Misaligned or chaotic? A strong break of axial symmetry in the local LRD J1025 revealed with VLT/FORS2 spectropolarimetry

Francesco D'Eugenio, Gabriele Pezzulli, Roberto Maiolino, Alessandro Marconi, Xihan Ji, Cristina Ramos Almeida, Andrea Ferrara, Piero Madau, Xiaojing Lin, José A. Acosta-Pulido, Fuyan Bian, Matilde Brazzini, Zheng Cai, Stefano Carniani, Xiaohui Fan, Ignas Juodžbalis, Robert G. Pascalau, Jan Scholtz, Charlotte Simmonds, Fengwu Sun, Sandro Tacchella

First listed 2026-08-03 | Last updated 2026-07-30

Abstract

Little Red Dots (LRDs) are compact active galactic nuclei (AGN) with unusual spectral energy distributions and broad Balmer emission, candidate signposts of rapid black-hole growth. We present VLT/FORS2 optical linear spectropolarimetry of the closest known LRD, SDSS J102530.29+140207.3, at z=0.1. In total light, we detect spatially extended narrow-H$α$ emission, probably tracing the host galaxy. We measure a nearly grey continuum polarisation $p_{\rm cont}=1.53\pm0.04$(rand.)$\pm$0.20(syst.) per cent, while broad H$α$ is less polarised, $p_{\rm Hα}=0.58-0.84$ per cent. We rule out polarisation by Milky Way dust and dilution by an unpolarised line. The polarised continuum with a depolarised line resembles local Seyfert-1 nuclei and favours a single dominant source over multi-source explanations. After Stokes-continuum subtraction, broad H$α$ shows no blue-to-red swing, but there is a significant (48$\pm$4)$^\circ$ continuum-to-line offset in polarisation angle. This implies a break of axial symmetry inside this object, posing interesting geometrical challenges to all existing LRD models and frameworks. We discuss different possible origins of this symmetry break and possible paths to discriminate between them with future observations.

Short digest

This paper uses VLT/FORS2 optical linear spectropolarimetry of SDSS J102530.29+140207.3 (J1025), the closest known little red dot, to probe the geometry behind its broad Balmer emission and unusual continuum. The continuum is nearly grey and polarized while broad Hα is less polarized, a Seyfert-1-like pattern that supports a single dominant central source rather than a multi-source explanation; extended narrow Hα is detected in total light and likely traces the host. Crucially, the broad line lacks a blue-to-red polarization-angle swing but is offset in polarization angle from the continuum, implying a strong break of axial symmetry and challenging existing geometrical models for LRDs.

Key figures to inspect

• Figure 1. This null-spectrum validation figure establishes that the Stokes-flux uncertainties are conservative relative to empirical off-target noise, supporting the significance of the continuum and broad-Hα polarization measurements on which the paper’s symmetry-break claim rests.