A study of extreme C iii]1908 & [O iii]88/[C ii]157 emission in Pox 186: implications for JWST plus ALMA (FUV plus FIR) studies of distant galaxies
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY(2024)
Abstract
Carbon spectral features are ubiquitous in the ultraviolet (UV) and far-infrared (FIR) spectra of the reionization-era galaxies. We probe the ionized carbon content of a dwarf galaxy Pox 186 using the UV, optical, mid-infrared, and FIR data taken with Hubble, Gemini, Spitzer, and Herschel, respectively. This local (z similar to 0.0040705) galaxy is likely an analogue of reionization-era galaxies, as revealed by its extreme FIR emission line ratio, [O iii] 88 mu m/[C ii] 157 mu m (>10). The UV spectra reveal extreme C iii] lambda lambda 1907, 1909 emission with the strongest equivalent width (EW) = 35.85 +/- 0.73 angstrom detected so far in the local (z similar to 0) Universe, a relatively strong C iv lambda lambda 1548, 1550 emission with EW = 7.95 +/- 0.45 angstrom, but no He ii lambda 1640 detection. Several scenarios are explored to explain the high EW of carbon lines, including high effective temperature, high carbon-to-oxygen ratio, slope, and upper mass of top-heavy initial mass function, hard ionizing radiation, and in-homogeneous dust distribution. Both C iii] and C iv line profiles are broadened with respect to the O iii] lambda 1666 emission line. Each emission line of C iv lambda lambda 1548, 1550 shows the most distinct double-peak structure ever detected, which we model via two scenarios, firstly a double-peaked profile that might emerge from resonant scattering and secondly, a single nebular emission line along with a weaker interstellar absorption. The study demonstrates that galaxies with extreme FIR properties may also show extreme UV properties, hence paving a promising avenue of using FIR+UV in the local (via Hubble+Herschel/SOFIA) and distant (via JWST + ALMA) Universe for unveiling the mysteries of the reionization-era.
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Key words
galaxies: abundances,galaxies: dwarf,galaxies: high-redshift
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