Astronomy

Last part of the paper:

For stellar models, the remarkably high 𝜉ion is untenable 27,36 under common initial mass functions (IMFs). Since this quantity is directly sensitive to the hottest stars, its extreme value may be ascribed to an extension of the IMF to very massive stars 37,38. The high average ionising-photon energy of a 𝑇 = 105 K blackbody moreover yields a 2× higher ratio of Lyα to LyC photons than standard case-B recombination24, thereby bringing the required 𝜉ion more closely in agreement with the theoretical maximum for such stars 39. Whilst at such high 𝜉ion (and relatively low 𝑓esc, LyC) a UV turnover could be produced by a prominent nebular continuum40, the extremely blue UV continuum (𝛽UV ≲ −2.7) appears incompatible with a 2𝛾- dominated spectrum. One explanation is to invoke an ISM density upwards of 𝑛 ≈ 104 cm−3, as may be expected from the compactness of JADES-GS-z13-1-LA. Considering nebular continuum would be reddened further by the free-bound contribution, however, it may again indicate significant LyC leakage, corroborating the suggestion that JADES-GS-z13-1-LA is located inside an ionised bubble.

One particularly intriguing class of objects predicted to radiate up to 40% of their bolometric luminosity as Lyα are entirely metalfree Population III (Pop III) stars 41–43 thought to reach significantly higher masses and effective temperatures than subsequent metal-4 enriched stellar populations. However, the absolute UV magnitude of JADES-GS-z13-1-LA, 𝑀UV ≈ −18.7 mag, would require a stellar mass of 𝑀∗ ≈ 106 M⊙ as a pure Pop III system, somewhat higher than typical predictions 44. We further note the absence of strong He ii 𝜆 1640 Å emission (Methods) may argue against the Pop III scenario45, although its strength rapidly evolves a few Myr after a star formation burst 42,43. A high LyC escape fraction would also suppress He ii, yet still leaves the UV turnover to be explained.

Whatever the origin of the Lyα emission of JADES-GS-z13-1-LA may be, it reveals the rather extreme character of one of the earliest galaxies known, despite having been found in a modest survey area 16 probing a comoving volume of 50 000 Mpc3 between 𝑧 = 11 and 𝑧 = 15. At just 330 Myr after the Big Bang, JADES-GS-z13-1-LA indicates the profound marks left on the IGM by the first generation of galaxies through the creation of reionised regions. Furthermore, it provides tangible evidence for the Wouthuysen-Field coupling of the spin temperature of neutral hydrogen to that of the gas via the emission of Lyα photons, the global evolution of which is anticipated to be uncovered soon by H i 21 cm experiments 46,47 to provide a complementary view of Cosmic Dawn.

Sadly, no mention of the obvious reason for this: aliens!

Any hypotheses out yet?