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arXiv 1012.1952astro-ph.HE
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Local Group星系的费米大面积望远镜观测:M31的探测和M33的搜寻

Fermi Large Area Telescope observations of Local Group galaxies: Detection of M31 and search for M33

LAT collaboration

摘要:

宇宙射线(CR)可以通过它们在星际介质中传播时产生的星系范围内的伽马射线发射来研究。通过对不同系统散射信号的比较,可以了解CR加速和输运过程中的关键参数。我们的目的是确定和比较的CR诱导的伽马射线发射的几个本星系群星系的属性。我们利用费米伽马射线太空望远镜上的大面积望远镜获得的2年几乎连续的巡天观测来搜索来自M31和M33的伽马射线发射。我们比较的结果与那些大麦云,小麦哲伦云,银河系,和星暴星系M82和NGC 253。我们检测到一个伽马射线信号在5西格玛意义上的能量范围200 MeV-20 GeV,这是一致的起源于M31。100 MeV以上的积分光子通量为9.1 +/- 1.9(stat)+/- 1.0(sys)x10 e-9 ph/cm 2/s。我们没有发现来自M33的发射的证据,并推导出大于100 MeV的光子通量的上限为5.1 × 10 ~(-9)ph/cm ~ 2/s(2sigma)。将这些结果与其他本星系群星系的性质进行比较,我们发现恒星形成率和伽马射线光度之间的相关性也适用于星暴星系。M31的伽马射线光度大约是银河系的一半,这意味着M31和银河系的平均CR密度之比为0.35 +/- 0.25。观测到的伽马射线光度和恒星形成率之间的相关性表明,M33的通量并不远低于目前LAT观测的上限。

英文摘要:

Cosmic rays (CRs) can be studied through the galaxy-wide gamma-ray emission that they generate when propagating in the interstellar medium. The comparison of the diffuse signals from different systems may inform us about the key parameters in CR acceleration and transport. We aim to determine and compare the properties of the CR-induced gamma-ray emission of several Local Group galaxies. We use 2 years of nearly continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to search for gamma-ray emission from M31 and M33. We compare the results with those for the Large Magellanic Cloud, the Small Magellanic Cloud, the Milky Way, and the starburst galaxies M82 and NGC253. We detect a gamma-ray signal at 5sigma significance in the energy range 200 MeV-20 GeV that is consistent with originating from M31. The integral photon flux above 100MeV amounts to 9.1 +/- 1.9 (stat) +/- 1.0 (sys) x10e-9 ph/cm2/s. We find no evidence for emission from M33 and derive an upper limit on the photon flux >100MeV of 5.1 x10e-9 ph/cm2/s (2sigma). Comparing these results to the properties of other Local Group galaxies, we find indications for a correlation between star formation rate and gamma-ray luminosity that also holds for the starburst galaxies. The gamma-ray luminosity of M31 is about half that of the Milky Way, which implies that the ratio between the average CR densities in M31 and the Milky Way amounts to 0.35 +/- 0.25. The observed correlation between gamma-ray luminosity and star formation rate suggests that the flux of M33 is not far below the current upper limit from the LAT observations.

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