LBDS-Lynx区域的深GMRT 150 MHz观测：超陡谱射电源
Deep GMRT 150 MHz observations of the LBDS-Lynx region: Ultra-Steep Spectrum Radio Sources
摘要：
近三十年来，高红移射电星系具有陡峭的射电频谱，因此超陡频谱射电源提供了高红移射电星系的候选者。几乎所有z > 3的射电星系都是用这种红移-光谱指数相关发现的。我们已经开始了一个方案，与GMRT利用这种相关性的通量密度水平约10至100倍深于已知的高红移射电星系，主要是使用现有的无线电目录确定。在我们的计划中，我们已经获得了深，高分辨率的无线电观测在150兆赫与GMRT的几个“深”领域，在更高的射频和其他波段的电磁波谱，目的是检测候选高红移射电星系的研究。在本文中，我们提出的结果，从深150 MHz的观测LBDS-Lynx场，这已经成像在327，610和1412 MHz的WSRT和1400和4860 MHz的VLA。使用GMRT制作的150 MHz图像的均方根噪声约为0.7 mJy/束，分辨率约为19”X 15”。这是LBDS-Lynx场最深的低频图像。在150 MHz时，该磁场的源目录有大约765个源，这些源低至初级波束响应的~20%，覆盖大约15度$^2$的区域。频谱指数是通过将在150兆赫探测到的每个源与在327、610、1400和4860兆赫的现有观测值进行互相关来估计的，还使用了现有的无线电调查，如在327兆赫的WENSS和在1400兆赫的NVSS和FIRST。我们发现大约150个射电源的频谱陡于1。其中约三分之二在SDSS中没有被探测到，因此是强有力的候选高红移射电星系，需要用深红外成像和光谱学进一步探索以估计红移。
英文摘要：
It has been known for nearly three decades that high redshift radio galaxies exhibit steep radio spectra, and hence ultra-steep spectrum radio sources provide candidates for high-redshift radio galaxies. Nearly all radio galaxies with z > 3 have been found using this redshift-spectral index correlation. We have started a programme with GMRT to exploit this correlation at flux density levels about 10 to 100 times deeper than the known high-redshift radio galaxies which were identified primarily using the already available radio catalogues. In our programme, we have obtained deep, high resolution radio observations at 150 MHz with GMRT for several 'deep' fields which are well studied at higher radio frequencies and in other bands of the electromagnetic spectrum, with an aim to detect candidate high redshift radio galaxies. In this paper we present results from the deep 150 MHz observations of LBDS-Lynx field, which has been already imaged at 327, 610 and 1412 MHz with the WSRT and at 1400 and 4860 MHz with the VLA. The 150 MHz image made with GMRT has a rms noise of ~0.7 mJy/beam and a resolution of ~19" X 15". It is the deepest low frequency image of the LBDS-Lynx field. The source catalog of this field at 150 MHz has about 765 sources down to ~20% of the primary beam response, covering an area of about 15 degree$^2$. Spectral index was estimated by cross correlating each source detected at 150 MHz with the available observations at 327, 610, 1400 and 4860 MHz and also using available radio surveys such as WENSS at 327 MHz and NVSS and FIRST at 1400 MHz. We find about 150 radio sources with spectra steeper than 1. About two-third of these are not detected in SDSS, hence are strong candidate high-redshift radio galaxies, which need to be further explored with deep infra-red imaging and spectroscopy to estimate the redshift.
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