Christopher P. O'Dea

To examine how active galactic nucleus (AGN) feedback shapes the intracluster medium (ICM) and fuels black hole accretion in the cool-core galaxy cluster A2597, we present deep (∼600 ks) Chandra X-ray observations complemented by archival GMRT radio and SINFONI near-infrared data. Radio-mode AGN activity has inflated seven X-ray cavities and driven one to three potential weak shocks ( M ∼ 1.05 − 1.14 ) extending to ∼150 kpc, suggesting recurrent outbursts occurring on ∼10 ⁷ yr timescales. We also detect a narrow, ∼57 kpc X-ray surface brightness deficit—a potential plasma depletion layer—likely shaped by residual sloshing motions that amplified magnetic fields and/or displaced gas within the cluster core. Although the AGN injects ∼10 ⁴⁴ erg s ⁻¹ of energy, comparable to the cluster’s cooling luminosity, radiative cooling persists at ∼15 M _⊙ yr ⁻¹ , replenishing the billion-solar-mass cold gas reservoir at the heart of the brightest cluster galaxy. Sustaining this level of activity requires a continuous fuel supply, yet the estimated Bondi accretion power (∼2 × 10 ⁴³ erg s ⁻¹ ) falls an order of magnitude short of the observed cavity power, suggesting that “hot” gas fueling is insufficient. Instead, archival Atacama Large Millimeter/submillimeter Array observations continue to support a chaotic cold accretion scenario, where turbulence-driven condensation fuels the AGN at rates exceeding Bondi accretion, sustaining a self-regulated feedback cycle that repeatedly shapes the core of A2597.

We present a study of quasar host galaxy 3C 297, which is home to a powerful bent-jet radio source suggesting vigorous interaction with a dense interstellar medium (ISM) and/or jet precession. Archival Hubble Space Telescope (HST) imaging showed interestingly perturbed morphology of the host with a bright ∼30 kpc arc feature, extended filamentary structure of line-emitting gas, and clumpy blue excess emission cospatial with the radio hotspots. Our Very Large Telescope (VLA)/SINFONI integral-field observations reveal complex, spatially resolved Hα + [N II] emission in this source. A prominent blueshifted wing in Hα indicates an ionized gas flow extending out to ∼8 kpc from the nuclear region. Combining our SINFONI narrow-Hα data with archival HST/UV and VLA imaging, we map the young stellar population in the host and compare the spatial distribution of star-forming regions with the ionized gas motion and jet structure. In the attempt to characterize the feedback mechanisms in this chaotic system, we suggest that the powerful radio source dominates the feedback, with possible contribution from radiation pressure due to accretion onto the black hole. We also propose that the expanding jet cocoon likely shocked the ISM, triggering a kpc-scale ionized gas outflow and new starbursts that enhanced ongoing merger-induced star formation.

Haystack and Owens Valley Radio Observatory observations recently revealed strong, intermittent, sinusoidal total flux-density variations that maintained their coherence between 1975 and 2021 in the blazar PKS 2131−021 (z = 1.283). This was interpreted as possible evidence of a supermassive black hole binary (SMBHB). Extended observations through 2023 show a coherence over 47.9 yr, with an observed period P _{15 GHz} = (1739.8 ± 17.4) days. We reject, with p-value = 2.09 × 10⁻⁷, the hypothesis that the variations are due to random fluctuations in the red noise tail of the power spectral density. There is clearly a physical phenomenon in PKS 2131−021 producing coherent sinusoidal flux-density variations. We find the coherent sinusoidal intensity variations extend from below 2.7 GHz to optical frequencies, from which we derive an observed period P _optical = (1764 ± 36) days. Across this broad frequency range, there is a smoothly varying monotonic phase shift in the sinusoidal variations with frequency. Hints of periodic variations are also observed at γ-ray energies. The importance of well-vetted SMBHB candidates to searches for gravitational waves is pointed out. We estimate the fraction of blazars that are SMBHB candidates to be >1 in 100. Thus, monitoring programs covering tens of thousands of blazars could discover hundreds of SMBHB candidates.

NGC 5972, a Voorwerp galaxy, features a helical-shaped extended emission-line region (EELR) with a radius >10 kpc and an S-shaped radio structure spanning about 470 kpc. We use the Very Large Telescope, Multi Unit Spectroscopic Explorer, Giant Metrewave Radio Telescope, and Very Large Array (VLA) to study the stellar and ionized gas kinematics and how the radio jet influences the gas in the galaxy. Our sensitive radio observations detect the southern jet for the first time, roughly coinciding with the southern EELR. The VLA images show a continuous inner jet connected to the outer east–west lobe, confirming the jet origin of the radio emission. Our kinematic analysis shows spatial correlations between the radio jet and the outflowing gas, supporting the jet-driven feedback mechanism. More interestingly, we observe enhanced velocity dispersion in the perpendicular direction along with a shell-like structure. Our Baldwin–Phillips–Telervich analysis shows that the [O III] emission overlapping with the radio jet is consistent with the shock+precursor model, whereas in the perpendicular region, a pure shock model fits well with the observations, indicating jet-induced shocks. Radio observations indicate episodic AGN activity characterized by surface brightness and spectral index discontinuities. Overall, based on our findings, we propose a jet-driven feedback mechanism as one of the key factors in the formation of the EELR in NGC 5972. Future high-resolution radio observations will be crucial to further investigate the origin of the EELR and quantify the extent to which the jet influences its formation and evolution.

