http://arxiv.org/abs/1510.03821
The abundance of oxygen in galaxies is widely used in furthering our understanding of galaxy formation and evolution. Unfortunately, direct measurements of O/H in the neutral gas are extremely difficult to obtain due to the fact that the only OI line available within the HST UV wavelength range (1150-3200A) is often saturated. As such, proxies for oxygen are needed to indirectly derive an O/H via the assumption that solar ratios based on local Milky Way sight lines hold in different environments. In this paper, we assess the validity of using two such proxies, PII and SII, within more typical star-forming environments. Using HST-COS FUV spectra of a sample of nearby star-forming galaxies, we find that P and S follow a trend, log(PII/SII)=1.73+/-0.18, which is in excellent agreement with the solar ratio of log(P/S)_sol=-1.71+/-0.04 over a large range of galaxy properties, i.e., metallicities in the range 0.03-3.2 Z_sol and HI column densities of log[N(HI)/cm^-2]=18.44-21.28. We additionally show evidence from literature data that both elements are individually found to trace oxygen according to their respective solar ratios across a wide-range of environments, such as stars, ionized gas in nearby galaxies, and neutral gas in DLAs and along Milky Way sight lines. Our findings demonstrate that the solar ratios of log(P/O)_sol=-3.28+/-0.06 and log(S/O)_sol=-1.57+/-0.06 can both be used to derive reliable O/H abundances in the neutral gas of local and high-redshift star-forming galaxies.
B. James and A. Aloisi
Wed, 14 Oct 15
9/66
Comments: 5 pages, 3 figures, submitted to ApJL
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