Herschel对本星系仙女座星系（HELGA）III的利用：M31的恒星形成规律
Herschel Exploitation of Local Galaxy Andromeda (HELGA) III: The Star Formation Law in M31
摘要：
本文详细研究了在~ 140 pc尺度下恒星形成率（SFR）与M31的星际介质（ISM）的关系。SFR是用远紫外和24 μ m辐射计算的，并对M31中的老恒星星族进行了校正。我们发现全球的SFR值为0.25+/-0.05Msun/yr，并将其与使用总远红外（FIR）光度发现的SFR进行比较。在年轻恒星主导尘埃加热的区域，人们普遍同意。原子氢（HI）和分子气体（由一氧化碳（CO）示踪）或粉尘质量用于示踪ISM中的总气体。我们表明，在Kennicutt（1998 b）的图中，SFR和气体质量的全球表面密度将M31置于一组低SFR星系中。SFR和气体表面密度之间的关系是在横跨M31的六个径向环空中测试的，假设与指数N呈幂律关系。用HI和CO追踪的气体总量的恒星形成定律给出了一个全球指数N=2.03+/-0.04，随半径的变化而显著变化;最高值出现在10 kpc环中。我们认为这种斜率是由于HI在~ 10 Msun/pc 2时使分子转向。当观察H2区域时，我们测量到更高的平均SFR，这表明H2和SF之间有更好的空间相关性。我们发现N~0.6与整个磁盘一致的结果-这是在低端的值在以前的工作中发现，并反对超线性SF法律小尺度。
英文摘要：
We present a detailed study of how the Star Formation Rate (SFR) relates to the interstellar medium (ISM) of M31 at ~140pc scales. The SFR is calculated using the far-ultraviolet and 24um emission, corrected for the old stellar population in M31. We find a global value for the SFR of 0.25+/-0.05Msun/yr and compare this with the SFR found using the total far-infrared (FIR) luminosity. There is general agreement in regions where young stars dominate the dust heating. Atomic hydrogen (HI) and molecular gas (traced by carbon monoxide, CO) or the dust mass is used to trace the total gas in the ISM. We show that the global surface densities of SFR and gas mass place M31 amongst a set of low-SFR galaxies in the plot of Kennicutt (1998b). The relationship between SFR and gas surface density is tested in six radial annuli across M31, assuming a power law relationship with index, N. The star formation law using total gas traced by HI and CO gives a global index of N=2.03+/-0.04, with a significant variation with radius; the highest values are observed in the 10kpc ring. We suggest that this slope is due to HI turning molecular at ~10Msun/pc2. When looking at H2 regions, we measure a higher mean SFR suggesting a better spatial correlation between H2 and SF. We find N~0.6 with consistent results throughout the disk - this is at the low end of values found in previous work and argues against a superlinear SF law on small scales.
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