Arina Arshinova | Searcharxiv

arXiv2026

Here Be SDRAGNs - Spiral Galaxies Hosting Large Double Radio Sources

We present a sample of large double radio sources hosted by spiral galaxies (Spiral Double Radio Active Galactic Nuclei, SDRAGNs). Candidates were selected during Radio Galaxy Zoo, and refined using Sloan Digital Sky Survey images. The most promising were targeted in the Zoo Gems Hubble Space Telescope program, yielding images for 36 candidates. We assess the likelihood of each spiral galaxy being the genuine host of the radio emission finding 15 new high-probability SDRAGNs. SDRAGN hosts are seen preferentially close to edge-on. SDRAGNs predominantly show FR II radio structures and optical pseudobulges. Accounting for sample selection effects, the radio-jet axes lie preferentially near the poles of the galaxy disks; we find a constant probability distribution for intrinsic pole-jet angles < 30 degrees, ramping to zero at 60 degrees. We have obtained optical spectra for all these new SDRAGNs. Among both previous and new SDRAGN samples, 8/25 show Seyfert 2 signatures, 6/25 show central star formation, and 5/25 show LINER emission strong enough to indicate AGN or shock ionization, broadly similar to radio galaxies in elliptical hosts with the addition of star formation (diluting or masking weak AGN signatures). SDRAGNs include FR II sources seen at unusually low radio power, and preferentially occur in significant galaxy overdensities on 1-Mpc scales. Our "false alarms" - systems where HST data show the spiral to not be the actual host galaxy - include radio sources seen through large parts of foreground spiral disks, potentially useful for Faraday-rotation studies of disk magnetic fields.

astro-ph.GA↗

arXiv2024

Polarization of active galactic nuclei with significant VLBI-Gaia displacements

Numerous studies have reported significant displacements in the coordinates of active galactic nuclei between measurements using radio interferometry techniques and those obtained by the Gaia space observatory. There is a consensus that these discrepancies do indeed manifest astrometrically resolved sub-components of AGN rather than random measurement noise. Among other evidence, it has been reported that AGN with VLBI-to-Gaia displacements (VGD) pointing downstream their parsec-scale radio jets exhibit higher optical polarization compared to sources with the opposite VGD orientation. We aim to verify this previously reported connection between optical polarization and VGD-jet angle using a larger dataset of polarimetric measurements and updated Gaia DR3 positions. We also seek additional evidence supporting the disc-jet dichotomy as an explanation of such a connection by using mm-wave polarization and multi-band optical polarization measurements. We performed optical polarimetric observations of 152 AGN using three telescopes. We cross-match public astrometric data from VLBI and Gaia experiments, obtain corresponding positional displacements, and join this catalog with the polarimetric and jet directions data. AGN with downstream VGD are confirmed to have significantly higher optical fractional polarization than the upstream sample. At the same time, the mm-wavelength polarization of the two samples demonstrates very similar distributions. Our results support the hypothesis that the VLBI-to-Gaia displacements pointing down the radio jet are likely caused by a component in the jet emitting highly polarized synchrotron radiation and dominating in the overall optical emission. The upstream-oriented VGD are likely to be produced by the low-polarized emission of the central engine sub-components dominating in the optical.

astro-ph.GA↗