A Multiwavelength Analysis of the Faint Radio Sky (COSMOS-XS): the Nature of the Ultra-faint Radio Population
A Multiwavelength Analysis of the Faint Radio Sky (COSMOS-XS): the Nature of the Ultra-faint Radio Population
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DOI：
10.3847/1538-4357/abb77a
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发表时间：
2020-09
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通讯作者：
H. Algera;D. V. D. Vlugt-D.-V.-D.-Vlugt-27732973;J. Hodge;I. Smail;M. Novak;J. Radcliffe;D. Riechers;H. Röttgering;V. Smolčić;Fabian Walter
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作者：
H. Algera;D. V. D. Vlugt-D.-V.-D.-Vlugt-27732973;J. Hodge;I. Smail;M. Novak;J. Radcliffe;D. Riechers;H. Röttgering;V. Smolčić;Fabian Walter
超深射电调查是对尘埃遮蔽的恒星形成的宝贵探测，但需要清楚地了解无线电活动星系核（agn）的相对贡献，以充分利用它们的潜力。我们研究了Karl G. Jansky Very Large Array COSMOS-XS巡天中探测到的μJy射电群的组成，该巡天基于在~ 350 arcmin2区域内以3ghz频率探测到的1540个源样本。这次超深探测包括在3 GHz和10 GHz的COSMOS场中进行单点探测，rms灵敏度分别为0.53和0.41 μJy beam−1。基于近紫外/光学到亚毫米数据的组合，我们发现97%的射电源存在多波长对应，并且通过光学/近红外波长的叠加分析，我们进一步表明，缺乏这种对应的源在本质上可能是高红移的（典型的z ~ 4−5）。利用COSMOS上的多波长数据，我们通过各种诊断方法识别agn，并发现这些agn占我们样本的23.2±1.3%，其余为未受污染的恒星形成星系。然而，超过一半的agn显示出与恒星形成一致的射电辐射，只有8.8±0.8%的射电源显示出明显的射电亮度过剩。在3 GHz的通量密度为~ 30 μJy时，恒星形成源的比例达到了~ 90%，这一比例与更低通量密度下的一致性一致。总的来说，我们的发现表明，像COSMOS-XS这样的超深射电巡天是获得恒星形成动力射电源的干净样本的一种非常有效的手段。
Ultra-deep radio surveys are an invaluable probe of dust-obscured star formation, but require a clear understanding of the relative contribution from radio active galactic nuclei (AGNs) to be used to their fullest potential. We study the composition of the μJy radio population detected in the Karl G. Jansky Very Large Array COSMOS-XS survey based on a sample of 1540 sources detected at 3 GHz over an area of ∼350 arcmin2. This ultra-deep survey consists of a single pointing in the well-studied COSMOS field at both 3 and 10 GHz and reaches rms sensitivities of 0.53 and 0.41 μJy beam−1, respectively. We find multiwavelength counterparts for 97% of radio sources, based on a combination of near-UV/optical to sub-millimeter data, and through a stacking analysis at optical/near-IR wavelengths we further show that the sources lacking such counterparts are likely to be high-redshift in nature (typical z ∼ 4−5). Utilizing the multiwavelength data over COSMOS, we identify AGNs through a variety of diagnostics and find these to make up 23.2 ± 1.3% of our sample, with the remainder constituting uncontaminated star-forming galaxies. However, more than half of the AGNs exhibit radio emission consistent with originating from star formation, with only 8.8 ± 0.8% of radio sources showing a clear excess in radio luminosity. At flux densities of ∼30 μJy at 3 GHz, the fraction of star formation-powered sources reaches ∼90%, and this fraction is consistent with unity at even lower flux densities. Overall, our findings imply that ultra-deep radio surveys such as COSMOS-XS constitute a highly effective means of obtaining clean samples of star formation-powered radio sources.