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arXiv 2102.00040astro-ph.GA
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turbulence与LITTLE中恒星形成的相关性研究

A Search for correlations between turbulence and star formation in LITTLE THINGS dwarf irregular galaxies

Deidre A. Hunter, Bruce G. Elmegreen, Haylee Archer, Caroline E. Simpson, Phil Cigan

摘要:

湍流有可能产生气体密度增加,启动云和恒星形成(SF),它可以由SF本地产生。为了研究湍流和SF之间的联系,我们在附近dIrr星系的LITTLE THINGS样本中寻找FUV图像跟踪的SF与动能密度(KED)和速度色散($v_{disp}$)跟踪的气体湍流之间的关系。我们进行2D之间的互相关FUV和KED图像,测量在环中的互相关,以产生相关系数作为半径的函数,并确定的互相关值的累积分布函数。我们还在逐像素的基础上绘制了局部过量KED、$v_{disp}$和HI质量表面密度$Σ_{\rm HI}$(从减去径向轮廓的相应值确定)与过量SF速率密度$Σ_{\rm SFR}$的关系图,对于所有具有正过量$Σ_{\rm SFR}$的区域。我们发现$Σ_{\rm SFR}$和KED的相关性很差。与SF相关的过量KED意味着超新星能量在这里的分辨率尺度上泵浦局部HI湍流的效率为$\sim0.5$ %,这是$\sim2$的一个因子,对于银河系尺度上的所有湍流都太小了。SF区的过剩$v_{disp}$也很小,只有$\sim0.37$ km s $^{-1}$。$Σ_{\rm HI}$中的局部过剩对应于$Σ_{\rm SFR}$中的过剩,这与星系内部$\sim1.6$ Gyr的HI消耗时间一致。这个时间尺度和CO的消耗时间之间的相似性意味着CO暗分子气体具有与内部圆盘中的HI相当的质量。

英文摘要:

Turbulence has the potential for creating gas density enhancements that initiate cloud and star formation (SF), and it can be generated locally by SF. To study the connection between turbulence and SF, we looked for relationships between SF traced by FUV images, and gas turbulence traced by kinetic energy density (KED) and velocity dispersion ($v_{disp}$) in the LITTLE THINGS sample of nearby dIrr galaxies. We performed 2D cross-correlations between FUV and KED images, measured cross-correlations in annuli to produce correlation coefficients as a function of radius, and determined the cumulative distribution function of the cross correlation value. We also plotted on a pixel-by-pixel basis the locally excess KED, $v_{disp}$, and HI mass surface density, $Σ_{\rm HI}$, as determined from the respective values with the radial profiles subtracted, versus the excess SF rate density $Σ_{\rm SFR}$, for all regions with positive excess $Σ_{\rm SFR}$. We found that $Σ_{\rm SFR}$ and KED are poorly correlated. The excess KED associated with SF implies a $\sim0.5$% efficiency for supernova energy to pump local HI turbulence on the scale of resolution here, which is a factor of $\sim2$ too small for all of the turbulence on a galactic scale. The excess $v_{disp}$ in SF regions is also small, only $\sim0.37$ km s$^{-1}$. The local excess in $Σ_{\rm HI}$ corresponding to an excess in $Σ_{\rm SFR}$ is consistent with an HI consumption time of $\sim1.6$ Gyr in the inner parts of the galaxies. The similarity between this timescale and the consumption time for CO implies that CO-dark molecular gas has comparable mass to HI in the inner disks.

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