A model for GN-z11: top-heavy stellar initial mass functions in forming galactic nuclei and ultra-compact dwarfs

TL;DR

This study models the chemical evolution of the high-redshift galaxy GN-z11, suggesting it is a forming galactic nucleus or ultra-compact dwarf with top-heavy IMFs and short star formation timescales, explaining its high nitrogen abundance.

Contribution

It introduces a chemical evolution model that reproduces GN-z11's observed properties using top-heavy IMFs and short star formation periods, highlighting the role of specific supernova contributions.

Findings

Reproduces observed nitrogen and oxygen abundances with short star formation timescales.

Highlights the importance of excluding massive supernovae in models to match nitrogen levels.

Suggests GN-z11 may host nitrogen-rich stellar populations linked to galaxy evolution.

Abstract

Recent JWST observations of the z=10.6 galaxy GN-z11 have revealed a very high gas-phase nitrogen abundance (higher than four times the solar value), a very small half-light radius(~ 60 pc), and a large stellar mass (M_s ~ 10^9 M_sun) for its size. We consider that this object is a forming galactic nucleus or ultra-compact dwarf galaxy rather than a proto globular cluster, and thereby investigate the chemical abundance pattern using one-zone chemical evolution models.The principal results of the models are as follows. The observed log (N/O) > -0.24, log (C/O)>-0.78, and 12+log (O/H) ~ 7.8 can be self-consistently reproduced by the models both with very short star formation timescales (< 10^7 yr) and with top-heavy stellar initial mass functions (IMFs). The adopted assumption of no chemical enrichment by massive (m>25 M_sun) core collapse supernovae (CCSNe) is also important for the reproduction of high gas-phase log (N/O), because such CCSNe can decrease high log (N/O) of gas polluted by OB and Wolf-Rayet stars. GN-z11 can have a significant fraction (>0.5) of nitrogen-rich ([N/Fe]>0.5) stars, which implies a possible link between nitrogen-rich stellar populations of the inner Galaxy and giant elliptical galaxies and high-z objects with high gas-phase log (N/O) like GN-z11.