A Ly[alpha] EMITTER WITH AN EXTREMELY LARGE REST-FRAME EQUIVALENT WIDTH OF ~900 A AT z = 6.5: A CANDIDATE POPULATION III-DOMINATED GALAXY?

We have identified a very interesting Ly[alpha] emitter (LAE), whose Ly[alpha] emission line has an extremely large observed equivalent width of EW sub(0) = 436 super(+422) sub(-149) A, which corresponds to an extraordinarily large intrinsic rest-frame equivalent width of EW super(int) sub(0) = 872 super(+844) sub(-298) A after the average intergalactic absorption correction. The object was spectroscopically confirmed to be a real LAE by its apparent asymmetric Ly[alpha] line profile detected at z = 6.538. The continuum emission of the object was definitely detected in our deep z' -band image; thus, its EW sub(0) was reliably determined. Follow-up deep near-infrared spectroscopy revealed emission lines of neither He II [lambda]1640 as an apparent signature of Population III (Pop III) nor C IV [lambda]1549 as proof of an active nucleus. No detection of the short-lived He II [lambda]1640 line is not necessarily inconsistent with the interpretation that the underlying stellar population of the object is dominated by Pop III.We found that the observed extremely large EW sub(0) of the Ly[alpha] emission and the upper limit on the EW sub(0) of the He II [lambda]1640 emission can be explained by population synthesis models favoring a very young age less than 2-4 Myr and massive metal-poor (Z < 10 super(-5)) or even metal-free stars. The observed large EW sub(0) of Ly[alpha] is insufficiently explained by Population I/II synthesis models with Z [> or =, slanted] 10 super(-3). However, we cannot conclusively rule out the possibility that this object is composed of a normal stellar population with a clumpy dust distribution, which could enhance the Ly[alpha] EW sub(0), though its significance is still unclear.