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arXiv 1409.0263astro-ph.GAastro-ph.CO
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射电活动星系核反馈到z=1的宇宙演化

The cosmic evolution of radio-AGN feedback to z=1

P. N. Best, L. M. Ker, C. Simpson, E. E. Rigby, J. Sabater

摘要:

为了研究射电活动星系核反馈的宇宙演化,首次测量了z=1时的“喷流模式"射电活动星系核的射电光度函数。8个射电源样品组合产生了211个0.5<z<1.0的射电响活动星系核目录,这些活动星系核在光谱上分为喷流型和辐射型(辐射有效)活动星系核。通过与斯隆数字巡天的大样本射电活动星系核的比较,独立地导出了射电活动星系核的射电光度函数的宇宙演化。辐射型射电活动星系核在所有光度下的空间密度都增加了一个数量级,这与活动星系核是由冷气体提供燃料的一致。而喷注型射电活动星系核的空间密度在低射电光度(L1.4 <1 e24 W/Hz)时随红移的增加而减小,在高射电光度时随红移的增加而增加。简单的模型来解释所观察到的演变。在最佳拟合模型中,喷流模式活动星系核的特征空间密度随红移而下降,这与大质量静止星系的空间密度下降一致,这些静止星系通过冷却热晕中的气体为它们提供燃料。在恒星形成的猝灭和喷流模式射电活动星系核活动的开始之间可能存在1.5-2 Gyr的时间延迟。在更高的射电光度下的行为可以解释为喷流模式射电活动星系核活动的特征光度随着红移(大约为(1+z)立方)的增加,或者喷流模式射电活动星系核的人口也包括一些贡献的冷气燃料源时,看到他们的吸积率低。更高的红移测量将区分这些可能性。

英文摘要:

This paper presents the first measurement of the radio luminosity function of 'jet-mode' (radiatively-inefficient) radio-AGN out to z=1, in order to investigate the cosmic evolution of radio-AGN feedback. Eight radio source samples are combined to produce a catalogue of 211 radio-loud AGN with 0.5<z<1.0, which are spectroscopically classified into jet-mode and radiative-mode (radiatively-efficient) AGN classes. Comparing with large samples of local radio-AGN from the Sloan Digital Sky Survey, the cosmic evolution of the radio luminosity function of each radio-AGN class is independently derived. Radiative-mode radio-AGN show an order of magnitude increase in space density out to z~1 at all luminosities, consistent with these AGN being fuelled by cold gas. In contrast, the space density of jet-mode radio-AGN decreases with increasing redshift at low radio luminosities (L_1.4 < 1e24 W/Hz) but increases at higher radio luminosities. Simple models are developed to explain the observed evolution. In the best-fitting models, the characteristic space density of jet-mode AGN declines with redshift in accordance with the declining space density of massive quiescent galaxies, which fuel them via cooling of gas in their hot haloes. A time delay of 1.5-2 Gyr may be present between the quenching of star formation and the onset of jet-mode radio-AGN activity. The behaviour at higher radio luminosities can be explained either by an increasing characteristic luminosity of jet-mode radio-AGN activity with redshift (roughly as (1+z) cubed) or if the jet-mode radio-AGN population also includes some contribution of cold-gas-fuelled sources seen at a time when their accretion rate was low. Higher redshifts measurements would distinguish between these possibilities.

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