Spectroscopic confirmation of two luminous galaxies at $z\sim14$ (2405.18485v2)

Abstract: The first observations of JWST have revolutionized our understanding of the Universe by identifying for the first time galaxies at $z\sim13$. In addition, the discovery of many luminous galaxies at Cosmic Dawn ($z>10$) has suggested that galaxies developed rapidly, in apparent tension with many standard models. However, most of these galaxies lack spectroscopic confirmation, so their distances and properties are uncertain. We present JADES JWST/NIRSpec spectroscopic confirmation of two luminous galaxies at redshifts of $z=14.32^{+0.08}_{-0.20}$ and $z=13.90\pm0.17$. The spectra reveal ultraviolet continua with prominent Lyman-$\alpha$ breaks but no detected emission lines. This discovery proves that luminous galaxies were already in place 300~million years after the Big Bang and are more common than what was expected before JWST. The most distant of the two galaxies is unexpectedly luminous and is spatially resolved with a radius of 260 parsecs. Considering also the very steep ultraviolet slope of the second galaxy, we conclude that both are dominated by stellar continuum emission, showing that the excess of luminous galaxies in the early Universe cannot be entirely explained by accretion onto black holes. Galaxy formation models will need to address the existence of such large and luminous galaxies so early in cosmic history.

• The paper confirms two luminous galaxies at z~14 through detailed spectroscopic analysis using JWST/NIRSpec.
• It employs multi-object spectroscopy and advanced filtering to eliminate low-redshift interlopers, ensuring robust redshift measurements.
• Key findings, including steep ultraviolet continua and substantial stellar masses, challenge prevailing models of early galaxy growth.

Spectroscopic Confirmation of Luminous Galaxies at High Redshift

The paper "Spectroscopic confirmation of two luminous galaxies at a redshift of 14" presents a detailed analysis and confirmation of two galaxies located at remarkably high redshifts, utilizing data from the James Webb Space Telescope (JWST). This paper is a significant advancement in our understanding of galaxy formation and evolution during the Cosmic Dawn, a period roughly 300 million years after the Big Bang.

Overview and Methodology

The researchers conducted spectroscopic observations with the JWST's NIRSpec to investigate three candidate galaxies with redshifts greater than 14, selected through the JWST Advanced Deep Extragalactic Survey (JADES). Utilizing a multi-object spectroscopic mode, they focused on two galaxies, JADES-GS-z14-0 and JADES-GS-z14-1, after confirming their high redshifts through the analysis of their spectral data. The team used various NIRCam and MIRI filters to meticulously eliminate low-redshift interlopers, supported by the probability analysis based on Hubble Space Telescope and previous JWST data.

Key Findings

The spectroscopic analysis confirmed redshifts of $z=14.32^{+0.08}_{-0.20}$ and $z=13.90\pm0.17$ for JADES-GS-z14-0 and JADES-GS-z14-1, respectively. These high-redshift values establish these galaxies as among the oldest known, thereby reinforcing existing theories about early galaxy formation. Each galaxy exhibited clear Lyman-$\alpha$ breaks in their spectra, with the analysis ruling out potential contamination or misidentification as lower-redshift objects.

Both galaxies showed ultraviolet continua with steep slopes, suggesting that their emissions are dominated by young stellar populations rather than accretion onto black holes. Notably, JADES-GS-z14-0 is especially luminous, with a size greater than typically expected for galaxies of this era, suggesting more rapid stellar mass accumulation and possibly challenging current cosmological models that predict slower growth.

Implications and Theoretical Context

These findings have profound implications for models of galaxy formation. The unexpectedly high number of luminous galaxies at these early cosmic times suggests that existing models may need revision to account for more efficient star formation or alternative mechanisms that could facilitate early growth. The presence of significant stellar mass in these galaxies indicates that they formed via rapid, efficient processes, possibly supported by unique conditions, such as high gas densities and elevated star formation efficiencies.

Future Directions in Research

This research invites further investigation into the nature and evolution of early galaxies. Follow-up observations, particularly with the Atacama Large Millimeter/submillimeter Array (ALMA) and further JWST spectroscopic data, are likely to provide additional insights into the physical conditions, such as metallicity and dust content, affecting star formation in the early universe. Additionally, theoretical models will need to incorporate these findings to refine our understanding of cosmic dawn and the role of dark matter halos in galaxy evolution.

In summary, this paper underscores the potential of the JWST in extending the frontier of observable high-redshift galaxies and challenging current theoretical frameworks. The confirmed existence and detailed observation of galaxies at such high redshifts provide invaluable data, crucial for piecing together the puzzle of early galaxy formation and evolution in the universe.