标题： 类星体射电亮度与椭圆核问题 显示英文标题

标题： Quasar Radio-Loudness and the Elliptical Core Problem

摘要： 射电亮与射电暗QSO之间的二分法不仅仅取决于宿主星系的形态。虽然螺旋星系几乎只宿主射电暗QSO，但椭圆星系既可以宿主射电亮QSO也可以宿主射电暗QSO。我们发现，吸积率和宿主星系尺度的结合决定了给定椭圆星系会宿主哪种类型的QSO。具有高X射线亮度（在0.5 keV处超过10^44.5 erg/s）的QSO大多是射电亮的。但是那些低亮度的QSO则根据半光半径r_e所测量的大小相对清晰地划分。大于约10千秒差距的QSO是射电亮的，而较小的则是射电暗的。最近的研究发现，有核和无核椭圆星系在这个极限附近也有所划分。这意味着对于低亮度QSO来说，射电亮的通常出现在有核椭圆星系中，而射电暗的则出现在无核椭圆星系和螺旋星系中。这种分离在低红移天体中表现得尤为明显，并且总体上，随着时间推移，无核射电亮QSO的数量有所减少。由于核心的存在与否可能与星系的合并历史有关，因此我们对射电亮和射电暗QSO之间的差异有了一个演化上的解释。 显示英文摘要

摘要： The dichotomy between radio-loud and radio-quiet QSOs is not simply one of host morphology. While spiral galaxies almost exclusively host radio-quiet QSOs, ellipticals can host either radio-louds or radio-quiets. We find that a combination of accretion rate and host scale determines which type of QSO a given elliptical galaxy will host. QSOs with high x-ray luminosities (above 10^44.5 erg/s at 0.5 keV) are mostly radio-loud. But those with low luminosities divide fairly neatly in size (measured by the half-light radius, r_e). Those larger than about 10 kpc are radio-loud, while smaller ones are radio-quiet. It has recently been found that core and coreless ellipticals are also divided near this limit. This implies that for low-luminosity QSOs, radio-louds are found in core ellipticals, while radio-quiets are in coreless ellipticals and spirals. This segregation also shows up strongly for low-redshift objects, and in general, there is a loss over time of coreless, radio-loud QSOs. Since the presence or absence of a core may be tied to the galactic merger history, we have an evolutionary explanation for the differences between radio-loud and radio-quiet QSOs.