Radio-loud active galactic nuclei at high redshifts and the cosmic microwave background
Radio-loud active galactic nuclei at high redshifts and the cosmic microwave background
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高红移和宇宙微波背景下的无线电响亮活跃星系核
DOI：
10.1093/mnras/stt2394
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发表时间：
2013
影响因子：
4.8
通讯作者：
H Germany
中科院分区：
文献类型：
--
作者：
G. G. A. Celotti;F. Tavecchio;F. Haardt;T. S. I. ;Italy.;Sissa;Trieste;Univ. Insubria;Infn;Milano;Eső;Garching;H Germany
发射电子与宇宙微波背景(CMB)之间的相互作用影响早期射电活动星系核(AGN)的可观测性质。在高红移z下，活动星系核的能量密度[UCMB/(1+z)4]可以超过射电活动星系核的磁密度(UB)。在这种情况下，相对论电子优先通过散射CMB光子来冷却，而不是通过同步辐射。这使得距离较远的源在射电中的亮度较低，而在X射线中的亮度比近距离的源更强。相反，在内喷流和热斑中，同步辐射不受CMB的影响。因此，射电光度的下降在未对准(相对于我们的视线)的高z源中更为严重，其射电通量由扩展的各向同性分量主导。在当前的流量受限的无线电调查中，这些源可能无法检测到，在那里它们可能会被使用。由于低能电子的冷却时间较长，因此在低无线电频率下，由CMB引起的无线电光度赤字不那么重要。因此，到目前为止在几GHz处还没有探测到的物体可以通过低频深度探测来探测到，例如LOFAR和SKA。在此之前，我们可以通过对其排列的代理，即blazar的普查来估计高z射电响亮活动星系核的数量，因为它们的射电辐射来自喷流内部强磁化的致密核心，并且它不受CMB光子的逆康普顿散射的影响。
The interaction between the emitting electrons and the Cosmic Microwave Background (CMB) affects the observable properties of radio‐loud Active Galactic Nuclei (AGN) at early epochs. At high redshifts z, the CMB energy density [UCMB / (1 + z) 4 ] can exceed the magnetic one (UB) in the lobes of radio‐loud AGN. In this case the relativisti c electrons cool preferentially by scattering off CMB photons, rather than by synchrotron emission. This makes more distant sources less luminous in radio and more luminous in X‐rays than their closer counterparts. In contrast, in the inner jet and the ho t spots, where UB > UCMB, synchrotron radiation is unaffected by the presence of the CMB. The decrease in radio luminosity is thus more severe in misaligned (with respect to our line of sight) high‐z sources, whose radio flux is dominated by the extended isotropic component. Th ese sources can fail detection in current flux limited radio surveys, where they are possibly u nder‐represented. As the cooling time is longer for lower energy electrons, the radio luminosity deficit due to the CMB is less important at low radio frequencies. Therefore objects not detected so far at a few GHz could be picked up by low frequency deep surveys, such as LOFAR and SKA. Until then, we can estimate the number of high‐z radio‐loud AGN through the census of their aligned proxies, i.e., blazars, since their observed radio emission arises i n the inner and strongly magnetized compact core of the jet, and it is not affected by inverse Compton scattering off CMB photons.