A massive interacting galaxy 510 million years after the Big Bang (2303.00306v2)

Abstract: JWST observations confirm the existence of galaxies as early as 300Myr and at a higher number density than expected based on galaxy formation models and HST observations. Yet, sources confirmed spectroscopically in the first 500Myr have estimated stellar masses $<5\times10^8M_\odot$, limiting the signal to noise ratio (SNR) for investigating substructure. We present a high-resolution spectroscopic and spatially resolved study of a rare bright galaxy at $z=9.3127\pm0.0002$ with a stellar mass of $(2.5^{+0.7}{-0.5})\times10^9M\odot$, forming $25^{+3}{-4}M\odot/yr$ and with a metallicity of $\sim0.1Z_\odot$- lower than in the local universe for the stellar mass but in line with expectations of chemical enrichment in galaxies 1-2Gyr after the Big Bang. The system has a morphology typically associated to two interacting galaxies, with a two-component main clump of very young stars (age$<10$Myr) surrounded by an extended stellar population ($130\pm20$Myr old, identified by modeling the NIRSpec spectrum) and an elongated clumpy tidal tail. The spectroscopic observations identify O, Ne and H emission lines, and the Lyman break, where there is evidence of substantial Ly$\alpha$ absorption. The [OII] doublet is resolved spectrally, enabling an estimate of the electron number density and ionization parameter of the interstellar medium and showing higher densities and ionization than in lower redshift analogs. For the first time at $z>8$, we identify evidence of absorption lines (Si, C and Fe), with low confidence individual detections but SNR$>6$ when stacked. The absorption features suggest that Ly$\alpha$ is damped by the interstellar and circumgalactic medium. Our observations provide evidence of rapid efficient build-up of mass and metals in the immediate aftermath of the Big Bang through mergers, demonstrating that massive galaxies with several billion stars exist earlier than expected.

• The paper confirms a massive galaxy at redshift 9.3127 using high-resolution JWST spectroscopy.
• The study reveals key measurements such as an ultraviolet luminosity of MUV = -21.66, a stellar mass of ~1.6×10^9 M⊙, and a star formation rate of ~19 M⊙ per year.
• The analysis shows that the galaxy’s interacting morphology, featuring dual stellar populations, suggests merger-induced processes in early cosmic evolution.

A Study of an Early Massive Interacting Galaxy

The paper titled "A massive interacting galaxy 510 million years after the Big Bang" investigates a significant discovery in astrophysics concerning the early Universe. Utilizing data from the James Webb Space Telescope (JWST), the authors confirm spectroscopically the presence of a massive galaxy at an exceptionally high redshift of 9.3127, corresponding to a time merely 510 million years after the Big Bang. This galaxy exhibits characteristics indicating it is undergoing an interaction, providing insights into galaxy formation processes shortly after the Universe's inception.

Key Observations and Measurements

The paper confirms the existence of this galaxy through high-resolution spectroscopic data, revealing significant details about its formation and composition. Among the key measurements are:

• Luminosity and Mass: The galaxy exhibits an ultraviolet (UV) luminosity ($M_{UV}=-21.66$) approximately twice the characteristic luminosity ($M_{UV}^*$), and a significant stellar mass of approximately $1.6 \times 10^9 M_{\odot}$.
• Star Formation and Metallicity: It is forming stars at a rate of $19^{+5}_{-6} M_{\odot}$ per year, with a measured metallicity about one-tenth that of the Sun.
• Morphology: The galaxy's structure hints at two interacting components, indicative of a potentially ongoing merger. This is marked by a central clump of extremely young stars (less than 10 million years old) and an extended, somewhat older (120 million years) stellar population.
• Emission and Absorption Lines: Spectra show distinct oxygen, neon, and hydrogen emission lines, alongside substantial Lyman-alpha absorption. The observed [O III] doublet lines provide a measure of electron density and ionization in the interstellar medium, pointing to conditions more intense than typically observed in lower-redshift analogs.

Implications of the Findings

These findings challenge existing models of early galaxy formation, which often underestimated the presence and abundance of such massive structures so soon after the Big Bang. The detection of this galaxy implies a rapid assembly period and efficient star formation and metal production. The evidence of merger-induced formation suggests that interactions played a significant role in the early mass build-up and potential morphological evolution of galaxies in the early Universe.

Theoretical Context and Future Directions

The higher-than-expected number density and bright-end emission of galaxies as observed by JWST could indicate previously missing elements in galaxy formation and evolution models. It raises questions about the precise mechanisms operating during the Universe's reionization era and suggests substantial interactions and mergers among nascent galaxies may have been more common than previously appreciated.

Future JWST observations, particularly with integral field spectroscopy, could provide more detailed kinematic maps of such early galaxies, improving our understanding of the role interactions played in shaping galaxy properties. These insights could also inform refinements in cosmological simulations, helping constrain the processes governing star formation and feedback in the early Universe.

In conclusion, the discovery and detailed analysis of such a galaxy not only advances our understanding of the early Universe but also sets the stage for future studies aiming to unravel the complexities of early cosmic structures and their evolution.