We present radio polarimetric images of 12 Seyfert and low-ionization nuclear emission-line region (LINER) galaxies belonging to the Centre for Astrophysics +12 μm sample exhibiting kiloparsec-scale radio outflows (KSRs). These observations have been carried out at 10 GHz with the Karl G. Jansky Very Large Array in D array and at 1.4 GHz with the BnA → A array configurations. We find signatures of organized magnetic (B) field structures in the cores, jets, and lobes of these galaxies. The linear polarization fraction varies from a few percent in the cores to 47% ± 18% in the lobes. The inferred B fields are toroidal in the cores of several sources making them consistent with the presence of either a sheath-like or a wind-like component surrounding the jet. The in-band spectral index images typically show the presence of flat/inverted spectrum cores and steep spectrum lobes. Radio cores with flatter spectra are found to have lower Eddington ratios, while the steeper ones have higher. A strong correlation is observed between the Seyfert/LINER radio outflow properties and the mass of the supermassive black holes; correlations with Eddington ratios are weaker. We find signatures of jet-medium interaction and both positive and negative active galactic nuclei (AGN) feedback in these sources. Overall, our study indicates that radio-quiet AGN with KSRs possess radio outflows driven by magnetic fields anchored to their black hole—accretion disk systems, which significantly impact their environments.

Context. The long-standing question concerning jetted subgalactic-size (JSS) radio sources is whether they will evolve into large radio galaxies, die before escaping the host galaxy, or remain indefinitely confined to their compact size. Aims. Our main goal is to propose a scenario that explains the relative number of JSS radio sources and their general properties. Methods. We studied the parsec-scale radio morphology of a complete sample of 21 objects using Very Long Baseline Array (VLBA) observations at various frequencies and analyzed the morphological characteristics of their optical hosts. Results. Many of these radio sources exhibit radio morphologies consistent with transverse motions of their bright edges and are found in dynamically disturbed galaxies. VLBA images suggest the possible presence of large-angle, short-period precessing jets, and an orbital motion of the radio-loud active galactic nucleus (AGN) in a dual or binary system. The majority of JSS radio sources appear to be in systems in different stages of their merging evolution. Conclusions. We propose a scenario where rapid jet redirection, through precession or orbital motion, prevents the jet from penetrating the interstellar medium (ISM) sufficiently to escape the host galaxy. Most JSS radio sources remain compact due to their occurrence in merging galaxies.

Modern wide field radio surveys typically detect millions of objects. Techniques based on machine learning are proving to be useful for classifying large numbers of objects. The self-organizing map (SOM) is an unsupervised machine learning algorithm that projects a many-dimensional dataset onto a two- or three-dimensional lattice of neurons. This dimensionality reduction allows the user to visualize common features of the data better and develop algorithms for classifying objects that are not otherwise possible with large datasets. To this aim, we use the PINK implementation of a SOM. PINK incorporates rotation and flipping invariance so that the SOM algorithm may be applied to astronomical images. In this cookbook we provide instructions for working with PINK, including preprocessing the input images, training the model, and offering lessons learned through experimentation. The problem of imbalanced classes can be improved by careful selection of the training sample and increasing the number of neurons in the SOM (chosen by the user). Because PINK is not scale-invariant, structure can be smeared in the neurons. This can also be improved by increasing the number of neurons in the SOM. We also introduce pyink, a Python package used to read and write PINK binary files, assist in common preprocessing operations, perform standard analyses, visualize the SOM and preprocessed images, and create image-based annotations using a graphical interface. A tutorial is also provided to guide the user through the entire process. We present an application of PINK to VLA Sky Survey (VLASS) images. We demonstrate that the PINK is generally able to group VLASS sources with similar morphology together. We use the results of PINK to estimate the probability that a given source in the VLASS QuickLook Catalogue is actually due to sidelobe contamination.

We present the first systematic search for UV signatures from radio source-driven active galactic nuclei (AGN) feedback in Compact Steep Spectrum (CSS) radio galaxies. Owing to their characteristic sub-galactic jets (1–20 kpc projected linear sizes), CSS hosts are excellent laboratories for probing galaxy scale feedback via jet-triggered star formation. The sample consists of seven powerful CSS galaxies, and two galaxies host to radio sources >20 kpc as the control, at low to intermediate redshifts (z < 0.6). Our new Hubble Space Telescope images show extended UV continuum emission in six out of seven CSS galaxies, with five CSS hosts exhibiting UV knots cospatial and aligned along the radio-jet axis. Young (≲ 10 Myr), massive (≳ 5 M _⊙) stellar populations are likely to be the dominant source of the blue excess emission in radio galaxies at these redshifts. Hence, the radio-aligned UV regions could be attributed to jet-induced starbursts. Lower near-UV star formation rates compared to other indicators suggest low scattered AGN light contribution to the observed UV. Dust attenuation of UV emission appears unlikely from high internal extinction correction estimates in most sources. Comparison with evolutionary synthesis models shows that our observations are consistent with recent (∼1−8 Myr old) star-forming activity likely triggered by current or an earlier episode of radio emission, or by a confined radio source that has frustrated growth, due to a dense environment. While follow-up spectroscopic and polarized light observations are needed to constrain the activity-related components in the observed UV, the detection of jet-induced star formation is a confirmation of an important prediction of the jet feedback paradigm.