从NVSS到RACS：识别真正紧凑且陡谱的射电源
From NVSS to RACS: Identifying truly Compact Galactic and Extragalactic sources with Steep Spectra
AI总结：
本文利用RACS数据识别紧凑陡谱射电源，发现部分源在NVSS未被检测到，揭示了高红移射电星系等天体的研究价值。
摘要：
紧凑、陡谱射电源是探测如脉冲星和高红移射电星系等奇异天体的关键示踪器。不同频率的全天空射电巡天，如TGSS和NVSS，通常被用来识别这些示踪器。更近期的RACS成像巡天，具有更高的角分辨率和更好的灵敏度，为更准确地识别和表征紧凑陡谱源提供了途径。本文利用公开的RACS 887 MHz和1.4 GHz图像，对在TGSS检测到但在NVSS未被检测到的171个紧凑源候选者进行了图像域表征。我们的详细表征结果识别出66个紧凑源、87个非紧凑、弥散或解析源，以及18个在RACS或NVSS图像中未被检测到的源，暗示谱指数大于-2.0。在66个紧凑源中，34个的谱指数大于-1.5。我们证明了样本中的大部分源在以前未被检测到，由于NVSS在银河平面的成像质量较差，导致谱指数限制不准确。我们展示了样本中所有源的谱指数和形态学分类，并讨论了它们在识别和研究如射电脉冲星、高红移射电星系及其他星系源方面的用途。
英文摘要：
Compact, steep-spectrum radio sources are key tracers of exotic astrophysical objects such as pulsars and high-redshift radio galaxies. All-sky radio surveys at different frequencies, like the TIFR-GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS), have been usually exploited to identify such tracers. The more recent imaging survey, Rapid ASKAP Continuum Survey (RACS), with higher angular resolution and better sensitivity offers an avenue for a far better identification and characterisation of compact, steep-spectrum sources. In this work, using publicly available RACS images at 887 MHz and 1.4 GHz, we present an image-domain characterisation of 171 compact source candidates between declinations -40 degrees and +41 degrees, that were detected and appeared compact at 147 MHz in TGSS but not detected at 1.4 GHz in NVSS. Our detailed characterisation resulted in the identification of 66 compact sources, 87 non-compact, diffuse or resolved sources, and 18 sources that are not detected in either of the RACS or NVSS images, implying spectral indices steeper than -2.0. Out of the 66 compact sources, 38 have spectral indices steeper than -1.5. We demonstrate that a large fraction of the sources in our sample were earlier not detected and resulted in incorrect spectral index limits due to poor imaging quality of NVSS in the Galactic plane. We present the spectral indices and morphological classification of all the sources in our sample and discuss their usefulness in identifying and studying interesting sources such as radio pulsars, high-redshift radio galaxies, and other extragalactic sources.
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