Connecting the little dots in polarized light
Abstract
Recent observations of the local Little Red Dot (LRD) analog SDSS~J1025+1402 have revealed that the optical continuum is polarized at the ~1.5% level, while broad Halpha has lower polarization (~0.7%) and a different polarization angle. We explain these properties in a scenario in which LRDs are dust-obscured Little Blue Dots (LBDs) viewed at high inclination and powered by super-Eddington accretion. In this framework, electron scattering in the geometrically thick inner accretion flow produces intrinsic continuum polarization, while unpolarized emission from the outer thin disk dilutes the signal, particularly at optical wavelengths. A circumnuclear dust screen contributes dichroic polarization to both the continuum and broad-line emission. Broad Halpha lacks the intrinsic disk component and therefore has lower polarization and a different position angle. We show that this model quantitatively reproduces the observed polarization properties, although degeneracies between accretion rate and inclination remain. These results illustrate the potential of spectropolarimetry as a probe of accretion-flow geometry and orientation in the little-dot population, complementary to spectral-energy-distribution fitting and line diagnostics.
Related
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BibTeX
@misc{madau2026connecting,
title = {{Connecting the little dots in polarized light}},
author = {Piero Madau and Roberto Maiolino and Francesco D'Eugenio},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.06239},
eprint = {2609.06239},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.06239},
}
RIS
TY - UNPB
TI - Connecting the little dots in polarized light
AU - Piero Madau
AU - Roberto Maiolino
AU - Francesco D'Eugenio
PY - 2026
DA - 2026/09/05
PB - arXiv
DO - 10.48550/arxiv.2609.06239
UR - https://arxiv.org/abs/2609.06239
AB - Recent observations of the local Little Red Dot (LRD) analog SDSS~J1025+1402 have revealed that the optical continuum is polarized at the ~1.5% level, while broad Halpha has lower polarization (~0.7%) and a different polarization angle. We explain these properties in a scenario in which LRDs are dust-obscured Little Blue Dots (LBDs) viewed at high inclination and powered by super-Eddington accretion. In this framework, electron scattering in the geometrically thick inner accretion flow produces intrinsic continuum polarization, while unpolarized emission from the outer thin disk dilutes the signal, particularly at optical wavelengths. A circumnuclear dust screen contributes dichroic polarization to both the continuum and broad-line emission. Broad Halpha lacks the intrinsic disk component and therefore has lower polarization and a different position angle. We show that this model quantitatively reproduces the observed polarization properties, although degeneracies between accretion rate and inclination remain. These results illustrate the potential of spectropolarimetry as a probe of accretion-flow geometry and orientation in the little-dot population, complementary to spectral-energy-distribution fitting and line diagnostics.
ER -