不需要z~7处的极端恒星质量：COS-87259的一个测试案例研究
No Need for Extreme Stellar Masses at z~7: A Test-case Study of COS-87259
摘要：
最近关于z>6的大质量（log（M/Msun）>11）星系存在的争论对星系形成理论提出了挑战。因此，了解SED拟合方法对再电离期星系质量估计的影响是至关重要的。在这项工作中，我们进行了一个案例研究的活动星系核宿主星系候选COS-87259光谱红移z=6.853，这是声称有一个非常高的恒星质量log（M/Msun）~11.2。我们测试了一套不同的SED拟合算法和恒星星族模型，我们独立测量测光在17个宽波段的这个来源。在五个不同的代码设置之间，COS-87259的恒星质量估计跨度log（M/Msun）=10.24-11.00，而拟合的约化卡方值在dchi 2 =1.2内都接近于1，因此SED拟合的质量基本上是不可区分的。只有当我们在Prospector中采用非参数恒星形成历史模型时，我们才能检索到超过log（M/Msun）=11的恒星质量。虽然推导出的恒星质量的变化时，使用以前报道的测光这个来源，非参数的SED拟合方法总是产生最高的值。由于这些模型越来越受欢迎的詹姆斯韦伯太空望远镜高红移科学，我们强调的绝对重要性，测试各种SED拟合例程，特别是显然非常大的星系在这样的高红移。
英文摘要：
Recent controversy regarding the existence of massive (log(M/Msun)>11) galaxies at z>6 poses a challenge for galaxy formation theories. Hence, it is of critical importance to understand the effects of SED fitting methods on stellar mass estimates of Epoch of Reionization galaxies. In this work, we perform a case study on the AGN host galaxy candidate COS-87259 with spectroscopic redshift z=6.853, that is claimed to have an extremely high stellar mass of log(M/Msun)~11.2. We test a suite of different SED fitting algorithms and stellar population models on our independently measured photometry in 17 broad bands for this source. Between five different code setups, the stellar mass estimates for COS-87259 span log(M/Msun)=10.24-11.00, whilst the reduced chi-squared values of the fits are all close to unity within dchi2=1.2, so that the quality of the SED fits is basically indistinguishable. Only when we adopt a nonparametric star formation history model within Prospector do we retrieve a stellar mass exceeding log(M/Msun)=11. Although the derived stellar masses change when using previously reported photometry for this source, the nonparametric SED-fitting method always yields the highest values. As these models are becoming increasingly popular for James Webb Space Telescope high-redshift science, we stress the absolute importance of testing various SED fitting routines particularly on apparently very massive galaxies at such high redshifts.
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