Testing metallicity indicators at z~1.4 with the gravitationally lensed galaxy CASSOWARY 20

Understand

We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ~6 Msol/yr) galaxy at z=1.433, magnified by a factor of 11.5 by the gravitational lensing produced by a massive foreground galaxy at z=0.741.

• We analysed the integrated physical properties of the HII regions of CSWA 20 using temperature- and density-sensitive emission lines.
• We find the abundance of oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the Sun.
• The unusually low C/O ratio may be an indication of a particularly rapid timescale of chemical enrichment.