The evolution of the galaxy UV luminosity function at redshifts z ~ 8-15 from deep JWST and ground-based near-infrared imaging (2207.12356v3)

Abstract: We reduce and analyse the available James Webb Space Telescope (JWST) ERO and ERS NIRCam imaging (SMACS0723, GLASS, CEERS) in combination with the latest deep ground-based near-infrared imaging in the COSMOS field (provided by UltraVISTA DR5) to produce a new measurement of the evolving galaxy UV luminosity function (LF) over the redshift range $z = 8 - 15$. This yields a new estimate of the evolution of UV luminosity density ($\rho_{\rm UV}$), and hence cosmic star-formation rate density ($\rho_{\rm SFR}$) out to within $< 300$\, Myr of the Big Bang. Our results confirm that the high-redshift LF is best described by a double power-law (rather than a Schechter) function up to $z\sim10$, and that the LF and the resulting derived $\rho_{\rm UV}$ (and thus $\rho_{\rm SFR}$), continues to decline gradually and steadily up to $z\sim15$ (as anticipated from previous studies which analysed the pre-existing data in a consistent manner to this study). We provide details of the 61 high-redshift galaxy candidates, 47 of which are new, that have enabled this new analysis. Our sample contains 6 galaxies at $z \ge 12$, one of which appears to set a new redshift record as an apparently robust galaxy candidate at $z \simeq 16.4$, the properties of which we therefore consider in detail. The advances presented here emphasize the importance of achieving high dynamic range in studies of early galaxy evolution, and re-affirm the enormous potential of forthcoming larger JWST programmes to transform our understanding of the young Universe.

• The paper demonstrates that the galaxy UV luminosity function at high redshifts is best described by a double power-law, suggesting earlier galaxy formation than previously thought.
• The authors combine multi-band JWST NIRCam data with UltraVISTA imaging to robustly identify 61 high-redshift galaxy candidates, including 47 new detections.
• The study’s results imply a gradual decline in star-formation rate density that aligns UV luminosity with dark matter halo distributions, refining early formation models.

Investigating the Evolution of the Galaxy UV Luminosity Function at High Redshifts

The paper titled "The evolution of the galaxy UV luminosity function at redshifts $z = 8 - 15$ from deep JWST and ground-based near-infrared imaging" presents a detailed analysis of the ultraviolet (UV) luminosity function of galaxies at some of the highest redshifts observed. This research utilizes data from the James Webb Space Telescope (JWST) Early Release Observations (ERO) and Early Release Science (ERS) programs, in conjunction with deep near-infrared images from UltraVISTA in the COSMOS field, providing a comprehensive dataset spanning redshifts from $z \sim 8$ to $z \sim 15$, thereby extending our understanding of galaxy formation to within 300 million years of the Big Bang.

Methodology and Sample Selection

The authors have utilized multi-band NIRCam imaging from JWST, covering fields such as SMACS0723, GLASS, and CEERS, alongside data from the COSMOS field, processed through the UltraVISTA Data Release 5 (DR5). Combining these datasets allowed the researchers to employ a robust photometric redshift analysis across a large sample of high-redshift galaxy candidates. A meticulous selection process yielded 61 high-redshift galaxy candidates, with a total of 47 being newly identified in this paper. Notably, among these new detections are six galaxies at $z \ge 12$, including one setting a new distance benchmark at $z \simeq 16.4$.

Luminosity Function Analysis

The analysis confirms that the high-redshift UV luminosity function (LF) is best described by a double power-law form, rather than the traditional Schechter function, at least up to $z \sim 10$. This finding, supported by data up to $z \sim 15$, suggests that galaxy formation commenced earlier than previously confirmed estimates, indicating a steady evolution in UV luminosity density ($\rho_{\rm UV}$) and hence, a gradual decline in star-formation rate density ($\rho_{\rm SFR}$) with increasing redshift.

Implications for Early Galaxy Formation

The results emphasize that during the highest redshift epochs, the LF aligns more closely with the distribution of the underlying dark matter halos, potentially indicating that mechanisms like mass quenching and dust obscuration are less influential in these early phases. This morphological insight is pivotal as it aligns with the theoretical expectations of early galaxy evolution, providing a crucial validation of current galaxy formation models under the $\Lambda$CDM framework.

Addressing Deviations from Previous Studies

This paper provides new insights, contradicting prior claims of a steep drop-off in $\rho_{\rm UV}$ at redshifts beyond $z \sim 8$, by demonstrating instead a consistent exponential decline, aligning more closely with analytical predictions for cosmic star formation history. Furthermore, the paper challenges the conclusions derived from earlier HST pure-parallel imaging, particularly regarding the overestimation of high-redshift galaxy abundance due to contamination risks.

Future Directions

The findings underscore the importance of reliable photometric data across multiple wavelengths to accurately determine redshifts and physical properties of distant galaxies. As JWST continues to provide unprecedented data, further studies will likely refine our understanding of galaxy formation processes in the early universe. Upcoming extensive JWST surveys will be instrumental in extending the dynamic range of LF studies, potentially uncovering even fainter and more distant galaxies that could further test the existing models of cosmic structure formation.

In conclusion, this paper elucidates the gradual evolution of high-redshift galaxies and reinforces the necessity of broad and deep space-based imaging to unlock the secrets of high-$z$ galaxies, reshaping our comprehension of the early universe. The integration of JWST data into this domain represents a transformative step, promising continued advancements in our grasp of galactic and cosmic evolution.