Are JWST/NIRCam color gradients in the lensed z=2.3 dusty star-forming galaxy El Anzuelo due to central dust attenuation or inside-out galaxy growth? (2303.05054v2)

Abstract: Gradients in the mass-to-light ratio of distant galaxies impede our ability to characterize their size and compactness. The long-wavelength filters of $JWST$'s NIRCam offer a significant step forward. For galaxies at Cosmic Noon ($z\sim2$), this regime corresponds to the rest-frame near-infrared, which is less biased towards young stars and captures emission from the bulk of a galaxy's stellar population. We present an initial analysis of an extraordinary lensed dusty star-forming galaxy (DSFG) at $z=2.3$ behind the $El~Gordo$ cluster ($z=0.87$), named $El~Anzuelo$ ("The Fishhook") after its partial Einstein-ring morphology. The FUV-NIR SED suggests an intrinsic star formation rate of $81^{+7}{-2}~M\odot~{\rm yr}^{-1}$ and dust attenuation $A_V\approx 1.6$, in line with other DSFGs on the star-forming main sequence. We develop a parametric lens model to reconstruct the source-plane structure of dust imaged by the Atacama Large Millimeter/submillimeter Array, far-UV to optical light from $Hubble$, and near-IR imaging with 8 filters of $JWST$/NIRCam, as part of the Prime Extragalactic Areas for Reionization and Lensing Science (PEARLS) program. The source-plane half-light radius is remarkably consistent from $\sim 1-4.5~\mu$m, despite a clear color gradient where the inferred galaxy center is redder than the outskirts. We interpret this to be the result of both a radially-decreasing gradient in attenuation and substantial spatial offsets between UV- and IR-emitting components. A spatial decomposition of the SED reveals modestly suppressed star formation in the inner kiloparsec, which suggests that we are witnessing the early stages of inside-out quenching.

• The paper estimates an intrinsic star formation rate of 81 M⊙/yr and dust attenuation of A_V≈1.6 via broadband SED analysis.
• It employs a parametric lens model with ALMA and JWST imaging to accurately reconstruct the source-plane structure.
• The analysis reveals a consistent half-light radius across 1–4.5 μm wavelengths, indicating early inside-out quenching in the galaxy’s core.

Analysis of JWST/NIRCam Color Gradients in a Lensed Dusty Star-Forming Galaxy

This paper investigates the color gradients observed in the $z=2.3$ dusty star-forming galaxy (DSFG), designated as "El Anzuelo," which is gravitationally lensed by the El Gordo cluster. The central question that the paper addresses is whether these color gradients are due to central dust attenuation or indicative of inside-out growth of the galaxy. The James Webb Space Telescope's Near Infrared Camera (JWST/NIRCam) provides detailed imaging, enabling a comprehensive analysis of the intrinsic properties of this galaxy.

Key Findings

• Star Formation Rate and Dust Attenuation: The analysis estimates an intrinsic star formation rate of 81 $(M_\odot~{\rm yr}^{-1})$ and dust attenuation of $A_V \approx 1.6$, consistent with other DSFGs on the star-forming main sequence. These measurements were derived from the far-ultraviolet (FUV) to near-infrared (NIR) spectral energy distribution (SED).
• Source-plane Structural Reconstruction: Using a parametric lens model, the researchers reconstructed the source-plane structure of El Anzuelo. The model combined data from the Atacama Large Millimeter/submillimeter Array (ALMA) and JWST/NIRCam imaging in eight filters, allowing for precise mapping of the stellar and dust continuum.
• Half-light Radius Consistency: Across wavelengths ranging from 1 to 4.5 micrometers, the source-plane half-light radius remains consistent. This finding is quite revealing, given the presence of a color gradient indicating that the galaxy center appears redder than its outskirts. This consistency suggests a radial gradient in dust attenuation and spatial offsets between UV- and IR-emitting regions.
• Spatial Decomposition and Early Quenching: A spatial decomposition of the SED reveals a suppressed star formation rate in the inner kiloparsec of the galaxy, suggesting the early stages of inside-out quenching. This implies that the galaxy may be transitioning towards quiescence from the inside out, a process observed in some galaxies as they evolve.

Implications

The findings have significant implications for understanding galaxy evolution at Cosmic Noon, a period when the cosmic star-formation history peaked. The results suggest complex interplay between dust distribution, star formation processes, and galaxy growth patterns. The consistent half-light radius across a broad wavelength range despite redder central colors underscores the need to consider both dust and stellar population effects in interpreting observations of distant galaxies.

The potential identification of inside-out quenching in El Anzuelo provides a case paper for theories on galaxy evolution dynamics, where central regions quench before the outskirts, possibly due to feedback processes or other mechanisms halting star formation.

Future Research Directions

The paper of El Anzuelo sets the stage for future developments in the paper of high-redshift galaxies facilitated by JWST. Further observations, potentially incorporating high-resolution spectroscopy, could differentiate between contributions from dust and old stellar populations to the observed color gradients. Additionally, exploring similar analyses in other lensed galaxies could validate the inside-out growth and quenching scenario, enriching our understanding of galaxy evolution across cosmic time.

Thus, the research contributes to the broader discourse on how early star-forming galaxies attain their mature forms and the role of processes like dust attenuation and quenching in shaping their structural and spectral properties. The integration of advanced observational tools with detailed modeling underscores the promise of contemporary astronomical research in unveiling the complexities of the universe's earlier epochs.