Horologium-Reticulum超星系团的射电观测-I。A3158：合并星系团中有多余的恒星形成星系？
Radio observations of the Horologium-Reticulum Supercluster -I. A3158: Excess star-forming galaxies in a merging cluster?
摘要：
我们提出的星系团A3158（z=0.0597），这是位于中央部分的时钟-网状超星系团（HRS）的1.4和2.5 GHz的澳大利亚望远镜紧凑阵列（ATCA）的观测。HRS中心部分的光谱数据表明，A3158在超星系团中处于一个动态的重要位置，它正在向HRS中心的双星系团系统A3125/A3128移动。在1.4GHz的频率下，在星系团周围35弧分半径范围内共观测到110个射电星系，其中30个在2.5GHz频率下也观测到，我们从ATCA光束全宽半功率区域内的88个源中选取源计数并计算了1.4GHz的射电光度函数（RLF）。根据Prandoni等人（2001年）的计算，将该区域的源计数与背景进行比较，发现有一些证据表明L（1.4）GHz < 2 x 10^22 W/Hz的星系过多。这一结果似乎表明了一个恒星形成的群体，并且与Owen et al.（2005）最近发现的合并星团A2125的结果相似。此外，我们还发现log P（1.4）= 22.5以下的早型星系（E和S 0）的射电光度函数低于复合星系团环境的射电光度函数（Ledlow & Owen，1996），但与Shapley超星系团中心星系团的早型射电光度函数相似（Venturi et al. 2000），后者被认为处于合并的后期阶段。这一结果意味着超星系团的核心是无线电发射，特别是来自活动星系核的无线电发射，在合并的后期阶段受到抑制的环境。因此，星系团的射电观测可能是星系团精确合并阶段的敏感指标，但仍需要更多的观测证据来确定这一趋势。
英文摘要：
We present 1.4 and 2.5 GHz Australia Telescope Compact Array (ATCA) observations of the galaxy cluster A3158 (z=0.0597) which is located within the central part of the Horologium-Reticulum Supercluster (HRS). Spectroscopic data for the central part of the HRS suggest that A3158 is in a dynamically important position within the supercluster and that it is moving toward the double cluster system A3125/A3128 which marks the centre of the HRS. A total of 110 radio galaxies are detected in a 35 arcminute radius about the cluster at 1.4 GHz, of which 30 are also detected at 2.5 GHz.We examine the source counts and compute the Radio Luminosity Function (RLF) at 1.4 GHz from the subset of 88 sources found within the fullwidth half-power area of the ATCA beam. Comparison of the source counts in the area over the background, as computed by Prandoni et al. (2001), shows some evidence of an excess of galaxies with L(1.4) GHz < 2 x 10^22 W/Hz. This result seems to indicate a star forming population and is a result similar to that found recently by Owen et al. (2005) for the merging cluster A2125. In addition we find that the radio luminosity function for early-type galaxies (E and S0) below log P(1.4) = 22.5 is lower than that found for a composite cluster environment (Ledlow & Owen, 1996) but is similar to the early-type RLF for clusters in the centre of the Shapley Super cluster (Venturi et al. 2000) which are believed to be in the latter stages of merging. This result implies that the cores of superclusters are environments where radio emission, particularly resultant from AGN, is suppressed in the later stages of merging. Thus, radio observations of clusters might be sensitive indicators of the precise merger stage of the cluster but more observational evidence is still required to establish this trend.
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