Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic Star-Formation Rate Density 300 Myr after the Big Bang (2312.10033v2)

Abstract: We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters spanning $0.4-0.9\mu\mathrm{m}$) and novel JWST images with 14 filters spanning $0.8-5\mu\mathrm{m}$, including 7 medium-band filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data at $>2.3\mu\mathrm{m}$ to construct an ultradeep image, reaching as deep as $\approx31.4$ AB mag in the stack and 30.3-31.0 AB mag ($5\sigma$, $r=0.1"$ circular aperture) in individual filters. We measure photometric redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts $z=11.5-15$. These objects show compact half-light radii of $R_{1/2}\sim50-200$pc, stellar masses of $M_{\star}\sim10^7-10^8 M_{\odot}$, and star-formation rates of $\mathrm{SFR}\sim0.1-1\,M_{\odot}\,\mathrm{yr}^{-1}$. Our search finds no candidates at $15<z<20$, placing upper limits at these redshifts. We develop a forward modeling approach to infer the properties of the evolving luminosity function without binning in redshift or luminosity that marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the impact of non-detections. We find a $z=12$ luminosity function in good agreement with prior results, and that the luminosity function normalization and UV luminosity density decline by a factor of $\sim2.5$ from $z=12$ to $z=14$. We discuss the possible implications of our results in the context of theoretical models for evolution of the dark matter halo mass function.

• The paper identifies eight high-redshift galaxy candidates with compact sizes (50–200 pc) and stellar masses around 10⁷–10⁸ M☉, revealing rapid early star formation.
• The study uses ultra-deep multi-filter imaging from JWST and HST, applying robust photometric redshift techniques to achieve a depth of 31.4 AB magnitude.
• The research finds a decline in UV luminosity density by roughly 2.5 times from z=12 to z=14, suggesting decreased star formation efficiency in the early universe.

Overview of "Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic Star-Formation Rate Density 300 Myr after the Big Bang"

The paper "Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic Star-Formation Rate Density 300 Myr after the Big Bang" explores the characterization of some of the earliest galaxies in the universe, leveraging observations from the JADES Origins Field (JOF) with the James Webb Space Telescope (JWST). This research aims to illuminate our understanding of galaxy formation during the first few hundred million years following the Big Bang, with a focus on the luminosity function and star-formation rate density at redshifts $z \approx 11.5-15$.

Methodology and Data

The paper utilizes ultra-deep imaging from both JWST and the Hubble Space Telescope (HST) to construct a comprehensive photometric dataset across a wide spectral range. This includes 14 JWST filters and 5 Hubble optical images, with exposure times reaching up to 46 hours per filter. By constructing an ultra-deep image through these combined datasets, the researchers achieve a depth of approximately 31.4 AB magnitude. Photometric redshifts are calculated for objects within this dataset, and robust selection criteria are applied to identify eight candidate galaxies at high redshifts ($z=11.5-15$).

Major Findings

• Galaxy Properties: The identified galaxy candidates exhibit compact sizes, with half-light radii ranging between 50-200 pc, and stellar masses of $\sim 10^7-10^8 M_\odot$. Their star-formation rates are estimated to be $\sim 0.1-1 M_\odot \text{yr}^{-1}$.
• Luminosity Function: The paper presents a forward modeling approach to infer properties of the evolving luminosity function without binning in redshift or luminosity. This approach accounts for photometric redshift uncertainties and impacts of non-detections and shows good agreement with prior $z=12$ findings. There is a noted decline in the normalization and UV luminosity density by a factor of approximately 2.5 from $z=12$ to $z=14$.
• Cosmic Star-Formation Rate Density: Consistent with previous observations and models, the cosmic star-formation rate density shows a decline towards high redshifts.

Implications

This research reinforces theories about early galaxy formation and the subsequent evolution of these structures. The observed decline in the luminosity function normalization suggests an alteration in the formation efficiency or availability of baryonic material in nascent galaxies as cosmic time advances towards $z=15$. The characterized compactness and active star formation suggest these early structures underwent rapid star formation phases, likely constrained by their local dynamical times.

Future Directions

The paper indicates several avenues for future research. These include extending the survey to larger areas to mitigate potential biases due to cosmic variance and further spectroscopic follow-ups. Confirming the photometric redshifts with spectroscopic analysis would also strengthen these findings. Additionally, exploring the role of dark matter halo evolution and its influence on early galaxy abundance could bridge connections between theoretical predictions and observed early-universe structures.

In essence, this detailed analysis of deep-field observations has enriched the understanding of galaxy formation dynamics in the early universe, offering robust measurements and interpretations that align with and expand upon existing astrophysical models. Future expansion of this work can further elucidate the formative processes of galaxies at the universe's infancy and assist in refining cosmological models to incorporate these early findings.