Galaxy Jets Consistently Collide with Dust Lanes at Right Angles

Researchers have long sought to understand how active galactic nuclei (AGN) interact with their host galaxies, and a key to unlocking this relationship may lie in the alignment of radio jets and dust structures. Emma Jane Weller and Pieter van Dokkum, both from Yale University, alongside their colleagues, present new findings from Hubble imaging of early-type radio galaxies, utilising an automated method to measure the orientation of dust features classified as lanes, disks or rings. Their study reveals a striking perpendicularity between dust lanes and radio jets, contrasting with the alignment observed in dust disks and rings, suggesting that external factors like gas-rich mergers significantly influence jet direction. This discovery offers valuable insight into how AGN feedback might regulate star formation and maintain the stability of massive galaxies over cosmic timescales.

Experiments reveal that dust lanes, indicative of recent mergers, exhibit a strong preference for being perpendicular to the host galaxy’s radio jets.

Conversely, more stable dust disks and rings tend to align closely with the major axes of their host galaxies, though their orientation relative to the jets varies. This perpendicular alignment of dust lanes and radio jets suggests that infalling dusty material from mergers actively influences the direction of the jet.
The team achieved precise measurements of position angles for both dust features and radio jets in a sample of early-type radio galaxies, utilising data from the HST and the VLA Sky Survey. This breakthrough establishes a potential mechanism for how jet orientation can change over time, driven by external influences like galactic mergers.

The research further supports the idea that AGN feedback plays a crucial role in maintaining quiescence within massive galaxies by regulating star formation. By differentiating between the origins of dust lanes and disks, the study unveils a more nuanced understanding of how galaxies evolve and interact with their central supermassive black holes. The work opens avenues for exploring the complex relationship between accretion processes, jet launching, and the overall evolution of galaxies.

Radio and optical data reduction for dust and jet orientation analysis are essential for understanding astrophysical phenomena

Scientists investigated the relationship between active galactic nuclei and their surrounding environments by meticulously measuring the orientations of radio jets and nuclear dust features in early-type radio galaxies. The study employed data from the NASA/IPAC Extragalactic Database to assemble a sample of 32 galaxies exhibiting clear nuclear dust absorption, ranging in redshift from approximately 0.003 to 0.1.

Galaxies with face-on dust disks or diffuse dust were excluded to ensure accurate position angle measurements. Researchers accessed radio data from the NVSS and FIRST surveys via NASA’s SkyView virtual observatory, prioritising NVSS for extended emission and FIRST for finer detail where available. Optical imaging data was sourced from ACS/HRC, ACS/WFC, and WFPC2/PC instruments.

The team developed an automated image processing procedure, beginning with establishing a brightness threshold at the 99.99th percentile to highlight key features. Photutils was then utilised to identify and characterise the brightest source as the host galaxy, determining its centre and major axis position angle.

To isolate dust features, scientists created a Gaussian model of the galaxy fit and subtracted it from the image, subsequently inverting the result. Applying Photutils with a 10 standard deviation threshold aimed to automatically identify dust, though manual adjustments were frequently necessary due to the irregular nature of the dust.

Radio jet position angles were determined using the Python Blob Detector and Source Finder package, initially identifying the nine brightest sources and selecting the one closest to the galaxy centre. The team prioritised measuring the position angle of the innermost jet, manually correcting measurements when PyBDSF identified larger-scale structures. Angular measurements were converted to physical scales using distances obtained from NED or calculated from redshifts and cosmological parameters established by the Planck Collaboration et al. (2020).

Dust morphology dictates alignment with radio jets in early-type galaxies, suggesting a common origin

Scientists have discovered a compelling relationship between dust features within early-type radio galaxies and the orientation of their radio jets. The research team employed newer Hubble imaging alongside an automated process to meticulously measure position angles, classifying dust features as lanes, disks, or rings.

Measurements reveal that dust lanes exhibit no preferred alignment with their host galaxies, but are preferentially oriented perpendicularly to the radio jets. In contrast, data shows that dust disks and rings consistently align with the major axes of their host galaxies, though their orientation relative to the jets varies.

The team measured position angles to determine these alignments, finding a clear distinction in behaviour between the different dust morphologies. Results demonstrate that the perpendicular alignment of dust lanes and jets occurs consistently across the observed sample. Experiments revealed that infalling dusty material, likely originating from minor mergers, significantly influences the angle of the radio jet.

This suggests a dynamic process where jet orientation can change over time, potentially impacting the role of AGN feedback in maintaining quiescence within massive galaxies. The breakthrough delivers a new understanding of how galactic mergers and accretion events shape the behaviour of active galactic nuclei.

Measurements confirm that the observed alignments are statistically significant, providing strong evidence for the proposed influence of infalling material. Tests prove that this work builds upon previous studies by utilising a larger sample and a more automated measurement technique, enhancing the reliability of the findings.

The study’s data will allow for improved modelling of AGN feedback mechanisms and the evolution of massive galaxies. Further research could explore the implications of these findings for understanding the long-term stability of jet orientation and its impact on galaxy evolution.

Dust morphology reveals merger history and jet orientation relationships in nearby galaxies

Scientists have investigated the alignment between dust features and radio jets in early-type radio galaxies, utilising new Hubble Space Telescope imaging and automated measurement techniques. They classified dust features into three categories: lanes, disks, and rings, recognising that lanes likely originate from gas-rich minor mergers, while disks and rings may form through settling lanes or internal processes.

The research demonstrates a clear distinction in alignment behaviour between these dust types. Dust lanes exhibit a tendency to be perpendicular to the radio jets, with no preferred alignment relative to the host galaxy itself. Conversely, dust disks and rings generally align with the major axes of their host galaxies, though their orientation relative to the jets is more variable.

These findings suggest that infalling material from galaxy mergers can influence the direction of the radio jet, potentially causing it to change over time. This connection between dust features and radio jets may be important for understanding how active galactic nuclei contribute to the maintenance of quiescence in massive galaxies.

The authors acknowledge that their analysis relies on classifying dust features, which can be subjective despite their automated approach. They also note the possibility of both internal and external formation mechanisms for dust disks and rings, which could explain the observed range of alignments. Future research could focus on modelling the dynamics of gas accretion during mergers to better understand how this process affects jet orientation, and on expanding the sample size to include a wider range of galaxy types and merger stages. This work offers valuable insights into the interplay between galactic mergers, dust distribution, and the behaviour of active galactic nuclei.