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arXiv 2107.09030astro-ph.GA
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AGN和恒星形成星系的GLEAM 200 MHz局部射电光度函数

The GLEAM 200 MHz Local Radio Luminosity Function for AGN and Star-forming Galaxies

T. M. O. Franzen, N. Seymour, E. M. Sadler, T. Mauch, S. V. White, C. A. Jackson, R. Chhetri, B. Quici, M. E. Bell, J. R. Callingham, K. S. Dwarakanath, B. For,… 展开作者

T. M. O. Franzen, N. Seymour, E. M. Sadler, T. Mauch, S. V. White, C. A. Jackson, R. Chhetri, B. Quici, M. E. Bell, J. R. Callingham, K. S. Dwarakanath, B. For, B. M. Gaensler, P. J. Hancock, L. Hindson, N. Hurley-Walker, M. Johnston-Hollitt, A. D. Kapinska, E. Lenc, B. McKinley, J. Morgan, A. R. Offringa, P. Procopio, L. Staveley-Smith, R. B. Wayth, C. Wu, Q. Zheng

备注：
28 pages, 18 figures, accepted for publication in PASA
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摘要：

银河系和河外全天空默奇森宽场阵列（GLEAM）是一个以76-227 MHz对整个南部天空进行的射电连续谱巡天（December $<+30°$），角分辨率为$\approx 2$ arcmin。在本文中，我们结合GLEAM数据与光谱从6dF银河系巡天构建一个样本的1,590个本地（中位数$z \approx 0.064$）无线电源与$S_{200\,\mathrm{MHz}} > 55$ mJy在整个区域的$\approx 16,700~\mathrm{deg}^{2}$。从光谱中，我们确定了每个星系射电辐射的主要物理过程：73%由活动星系核（AGN）提供燃料，27%由恒星形成提供燃料。我们提出了活动星系核和恒星形成星系在200 MHz的局部射电光度函数，并计算了这两个群体在76 MHz和$\sim 1$ GHz之间的典型射电光谱。对于活动星系核，200 MHz和$\sim 1$ GHz之间的中位光谱指数$α_{\mathrm{high}}$为$-0.600 \pm 0.010$（其中$S \propto ν^α$），GLEAM带内的中位光谱指数$α_{\mathrm{low}}$为$-0.704 \pm 0.011$。对于恒星形成星系，$α_{\mathrm{high}}$的中值为$-0.650 \pm 0.010$，$α_{\mathrm{low}}$的中值为$-0.596 \pm 0.015$。在活动星系核中，平谱源在较低的射电光度下更常见，这表明存在着一个重要的弱射电活动星系核群体，即使在低频下也仍然以核心为主。然而，大约4%的本地射电活动星系核在低频（$α_{\mathrm{low}} < -1.2$）具有超陡射电频谱。这些超陡谱源的射电光度范围很广，需要进一步的工作来澄清它们的性质。

英文摘要：

The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76-227 MHz of the entire southern sky (Declination $<+30°$) with an angular resolution of $\approx 2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1,590 local (median $z \approx 0.064$) radio sources with $S_{200\,\mathrm{MHz}} > 55$ mJy across an area of $\approx 16,700~\mathrm{deg}^{2}$. From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73 per cent are fuelled by an active galactic nucleus (AGN) and 27 per cent by star formation. We present the local radio luminosity function for AGN and star-forming galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and $\sim 1$ GHz. For the AGN, the median spectral index between 200 MHz and $\sim 1$ GHz, $α_{\mathrm{high}}$, is $-0.600 \pm 0.010$ (where $S \propto ν^α$) and the median spectral index within the GLEAM band, $α_{\mathrm{low}}$, is $-0.704 \pm 0.011$. For the star-forming galaxies, the median value of $α_{\mathrm{high}}$ is $-0.650 \pm 0.010$ and the median value of $α_{\mathrm{low}}$ is $-0.596 \pm 0.015$. Among the AGN population, flat-spectrum sources are more common at lower radio luminosity, suggesting the existence of a significant population of weak radio AGN that remain core-dominated even at low frequencies. However, around 4 per cent of local radio AGN have ultra-steep radio spectra at low frequencies ($α_{\mathrm{low}} < -1.2$). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.

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