GOODS NICMOS调查中块状镓的主要形成模式--气体吸积
Gas Accretion as a Dominant Formation Mode in Massive Galaxies from the GOODS NICMOS Survey
摘要：
解决所有驱动星系形成的过程的能力是河外天文学最基本的目标之一。虽然恒星形成率和合并历史现在越来越确定，但星系际介质的气体吸积在为恒星形成提供气体方面的作用仍然很大程度上未知。本文利用GOODS NICMOS巡天（GNS）的观测结果，给出了1.5 < z < 3历元内，初始恒星质量M *>10^{11} Msol，并遵循相同的并合调整后的同动数密度的大质量星系吸积气体的间接证据。我们发现，这些大质量星系的气体质量分数的测量是不一致的，所观察到的恒星形成历史相同的星系人口。我们进一步证明，这一额外的气体质量不能占冷气体通过较小的和主要的合并。在这些计算中，我们还考虑了气体流出和气体再循环的影响，由于恒星演化。我们认为，以维持恒星形成在观察到的速率必须有额外的方法来增加冷气体质量，并建立这种气体供应的最有可能的方法是从星系际介质吸积。我们计算出在1.5 < z < 3.0之间的大质量星系的平均气体质量吸积率为\dot{M} = 96+/-19 Msol/yr。我们表明，在这个时期，对于这些非常大质量的星系，49+/-20%的重子质量组装是气体吸积和未解决的合并的结果。然而，这个时期所有恒星形成的66+/-20%是气体吸积的结果。这表明，对于大多数质量在1.5< z< 3的星系，气体吸积是引发新恒星质量组装的主要方法。
英文摘要：
The ability to resolve all processes which drive galaxy formation is one of the most fundamental goals in extragalactic astronomy. While star formation rates and the merger history are now measured with increasingly high certainty, the role of gas accretion from the intergalactic medium in supplying gas for star formation still remains largely unknown. We present in this paper indirect evidence for the accretion of gas into massive galaxies with initial stellar masses M_*>10^{11} M_sol and following the same merger adjusted co-moving number density at lower redshifts during the epoch 1.5 < z < 3, using results from the GOODS NICMOS Survey (GNS). We show that the measured gas mass fractions of these massive galaxies are inconsistent with the observed star formation history for the same galaxy population. We further demonstrate that this additional gas mass cannot be accounted for by cold gas delivered through minor and major mergers. We also consider the effects of gas outflows and gas recycling due to stellar evolution in these calculations. We argue that to sustain star formation at the observed rates there must be additional methods for increasing the cold gas mass, and that the likeliest method for establishing this supply of gas is by accretion from the intergalactic medium. We calculate that the average gas mass accretion rate into these massive galaxies between 1.5 < z < 3.0, is \dot{M} = 96+/-19 M_sol/yr after accounting for outflowing gas. We show that during this epoch, and for these very massive galaxies, 49+/-20% of baryonic mass assembly is a result of gas accretion and unresolved mergers. However, 66+/-20% of all star formation in this epoch is the result of gas accretion. This reveals that for the most massive galaxies at 1.5< z< 3 gas accretion is the dominant method for instigating new stellar mass assembly.
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