Blue monsters. Why are JWST super-early, massive galaxies so blue?

The recent James Webb Space Telescope tentative discovery of a population of super-early (redshift z > 10), relatively massive (stellar mass M-* = 10(8)-10(9)M(circle dot)) and evolved (metallicity Z approximate to 0.1 Z(circle dot)) galaxies, which nevertheless show blue (beta similar or equal to -2.6) spectra, and very small dust attenuation (A(V) less than or similar to 0.02), challenges our interpretation of these systems. To solve the puzzle, we propose two solutions in which dust is either (a) ejected by radiation pressure, or (b) segregated with respect to UV-emitting regions. We clarify the conditions for which the two scenarios apply, and show that they can be discriminated by ALMA observations, such as the recent non-detection of the 88 mu m dust continuum in GHZ2 (z similar or equal to 12) favouring dust ejection.

Automated summary

The recent discovery by the James Webb Space Telescope challenges our current understanding of a population of super-early, massive, and evolved galaxies. These galaxies exhibit blue spectra and minimal dust attenuation, which contradicts our current interpretation. To explain this puzzle, two possible solutions are proposed: dust ejection due to radiation pressure or dust segregation with respect to UV-emitting regions. ALMA observations, including the recent non-detection of 88 μm dust continuum in GHZ2, can help differentiate between these two scenarios, favoring dust ejection.