NIRSpec View of the Appearance and Evolution of Balmer Breaks and the Transition from Bursty to Smooth Star Formation Histories from Deep Within the Epoch of Reionization to Cosmic Noon
arxiv(2024)
摘要
Theoretical models and observational evidence suggest that high-redshift
galaxies grow under the bursty mode of star formation, with large temporal star
formation rate (SFR) fluctuations around some mean value. From an observational
perspective, it has not been clear at which redshift and stellar population
characteristics the transition from bursty to smooth star formation occurs.
Here, we investigate these using a uniformly reduced sample of NIRSpec prism
spectra of 631 galaxies at 3 < z_ spec < 14, stacked in 8 redshift and 8
UV slope bins. We evaluate the burstiness of star formation histories using the
Balmer break strengths as well as the ratios of SFRs as measured from the
emission lines to those measured from the UV continua. The break strength
increases monotonically from z = 10 to z = 3, and from β_ UV =
-3.0 to β_ UV = 0.0. The break strength is tightly anti-correlated
with specific SFR (sSFR), and in dusty galaxies, strongly correlated with dust
attenuation. Based on the SFR ratios, we find that bursty star formation
thrives in the highest redshift, bluest, and lowest stellar mass galaxies,
which exhibit the highest sSFRs. The burstiness appears to plateau at z > 6,
suggesting that we might be observing the peak of star formation burstiness at
these redshifts. The z < 4 galaxies do not appear particularly bursty,
suggesting that the smooth mode of star formation starts taking over right
before cosmic noon. As galaxies mature and develop redder UV colors and more
pronounced Balmer breaks, their ability to sustain star formation over longer
timescales increases, signalling their transition from bursty to smooth star
formation.
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