A surprising abundance of massive quiescent galaxies at 3 < z < 5 in the first data from JWST CEERS (2208.00986v3)

Abstract: We report a robust sample of 10 massive quiescent galaxies at redshift, $z > 3$, selected using the first data from the JWST CEERS programme. Three of these galaxies are at $4 < z < 5$, constituting the best evidence to date for quiescent galaxies significantly before $z=4$. These extreme galaxies have stellar masses in the range log${10}(M/$M$\odot) = 10.1-11.1$, and formed the bulk of their mass around $z \simeq 10$, with two objects having star-formation histories that suggest they had already reached log${10}(M_/$M$_\odot) > 10$ by $z\gtrsim8$. We report number densities for our sample, demonstrating that, based on the small area of JWST imaging so far available, previous work appears to have underestimated the number of quiescent galaxies at $3 < z < 4$ by a factor of $3-5$, due to a lack of ultra-deep imaging data at $\lambda>2\,\mu$m. This result deepens the existing tension between observations and theoretical models, which already struggle to reproduce previous estimates of $z>3$ quiescent galaxy number densities. Upcoming wider-area JWST imaging surveys will provide larger samples of such galaxies and more-robust number densities, as well as providing opportunities to search for quiescent galaxies at $z>5$. The galaxies we report are excellent potential targets for JWST NIRSpec spectroscopy, which will be required to understand in detail their physical properties, providing deeper insights into the processes responsible for forming massive galaxies and quenching star formation during the first billion years.

• The paper reports the detection of 10 robust quiescent galaxy candidates, including 3 found beyond z = 4, marking some of the earliest massive quiescent systems.
• The study employs deep NIRCam imaging and precise SED fitting using Bagpipes to identify galaxies with stellar masses between log₁₀(M*/M☉) 10.1 and 11.1.
• The findings challenge current galaxy formation models by showing a 3–5 times higher number density of quiescent galaxies compared to pre-JWST estimates, suggesting rapid quenching processes.

A Surprising Abundance of Massive Quiescent Galaxies at $3 < z < 5$

The paper by Carnall et al. presents findings from the James Webb Space Telescope (JWST) Cosmic Evolution Early Release Science (CEERS) program regarding the discovery of massive quiescent galaxies in the $3 < z < 5$ redshift range. The paper identifies ten robust candidates of quiescent galaxies, three of which are located beyond $z = 4$, marking them as some of the earliest known massive quiescent galaxies in the universe's history.

Key Findings

The authors highlight the significance of their discovery by contrasting the number densities of these quiescent galaxies with pre-JWST estimates. The new JWST data reveal a number density that is 3–5 times higher than previously estimated for galaxies of similar redshift and quiescence. This increase is attributed to the superior depth and wavelength coverage of JWST, which facilitates the detection of the Balmer break—a key feature for identifying quiescent stars—at these high redshifts.

Methodology

To achieve their results, the researchers utilized deep NIRCam imaging from the JWST in combination with spectral energy distribution (SED) fitting through the Bagpipes code. Artifact removal, photometry calibration, and several reliability checks—including comparisons with existing catalogs—were employed to ensure robust candidate selection. The detected galaxies were characterized by their stellar masses in the range of log$_{10}(M_*/M_\odot) = 10.1-11.1$.

Implications

The findings challenge existing galaxy formation models, many of which are unable to reproduce the observed abundance of massive quiescent galaxies at such high redshifts. This discrepancy suggests that current simulations might be lacking crucial physical processes responsible for rapid quenching events in the early universe.

Furthermore, these quiescent galaxies, having formed the bulk of their stars at $z>6$, prompt a reevaluation of star formation and quenching timelines. In particular, they may represent a transitional phase linking early, rapidly forming galaxies—such as those identified by Labbe et al.—and more evolved quiescent systems at lower redshifts.

Future Directions

The paper sheds light on the capabilities of forthcoming JWST surveys, particularly those with a larger field of view like the Public Release Imaging for Extragalactic Research (PRIMER). The authors stress the necessity of expanded datasets to confirm these results and to further our understanding of early galaxy evolution. Potential advancements include achieving mass-complete selections through longer wavelength observations and obtaining spectroscopic data to dissect the physical properties and histories of these galaxies.

Conclusion

Carnall et al. provide compelling evidence for the existence of massive quiescent galaxies at redshifts as high as $z=5$. The work significantly impacts our understanding of galaxy evolution, challenging existing theoretical models, and setting the stage for future observations and studies aimed at unraveling the complexities of galaxy formation in the early universe.