El-Badry Kareem, Bradford Jeremy, Quataert Eliot, Geha Marla, Boylan-Kolchin Michael, Weisz Daniel R, Wetzel Andrew, Hopkins Philip F, Chan T K, Fitts Alex, Kereš Dušan, Faucher-Giguére Claude-André
Department of Astronomy and Theoretical Astrophysics Center, University of California Berkeley, Berkeley, CA 94720, USA.
Department of Astronomy, Yale University, New Haven, CT 06520, USA.
Mon Not R Astron Soc. 2018 Jun;477(2):1536-1548. doi: 10.1093/mnras/sty730. Epub 2018 Mar 24.
The shape of a galaxy's spatially unresolved, globally integrated 21-cm emission line depends on its internal gas kinematics: galaxies with rotationally supported gas discs produce double-horned profiles with steep wings, while galaxies with dispersion-supported gas produce Gaussian-like profiles with sloped wings. Using mock observations of simulated galaxies from the FIRE project, we show that one can therefore constrain a galaxy's gas kinematics from its unresolved 21-cm line profile. In particular, we find that the kurtosis of the 21-cm line increases with decreasing and that this trend is robust across a wide range of masses, signal-to-noise ratios, and inclinations. We then quantify the shapes of 21-cm line profiles from a morphologically unbiased sample of ~2000 low-redshift, HI-detected galaxies with = 10 M and compare to the simulated galaxies. At ≳ 10 M, both the observed and simulated galaxies produce double-horned profiles with low kurtosis and steep wings, consistent with rotationally supported discs. Both the observed and simulated line profiles become more Gaussian like (higher kurtosis and less-steep wings) at lower masses, indicating increased dispersion support. However, the simulated galaxies transition from rotational to dispersion support more strongly: at 10 M, most of the simulations produce more Gaussian-like profiles than typical observed galaxies with similar mass, indicating that gas in the low-mass simulated galaxies is, on average, overly dispersion supported. Most of the lower-mass-simulated galaxies also have somewhat lower gas fractions than the median of the observed population. The simulations nevertheless reproduce the observed line-width baryonic Tully-Fisher relation, which is insensitive to rotational versus dispersion support.
星系空间上无法分辨的整体21厘米发射线的形状取决于其内部气体运动学：具有旋转支撑气体盘的星系会产生带有陡峭边缘的双角轮廓，而具有弥散支撑气体的星系会产生带有倾斜边缘的类似高斯的轮廓。通过对FIRE项目模拟星系的模拟观测，我们表明，因此可以从星系无法分辨的21厘米线轮廓来约束其气体运动学。特别是，我们发现21厘米线的峰度随着[具体参数未给出]的减小而增加，并且在广泛的质量、信噪比和倾角范围内，这一趋势是稳健的。然后，我们从约2000个低红移、检测到中性氢、质量为[具体质量未给出]的形态无偏样本中量化21厘米线轮廓的形状，并与模拟星系进行比较。在质量约大于等于[具体质量未给出]时，观测到的和模拟的星系都产生了具有低峰度和陡峭边缘的双角轮廓，这与旋转支撑盘一致。在较低质量时，观测到的和模拟的线轮廓都变得更像高斯分布（峰度更高，边缘不那么陡峭），表明弥散支撑增加。然而，模拟星系从旋转支撑到弥散支撑的转变更为强烈：在质量为[具体质量未给出]时，大多数模拟产生的轮廓比具有相似质量的典型观测星系更像高斯分布，这表明低质量模拟星系中的气体平均而言过度受到弥散支撑。大多数低质量模拟星系的气体分数也略低于观测样本的中值。不过，模拟结果再现了观测到的线宽重子塔利 - 费希尔关系，该关系对旋转支撑与弥散支撑不敏感。
