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The MUSE Hubble Ultra Deep Field Survey: XII. Mg II emission and absorption in star-forming galaxies
The physical origin of the near-ultraviolet Mg II emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn fr...
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Published in: | Astronomy and astrophysics (Berlin) 2018-09, Vol.617, p.A62 |
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Main Authors: | , , , , , , , , , , , , , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites |
Online Access: | Get full text |
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Summary: | The physical origin of the near-ultraviolet Mg
II
emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 <
z
< 2.34 drawn from the MUSE
Hubble
Ultra Deep Survey. The spectra of these galaxies show a wide variety of profiles of the Mg
II
λλ
2796, 2803 resonant doublet, from absorption to emission. We present a study on the main drivers for the detection of Mg
II
emission in galaxy spectra. By exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with Mg
II
in emission are consistent with nebular emission from H
II
regions. From a simultaneous analysis of MUSE spectra and ancillary
Hubble
Space Telescope information through spectral energy distribution fitting, we find that galaxies with Mg
II
in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. This leads us to suggest that Mg
II
emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. We show that these differences in Mg
II
emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ISM) of galaxies showing Mg
II
in absorption, which confirms the extreme sensitivity of Mg
II
to the presence of the neutral ISM. We conclude with an analogy between the Mg
II
doublet and the Ly
α
line that lies in their resonant nature. Further investigations with current and future facilities, including the
James Webb
Space Telescope, are promising because the detection of Mg
II
emission and its potential connection with Ly
α
could provide new insights into the ISM content in the early Universe. |
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ISSN: | 0004-6361 1432-0746 1432-0746 1432-0756 |
DOI: | 10.1051/0004-6361/201833281 |