HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ∼ 1 — II. Old stellar populations in central cluster galaxies
HST, radio and infrared observations of 28 3CR radio galaxies at redshift z ∼ 1 — II. Old stellar populations in central cluster galaxies
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中心星团星系红移 28 个 3CR 射电星系的 HST、射电和红外观测
DOI：
10.1046/j.1365-8711.1998.01245.x
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发表时间：
1997
影响因子：
4.8
通讯作者：
H. Röttgering
中科院分区：
文献类型：
--
作者：
P. Best;M. Longair;H. Röttgering
哈勃太空望远镜拍摄的3CR射电星系在红移为0.6 < z < 1.8时的图像显示了显著的结构变化，通常沿着射电轴排列，表明射电源强烈影响这些星系的光学外观。在本文中，我们调查的主机星系这种对齐的发射，结合HST数据与地面红外图像。 对星系光谱能量分布的研究表明，排列的蓝色成分对K波段光的贡献一般很小（约10%）。星系的径向强度分布在半径约为35 kpc处符合德·沃库勒定律，表明K波段的光主要由椭圆星系的光所控制。除了de Vaucouleurs剖面外，没有证据表明存在核点源，其贡献占总K波段通量密度的15%，除了两个情况，3C 22和3C 41。我们得出的结论是，K带发射的遥远的3CR星系的星光占主导地位。遥远的3CR星系在投影基平面上的星等、颜色和位置表明，它们的恒星群是在高红移下形成的，此后一直在被动地演化。 大的特征半径推导出的3CR星系，表明它们必须高度动态演化，即使在红移为1。在半径大于1.35 kpc时，一个组合的星系轮廓清楚地显示出比德·沃库勒定律更多的辐射，这表明至少有一些星系具有CD型晕。这支持了其他独立的证据的假设，遥远的3CR星系位于中等丰富（原）集群。由于3CR星表中邻近的FR II星系处于更弥散的环境中，并且不具有cD晕，因此3CR星系的星系环境必须随红移而变化。因此，3CR星系的K-z关系不能用标准的“封闭盒，被动演化的恒星种群”模型来解释，即拥有遥远3CR源的星系将演化为拥有附近3CR FR II源的星系。 在红移z <$1处，3CR星系的恒星星族的绝对K星等比低射电功率的6C星系亮，这表明3CR星系包含更大质量的恒星;这与它们位于星系团的中心是一致的。强大的高红移射电星系拥有无线电波束，其动力学功率接近中央超大质量黑洞的爱丁顿极限光度。由于黑洞的质量很可能与宿主星系的质量成比例，3CR星系将比6C星系包含更多质量的中央引擎，这说明它们的无线电发射更强大。在红移z = 0.6时，射电源的射束功率受到中央引擎燃料可用性的限制，而不是黑洞质量的限制，因此射电源和宿主星系的质量之间没有相关性。
Hubble Space Telescope images of 3CR radio galaxies at redshifts 0.6 < z < 1.8 have shown a remarkable variety of structures, generally aligned along the radio axis, indicating that the radio source strongly influences the optical appearance of these galaxies. In this paper we investigate the host galaxies underlying this aligned emission, combining the HST data with ground-based infrared images. An investigation of the spectral energy distributions of the galaxies shows that the contribution of the aligned blue component to the K-band light is generally small (∼ 10 per cent). The radial intensity profiles of the galaxies are well matched at radii ≲ 35 kpc by de Vaucouleurs’ law, demonstrating that the K-band light is dominated by that of an elliptical galaxy. There is no evidence for a nuclear point source, in addition to the de Vaucouleurs profile, with a contribution ≳ 15 per cent of the total K-band flux density, except in two cases, 3C 22 and 3C 41. We conclude that the K-band emission of the distant 3CR galaxies is dominated by starlight. The magnitudes, colours and location of the distant 3CR galaxies on the projected fundamental plane indicate that their stellar populations formed at high redshift and have since been evolving passively. Large characteristic radii are derived for the 3CR galaxies, indicating that they must be highly evolved dynamically, even at a redshift of 1. At radii larger than ∼ 35 kpc, a combined galaxy profile clearly shows an excess of emission as compared with de Vaucouleurs' law, indicating that at least some of the galaxies possess cD-type haloes. This supports other independent evidence for the hypothesis that the distant 3CR galaxies lie in moderately rich (proto-)clusters. Since the nearby FR II galaxies in the 3CR catalogue lie in more diffuse environments and do not possess cD haloes, the galactic environments of the 3CR galaxies must change with redshift. The K–z relation of the 3CR galaxies cannot, therefore, be interpreted using a standard ‘closed-box, passively evolving stellar population’ model, whereby the galaxies that host distant 3CR sources will evolve into the galaxies that host nearby 3CR FR II sources. At redshifts z ∼ 1, the absolute K magnitudes of the stellar populations of the 3CR galaxies are brighter than those of the lower radio power 6C galaxies, indicating that the 3CR galaxies contain a greater mass of stars; this is consistent with them lying towards the centres of clusters. Powerful high-redshift radio galaxies possess radio beams the kinetic power of which is close to the Eddington limiting luminosity of a central supermassive black hole. Since the mass of the black hole is likely to scale in proportion to the mass of the host galaxy, the 3CR galaxies will contain more massive central engines than the 6C galaxies, which accounts for their more powerful radio emission. At redshifts z ≲ 0.6, the beam power of the radio sources is limited by the availability of fuel for the central engine rather than by the black hole mass, and so no correlation is expected between the radio power and the mass of the host galaxy.