Numerical calibration of the HCN–star formation correlation
Numerical calibration of the HCN–star formation correlation
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DOI：
10.1093/mnras/sty1662
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发表时间：
2018-01
影响因子：
4.8
通讯作者：
Adam Onus;M. Krumholz;C. Federrath
中科院分区：
文献类型：
--
作者：
Adam Onus;M. Krumholz;C. Federrath
HCN(1美元-0美元)排放追踪致密气体，并与从小银河系云到整个星系的尺度上的恒星形成率(SFR)密切相关。观测到的关联对稠密气体中恒星形成的效率提供了很强的约束，但对这种约束的定量解释需要从HCN排放到气体质量和密度的映射。在这篇文章中，我们通过对致密的恒星形成云的高分辨率模拟的后处理来提供所需的定标，以计算它们的HCN排放($L Hcn}$)，并确定这种发射如何与下面的气体密度分布和恒星形成效率有关。结果表明，HCN的发光度加权平均数密度为0.8-1.7倍10^4，rm cm-3；HCN发光度与稠密气体质量有关，其换算因子为α-RmHcn\约14，RmModot/(K，Km，S^-1，{Pc}^2)。我们还测量了每全球平均自由落体时间的恒星形成率($\epsilon}_{ff}$)与SFR$-$hcn之间的新的经验关系，${\rm sfr}/L{\rmhcn}=5.73\x 10^{-5}\，{\epsilon}^{1.32}_{\rm ff}\，\rm M{\odot}\，{yr}^{-1}/(K\，Km\，S^{-1}\，{PC}^2)$。观测到的sfr$-$hcn关联强烈地约束了系统不确定性因子为$sim 2$的系统不确定性。银河系内云与云之间的散射是几个因素之一。我们得出结论：L Hcn是稠密气体的有效示踪剂，IR Hcn关联对稠密气体中恒星形成的微物理有很强的诊断作用。
HCN(1$-$0) emission traces dense gas and correlates very strongly with star formation rates (SFRs) on scales from small Milky Way clouds to whole galaxies. The observed correlation offers strong constraints on the efficiency of star formation in dense gas, but quantitative interpretation of this constraint requires a mapping from HCN emission to gas mass and density. In this paper we provide the required calibration by postprocessing high-resolution simulations of dense, star-forming clouds to calculate their HCN emission ($L_{\rm HCN}$) and to determine how that emission is related to the underlying gas density distribution and star formation efficiency. We find that HCN emission traces gas with a luminosity-weighted mean number density of $0.8-1.7 \times 10^4\,{\rm cm}^{-3}$ and that HCN luminosity is related to mass of dense gas of $\gtrsim 10^4\,{\rm cm}^{-3}$ with a conversion factor of ${\alpha}_{\rm HCN} \approx 14\,\rm M_{\odot}/(K\,km\,s^{-1}\,{pc}^2)$. We also measure a new empirical relationship between the star formation rate per global mean freefall time (${\epsilon}_{ff}$) and the SFR$-$HCN relationship, ${\rm SFR}/L_{\rm HCN} = 5.73 \times 10^{-5}\,{\epsilon}^{1.32}_{\rm ff}\,\rm M_{\odot}\,{yr}^{-1}/(K\,km\,s^{-1}\,{pc}^2)$. The observed SFR$-$HCN correlation strongly constrains ${\epsilon}_{\rm ff} \approx 1\%$ with a factor of $\sim 2$ systematic uncertainty. The scatter in ${\epsilon}_{\rm ff}$ from cloud to cloud within the Milky Way is a factor of a few. We conclude that $L_{\rm HCN}$ is an effective tracer of dense gas and that the IR$-$HCN correlation is a very strong diagnostic of the microphysics of star formation in dense gas.