Radio Jet Research Articles

RadioSED I: Bayesian inference of radio SEDs from inhomogeneous surveys

Abstract We present here RadioSED, a Bayesian inference framework tailored to modelling and classifying broadband radio spectral energy distributions (SEDs) using only data from publicly-released, large-area surveys. We outline the functionality of RadioSED, with its focus on broadband radio emissions which can trace kiloparsec-scale absorption within both the radio jets and the circumgalactic medium of Active Galactic Nuclei (AGN). In particular, we discuss the capability of RadioSED to advance our understanding of AGN physics and composition within youngest and most compact sources, for which high resolution imaging is often unavailable. These young radio AGN typically manifest as peaked spectrum (PS) sources which, before RadioSED, were difficult to identify owing to the large, broadband frequency coverage typically required, and yet they provide an invaluable environment for understanding AGN evolution and feedback. We discuss the implementation details of RadioSED, and we validate our approach against both synthetic and observational data. Since the surveys used are drawn from multiple epochs of observation, we also consider the output from RadioSED in the context of AGN variability. Finally, we show that RadioSED recovers the expected SED shapes for a selection of well-characterised radio sources from the literature, and we discuss avenues for further study of these and other sources using radio SED fitting as a starting point. The scalability and modularity of this framework make it an exciting tool for multiwavelength astronomers as next-generation telescopes begin several all-sky surveys. Accordingly, we make the code for RadioSED, which is written in python, available on Github.

JWST Reveals Powerful Feedback from Radio Jets in a Massive Galaxy at z = 4.1

We report observations of a powerful ionized gas outflow in the z = 4.1 luminous radio galaxy TNJ1338-1942 hosting an obscured quasar using the Near Infrared Spectrograph (NIRSpec) on board JWST. We spatially resolve a large-scale (∼15 kpc) outflow and measure outflow rates. The outflowing gas shows velocities exceeding 900 km s−1 and broad line profiles with widths exceeding 1200 km s−1 located at an ∼10 kpc projected distance from the central nucleus. The outflowing nebula spatially overlaps with the brightest radio lobe, indicating that the powerful radio jets are responsible for the outflow kinematics. The gas is possibly ionized by the obscured quasar with a contribution from shocks induced by the jets. The mass outflow rate map shows that the region with the broadest line profiles exhibits the strongest outflow rates. The total mass outflow rate is ∼500 M ⊙ yr−1, and the mass loading factor is ∼1, indicating that a significant part of the gas is displaced outwards by the outflow. Our hypothesis is that the overpressured shocked jet fluid expands laterally to create an expanding ellipsoidal “cocoon” that causes the surrounding gas to accelerate outwards. The total kinetic energy injected by the radio jet is about 3 orders of magnitude larger than the energy in the outflowing ionized gas. This implies that kinetic energy must be transferred inefficiently from the jets to the gas. The bulk of the deposited energy possibly lies in the form of hot X-ray-emitting gas.

An IXPE-led X-Ray Spectropolarimetric Campaign on the Soft State of Cygnus X-1: X-Ray Polarimetric Evidence for Strong Gravitational Lensing

We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.

A high-resolution radio morphology and polarization of the kiloparsec-scale X-ray jet of PKS 1127−145

We report on new multifrequency Very Large Array (VLA) radio observations and Chandra X-ray observations of a radio-loud quasar with a ∼300 kpc-long jet, PKS 1127−145, during a flaring event detected in γ-rays by the Fermi Large Area Telescope in December 2020. The high angular resolution of the new radio images allows us to disentangle for the first time the kiloparsec-scale inner jet from the core contribution. The inner radio jet, up to 15 kpc from the core, is highly polarized (33 percent) and the magnetic field is parallel to the jet axis. At about 18 arcsecs from the core, the jet slightly bends and we observe a re-brightening of the radio emission and a 90-degree rotation of the magnetic field, likely highlighting the presence of a shock that is compressing the magnetic field to a plane perpendicular to the jet axis, where efficient particle acceleration takes place. At the same position, the X-ray emission fades, suggesting a deceleration of the bulk velocity of the jet after the bend. A change in velocity and collimation of the jet is supported by the widening of the jet profile and the detection of a limb-brightened structure connecting the bending region with the jet termination. The limb-brightened structure might indicate the coexistence of both longitudinal and transverse velocity gradients at the jet bending. There is no evidence of significant brightening of the kiloparsec-scale jet in the radio or X-ray band during the γ-ray flare. The X-ray flux, F2 − 10 keV = (6.24 ± 0.57)×10−12 ergs s−1 cm−2, measured by Chandra from the quasar core is consistent with the flux measured by the X-ray Telescope on board the Neil Gehrels Swift Observatory after the high-energy flare. Our results indicate that the γ-ray flaring region is located within the VLA source core.

