EPOCHS. III. Unbiased UV Continuum Slopes at 6.5 < <i>z</i> < 13 from Combined PEARLS GTO and Public JWST/NIRCam Imaging
Duncan Austin, Christopher J. Conselice, Nathan Adams, Thomas Harvey, Qiao Duan, James Trussler, Qiong Li, Ignas Juodžbalis, Katherine Ormerod, Leonardo Ferreira, Lewi Westcott, Honor Harris, Stephen M. Wilkins, Rachana Bhatawdekar, Joseph Caruana, Dan Coe, Seth H. Cohen, Simon P. Driver, Jordan C. J. D’Silva, Brenda Frye, Lukas J. Furtak, Norman A. Grogin, Nimish P. Hathi, Benne W. Holwerda, Rolf A. Jansen, Anton M. Koekemoer, Madeline A. Marshall, M. Nonino, Rafael Ortiz, Nor Pirzkal, A. S. G. Robotham, Russell E. Ryan, Jake Summers, Christopher N. A. Willmer, Rogier A. Windhorst, Haojing Yan, Erik Zackrisson
Abstract
Abstract We present an analysis of rest-frame UV continuum slopes, β , using a sample of 1011 galaxies at 6.5 < z < 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 < −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 < 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.