A comprehensive metallicity analysis of J0332-3557: establishing a z ~ 4 anchor for direct gas metallicity and C/O abundance investigations
Abstract
We provide one of the most comprehensive metallicity studies at z 4 by analyzing the UV/optical HST photometry, and rest-frame VLT-FORS2 ultraviolet and VLT-XSHOOTER optical spectra of J0332-3557, a gravitationally lensed galaxy magnified by a factor of 20. With a 5σ detection of the auroral O III]1666 line, we are able to derive a direct gas metallicity estimate for our target. We find Zgas = 12 + log(O/H) = 8.26 0.06, which is compatible with an increasing of both the gas fraction and the outflow metal loading factor from z 0 to z 4. J0332-3557 is the most metal-rich individual galaxy at z 4 for which the C/O ratio has been measured. We derive a low log(C/O) = - 1.02 0.2, which suggests that J0332-3557 is in the early stages of ISM carbon enrichment driven mostly by massive stars. The low C/O abundance also indicates that J0332-3557 is characterized by a low star formation efficiency, higher yields of oxygen, and longer burst duration. We find that EW(C III])1906,9 is as low as 3 . The main drivers of the low EW(C III])1906,9 are the higher gas metallicity and the low C/O abundance. J0332-3557 is characterized by one diffuse and two more compact regions 1 kpc in size. We find that the carbon emission mostly originates in the compact knots. Our study on J0332-3557 serves as an anchor for studies investigating the evolution of metallicity and C/O abundance across different redshifts.
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