The twin-jet system in the FRII radio galaxy 3C 452: A sub-parsec scale VLBI study

Abstract

We present a comprehensive multifrequency VLBI analysis of the FRII, high-excitation radio galaxy 3C 452, aiming to resolve and analyze for the first time its twin-jet structure on sub-parsec scales. Our data set comprises High Sensitivity Array (HSA) observations at 4.9, 8.4, 15.4, 23.6, and 43.2 GHz. Through fitting methods performed in both the visibility and the image plane, we trace the jet expansion from scales of a few thousand to nearly $10^5$ Schwarzschild radii ($R_S$) on both the approaching and receding jets. Additionally, we derive the core brightness temperatures and Doppler factors to constrain the jet's orientation and intrinsic speed. Our study provides the first detailed description of the twin-jet system in 3C 452 on VLBI scales, confirming it as a rare FRII source with jets detected down to millimeter wavelengths. We resolve both jet and counter-jet down to scales of a few thousand $R_S$, revealing a symmetric, parabolically expanding structure with power-law indices $k \approx 0.66$ (jet) and $k \approx 0.47$ (counter-jet). The brightness temperature analysis yields low Doppler factors ($δ\sim 0.03$-$0.83$), indicative of Doppler de-boosting due to the large viewing angle ($θ\approx 70^\circ$) and/or a magnetically dominated jet base. A spectral index analysis reveals a strongly inverted core spectrum ($α> 2$) with additional absorption at the highest frequencies, followed by a sharp steepening ($α\sim -2.5$) to optically thin values in the innermost jet. Finally, a comparison between broad- and narrow-line high-excitation radio galaxies shows that jets in narrow-line sources such as 3C 452 and Cygnus A complete collimation at $\leq 10^5 R_S$, whereas broad-line sources exhibit shape transitions at $10^6$-$10^7 R_S$, suggesting that orientation plays an important role in the observed collimation scales.

Figures (12)

• Figure 1: The twin-jet structure of 3C 452 from kiloparsec to sub-parsec scales. The top image was obtained from VLA data at 1.4 GHz Leahy1996_Atlas. The following maps show the VLBI structure at different frequencies (4.9 GHz, 8.4 GHz, 15.4 GHz, 23.6 GHz, 43.2 GHz) based on the analyzed data of our project code BM516B presented in Sect. \ref{['sec:data set']}. Images were produced using natural weighting. The maps have been aligned to the central brightest feature. The complete series of images considered in the article is presented in the Appendix \ref{['app:appendix']}.
• Figure 2: Stacked VLBI images of 3C 452 at 4.9 (upper left), 8.4 (upper right), 15.4 (middle left), 23.6 (middle right), and 43.2 (bottom) GHz. Restored with circular beams of 1.48, 0.8, 0.45, 0.34, and 0.18 mas, respectively. The respective peak flux density and rms values are displayed on the top of each panel. Images were produced using uniform weighting.
• Figure 3: Flux density profiles of the receding counter-jet (left panel) and approaching jet (right panel) and as a function of distance from the common reference frame, measured from the stacked images at each frequency. The profiles were derived using pixel-based Gaussian fitting across transverse jet slices, as described in Sect. \ref{['sec:stacked images']}.
• Figure 4: Jet-to-counter-jet intensity ratio as a function of frequency. Ratios are derived for three datasets: BB393, BM516A, and BM516B. All images were aligned to the common reference frame, identified as the midpoint between the jet and counter-jet cores in the 43 GHz map (Sect. \ref{['sec:alignment']}). BB393 observations were published in 2025AA...695A.118B
• Figure 5: Jet-to-counter-jet intensity ratio as a function of distance from the common reference frame, shown for all observing frequencies. The analysis includes data from projects BB393, BM516A, and BM516B.