An extremely metal-poor star complex in the reionization era: Approaching Population III stars with JWST

We present JWST/Near Infrared Spectrograph (NIRSpec) integral field spectroscopy (IFS) of a lensed Population III candidate stellar complex (dubbed Lensed And Pristine 1, LAP1), with a lensing-corrected stellar mass of less than or similar to 10(4) M-circle dot and an absolute luminosity of M-UV>-11.2 (m(UV)>35.6), confirmed at redshift 6.639 +/- 0.004. The system is strongly amplified (mu greater than or similar to 100) by straddling a critical line of the Hubble Frontier Field galaxy cluster MACS J0416. Although the stellar continuum is currently not detected in the Hubble and JWST/Near Infrared Camera (NIRCam) and Near Infrared Imager and Slitless Spectrograph (NIRISS) imaging, arclet-like shapes of Lyman and Balmer lines, Ly alpha, H gamma, H beta and H alpha are detected with NIRSpec IFS with signal-to-noise ratios (S/N) of approximately 5-13 and large equivalent widths (> 300-2000 angstrom), along with a remarkably weak [OIII]lambda lambda 4959, 5007 at S/N similar or equal to 4. LAP1 shows a large ionizing photon production efficiency, log(xi(ion)[erg Hz(-1)]) > 26. From the metallicity indexes R23 = ([OIII] + [OII])/H beta less than or similar to 0.74 and R3 = ([OIII]/H beta) = 0.55 +/- 0.14, we derive an oxygen abundance of 12+log(O/H)less than or similar to 6.3. Intriguingly, the H alpha emission is also measured in mirrored subcomponents where no [OIII] is detected, providing even more stringent upper limits on the metallicity if in situ star formation is ongoing in this region (12+log(O/H) < 6). The formal stellar mass limit of the subcomponents would correspond to similar to 10(3) M-circle dot or M-UV fainter than -10. Alternatively, this metal-free, pure line-emitting region could be the first case of a fluorescing HI gas region induced by transverse escaping ionizing radiation from a nearby star complex. The presence of large equivalent-width hydrogen lines and the deficiency of metal lines in such a small region make LAP1 the most metal-poor star-forming region currently known in the reionization era and a promising site that may host isolated, pristine stars.