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 $z \sim 4-8$ in the GOODS fields, leveraging ultra-deep JADES NIRCam short-wavelength (SW) data. We examine the morphology of $30$ LRDs; the remaining $69$ are predominantly compact, i.e., are strongly dominated by sources $< 400\ \mathrm{parsec}$ in diameter and lack extended components even in stacked SW band images. Among the LRDs selected for morphological analysis, $50\%$ show at least two distinct, associated sources or galaxy components, while the others appear as single sources with highly asymmetric structures. We find median stellar masses of $\mathrm{log}_{10}(M_{\ast}/M_{\odot}) = 9.07_{-0.08}^{+0.11}$ for pure stellar models with $A_{V} \sim 1.16_{-0.21}^{+0.11}\ \mathrm{mag}$ , and $\mathrm{log}_{10}(M_{\ast}/M_{\odot}) = 9.67_{-0.27}^{+0.17}$ for models including AGNs, where $A_{V} \sim 2.74_{-0.71}^{+0.55}\ \mathrm{mag}$ , consistent with recent results showing LRDs tend to have high stellar masses and dust content when fitted with AGN models. NIRSpec spectra are available for $15$ sources, $6$ of which fall within the morphological analysis sample and show multiple components. Among these $15$ , broad H-alpha emission is detected in $40\%$ , with full-width half-maximum (FWHM) ranging from $1200$ to $2900\ \mathrm{km/s}$ . One source exhibits broad H-beta emission with $\mathrm{FWHM} = 2000 \pm 500\ \mathrm{km/s}$ . Analysis of line ratios probing the interstellar medium (ISM) reveals a composite nature, indicating AGN activity combined with stellar processes. These findings suggest LRDs have a mixed nature, with AGN signatures in some cases linked to disturbed morphologies observed at rest-frame UV wavelengths.

eprint arXiv:2411.14383