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arXiv 1004.2699astro-ph.CO
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三叶草类星体中的弱13 CO：年轻的，早期星暴的证据

Weak 13CO in the Cloverleaf Quasar: evidence for a young, early generation starburst

C. Henkel, D. Downes, A. Weiss, D. Riechers, F. Walter

备注：
7 pages, 5 figures, accepted for publication in A&A (Main Journal)
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摘要：

在高红移下对12 CO的观测表明，在早期宇宙中至少有一些星系的核区域存在快速的金属富集。然而，浓缩可能仅限于由短寿命大质量恒星合成的核，不包括经典的次级核，如13 CO。为了验证这一观点，我们在红移2.5的三叶草类星体上探测到了13 CO J=3-2的谱线，其速度为0.3 Jy km/s。这是13 CO在高红移的第一个观测证据。12 CO/13 CO J=3-2的光度比至少有40比银河系分子云和超亮星系Arp 220的光度比高得多，但可能与NGC 6240的光度比相似。大速度梯度（LVG）模型模拟七个12 CO转换和13 CO线产量12 CO/13 CO丰度比超过100的立体式。这是可能的，所测量的比率是由一个强大的亚毫米辐射场，这降低了13 CO线和背景之间的对比度的影响。然而，更有可能的是，该比率是由13 CO的真正缺乏引起的。一个潜在的冲突与光学数据，表明高丰度也为次级核类星体的高红移，可能会得到解决，如果大部分的CO排放源足够远离活动星系核。

英文摘要：

Observations of 12CO at high redshift indicate rapid metal enrichment in the nuclear regions of at least some galaxies in the early universe. However, the enrichment may be limited to nuclei that are synthesized by short-lived massive stars, excluding classical secondary nuclei like 13CO. Testing this idea, we tentatively detect the 13CO J=3-2 line at a level of 0.3 Jy km/s toward the Cloverleaf Quasar at redshift 2.5. This is the first observational evidence for 13CO at high redshift. The 12CO/13CO J=3-2 luminosity ratio is with at least 40 much higher than ratios observed in molecular clouds of the Milky Way and in the ultraluminous galaxy Arp 220, but may be similar to that observed toward NGC 6240. Large Velocity Gradient (LVG) models simulating seven 12CO transitions and the 13CO line yield 12CO/13CO abundance ratios in excess of 100 for the Cloverleaf. It is possible that the measured ratio is affected by a strong submillimeter radiation field, which reduces the contrast between the 13CO line and the background. It is more likely, however, that the ratio is caused by a real deficiency of 13CO. A potential conflict with optical data, indicating high abundances also for secondary nuclei in quasars of high redshift, may be settled if the bulk of the CO emission is originating sufficiently far from the active galactic nucleus.

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