DRIVERS OF H i TURBULENCE IN DWARF GALAXIES
DRIVERS OF H i TURBULENCE IN DWARF GALAXIES
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DOI：
10.1088/0004-637x/773/2/88
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
A. Stilp;J. Dalcanton;E. Skillman;S. Warren;J. Ott;B. Koribalski
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作者：
A. Stilp;J. Dalcanton;E. Skillman;S. Warren;J. Ott;B. Koribalski
中性氢（Hi）的速度色散被认为是由星际介质（ISM）中的湍流决定的。虽然湍流被广泛认为是由星星形成驱动的，但最近的研究表明，这种驱动机制可能在低星星形成表面密度（SARSFR）的区域并不占主导地位，例如矮星系或螺旋星系的外部区域。我们已经产生了平均H i线配置文件中的一些附近的矮星和低质量的螺旋线共同添加H i光谱的子区域中的一个共同的半径或crossFR。我们发现单个空间分辨的“超轮廓”由中央窄峰（0.55 -15 km s-1）和两侧的高速翼组成，类似于对整个星系计算的全球对应物。假设的中心峰值反映了H i湍流速度色散，我们比较措施H i运动学确定的superprofiles本地ISM属性，包括表面质量密度和措施的星星形成。超轮廓的机翼形状与局部ISM性质没有任何相关性，这表明它们可能是H i视线谱的一个内在特征。另一方面，H i速度色散与重子和H i表面质量密度的相关性最强，这指向湍流的引力起源，但尚不清楚哪些引力不稳定性（如果有的话）能够在这些系统中有效地运行。星星形成能量通常产生在一个足以驱动H i湍流运动的水平，在现实的耦合效率的制度中，在该制度中，SFR为10−4 M yr−1 kpc−2，这是典型的内螺旋盘。另一方面，在低星星形成强度下，星星形成不能提供足够的能量来驱动所观察到的湍流，也不能唯一地确定湍流速度色散。然而，即使在低强度，星星的形成似乎提供了一个较低的阈值H i速度色散。我们发现一个显着的耦合效率降低，增加的BISSFR，这将是一致的图片星星形成耦合到ISM与恒定的效率，但较少的能量被发现在中性相在较高的BISSFR。我们已经研究了一些潜在的驱动程序的H i湍流，包括星星的形成，引力不稳定性，磁旋转不稳定性，吸积驱动的湍流，并发现，单独地，没有这些驱动程序是能够驱动所观察到的水平的湍流在低COSFR制度。我们将讨论解决这个难题的可能方案。
Neutral hydrogen (H i) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation, recent studies have shown that this driving mechanism may not be dominant in regions of low star formation surface density (ΣSFR), such those as found in dwarf galaxies or the outer regions of spirals. We have generated average H i line profiles in a number of nearby dwarfs and low-mass spirals by co-adding H i spectra in subregions with either a common radius or ΣSFR. We find that the individual spatially resolved “superprofiles” are composed of a central narrow peak (∼5–15 km s−1) with higher velocity wings to either side, similar to their global counterparts as calculated for the galaxy as a whole. Under the assumption that the central peak reflects the H i turbulent velocity dispersion, we compare measures of H i kinematics determined from the superprofiles to local ISM properties, including surface mass densities and measures of star formation. The shape of the wings of the superprofiles do not show any correlation with local ISM properties, which indicates that they may be an intrinsic feature of H i line-of-sight spectra. On the other hand, the H i velocity dispersion is correlated most strongly with baryonic and H i surface mass density, which points toward a gravitational origin for turbulence, but it is unclear which, if any, gravitational instabilities are able to operate efficiently in these systems. Star formation energy is typically produced at a level sufficient to drive H i turbulent motions at realistic coupling efficiencies in regimes where ΣSFR ≳ 10−4 M☉ yr−1 kpc−2, as is typically found in inner spiral disks. At low star formation intensities, on the other hand, star formation cannot supply enough energy to drive the observed turbulence, nor does it uniquely determine the turbulent velocity dispersion. Nevertheless, even at low intensity, star formation does appear to provide a lower threshold for H i velocity dispersions. We find a pronounced decrease in coupling efficiency with increasing ΣSFR, which would be consistent with a picture where star formation couples to the ISM with constant efficiency, but that less of that energy is found in the neutral phase at higher ΣSFR. We have examined a number of potential drivers of H i turbulence, including star formation, gravitational instabilities, the magneto-rotational instability, and accretion-driven turbulence, and found that, individually, none of these drivers is capable of driving the observed levels of turbulence in the low ΣSFR regime. We discuss possible solutions to this conundrum.