Early Bright Galaxies from Helium Enhancements in High-Redshift Star Clusters

The first few cycles of JWST have identified an overabundance of UV-bright galaxies and a general excess of UV luminosity density at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≳</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math> compared to expectations from most (pre-JWST) theoretical models. Moreover, some of the brightest high-redshift spectroscopically confirmed galaxies exhibit peculiar chemical abundance patterns, most notably extremely high N/O ratios. Since N/O has been empirically shown to scale strongly with He/H, as expected for hot hydrogen burning, these same bright high-redshift galaxies are likely also helium-enhanced. Under simplistic assumptions for stellar evolution, the bolometric luminosity of a star scales as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>L</mml:mi> <mml:mo>∝</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="true" form="prefix">(</mml:mo> <mml:mn>4</mml:mn> <mml:mo>−</mml:mo> <mml:mfrac> <mml:mn>9</mml:mn> <mml:mn>2</mml:mn> </mml:mfrac> <mml:mi>Y</mml:mi> <mml:mo>+</mml:mo> <mml:mfrac> <mml:mn>5</mml:mn> <mml:mn>4</mml:mn> </mml:mfrac> <mml:msup> <mml:mi>Y</mml:mi> <mml:mn>2</mml:mn> </mml:msup> <mml:mo stretchy="true" form="postfix">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> — hence a higher He/H leads to brighter stars. In this Letter, we evolve a series of MESA models to the zero-age main-sequence and highlight that the helium enhancements at the levels measured and inferred for high-redshift galaxies can boost the 1500 A UV luminosity by up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>50</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> , while simultaneously increasing the stellar effective temperature. The combination of helium enhancements with nebular continuum emission expected for intense bursts of star formation have the potential to help reduce the tension between JWST observations and certain galaxy formation models.