The Perpendicularity of Dust Lanes and Radio Jets in Early-Type Galaxies: Implications for AGN Feedback

TL;DR

This study investigates how the orientations of dust features in early-type galaxies relate to the directions of radio jets to illuminate AGN feedback and jet reorientation. Leveraging archival HST optical images and VLA NVSS/FIRST data, the authors implement an automated PA-measurement pipeline to classify dust as lanes, disks, or rings and quantify their relative angles to jets and host galaxies. They find dust lanes are predominantly perpendicular to jets and largely unaligned with the host major axis, while disks and rings align with the galaxy major axis but show varying jet associations; large lanes may align with the galaxy axis, hinting at merger-driven dynamics. A merger-driven scenario is proposed: successive gas-rich mergers alter the angular momentum of infalling material, reorienting jets and enabling broader halo heating, which has implications for sustaining quiescence in massive galaxies. Overall, the work links small-scale dust morphologies to jet dynamics and provides a nuanced picture of AGN feedback in shaping galaxy evolution.

Abstract

The orientation of radio jets relative to their host galaxies offers an interesting avenue for probing the connection between active galactic nuclei (AGN) and their surroundings. Several studies have also investigated the orientation of nuclear dust features. We follow up on this previous work with newer Hubble Space Telescope imaging of early-type radio galaxies, and a largely automated process for measuring position angles. We classify the dust features as lanes, disks, or rings. Lanes are irregular structures that likely form from gas-rich minor mergers, while disks and rings are more well-defined and may form from settling lanes or internal mechanisms. We find that dust lanes do not have a preferred alignment relative to their host galaxies, but are preferentially perpendicular to the jets. In contrast, dust disks and rings tend to be closely aligned with the major axes of their host galaxies, but have varying orientations relative to the jets. Our results suggest that infalling dusty material from mergers can influence the angle of the radio jet. This would allow the jet orientation to change over time, and may help explain the role of AGN feedback in maintaining quiescence in massive galaxies.

Figures (8)

• Figure 1: Image gallery of the galaxy sample, Part 1/4. We applied an asinh scaling to the images for visualization. For each galaxy, we show the optical HST image on the left and the radio image on the right. Optical image: We report the measured dust and galaxy PAs, the dust morphology, the HST instrument and filter used, and the angular and physical side length of the box. We mark the dust and galaxy PAs in the image with red and blue lines, respectively, centered on the galaxy position. A solid red line indicates an automatic dust fit, while a dashed red line indicates a manual fit. Radio image: We report the measured jet PA, the survey used, and the angular and physical side length of the box. We mark the center of the galaxy with a blue point and the center of the jet with an orange point. A solid orange line indicates an automatically measured jet PA, while a dashed orange line indicates a manual measurement. Superscripts: These indicate the following adjustments: (a/b) In the optical/radio image, we adjusted the upper limit of the color map, the linear width parameter of the asinh scaling, or both; (c) We cut the optical image to avoid a bright spot or defect; (d) We used the second optical image in the observational table rather than the first.
• Figure 2: Image gallery of the galaxy sample, Part 2/4.
• Figure 3: Image gallery of the galaxy sample, Part 3/4.
• Figure 4: Image gallery of the galaxy sample, Part 4/4.
• Figure 5: Galaxy, dust, and jet PAs from previous papers compared to the PAs measured in this work. The black line marks equality between the literature and measured PAs. The open markers indicate galaxies that fall on the high end of our covered redshift range. For points with literature PA $<15^\circ$ and measured PA $>165^\circ$, or vice versa, we shifted the literature PA by $\pm 180^\circ$ to simplify visual comparison with the measured PA.