Аннотация
We present measurements of the electron-temperature based oxygen abundance
for a highly star-forming galaxy at z=3.08, COSMOS-1908. This is the highest
redshift at which OIII$łambda$4363 has been detected, and the first time
that this line has been measured at z>2. We estimate an oxygen abundance of
12+log(O/H)$=8.00^+0.13_-0.14$. This galaxy is a low-mass ($10^9.3$
M$_ødot$), highly star-forming ($\sim50$ M$_ødot$ yr$^-1$) system that
hosts a young stellar population ($\sim160$ Myr). We investigate the physical
conditions of the ionized gas in COSMOS-1908 and find that this galaxy has a
high ionization parameter, little nebular reddening ($E(B-V)_gas<0.14$),
and a high electron density ($n_e\sim500$ cm$^-3$). We compare the ratios of
strong oxygen, neon, and hydrogen lines to the direct-method oxygen abundance
for COSMOS-1908 and additional star-forming galaxies at z=0-1.8 with
OIII$łambda$4363 measurements, and show that galaxies at z$\sim$1-3 follow
the same strong-line correlations as galaxies in the local universe. This
agreement suggests that the relationship between ionization parameter and O/H
is similar for z$\sim$0 and high-redshift galaxies. These results imply that
metallicity calibrations based on lines of oxygen, neon, and hydrogen do not
strongly evolve with redshift and can reliably estimate abundances out to
z$\sim$3, paving the way for robust measurements of the evolution of the
mass-metallicity relation to high redshift.
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