正常和LSB星系盘稀薄区的气体密度和恒星形成
Gas density and star formation in the rarified regions of discs of normal and LSB galaxies
摘要：
假设11个高表面亮度（HSB）旋涡星系、7个低表面亮度（LSB）星系和3个S0星系的气体层处于边缘稳定星盘平面的平衡状态，计算了它们的方位平均中平面气体体积密度$ρ_g$的径向分布。我们比较了表面恒星形成率（$Σ_{SFR}$）和恒星形成效率（$SFE=Σ_{SFR}/Σ_{gas}$）与$ρ_g$和恒星表面密度$Σ_s$假设后者是成比例的光盘表面亮度。HSB和LSB星系都遵循单一的序列$Σ_{SFR}-ρ_{g}$和$SFE-Σ_s$或$SFE-ρ_s$。这意味着，在正常旋涡星系的外盘和LSB星系的内区，如果它们的恒星盘具有相似的密度，则恒星形成的条件是相似的。$SFE$和$ρ_s$之间的关系与Ostriker等人提出的自调节恒星形成理论模型中所期望的规律$SFE$ $\sim ρ_s^{1/2}$接近。\cite{OstrikerAll10}。另一种解释是，提出PDMATHAMT是成比例的频率的垂直振荡的气体云周围的磁盘中平面。在LSB星系的最稀薄的地区，恒星形成的效率几乎是独立的气体和恒星盘密度高于平均值从外推的幂律适合HSB样本星系的预期。显然，在这些区域与极低的$ρ_{g}$ SFE依赖于当地的密度波动，而不是在方位平均光盘参数。
英文摘要：
We calculated the radial profiles of the azimuthally averaged midplane gas volume density $ρ_g$ for 11 high surface brightness (HSB) spiral galaxies, 7 low surface brightness (LSB) galaxies and 3 S0 galaxies assuming their gaseous layers to be in the equilibrium state in the plane of marginally stable stellar discs. We compared the surface star formation rate ($Σ_{SFR}$) and star formation efficiency ($SFE=Σ_{SFR}/Σ_{gas}$) with $ρ_g$ and stellar surface density $Σ_s$ assuming the latter to be proportional to disc surface brightness. Both HSB and LSB galaxies follow a single sequence $Σ_{SFR}-ρ_{g}$ and $SFE-Σ_s$ or $SFE-ρ_s$. It means that the conditions of star formation are similar in the outer discs of normal spiral galaxies and in the inner regions of LSB galaxies if their stellar discs have similar densities. The relationship between $SFE$ and $ρ_s$ is close to the law $SFE$ $\sim ρ_s^{1/2}$ expected in the theoretical model of self-regulated star formation proposed by Ostriker et al.\cite{OstrikerAll10}. The alternative explanation is to propose that $SFE$ is proportional to a frequency of vertical oscillation of gas clouds around the disc midplane. In the most rarified regions of LSB galaxies the efficiency of star formation is nearly independent on gas and stellar disc densities being higher in the mean than it is expected from the extrapolation of the power law fit for HSB sample galaxies. Evidently in these regions with extremely low $ρ_{g}$ SFE depends on local density fluctuations rather than on the azimuthally averaged disc parameters.
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