Limitations on Morphological Fitting for JWST "Little Red Dots"
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arXiv
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| Auteurs principaux: | , , , |
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| Format: | Preprint |
| Publié: |
2025
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| _version_ | 1866911176214970368 |
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| author | Whalen, Kelly E. Weaver, Kimberly A. Hickox, Ryan C. Lambrides, Erini |
| author_facet | Whalen, Kelly E. Weaver, Kimberly A. Hickox, Ryan C. Lambrides, Erini |
| contents | Early results from JWST uncover a peculiar class of objects referred to as ``little red dots'' (LRDs). The extremely compact morphology of LRDs is often invoked to point towards an AGN-dominated picture in the context of their conflicting multiwavelength properties. In this work, we assess the capability of pysersic and GALFIT -- commonly used tools in LRD morphological studies -- to recover input parameters for a simulated suite of LRD-like objects in the F444W band. We find that: 1) these tools have difficulty recovering input parameters for simulated images with SNR $\lesssim 25$; 2) estimated PSF fraction could be a more robust physically-motivated description of LRD compactness; and 3) almost all permutations of modeled LRDs with SNR $\lesssim 50$ cannot be differentiated from a point source, regardless of intrinsic extent. This has serious implications on how we interpret morphological results for increasingly large photometric samples of LRDs, especially at extremely high-$z$ or in relatively shallow fields. We present results of Sersic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that $\sim85\%$ of observed LRDs are PSF-dominated, consistent with the AGN-dominated interpretation. The remaining $\sim15\%$ have low estimated PSF fractions (two-component fit) and sizes $\gtrsim 150$ pc (Sersic). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of sources consistent with the AGN-dominated hypothesis, and a secondary population of sources more consistent with arising perhaps from extremely compact starbursts. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_21236 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Limitations on Morphological Fitting for JWST "Little Red Dots" Whalen, Kelly E. Weaver, Kimberly A. Hickox, Ryan C. Lambrides, Erini Astrophysics of Galaxies Early results from JWST uncover a peculiar class of objects referred to as ``little red dots'' (LRDs). The extremely compact morphology of LRDs is often invoked to point towards an AGN-dominated picture in the context of their conflicting multiwavelength properties. In this work, we assess the capability of pysersic and GALFIT -- commonly used tools in LRD morphological studies -- to recover input parameters for a simulated suite of LRD-like objects in the F444W band. We find that: 1) these tools have difficulty recovering input parameters for simulated images with SNR $\lesssim 25$; 2) estimated PSF fraction could be a more robust physically-motivated description of LRD compactness; and 3) almost all permutations of modeled LRDs with SNR $\lesssim 50$ cannot be differentiated from a point source, regardless of intrinsic extent. This has serious implications on how we interpret morphological results for increasingly large photometric samples of LRDs, especially at extremely high-$z$ or in relatively shallow fields. We present results of Sersic and two-component fitting to a sample of observed LRDs to compare with our mock sample fitting. We find that $\sim85\%$ of observed LRDs are PSF-dominated, consistent with the AGN-dominated interpretation. The remaining $\sim15\%$ have low estimated PSF fractions (two-component fit) and sizes $\gtrsim 150$ pc (Sersic). This morphological diversity of LRDs suggests that that the population likely is not homogeneous. It possibly has a primary subset of sources consistent with the AGN-dominated hypothesis, and a secondary population of sources more consistent with arising perhaps from extremely compact starbursts. |
| title | Limitations on Morphological Fitting for JWST "Little Red Dots" |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2509.21236 |