UV slopes of star-forming galaxies in strong-lensing fields at the epoch of reionisation with JWST

Résumé fourni par la source

UV slopes (β) are a powerful diagnostic for galaxies at the epoch of reionisation, tracing star formation, interstellar medium ionisation, and the escape fraction f_esc of ionising photons. Studies at low and intermediate z suggested a gradual reddening of the UV slope with time and steeper slopes for fainter galaxies. The James Webb Space Telescope ( ) enabled measurements of the UV slope for statistically significant samples of galaxies deep into the epoch of reionisation up to redshift z JWST and for increasingly faint galaxies. Recent studies of β with JWST at z>7 revealed a flattening of the trend of the UV slope with respect to redshift and UV magnitude. We measure β at z>7.5 using the strong lensing around massive galaxy clusters to observe high-redshift and faint galaxies. The low-brightness regime is of particular interest for reionisation, as most of the recent models of this process posit that numerous faint galaxies are the prime drivers of reionisation We used NIRCam and NIRSpec observations from CANUCS, Technicolor, JUMPS, Silver Bullet, UNCOVER, and MEGASCIENCE in seven strong-lensing fields in order to find galaxies down to M_ UV ∼-16 and 7.5 =-2.3 an average redshift $ =8.5 =-18 and an average AB magnitude M_ UV We found no significant evolution of β in our redshift range, suggesting a flattening of the β-z trend above z We found a weak trend between β and M_UV. The flat trend of β at z>7.5 indicates a similarity in average galaxy properties between 300 and 600 Myr after the Big Bang. The weak trend between β and M_UV suggests an analogous composition for the interstellar medium of low- and high-mass galaxies, likely due to a lack of time to build up a dust reservoir.

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