Testing metallicity indicators at z similar to 1.4 with the gravitationally lensed galaxy CASSOWARY 20(star)

TY - JOUR

T1 - Testing metallicity indicators at z similar to 1.4 with the gravitationally lensed galaxy CASSOWARY 20(star)

AU - James, B. L.

AU - Pettini, M.

AU - Christensen, Lise Bech

AU - Auger, M.W.

AU - Becker, G.D.

AU - King, L. J.

AU - Quider, A. M.

AU - Shapley, A. E.

AU - Steidel, C. C.

PY - 2014/5/1

Y1 - 2014/5/1

N2 - We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ̃ 6 M⊙ yr-1) 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 time-scale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from HII regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ̃2 uncertainty of each method. The interstellar medium (ISM) of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the ISM with speeds of up 750 km s-1, similar to the values measured in other high-z galaxies sustaining much higher rates of star formation.

AB - We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ̃ 6 M⊙ yr-1) 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 time-scale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from HII regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ̃2 uncertainty of each method. The interstellar medium (ISM) of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the ISM with speeds of up 750 km s-1, similar to the values measured in other high-z galaxies sustaining much higher rates of star formation.

M3 - Journal article

SN - 0035-8711

VL - 440

SP - 1794

EP - 1809

JO - Royal Astronomical Society. Monthly Notices

JF - Royal Astronomical Society. Monthly Notices

IS - 2

ER -