The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations
The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations
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DOI：
10.1086/309512
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发表时间：
2000-10-10
影响因子：
4.9
通讯作者：
Welch, D
中科院分区：
文献类型：
--
作者：
Alcock, C;Allsman, RA;Welch, D
我们报告了我们对大麦哲伦星云(LMC)微透镜的探索。对LMC中1190万颗恒星5.7年的测光分析揭示了13-17次微透镜事件。对我们的探测效率的详细处理表明，这比已知恒星群体通过透镜所预期的类似2-4次事件要多得多。这些事件的时间尺度((T)Over Top)从34天到230天不等。我们估计从2<；<；400天的事件到LMC的微透镜光学厚度为(400)(2)=1.2(-0.3)(+0.4)x 10(-7)，另外还有20%到30%的系统误差。事件的空间分布与LMC/LMC圆盘自透镜略有不同，但与银河系或LMC晕等扩展透镜分布一致。在部分由致密天体组成的银河系暗物质晕的背景下进行解释，最大似然分析给出了典型晕模型的男性晕部分为20%，95%的可信区间为8%-50%。在95%的置信度水平下，100%的男子气概光环被排除在外，除了我们最极端的光环模型。根据晕模型的不同，最有可能的MACHO质量在0.15-0.9Mo之间，而50kpc的MACHO的总质量为9(-3)(+4)×10(10)M，与晕模型无关。这些结果与我们之前的结果略有一致，但比之前的结果低了大约2倍。这主要是由于泊松噪声，因为在曝光时间增加3.4倍和对长时间尺度事件的敏感性增加的情况下，我们没有发现类似到4个以上事件的预期因素。除了更大的数据集，这项工作还包括改进的效率确定、改进的似然分析和更彻底的系统误差测试，特别是在处理微透镜的潜在背景方面。我们注意到背景的一个重要来源是LMC后面星系中的超新星(SNE)。
We report on our search for microlensing toward the Large Magellanic Cloud (LMC). Analysis of 5.7 yr of photometry on 11.9 million stars in the LMC reveals 13-17 microlensing events. A detailed treatment of our detection efficiency shows that this is significantly more than the similar to2-4 events expected from lensing by known stellar populations. The timescales ((t) over cap) of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < < 400 days to be (400)(2) = 1.2(-0.3)(+0.4) x 10(-7), with an additional 20% to 30% of systematic error. The spatial distribution of events is mildly inconsistent with LMC/LMC disk self-lensing, but is consistent with an extended lens distribution such as a Milky Way or LMC halo. Interpreted in the context of a Galactic dark matter halo, consisting partially of compact objects, a maximum-likelihood analysis gives a MACHO halo fraction of 20% for a typical halo model with a 95% confidence interval of 8%-50%. A 100% MACHO halo is ruled out at the 95% confidence level for all except our most extreme halo model. Interpreted as a Galactic halo population, the most likely MACHO mass is between 0.15 and 0.9 Mo, depending on the halo model, and the total mass in MACHOs out to 50 kpc is found to be 9(-3)(+4) x 10(10) M., independent of the halo model. These results are marginally consistent with our previous results, but are lower by about a factor of 2. This is mostly due to Poisson noise, because with 3.4 times more exposure and increased sensitivity to long-timescale events, we did not find the expected factor of similar to4 more events. In addition to a larger data set, this work also includes an improved efficiency determination, improved likelihood analysis, and more thorough testing of systematic errors, especially with respect to the treatment of potential backgrounds to microlensing. We note that an important source of background are supernovae (SNe) in galaxies behind the LMC.