A massive reservoir of low-excitation molecular gas at high redshift
A massive reservoir of low-excitation molecular gas at high redshift
复制标题
高红移低激发分子气体的巨大储层
作者：
P. Papadopoulos;R. Ivison;C. Carilli;G. Lewis
分子氢（H2）是星系的重要组成部分，因为它促进了星星的形成和气体在活动星系核（AGN）上的吸积，这两个过程可以产生富气体星系的大红外光度。从示踪分子一氧化碳（CO）的光谱线发射的观测被用来探测这种气体的性质。但是在局域宇宙中已经研究过的谱线--主要是J = 1 → 0和J = 2 → 1的低转动跃迁--迄今为止在高红移星系中还无法观测到。相反，更高的转变已经被使用，尽管激发这些更高的转变所需的密度和温度可能不会被大部分气体达到。因此，过去的观测可能低估了分子气体的总量。利用12 CO的两条最低激发线（J = 1 → 0和J = 2 → 1），在红移z = 3.91的红外发光类星体APM 08279 +5255周围发现了大量的低激发分子气体。这些地图证实了核附近存在热而致密的气体，并揭示了一个扩展的低激发分子气体库，其质量比高激发观测所追踪的气体大10到100倍。这提出了在高红移（z > 3）星系的环境中可能存在大量低激发分子气体的可能性。
Molecular hydrogen (H2) is an important component of galaxies because it fuels star formation and the accretion of gas onto active galactic nuclei (AGN), the two processes that can generate the large infrared luminosities of gas-rich galaxies. Observations of spectral-line emission from the tracer molecule carbon monoxide (CO) are used to probe the properties of this gas. But the lines that have been studied in the local Universe—mostly the lower rotational transitions of J = 1 → 0 and J = 2 → 1—have hitherto been unobservable in high-redshift galaxies. Instead, higher transitions have been used, although the densities and temperatures required to excite these higher transitions may not be reached by much of the gas. As a result, past observations may have underestimated the total amount of molecular gas by a substantial amount. Here we report the discovery of large amounts of low-excitation molecular gas around the infrared-luminous quasar APM08279+5255 at redshift z = 3.91, using the two lowest excitation lines of 12 CO (J = 1 → 0 and J = 2 → 1). The maps confirm the presence of hot and dense gas near the nucleus, and reveal an extended reservoir of molecular gas with low excitation that is 10 to 100 times more massive than the gas traced by the higher-excitation observations. This raises the possibility that significant amounts of low-excitation molecular gas may exist in the environments of high-redshift (z > 3) galaxies.