Annalisa Citro: A comprehensive metallicity analysis of a z~3.8 gravitationally lensed galaxy скачать в хорошем качестве

Annalisa Citro: A comprehensive metallicity analysis of a z~3.8 gravitationally lensed galaxy

We provide one of the most comprehensive metallicity studies at z~4 by analyzing the 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 5 sigma detection of the auroral O III] 1666 line, we are able to obtain a direct gas metallicity estimate of a galaxy at z~4. We find that the derived gas metallicity (Zg = 12+log(O/H)=8.26 ± 0.06) is compatible with an increase of both the gas fraction and the outflow metal loading factor. Our estimate of Zg is also compatible with a redshift invariant fundamental metallicity relation. We find that J0332 has a low log(C/O)= -1.02 ±0.2. This supports the scenario of a star formation history characterized by a low star formation efficiency, higher yields of oxygen and longer burst duration. Also, a low C/O at the metallicity and age (100 Myr) of J0332 suggests that Carbon is mainly released into the interstellar medium by long-lived intermediate mass stars instead of winds from massive stars. Although characterized by a low metallicity, a high ionization parameter, a vigorous star formation and a low C/O, J0332 shows a low EW(C III]) ~ 3 A. This result is puzzling and similar to what is found in the nearby galaxy I Zw 18. We present a spatially resolved analysis of J0332 on ~ 1 kpc spatial scales and find that the Carbon emission is not ubiquitous throughout the galaxy, but originates mostly from a bright, compact knot. This suggests that large variations in the physical conditions are present throughout the galaxy.