JWST Measurements of Neutral Hydrogen Fractions and Ionized Bubble Sizes at z = 7–12 Obtained with Lyα Damping Wing Absorptions in 27 Bright Continuum Galaxies

Abstract

Abstract We present volume-averaged neutral hydrogen fractions x H I and ionized bubble radii R b measured with Ly α damping wing absorption of galaxies at the epoch of reionization. We combine JWST/NIRSpec spectra taken by the CEERS, GO-1433, DDT-2750, and JADES programs and obtain a sample containing 27 bright UV-continuum ( M UV &lt; −18.5 mag) galaxies at 7 &lt; z &lt; 12. We construct four composite spectra binned by redshift and find the clear evolution of the softening break toward high redshift at rest-frame 1216 Å, suggesting an increase of Ly α damping wing absorption. We estimate Ly α damping wing absorption in the galaxy spectra with realistic templates including Ly α emission and circumgalactic medium absorptions. Assuming the standard inside-out reionization picture having an ionized bubble with radius R b around a galaxy embedded in the intergalactic medium with x H I , we obtain x H I ( R b ) values generally increasing (decreasing) from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathsize="small" mathvariant="normal">I</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.53</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.47</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.92</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>b</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mn>1.67</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.69</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.24</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.89</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> comoving Mpc) at redshift <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>7.12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>9.91</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.15</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.49</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . The redshift evolution of x H I indicates a moderately late reionization history consistent with the one previously suggested from the electron scattering of cosmic microwave background and the evolution of UV luminosity function with an escape fraction f esc ∼ 0.2. Our R b measurements suggest that bubble sizes could be up to a few dex larger than the cosmic average values estimated by analytic calculations for a given x H I , while our R b measurements are roughly comparable with the values for merged ionized bubbles around bright galaxies predicted by recent numerical simulations.