Studying C ii emission in low-mass galaxies at z ∼ 7

ABSTRACT We report on a CII₁₅₈ ₌ search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly α emitting galaxies at z ∼ 7. Our targets are ultraviolet (UV) faint systems with stellar masses on the order of M* ∼ 109 M⊙. We detect a single C ii line emission (4σ) from the brightest (L ∼ 2. 4 × 1010L⊙) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (zC ii = 6. 3151 ± 0. 0005) for MACS0454-1251 and measure a Ly α velocity offset of v 300 70 km\, s^-1. The remaining two galaxies we detect no C ii but provide 3σ upper limits on their C ii line luminosities which we use to investigate the L ₂₈₈ - SFR relation. Overall our single C ii detection shows agreement with the relation for local dwarf galaxies. Our C ii deficient galaxies could potentially be exhibiting low metallicities (Z Z⊙). Another possible explanation for weaker C ii emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of T₃=35 K dust masses (Mdust) range from 4. 8 × 107 M⊙ to 2. 3 × 108 M⊙. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing C ii emission.