近螺旋星系中由非线性过程触发的亚kpc尺度恒星形成
Star Formation On Sub-kpc Scale Triggered By Non-linear Processes In Nearby Spiral Galaxies
摘要：
利用CARMA和NOBEYAMA近星系（CANON）CO巡天的新CO（$J$ =1-0）数据，研究了恒星形成规律的超线性相关。该样本包括10个附近的螺旋星系，其中结构在sub-kpc尺度的空间分辨。结合H $α$和24 $μ$ m图像追踪的恒星形成率表面密度，CO（$J$ =1-0）数据提供了一个超线性斜率$N$ = 1.3。当从H $α$和24 $μ$ m图像中减去弥漫的恒星和尘埃背景辐射时，斜率变得更陡（$N$ = 1.8）。最近的研究发现，在许多旋涡星系中，CO（$J$ =2-1）的恒星形成效率（SFE）是恒定的，与此相反，这些结果表明，SFE不是与环境无关的，而是随着分子气体表面密度的增加而增加。我们认为，CO（$J$ =2-1）的激发可能是增强的地区，具有较高的恒星形成和不线性跟踪的分子气体质量。此外，在恒星形成率为零的区域，散射辐射对超临界流体能量测量的影响最大。这两种效应可以使幂律相关变平，产生表观线性斜率。CO（$J$ =1-0）分析的超线性斜率表明，在高气体密度区域，恒星形成被非线性过程增强，例如，引力坍缩和云-云碰撞。
英文摘要：
We report a super-linear correlation for the star formation law based on new CO($J$=1-0) data from the CARMA and NOBEYAMA Nearby-galaxies (CANON) CO survey. The sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined with the star formation rate surface density traced by H$α$ and 24 $μ$m images, CO($J$=1-0) data provide a super-linear slope of $N$ = 1.3. The slope becomes even steeper ($N$ = 1.8) when the diffuse stellar and dust background emission is subtracted from the H$α$ and 24 $μ$m images. In contrast to the recent results with CO($J$=2-1) that found a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO($J$=2-1) is likely enhanced in the regions with higher star formation and does not linearly trace the molecular gas mass. In addition, the diffuse emission contaminates the SFE measurement most in regions where star formation rate is law. These two effects can flatten the power law correlation and produce the apparent linear slope. The super linear slope from the CO($J$=1-0) analysis indicates that star formation is enhanced by non-linear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions.
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