Cosmic clocks: a tight radius-velocity relationship for HI-selected galaxies
Cosmic clocks: a tight radius-velocity relationship for HI-selected galaxies
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宇宙钟：HI选定星系的紧密半径-速度关系
DOI：
10.1093/mnras/sty275
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发表时间：
2018
影响因子：
4.8
通讯作者：
Hanish D J
中科院分区：
文献类型：
--
作者：
Meurer Gerhardt R;Obreschkow Danail;Wong O Ivy;Zheng Zheng;Audcent Rossi Fiona M;Hanish D J
高选择星系的最大可探测半径Rmax与自转速度呈线性关系。这一结果涵盖了测量的光学，紫外线和Hiemission的星系跨越一个因素的30的大小和速度，从小矮不规则的最大的螺旋。因此，星系的行为就像时钟一样，在它们圆盘的最外围旋转一圈。一个大的光学选择样本的观测是一致的，这意味着这种关系是通用的低红移宇宙中的盘星系。从星系形成和演化的简单模型中，可以预期一个线性的半径-速度关系。与目前宇宙的平均密度相比，Rmax内的总质量已经坍缩了37倍。采用标准假设，我们发现平均晕自旋参数λ在0.020-0.035的范围内。λ中的色散为0.16 dex，小于模拟的预期值。这可能是由于我们选择盘星系而不是所有晕的偏见。在Rmax下，恒星和原子气体的质量密度估计值相似（约0.5 M <$pc−2），表明外盘高度演化。气体的消耗和恒星人口的建立时间尺度是数百个Gyr，因此星星的形成并不是驱动目前外盘演化的动力。Rmax和光盘scalelength之间的估计比率是一致的长期预测单片崩溃模型。因此，目前还不清楚盘的范围是否来自持续的吸积，快速的初始崩溃，长期的演变，或其组合。
Hi-selected galaxies obey a linear relationship between their maximum detected radiusRmaxand rotational velocity. This result covers measurements in the optical, ultraviolet, and Hiemission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear radius–velocity relationship is expected from simple models of galaxy formation and evolution. The total mass withinRmaxhas collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions, we find a mean halo spin parameter λ in the range 0.020–0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all haloes. The estimated mass densities of stars and atomic gas atRmaxare similar (∼0.5 M⊙pc−2), indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio betweenRmaxand disc scalelength is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution, or a combination thereof.