We report the detection of CO($J$=2$\to$1) emission from three massive dusty starburst galaxies at $z$$>$5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 ($z$=5.183) and AzTEC-3 ($z$=5.298), were previously known. We revise a previous redshift estimate for the third source GN10 ($z$=5.303), which we have independently confirmed through detections of CO $J$=1$\to$0, 5$\to$4, 6$\to$5, and [CII] 158 $\mu$m emission with the VLA and the NOrthern Extended Milllimeter Array (NOEMA). We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at $z$$>$5. Given our survey area of $\sim$60 arcmin$^2$, our results appear to imply a $\sim$6-55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these $z$$>$5 galaxies show star-formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions - consistent with the more extended sizes of the [CII] emission compared to the dust continuum and higher [CII]-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between $z$$>$5 dusty starbursts, which typically have dust temperatures $\sim$57%$\pm$25% warmer than starbursts at $z$=2-3 due to their enhanced star formation activity.

中文翻译：

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COLDz：大爆炸后约 10 亿年的巨大尘埃星暴星系的高空间密度

我们报告了通过 NSF 的 Karl G. Jansky 甚大阵列 (VLA) CO 光度的分子线扫描，检测到来自三个巨大尘埃星暴星系的 CO($J$=2$\to$1) 发射，$z$$>$高红移 (COLDz) 测量中的密度。其中两个来源 HDF 850.1 ($z$=5.183) 和 AzTEC-3 ($z$=5.298) 的红移以前是已知的。我们修改了先前对第三个源 GN10 ($z$=5.303) 的红移估计，我们已经通过检测 CO$J$=1$\to$0、5$\to$4、6$\to$5 独立确认了这一点， [CII] 使用 VLA 和北方扩展毫米波阵列 (NOEMA) 的 158 $\mu$m 发射。我们发现 COLDz 中目前独立确认的两个 CO 源是“光学暗的”，其中三个是 $z$$>$5 的尘埃遮蔽星系。鉴于我们的调查区域为 $\sim$60 arcmin$^2$，我们的结果似乎表明，在大爆炸后的最初 10 亿年内，这种遥远的尘埃系统的空间密度比之前认为的高 6-55 倍。这些$z$$>$5 星系中至少有两个显示出与所谓的“最大”星暴一致的恒星形成率表面密度，但我们发现它们之间的 CO 激发存在显着差异。这一结果可能表明，大块气藏的不同部分位于致密的恒星形成核区——与尘埃连续体相比 [CII] 发射的更大尺寸和更高的 [CII] 到远距离一致- 那些具有较低气体激发的星系的红外光度比。因此，我们发现 $z$$>$5 尘埃星暴之间的恒星形成条件存在很大差异，