arXiv 1812.033922018-12-08astro-ph.GA

VLA-COSMOS 3 GHz大型项目：高度恒星形成星系的平均无线电频谱能量分布

The VLA-COSMOS 3 GHz Large Project: Average radio spectral energy distribution of highly star-forming galaxies

K. Tisanić, V. Smolčić, J. Delhaize, M. Novak, H. Intema, I. Delvecchio, E. Schinnerer, G. Zamorani, M. Bondi, E. Vardoulaki

备注：: 21 pages, 15 figures
发表信息：: A&A 621, A139 (2019)
DOI：: 10.1051/0004-6361/201834002

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摘要：

我们构造了z~4范围内的高恒星形成星系（HSFGs）的平均射电谱能量分布（SED）。红外线和无线电的亮度是由一个紧密的相关性，这是由所谓的q参数定义。这种红外-射电相关性为使用射电光度作为恒星形成示踪剂提供了基础。最近的叠加和生存分析研究发现q随着红移的增加而减小。本文指出，通过对恒星形成星系（SFG）的单次幂律假设来计算静止标架射电光度可能是导致红移趋势的一个原因，为了验证这一点，我们对一个HSFG样本的射电SED形状进行了约束。为了实现广泛的休息帧频率范围内，我们结合了以前发表的VLA观测COSMOS场在1.4 GHz和3 GHz与未发表的GMRT观测在325 MHz和610 MHz的生存分析占非检测GMRT地图。我们选取了一个宽红移范围（0.3<z<4，SFR> 100 M ~ 0/yr）的HSFG样本，构造了平均射电SED。通过拟合破幂律，我们发现谱指数从低于4.3 GHz的静止帧频率的$α_1=0.42\pm0.06$到高于4.3 GHz的$α_2=0.94\pm0.06$变化。我们的研究结果与以前的低红移研究结果一致，即HSFG的SED不同于正常SFG的SED（SFR<10 M0/yr）。差异主要是在10 GHz左右的陡峭频谱中，这可能表明热自由-自由发射的比例较小。最后，我们还讨论了应用这种破碎的幂律SED代替一个简单的幂律在HSFG的K-校正和一个典型的无线电SED从文献中得出的正常SFG的影响。我们发现，无线电SED的形状是不太可能的SFG的q-z趋势的根本原因。

英文摘要：

We construct the average radio spectral energy distribution (SED) of highly star-forming galaxies (HSFGs) up to z~4. Infrared and radio luminosities are bound by a tight correlation that is defined by the so-called q parameter. This infrared-radio correlation provides the basis for the use of radio luminosity as a star-formation tracer. Recent stacking and survival analysis studies find q to be decreasing with increasing redshift. It was pointed out that a possible cause of the redshift trend could be the computation of rest-frame radio luminosity via a single power-law assumption of the star-forming galaxies' (SFGs) SED.To test this, we constrained the shape of the radio SED of a sample of HSFGs. To achieve a broad rest-frame frequency range, we combined previously published VLA observations of the COSMOS field at 1.4 GHz and 3 GHz with unpublished GMRT observations at 325 MHz and 610 MHz by employing survival analysis to account for non-detections in the GMRT maps. We selected a sample of HSFGs in a broad redshift range (0.3<z<4,SFR>100M0/yr) and constructed the average radio SED. By fitting a broken power-law, we find that the spectral index changes from $α_1=0.42\pm0.06$ below a rest-frame frequency of 4.3 GHz to $α_2=0.94\pm0.06$ above 4.3 GHz. Our results are in line with previous low-redshift studies of HSFGs (SFR>10M0/yr) that show the SED of HSFGs to differ from the SED found for normal SFGs (SFR<10M0/yr). The difference is mainly in a steeper spectrum around 10 GHz, which could indicate a smaller fraction of thermal free-free emission. Finally, we also discuss the impact of applying this broken power-law SED in place of a simple power-law in K-corrections of HSFGs and a typical radio SED for normal SFGs drawn from the literature. We find that the shape of the radio SED is unlikely to be the root cause of the q-z trend in SFGs.

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