Nebular dominated galaxies: insights into the stellar initial mass function at high redshift
arxiv(2023)
摘要
We identify a low-metallicity (12+log( O/ H)=7.59)
Lyα-emitting galaxy at z=5.943 with evidence of a strong Balmer jump,
arising from nebular continuum. While Balmer jumps are sometimes observed in
low-redshift star-forming galaxies, this galaxy also exhibits a steep turnover
in the UV continuum. Such turnovers are typically attributed to absorption by a
damped Lyα system (DLA); however, the shape of the turnover and the high
observed Lyα escape fraction (f_ esc,Lyα ∼27%) is also
consistent with strong nebular two-photon continuum emission. Modelling the UV
turnover with a DLA requires extreme column densities (N_
HI>10^23 cm^-2), and simultaneously explaining the high f_
esc,Lyα requires a fine-tuned geometry. In contrast, modelling the
spectrum as primarily nebular provides a good fit to both the continuum and
emission lines, motivating scenarios in which (a) we are observing only nebular
emission or (b) the ionizing source is powering extreme nebular emission that
outshines the stellar emission. The nebular-only scenario could arise if the
ionising source has `turned off' more recently than the recombination timescale
(∼1,000 yr), hence we may be catching the object at a very specific time.
Alternatively, hot stars with T_ eff≳10^5 K (e.g. Wolf-Rayet or
low-metallicity massive stars) produce enough ionizing photons such that the
two-photon emission becomes visible. While several stellar SEDs from the
literature fit the observed spectrum well, the hot-star scenario requires that
the number of ≳50 M_⊙ stars relative to ∼5-50
M_⊙ stars is significantly higher than predicted by typical stellar
initial mass functions (IMFs). The identification of more galaxies with similar
spectra may provide evidence for a top-heavy IMF at high redshift.
更多查看译文
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要