CHILES VERDES：在COSMOS场中，无线电变化的深度和节奏前所未有
CHILES VERDES: Radio variability at an unprecedented depth and cadence in the COSMOS field
摘要：
虽然它是公认的，一些河外射电源是随时间变化的，这种无线电变化的属性，以及它与宿主星系属性的连接，仍然有待探索-特别是对于微弱的来源。在这里，我们提出了一个无线电变量源的分析，从智利变量和爆炸性无线电动态演化调查（智利绿色）-1.4 GHz宇宙\ion{H}{1}大型河外星系调查（智利）的合作伙伴项目。CHILES VERDES提供了前所未有的调查深度，持续时间和节奏的组合，在2013年至2019年期间，在经过充分研究的河外深场COSMOS的0.44度$^2$部分获得了960小时的1- 2 GHz连续VLA数据。我们确定了18个中等变率源（显示$10-30\%$通量密度变化）和40个低变率源（2-10 $\%$通量密度变化）。根据与COSMOS多波长星表的交叉匹配，它们主要是射电光度在$10^{22}-10^{27}$ W Hz $^{-1}$范围内的活动星系核（AGN）。中等变率的源跨越红移$z=0.22-1.56$，具有大部分平坦的射电频谱（$α>-0.5$），并且在从几天到几年的时间尺度上变化。低变率源具有类似的性质，但通常比中等变率源具有更高的射电光度，延伸到$z = 2.8$，并具有更陡的射电频谱（$α<-0.5$）。在我们的分析中，没有恒星形成星系显示出统计学上的显著变化。观察到的变化可能源于闪烁短（$\sim$周）的时间尺度上，多普勒增强的内在AGN的变化长（月-年）的时间尺度。
英文摘要：
Although it is well-established that some extragalactic radio sources are time-variable, the properties of this radio variability, and its connection with host galaxy properties, remain to be explored---particularly for faint sources. Here we present an analysis of radio variable sources from the CHILES Variable and Explosive Radio Dynamic Evolution Survey (CHILES VERDES)---a partner project of the 1.4 GHz COSMOS \ion{H}{1} Large Extragalactic Survey (CHILES). CHILES VERDES provides an unprecedented combination of survey depth, duration, and cadence, with 960 hrs of 1--2 GHz continuum VLA data obtained over 209 epochs between 2013 and 2019 in a 0.44 deg$^2$ section of the well-studied extragalactic deep field, COSMOS. We identified 18 moderate-variability sources (showing $10-30\%$ flux density variation) and 40 lower variability sources (2-10$\%$ flux density variation). They are mainly active galactic nuclei (AGN) with radio luminosities in the range of $10^{22}-10^{27}$ W Hz$^{-1}$ based on cross-matching with COSMOS multi-wavelength catalogs. The moderate-variability sources span redshifts $z=0.22-1.56$, have mostly flat radio spectra ($α>-0.5$), and vary on timescales ranging from days to years. Lower-variability sources have similar properties, but have generally higher radio luminosities than the moderate-variability sources, extend to $z = 2.8$, and have steeper radio spectra ($α<-0.5$). No star-forming galaxy showed statistically significant variability in our analysis. The observed variability likely originates from scintillation on short ($\sim$week) timescales, and Doppler-boosted intrinsic AGN variability on long (month--year) timescales.
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