Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
Limits on the Macho content of the Galactic Halo from the EROS-2 Survey of the Magellanic Clouds
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DOI：
10.1051/0004-6361:20066017
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发表时间：
2007-07-01
影响因子：
6.5
通讯作者：
Zylberajch, S.
中科院分区：
文献类型：
--
作者：
Tisserand, P.;Le Guillou, L.;Zylberajch, S.
目标。EROS-2项目的设计是为了验证一个假设，即大质量致密的光晕物体（所谓的“machos”）可能是银河系暗物质光晕的主要组成部分。为此，EROS-2在6.7年的时间里对麦哲伦星云中的33 × 106颗恒星进行了监测，以寻找由这些天体引起的微透镜事件。在这项工作中，我们只使用了分布在LMC 84度(2)和SMC 9度(2)上的7 × 10(6)颗明亮恒星的子样本。只使用明亮恒星的策略有助于区分由变星引起的背景事件，并允许简单地确定源混淆（混合）的影响。大立体角的使用使得测量对可能使光学深度强烈依赖方向的影响相对不敏感。使用这些明亮的恒星样本，只发现了一个候选事件，而如果光晕完全被质量为0.4 M的天体所占据，预计会有39个类似的事件。结合EROS-1的结果，这意味着由于这些透镜对大麦哲伦云（LMC）的光学深度为tau < 0.36 x 10(-7) (95% CL)，对应于晕质量的一小部分小于8%。这个光学深度远远小于MACHO合作在LMC中心区域测量到的深度。更一般地说，质量范围在0.6 x 10(-7) M-圆点< M < 15 M-圆点被排除为银河系光晕的主要居住者。
Aims. The EROS-2 project was designed to test the hypothesis that massive compact halo objects (the so-called "machos") could be a major component of the dark matter halo of the Milky Way galaxy. To this end, EROS-2 monitored over 6.7 years 33 x 106 stars in the Magellanic clouds for microlensing events caused by such objects.Methods. In this work, we use only a subsample of 7 x 10(6) bright stars spread over 84 deg(2) of the LMC and 9 deg(2) of the SMC. The strategy of using only bright stars helps to discriminate against background events due to variable stars and allows a simple determination of the effects of source confusion (blending). The use of a large solid angle makes the survey relatively insensitive to effects that could make the optical depth strongly direction dependent.Results. Using this sample of bright stars, only one candidate event was found, whereas similar to 39 events would have been expected if the Halo were entirely populated by objects of mass M similar to 0.4 M-circle dot. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (LMC) due to such lenses is tau < 0.36 x 10(-7) (95% CL), corresponding to a fraction of the halo mass of less than 8%. This optical depth is considerably less than that measured by the MACHO collaboration in the central region of the LMC. More generally, machos in the mass range 0.6 x 10(-7) M-circle dot < M < 15 M-circle dot are ruled out as the primary occupants of the Milky Way Halo.