遥远宇宙中的低功率射电星系：在COSMOS场中寻找1<z<2的FRI
Low-power Radio Galaxies in the Distant Universe: A search for FRI at 1<z<2 in the COSMOS field
摘要：
本文提出了在COSMOS场中寻找1 < z < 2的FRI射电星系的方法。在没有光谱红移测量的情况下，选择方法是基于多个步骤，这些步骤利用了无线电和光学约束。基本假设是：1）低功率FRI和更强大的FRI之间的无线电功率的中断不随红移而改变，2）遥远宇宙中低功率射电星系的宿主星系的光度特性与相同红移仓中的FRI相似，就像附近的射电星系一样。我们描述了我们的搜索结果，产生37个低功率的射电星系候选人，可能是FRIs。我们表明，这些低光度的射电星系中的很大一部分显示出紧凑的无线电形态，这并不对应于FRI形态分类。此外，我们的物体显然与显示出明显相互作用迹象的星系有关，这与在低z FRI宿主中观察到的典型行为不一致。紧凑的射电形态可能意味着我们正在观察本质上很小并且可能很年轻的物体，这些物体最终将演变成我们在局部宇宙中观察到的巨大的FRI。其中一个物体在HST图像中显示为点状。这可能属于FRI-QSO的人口，然而，这将代表一小部分的高z FRIs的整体人口。至于本地FRIs，我们的对象的很大一部分可能与集团或集群，使他们的“灯塔”高红移星系团。我们在本文中提出的候选高z FRI的搜索构成了对未来高分辨率和高灵敏度仪器观测对象的初步研究
英文摘要：
We present a search for FRI radio galaxies between 1 < z < 2 in the COSMOS field. In absence of spectroscopic redshift measurements, the selection method is based on multiple steps which make use of both radio and optical constraints. The basic assumptions are that 1) the break in radio power between low-power FRIs and the more powerful FRIIs does not change with redshift, and 2) that the photometric properties of the host galaxies of low power radio galaxies in the distant universe are similar to those of FRIIs in the same redshift bin, as is the case for nearby radio galaxies. We describe the results of our search, which yields 37 low-power radio galaxy candidates that are possibly FRIs. We show that a large fraction of these low-luminosity radio galaxies display a compact radio morphology, that does not correspond to the FRI morphological classification. Furthermore, our objects are apparently associated with galaxies that show clear signs of interactions, at odds with the typical behavior observed in low-z FRI hosts. The compact radio morphology might imply that we are observing intrinsically small and possibly young objects, that will eventually evolve into the giant FRIs we observe in the local universe. One of the objects appears as point-like in HST images. This might belong to a population of FRI-QSOs, which however would represent a tiny minority of the overall population of high-z FRIs. As for the local FRIs, a large fraction of our objects are likely to be associated with groups or clusters, making them "beacons" for high redshift clusters of galaxies. Our search for candidate high-z FRIs we present in this paper constitutes a pilot study for objects to be observed with future high-resolution and high-sensitivity instruments (shortened)
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