Possible Systematic Rotation in the Mature Stellar Population of a z = 9.1 Galaxy

Abstract

<jats:title>Abstract</jats:title> <jats:p>We present new observations with the Atacama Large Millimeter/submillimeter Array for a gravitationally lensed galaxy at <jats:italic>z</jats:italic> = 9.1, MACS1149-JD1. [O <jats:sc>iii</jats:sc>] 88 <jats:italic>μ</jats:italic>m emission is detected at 10<jats:italic>σ</jats:italic> with a spatial resolution of ∼0.3 kpc in the source plane, enabling the most distant morphokinematic study of a galaxy. The [O <jats:sc>iii</jats:sc>] emission is distributed smoothly without any resolved clumps and shows a clear velocity gradient with Δ<jats:italic>V</jats:italic> <jats:sub>obs</jats:sub>/2<jats:italic>σ</jats:italic> <jats:sub>tot</jats:sub> = 0.84 ± 0.23, where Δ<jats:italic>V</jats:italic> <jats:sub>obs</jats:sub> is the observed maximum velocity difference and <jats:italic>σ</jats:italic> <jats:sub>tot</jats:sub> is the velocity dispersion measured in the spatially integrated line profile, suggesting a rotating system. Assuming a geometrically thin self-gravitating rotation disk model, we obtain <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\mathrm{rot}}/{\sigma }_{V}={0.67}_{-0.26}^{+0.73}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>rot</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>0.67</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.26</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.73</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7447ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>V</jats:italic> <jats:sub>rot</jats:sub> and <jats:italic>σ</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> are the rotation velocity and velocity dispersion, respectively, still consistent with rotation. The resulting disk mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.65}_{-0.40}^{+1.37}\times {10}^{9}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.65</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.40</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.37</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac7447ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> is consistent with being associated with the stellar mass identified with a 300 Myr old stellar population independently indicated by a Balmer break in the spectral energy distribution. We conclude that the most of the dynamical mass is associated with the previously identified mature stellar population that formed at <jats:italic>z</jats:italic> ∼ 15.</jats:p>