Presence of strong two-photon emission and very hot stars in SXDF-NB1006-2

Determine whether the galaxy SXDF-NB1006-2 at redshift z = 7.212 exhibits strong two-photon continuum emission and whether its ionizing radiation field includes very hot stars with effective temperatures of approximately 10^5 K, as suggested by the modeled Balmer jump and the measured F277W/F356W flux ratio.

Background

The authors’ spectral energy distribution modeling predicts a prominent Balmer jump and strong nebular continuum, which can be produced by two-photon emission. They quantify the Balmer jump strength via the F277W/F356W flux ratio and find a value consistent with a two-photon emission model that explains a UV turnover feature at z ~ 6.

Such strong two-photon emission is plausibly powered by very hot stars (~105 K). However, the current JWST/NIRSpec spectrum does not detect the continuum at the relevant wavelengths, and the authors explicitly state they cannot confirm the presence of this emission or the associated very hot stellar populations with the available data.

References

With the current data, we cannot confirm if there is strong two-photon emission in our target, but future observations will be crucial to examine the presence of strong two-photon emission and very hot stars.

— RIOJA. Young Starburst and Ionized Gas Outflows in a $z = 7.212$ Galaxy Uncovered by JWST NIRCam and NIRSpec Observations  (2510.25721 - Ren et al., 29 Oct 2025) in Section 3.3 (SED Fitting Results)