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We investigate the degree of dust obscured star formation in 49 massive (log10(M⋆/M⊙) > 9) Lyman-break galaxies (LBGs) at z = 6.5–8 observed as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Survey (REBELS) large program. By creating deep stacks of the photometric data and the REBELS ALMA measurements we determine the average rest-frame ultraviolet (UV), optical, and far-infrared (FIR) properties which reveal a significant fraction (fobs = 0.4–0.7) of obscured star formation, consistent with previous studies. From measurements of the rest-frame UV slope, we find that the brightest LBGs at these redshifts show bluer (β ≃ −2.2) colours than expected from an extrapolation of the colour–magnitude relation found at fainter magnitudes. Assuming a modified blackbody spectral energy distribution (SED) in the FIR (with dust temperature of $T_{\rm d} = 46\, {\rm K}$ and βd = 2.0), we find that the REBELS sources are in agreement with the local ‘Calzetti-like’ starburst Infrared-excess (IRX)–β relation. By re-analysing the data available for 108 galaxies at z ≃ 4–6 from the ALMA Large Program to Investigate C+ at Early Times (ALPINE) using a consistent methodology and assumed FIR SED, we show that from z ≃ 4–8, massive galaxies selected in the rest-frame UV have no appreciable evolution in their derived IRX–β relation. When comparing the IRX–M⋆ relation derived from the combined ALPINE and REBELS sample to relations established at z < 4, we find a deficit in the IRX, indicating that at z > 4 the proportion of obscured star formation is lower by a factor of ≳ 3 at a given a M⋆. Our IRX–β results are in good agreement with the high-redshift predictions of simulations and semi-analytic models for z ≃ 7 galaxies with similar stellar masses and star formation rates.

 

Abstract A metallic state with a vanishing activation gap, at a filling factor $$\nu = 8/5$$ ν = 8 / 5 in the untilted specimen with $$n= 2 \times 10^{11} cm^{-2}$$ n = 2 × 10 11 c m - 2 , and at $$\nu = 4/3$$ ν = 4 / 3 at $$n=1.2 \times 10^{11} cm^{-2}$$ n = 1.2 × 10 11 c m - 2 under a $$\theta = 66^{0}$$ θ = 66 0 tilted magnetic field, is examined through a microwave photo-excited transport study of the GaAs/AlGaAs 2 dimensional electron system (2DES). The results presented here suggest, remarkably, that at the possible degeneracy point of states with different spin polarization, where the 8/5 or 4/3 FQHE vanish, there occurs a peculiar marginal metallic state that differs qualitatively from a quantum Hall insulating state and the usual quantum Hall metallic state. Such a marginal metallic state occurs most prominently at $$\nu =8/5$$ ν = 8 / 5 , and at $$\nu =4/3$$ ν = 4 / 3 under tilt as mentioned above, over the interval $$1 \le \nu \le 2$$ 1 ≤ ν ≤ 2 , that also includes the $$\nu = 3/2$$ ν = 3 / 2 state, which appears perceptibly gapped in the first instance. 

ABSTRACT We examined the influence of the microwave power on the diagonal resistance in the GaAs/AlGaAs two dimensional electron system (2DES), in order to extract the electron temperature and determine microwave induced heating as a function of the microwave power. The study shows that microwaves produce a small discernable increase in the electron temperature both at null magnetic field and at finite magnetic fields in the GaAs/AlGaAs 2DES. The heating effect at null field appears greater in comparison to the examined finite field interval, although the increase in the electron temperature in the zero-field limit appears smaller than theoretical predictions.