Radio Spectra and Sizes of Atacama Large Millimeter/submillimeter Array-identified Submillimeter Galaxies: Evidence of Age-related Spectral Curvature and Cosmic-Ray Diffusion?
Radio Spectra and Sizes of Atacama Large Millimeter/submillimeter Array-identified Submillimeter Galaxies: Evidence of Age-related Spectral Curvature and Cosmic-Ray Diffusion?
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DOI：
10.3847/1538-4357/ab32e7
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发表时间：
2019-04
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通讯作者：
A. Thomson;I. Smail;A. Swinbank;J. Simpson;V. Arumugam;S. Stach;E. Murphy;W. Rujopakarn;O. Almaini;F. An;A. Blain;Chian-Chou Chen;E. Cooke;U. Dudzevičiūtė;A. Edge;D. Farrah;B. Gullberg;W. Hartley;E. Ibar;D. Maltby;M. Michałowski;Chris Simpson;P. V. D. Werf;J. Wardlow
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作者：
A. Thomson;I. Smail;A. Swinbank;J. Simpson;V. Arumugam;S. Stach;E. Murphy;W. Rujopakarn;O. Almaini;F. An;A. Blain;Chian-Chou Chen;E. Cooke;U. Dudzevičiūtė;A. Edge;D. Farrah;B. Gullberg;W. Hartley;E. Ibar;D. Maltby;M. Michałowski;Chris Simpson;P. V. D. Werf;J. Wardlow
我们分析了41个6 GHz探测到的阿塔卡玛大型毫米/亚毫米阵列（阿尔马）确定的亚毫米星系（SMG）的多频射电光谱特性，在610 MHz，1.4 GHz和6 GHz的巨型米波射电望远镜和甚大阵列观测。结合高分辨率（~ 0.″5）6 GHz射电和阿尔马870 μm成像（跟踪静止帧~ 20 GHz，和~ 250 μm尘埃连续谱），通过对样品测量的对数通量比qIR研究了远红外/射电相关。我们发现SMG的高频射电尺寸比冷尘埃辐射的尺寸大1.9 ± 0.4×（1.2 -3 kpc），并发现我们的源的子集在1.4 GHz扩展到1.10 kpc尺度的证据。通过结合在三个频率测量的无线电通量密度，我们可以超越简单的线性拟合高红移恒星形成星系的无线电光谱，并搜索光谱曲率，这已经在本地星暴星系中观察到。我们的样本中至少有四分之一（10/41）的样本显示出频谱中断的证据，具有中值，但相对于从低频数据简单外推的高频通量赤字。我们在与年龄相关的同步辐射损失的背景下，在这个源的子集内探索这一结果，表明弱磁场（B = 35 μG）和年轻的年龄（tSB = 40-80百万年）的中央星暴的组合可以再现所观察到的光谱中断。假设这些代表了演化（但仍在进行中）的恒星爆发，并且我们在这些系统当前星星形成过程的大约一半时间内观测到这些系统，这意味着恒星爆发的持续时间为1亿年，与通过气体耗尽时间尺度得出的估计值合理一致。
We analyze the multifrequency radio spectral properties of 41 6 GHz-detected Atacama Large Millimeter/submillimeter Array (ALMA)-identified, submillimeter galaxies (SMGs), observed at 610 MHz, 1.4 GHz, and 6 GHz with the Giant Metrewave Radio Telescope and the Very Large Array. Combining high-resolution (∼0.″5) 6 GHz radio and ALMA 870 μm imaging (tracing rest frame ∼20 GHz, and ∼250 μm dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio qIR, measuring for our sample. We show that the high-frequency radio sizes of SMGs are ∼1.9 ± 0.4× (∼2–3 kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on ∼10 kpc scales at 1.4 GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample shows evidence of a spectral break, with a median , but —a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields (B ∼ 35 μG) and young ages (tSB ∼ 40–80 Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts, and we are observing these systems roughly halfway through their current episode of star formation, this implies starburst durations of ≲100 Myr, in reasonable agreement with estimates derived via gas depletion timescales.