等质量恒星中的二次氮产生在 Nv/Civ 和 Nv/Heii 线比中产生特征特征，这在类似红移的类星体的宽线区域中已经见过。我们发现 Lyα 和 N v 发射线的强度与紫外线连续偏振程度之间存在有趣的相关性，这可能代表与球体化学富集相关的灰尘扩散。
In classifying the ensemble of powerful extragalactic radio sources, considerable evidence has accumulated that radio galaxies and quasars are orientation-dependent manifestations of the same parent population: massive spheroidal galaxies containing correspondingly massive black holes. One of the key factors in establishing this unification has been the signature of a hidden quasar detected in some radio galaxies in polarized light. The obscuration of our direct view of the active nucleus usually, but not necessarily exclusively, by a thick nuclear disk or torus can act conveniently as a "natural coronograph" that allows a much clearer view of the host of a radio galaxy than of a quasar. In this study, we exploit the opportunity to eliminate the quasar glare by performing sensitive spectropolarimetry with the Keck II telescope of a sample of radio galaxies with redshifts around 2.5. This represents the epoch when quasars were many times more common that they are now and is likely to be the period during which their host galaxies were being assembled into what become the most massive galaxies in the Universe today. We show that dust-reflected quasar light generally dominates the restframe ultraviolet continuum of these sources and that a highly clumped scattering medium results in almost grey scattering of the active galactic nucleus photons. The observations, however, do not exclude a substantial star formation rate averaged over a Gyr of evolution. The sub-mm reradiation from the scattering dust is likely to represent only a small fraction (∼10% ) of the total far infrared luminosity. An analysis of the emission lines excited in the interstellar medium of the host galaxy by the hard quasar radiation field reveals evidence of a dramatic chemical evolution within the spheroid during this epoch. Secondary nitrogen production in intermediate mass stars produces a characteristic signature in the Nv/Civ and Nv/Heii line ratios which has been seen previously in the broad line region of quasars at similar redshifts. We find intriguing correlations between the strengths of the Lyα and N v emission lines and the degree of ultraviolet continuum polarization which may represent the dispersal of dust associated with the chemical enrichment of the spheroid.