Simulations reveal how early universe radiation shapes tiny galaxies today
Researchers modeled how intense radiation in the early universe prevented the smallest dwarf galaxies from forming stars, fundamentally changing where galaxies appear today. The findings help explain astronomical observations and refine models that predict cosmic structure—crucial for next-generation space telescopes and our understanding of galaxy formation.
Originaltitel: LYRA ultra-faints: the emergence of faint dwarf galaxies in the presence of an early Lyman–Werner background
<p>We present a suite of zoom-in cosmological hydrodynamical simulations of dwarf galaxies using the LYRA galaxy formation model with an extremely high-mass resolution of 4M<sub>☉</sub>, evolved to <em>z </em>= 0. The suite contains 65 haloes selected from Local Group like environments, spanning <em>M</em><sub>200c </sub>= 10<sup>7</sup>–5 × 10<sup>9</sup> M<sub>☉</sub>. The sample includes small ultra-faints with <em>M</em><sub>∗ </sub>∼ 100M<sub>☉</sub> through to classical dwarfs with <em>M</em><sub>∗ </sub>∼ 5 × 10<sup>6</sup>M<sub>☉</sub>, as well as haloes that remain dark to the present day. We explore two prescriptions for the high-redshift (<em>z</em> > 7) Lyman–Werner background (LWB), differing in intensity and redshift evolution. Star formation begins early (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%20%5E%7B%3E%7D_%7B%5Csim%7D%208" data-classname="equation" />) in progenitors with <em>M</em><sub>200c</sub> ∼ 10<sup>5</sup>–10<sup>6</sup> M<sub>☉</sub>, where molecular hydrogen enables warm moderate-density gas to efficiently cool. The LWB strongly influences the <em>z</em> = 0 halo occupation fraction, shifting the dark-to-luminous transition from M<sub>200c</sub> ∼ 10<sup>7 </sup>M<sub>☉</sub> (weaker LWB) to <em>M</em><sub>200c</sub> ∼ 10<sup>8 </sup>M<sub>☉</sub> (stronger LWB). Galaxies with <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?M_%7B%5Cast%7D%20%5C:%20%5E%7B%3E%7D_%7B%5Csim%7D%20%5C:%2010%5E%7B5%7D%20%5C:%20M_%7B%5Codot%7D" data-classname="equation" data-title="" /> are mostly insensitive to the LWB choice, whereas lower mass systems respond strongly, producing markedly different stellar mass–halo mass (SMHM) relations. The weaker LWB yields a very shallow SMHM slope with nearly constant scatter, while the stronger background introduces a pronounced break at <em>M</em><sub>200c</sub> ∼ 10<sup>9 </sup>M<sub>☉</sub>, where haloes of similar mass host galaxies with <em>M</em><sub>∗ </sub>∼ 10<sup>3</sup>–10<sup>5</sup> M<sub>☉</sub> or remain dark. Both models produce a minimum stellar mass floor at <em>M</em><sub>∗ </sub>∼ 10<sup>3</sup> M<sub>☉</sub>, originating from galaxies that undergo a single burst of star formation at high redshift before self-quenching from their first supernovae.</p>