In a recent study led by Sandra Zamora and colleagues from the University of Rome and other international institutions, researchers have delved into the physical conditions and feedback mechanisms of a distant galaxy, EGSY8p7/CEERS-1019, located at a redshift of 8.6. This galaxy, with a stellar mass of about 10^9.3 solar masses, offers a unique window into the early universe, providing insights that could be valuable for understanding the evolution of massive galaxies and their impact on the interstellar medium.
The team utilized the James Webb Space Telescope’s NIRSpec instrument to obtain spatially resolved spectroscopy of EGSY8p7/CEERS-1019, achieving higher sensitivity and spectral resolution than previous studies. They identified broad emission components of Hβ and [OIII] that are extended over a distance of approximately 1 kiloparsec, located between two rest-frame UV clumps of the galaxy. The morphology and kinematics of these components suggest that the broad emission arises from outflowing gas driven by stellar feedback, rather than from an active galactic nucleus (AGN) broad-line region.
The researchers found that the kinetic energy injection rate from stellar feedback is significantly higher than that of the outflow, while the radiation pressure rate is comparable to the outflow momentum rate. This indicates that stellar feedback alone can drive the outflow, with radiation pressure potentially providing the necessary momentum transfer. The study derived a low mass-loading factor (η=0.16) and a low ionizing photon escape fraction (fesc=0.021±0.014), suggesting that most of the gas remains confined within the galaxy. The high electron density measured (ne=2200 cm^-3) supports this interpretation.
Comparisons of diagnostic emission-line ratios with photoionization and shock models further support a star-formation-driven ionization scenario, ruling out any excitation by AGN radiation. The absence of detectable Wolf-Rayet features suggests that alternative mechanisms must be considered to explain the high nitrogen-to-oxygen (N/O) ratio observed in this galaxy.
For the energy sector, understanding the feedback mechanisms and physical conditions in early massive galaxies can provide insights into the processes that govern star formation and galaxy evolution. This knowledge can inform models of cosmic reionization and the intergalactic medium, which are crucial for understanding the distribution and properties of dark matter and dark energy. Additionally, the study of outflowing gas and its impact on the interstellar medium can offer valuable insights into the regulation of star formation and the enrichment of the intergalactic medium with heavy elements.
This research was published in the journal Astronomy & Astrophysics.
This article is based on research available at arXiv.