8点钟弧透镜系统的甚大天线阵观测：射电发射和恒星形成率的极限
Very Large Array observations of the 8 o'clock arc lens system: Radio emission and a limit on the star-formation rate
摘要：
8点钟方向的弧是一个引力透镜莱曼破裂星系（LBG），红移z=2.73，恒星形成速率（SFR）为270太阳质量/年（来自光学和近红外光谱）。考虑到系统的放大率~12和SFR，预计在1.4 GHz处任何相关无线电发射的通量密度仅为0.1 mJy。然而，透镜系统被发现与NRAO甚大阵（VLA）巡天中检测到的射电源一致，通量密度为~5 mJy。如果这个通量密度归因于透镜LBG，那么它将意味着SFR ~11000太阳质量/年，与光学和近红外导出的值形成对比。我们想研究这个系统的无线电特性，并从LBG的透镜无线电发射中独立地确定LBG的SFR。我们已经进行了新的高分辨率成像与VLA ain A和B-配置在1.4和5 GHz。我们发现，无线电辐射是由一个无线电大声与透镜星系活动星系核为主。来自活动星系核的射电喷流部分覆盖了LBG的透镜弧，我们没有探测到任何来自弧的未被遮蔽区域的射电辐射，其通量密度限制为3 σ 108微焦耳/束。利用射电数据，我们将LBG的SFR限制在<750太阳质量/年，这与光学和近红外光谱的结果一致。我们预计，扩展的VLA的灵敏度将足以检测许多高红移的引力透镜后，只有几个小时的观测时间的LBG。EVLA提供的高角分辨率也将允许对透镜星系进行详细研究，并确定是否有来自透镜的无线电发射。
英文摘要：
The 8 o'clock arc is a gravitationally lensed Lyman Break Galaxy (LBG) at redshift z=2.73 that has a star-formation rate (SFR) of 270 solar-mass/year (derived from optical and near-infrared spectroscopy). Taking the magnification of the system ~12 and the SFR into account, the expected flux density of any associated radio emission at 1.4 GHz is predicted to be just 0.1 mJy. However, the lens system is found to be coincident with a radio source detected in the NRAO Very Large Array (VLA) Sky Survey with a flux density of ~5 mJy. If this flux density is attributed to the lensed LBG then it would imply a SFR ~11000 solar-mass/year, in contrast with the optical and near-infrared derived value. We want to investigate the radio properties of this system, and independently determine the SFR for the LBG from its lensed radio emission. We have carried out new high resolution imaging with the VLA ain A and B-configurations at 1.4 and 5 GHz. We find that the radio emission is dominated by a radio-loud AGN associated with the lensing galaxy. The radio-jet from the AGN partially covers the lensed arc of the LBG, and we do not detect any radio emission from the unobscured region of the arc down to a 3 sigma flux-density limit of 108 micro-Jy/beam. Using the radio data, we place a limit of <750 solar-mass/year for the SFR of the LBG, which is consistent with the results from the optical and near-infrared spectroscopy. We expect that the sensitivity of the Expanded VLA will be sufficient to detect many high redshift LBGs that are gravitationally lensed after only a few hours of observing time. The high angular resolution provided by the EVLA will also allow detailed studies of the lensed galaxies and determine if there is radio emission from the lens.
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