Candidate Population III stellar complex at <i>z</i> = 6.629 in the MUSE Deep Lensed Field
E. Vanzella, M. Meneghetti, G. B. Caminha, M. Castellano, F. Calura, P. Rosati, C. Grillo, Mark Dijkstra, Max Grönke, E. Sani, A. Mercurio, P. Tozzi, M. Nonino, S. Cristiani, M. Mignoli, L. Pentericci, R. Gilli, Tommaso Treu, K. I. Caputi, G. Cupani, A. Fontana, A. Grazian, I. Balestra
Abstract
ABSTRACT We discovered a strongly lensed (μ ≳ 40) Ly α emission at z = 6.629 (S/N ≃ 18) in the MUSE Deep Lensed Field (MDLF) targeting the Hubble Frontier Field (HFF) galaxy cluster MACS J0416. Dedicated lensing simulations imply that the Ly α emitting region necessarily crosses the caustic. The arc-like shape of the Ly α extends 3 arcsec on the observed plane and is the result of two merged multiple images, each one with a de-lensed Ly α luminosity L ≲ 2.8 × 1040 erg s−1 arising from a confined region (≲150 pc effective radius). A spatially unresolved Hubble Space Telescope(HST) counterpart is barely detected at S/N ≃ 2 after stacking the near-infrared bands, corresponding to an observed (intrinsic) magnitude m1500 ≳ 30.8 (≳35.0). The inferred rest-frame Ly α equivalent width is EW0 &gt; 1120 Å if the IGM transmission is TIGM &lt; 0.5. The low luminosities and the extremely large Ly α EW0 match the case of a Population III (Pop III) star complex made of several dozens stars (∼104 M⊙) that irradiate an H ii region crossing the caustic. While the Ly α and stellar continuum are among the faintest ever observed at this redshift, the continuum and the Ly α emissions could be affected by differential magnification, possibly biasing the EW0 estimate. The aforementioned tentative HST detection tends to favour a large EW0, making such a faint Pop III candidate a key target for the James Webb Space Telescope and Extremely Large Telescopes.