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

Abstract

We report on a [CII] 158 μm search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly αemitting galaxies at z 7. Our targets are ultraviolet (UV) faint systems with stellar masses on the order of M 10 9 M. We detect a single [C II ] line emission (4 σ) from the brightest ( L 2.4 ×10 10 L) galaxy in our sample, MACS0454- 1251. We determine a systemic redshift ( z [C II ] = 6.3151 ±0.0005) for MACS0454-1251 and measure a Ly αvelocity offset of v ≈300 ±70 km s −1 . The remaining two galaxies we detect no [C II ] but provide 3 σupper limits on their [C II ] line luminosities which we use to investigate the L [CII] −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 T d = 35K dust masses ( M dust ) range from < 4.8 ×10 7 M to 2.3 ×10 8 M. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing [C II ] emission..