First Direct Carbon Abundance Measured at <i>z</i>  &gt; 10 in the Lensed Galaxy MACS0647-JD

Abstract Investigating the metal enrichment in the early Universe helps us constrain theories about the first stars and study the ages of galaxies. The lensed galaxy MACS0647−JD at z = 10.17 is the brightest galaxy known at z &gt; 10. Previous work analyzing JWST NIRSpec and MIRI data yielded a direct metallicity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.14em"/> <mml:mo>=</mml:mo> <mml:mn>7.79</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.09</mml:mn> </mml:math> (∼0.13 Z ⊙ ) and electron density <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>/</mml:mo> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>2.9</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> , the most distant such measurements to date. Here we estimate the direct C/O abundance for the first time at z &gt; 10, finding a subsolar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">C</mml:mi> <mml:mo>/</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.14em"/> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . This is higher than other z &gt; 6 galaxies with direct C/O measurements, likely due to higher metallicity. It is also slightly higher than galaxies in the local Universe with similar metallicity. This may suggest a very efficient and rapid burst of star formation, a low effective oxygen abundance yield, or the presence of unusual stellar populations, including supermassive stars. Alternatively, the strong C iii ] λλ 1907,1909 emission (14 ± 3 Å rest-frame equivalent width may originate from just one of the two component star clusters JDB ( r ∼ 20 pc). Future NIRSpec integral field unit spectroscopic observations of MACS0647−JD will be promising for disentangling C/O in the two components to constrain the chemistry of individual star clusters just 460 Myr after the Big Bang.