EPOCHS. III. Unbiased UV Continuum Slopes at 6.5 &lt; <i>z</i> &lt; 13 from Combined PEARLS GTO and Public JWST/NIRCam Imaging

Abstract We present an analysis of rest-frame UV continuum slopes, β , using a sample of 1011 galaxies at 6.5 &lt; z &lt; 13 from the EPOCHS photometric sample collated from the GTO PEARLS and public ERS/GTO/GO (JADES, CEERS, NGDEEP, GLASS) JWST/NIRCam imaging across <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>178.9</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">arcmin</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> of unmasked blank sky. We correct our UV slopes for the photometric error coupling bias using 200,000 power-law spectral energy distributions for each β = {−1, −1.5, −2, −2.5, −3} in each field, finding biases as large as Δ β ≃ −0.55 for the lowest signal-to-noise ratio galaxies in our sample. Additionally, we simulate the impact of rest-UV line emission (including Ly α ) and damped Ly α systems on our measured β , finding biases as large as 0.5–0.6 for the most extreme systems. We find a decreasing trend with redshift of β = −1.51 ± 0.08 − (0.097 ± 0.010) × z , with potential evidence for Population III stars or top-heavy initial mass functions in a subsample of 68 β + σ β &lt; −2.8 galaxies. At z ≃ 11.5, we measure an extremely blue β ( M UV = −19) = −2.73 ± 0.06, deviating from simulations, indicative of low-metallicity galaxies with nonzero Lyman continuum escape fractions f esc,LyC ≳ 0 and minimal dust content. The observed steepening of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mi>β</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>d</mml:mi> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> from 0.22 ± 0.02 at z ≃ 7 to 0.81 ± 0.13 at z ≃ 11.5 implies that dust produced in core-collapse supernovae at early times may be ejected via outflows from low-mass galaxies. We also observe a flatter d β / d M UV = 0.03 ± 0.02 at z ≃ 7 and a shallower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mi>β</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>d</mml:mi> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> at z &lt; 11 than seen by the Hubble Space Telescope, unveiling a new population of low-mass, faint galaxies reddened by dust produced in the stellar winds of asymptotic giant branch stars or carbon-rich Wolf–Rayet binaries.