The average ultraviolet continuum slope of galaxies at z >12 is consistent with dust‑free conditions, although some individual galaxies exhibit redder slopes
arXiv: 2611.17208v1
A new study measured the ultraviolet continuum slopes of 55 galaxies selected from more than 0.6 deg² of JWST/NIRCam imaging. The galaxies have redshifts z≳12, the highest to be characterised in a statistically meaningful sample.
The UV continuum slope (β) was obtained by fitting a power‑law model to the broadband photometry up to 3000 Å rest‑frame. A nested‑sampling algorithm (dynesty) was used, with a flat prior −10 ≤ β ≤ 10 and the redshift simultaneously fitted from the full spectral energy distribution.
Across five redshift bins, the inverse‑variance weighted mean β ranges from ⟨β⟩ = −2.19±0.06 at z < 10 to ⟨β⟩ = −2.58±0.11 in the 13 ≤ z < 14 bin. In the 11.5–12.3 < z < 13 bins the mean slopes of −2.55±0.05 and −2.50±0.05 match the theoretical attenuation‑free limit of β≈−2.6, suggesting that typical galaxies in this era are essentially dust‑free.
A table listing five redshift intervals (z<10, 10–11, 11–12, 12–13, 13–14) with the number of galaxies, mean redshift ⟨z⟩, and corresponding mean UV continuum slope ⟨β⟩, including uncertainties.
Redshift Range
Number
⟨z⟩
⟨β⟩
z<10
37
9.27±0.04
−2.19±0.06
10≤z<11
41
10.42±0.03
−2.36±0.05
11≤z<12
37
11.52±0.04
−2.55±0.05
12≤z<13
37
12.30±0.04
−2.50±0.05
13≤z<14
13
13.28±0.19
−2.58±0.11
Table 1. Inverse‑variance weighted mean UV continuum slopes ⟨β⟩ for five redshift bins from the studied galaxy sample.Bondestam, C., McLeod, D. J., Cullen, F., McLure, R. J., Dunlop, J. S., Antonogiannaki, S. et al. · arXiv:2611.17208v1 · Table 1: · CC BY 4.0
The measured β values have a floor uncertainty of 0.25. Spectroscopic confirmation is limited to six bright objects at z > 12, so the mean values at the highest redshifts could be biased.
Table 1 shows the weighted averages for the five redshift ranges, directly supporting the trend toward bluer, dust‑free spectra with increasing redshift.
The average ultraviolet continuum slope of galaxies at z >12 is consistent with dust‑free conditions, although some individual galaxies exhibit redder slopes | arXiv News