Not Just a Dot: The Complex UV Morphology and Underlying Properties of Little Red Dots

We analyze $99$ photometrically selected Little Red Dots (LRDs) at $z \approx 4-8$ in the GOODS fields, leveraging ultra-deep JADES NIRCam short-wavelength (SW) data. Among the $99$ selected LRDs, we examine the morphology of $30$ . The remaining $69$ appear predominantly compact, with sizes $\lesssim 400\ \mathrm{parsec}$ and no extended components even in stacked SW images. However, their unresolved nature may partly reflect current depth limitations, which could prevent the detection of faint diffuse components. Among the $30$ morphologically analyzed LRDs, $50\%$ show multiple associated clumps, while the rest exhibit highly asymmetric structures, despite appearing as single sources. This diversity in rest-frame UV morphologies may point to interactions or strong internal feedback. We find median stellar masses of $\mathrm{log}_{10}(M_{\ast}/M_{\odot}) = 9.07_{-0.08}^{+0.11}$ for pure stellar models with $A_{V} \approx 1.16_{-0.21}^{+0.11}\ \mathrm{mag}$ , and $\mathrm{log}_{10}(M_{\ast}/M_{\odot}) = 9.67_{-0.27}^{+0.17}$ for models including active galactic nuclei (AGNs), where $A_{V} \approx 2.74_{-0.71}^{+0.55}\ \mathrm{mag}$ , in line with recent studies suggesting higher masses and dust content for AGN-fitted LRDs. NIRSpec spectra are available for $15$ sources, six of which are also in the morphological sample. Broad $\mathrm{H}-\alpha$ is detected in $40\%$ , with full-width half-maximum (FWHM) ranging from $1200$ to $2900\ \mathrm{km/s}$ , and one source exhibits broad $\mathrm{H}-\beta$ emission. Emission line ratios indicate a composite nature, consistent with both AGN and stellar processes. Altogether, these results suggest that LRDs are a mixed population, and their rest-frame UV morphology reflects this complexity. Morphological studies of larger samples could provide a new way to understand what drives their properties and evolution.

The Astrophysical Journal, Volume 992, Issue 1, id.71, 20 pages