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arXiv 0706.0210astro-ph
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关于小星系的形态、气体分数和恒星形成率

On the morphologies, gas fractions, and star formation rates of small galaxies

Tobias Kaufmann, Coral Wheeler, James S. Bullock

摘要:

我们利用一系列N体/光滑粒子流体动力学模拟和分析论证表明,在T_F ~ 10^4 K的星际介质中存在一个有效的温度底,这自然地解释了低质量星系比大星系更接近球形、更富含气体和更低的重子转化成恒星的效率的趋势。这种趋势的出现是因为在小的暗物质晕中,气体压力的支持比角动量的支持更重要。我们认为旋转速度约为40 km/s的矮星系并不起源于薄盘,而是出生于厚而蓬松的系统。如果被吸积到更大的晕上,这种纤细的矮星将比缩小的更大的螺旋更容易受到气体损失或潮汐变化的影响。对于一个恒定的温度地板,压力支持变得不那么重要,在大晕,这产生了一种趋势,大规模的孤立星系有更薄的磁盘和更有效的恒星形成比他们的质量较小的同行,观察。

英文摘要:

We use a series of N-body/smoothed particle hydrodynamics simulations and analytic arguments to show that the presence of an effective temperature floor in the interstellar medium at T_F ~ 10^4 K naturally explains the tendency for low-mass galaxies to be more spheroidal, more gas rich, and less efficient in converting baryons into stars than larger galaxies. The trend arises because gas pressure support becomes important compared to angular momentum support in small dark matter haloes. We suggest that dwarf galaxies with rotational velocities ~ 40 km/s do not originate as thin discs, but rather are born as thick, puffy systems. If accreted on to larger haloes, tenuous dwarfs of this kind will be more susceptible to gas loss or tidal transformation than scaled-down versions of larger spirals. For a constant temperature floor, pressure support becomes less important in large haloes, and this produces a tendency for massive isolated galaxies to have thinner discs and more efficient star formation than their less massive counterparts, as observed.

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