A Hot Core in the Group-dominant Elliptical Galaxy NGC 777

NGC 777 provides an example of a phenomenon observed in some group-central ellipticals, in which the temperature profile shows a central peak, despite the short central cooling time of the intragroup medium. We use deep Chandra X-ray observations of the galaxy, supported by uGMRT 400 MHz radio imaging, to investigate the origin of this hot core. We confirm the centrally peaked temperature profile and find that the entropy and cooling time both monotonically decline to low values (2.62 −0.18+0.19 keV cm2 and 71.3−13.1+12.8 Myr, respectively) in the central ∼700 pc. Faint diffuse radio emission surrounds the nuclear point source, with no clear jets or lobes but extending to ∼10 kpc on the northwest–southeast axis. This alignment and extent agree well with a previously identified filamentary Hα + [N ii] nebula. While cavities are not firmly detected, we see X-ray surface brightness decrements on the same axis at 10–20 kpc radii, which are consistent with the intragroup medium having been pushed aside by expanding radio lobes. Any such outburst must have occurred long enough ago for lobe emission to have faded below detectability. Cavities on this scale would be capable of balancing radiative cooling for at least ∼240 Myr. We consider possible causes of the centrally peaked temperature profile, including gravitational heating of gas as the halo relaxes after a period of active galactic nucleus jet activity, and heating by particles leaking from the remnant relativistic plasma of the old radio jets.

Non-thermal emission from microquasar jets: The case of GRS 1915+105

Microquasars (μQs) represent a prominent population of Galactic sources, from which broadband non-thermal emission was detected. At present, the potential of μQs as sources of gamma-ray emission is poorly understood and constrained. In most cases, even the power of μQ jets remains largely uncertain, and this hinders the study of gamma-ray generation in these sources. Using observational data obtained in the radio band, we derive an estimate of the jet power in one of the most famous Galactic μQ, in GRS 1915+105. Compared to other studies of this subject, we additionally consider constraints related to the energy dissipated at internal shocks in the jet, the conditions at which are obtained using properties of the radio blobs detected in the jets. We show that even if one subtracts the rest-energy of matter in the jet, the jet power in this source should be very high, 1039ergs−1, or even higher. The properties of the detected radio emission favor jets with a Gauss-strength magnetic field at parsec distances from the black hole. Such a strong magnetic field should suppress inverse Compton (IC) emission from relativistic electrons, at least from parsec-scale jet. On the other hand, this strong magnetic field makes μQ jets perfect proton accelerators. If present, protons should easily be accelerated in the ultra-high-energy regime. However, due to a diluted target, protons should not lose a notable fraction of their energy in the jet, injected into the interstellar medium at the jet termination. This should significantly enhance the density of cosmic rays in the vicinity of GRS 1915+105. This may manifest itself as an extended gamma-ray source or as several compact sources if the target gas has a highly inhomogeneous distribution. This analysis has direct implication for studying Galactic μQ with such gamma-ray observatories as LHAASO, CTA, and SWGA in the next decades.

JWST/NIRSpec and MIRI observations of an expanding, jet-driven bubble of warm H2 in the radio galaxy 3C 326 N

The physical link between AGN activity and the suppression of star formation in their host galaxies is one of the major open questions of the AGN feedback scenario. The Spitzer space mission revealed a subset of powerful nearby radio galaxies with unusually bright line emission from warm ($T 100$ K) molecular hydrogen, while typical star-formation tracers such as polycyclic aromatic hydrocarbons (PAHs) or a dust continuum have been exceptionally faint or undetected. Here, we present JWST NIRSpec and MIRI MRS IFU observations of one of the best studied galaxies of this class, 3C 326 N at z=0.09. We identified a total of 19 lines of the S, O, and Q series of ro-vibrational H$_2$ emission with NIRSpec at a 0.11 spatial resolution, probing a small quantity odot $) of gas at temperatures of $T 1000$ K. We also mapped the rotational mid-infrared lines of H$_2$ 0--0 S(3), S(5), and S(6) at a spatial resolution of 0.4 with MIRI/MRS, probing most of the $2 odot $ of warm H$_2$ in this galaxy. The CO band heads show a stellar component consistent with a 'slow-rotator' that is typical of a massive ($3 $\,M$_ galaxy, offering a reliable systemic redshift of $z=0.08979 0.0003$. The extended line emission shows a bipolar bubble expanding through the molecular disk at velocities of up to $, delineated by several bright clumps along the northern outer rim, potentially coming from gas fragmentation. Throughout the disk, H$_2$ is very broadly dispersed, with an FWHM of $ 100-1300$ km $ and complex, dual-component Gaussian line profiles. The extended FeII lambda 1.644 and Paalpha follow the same morphology, however NeIII lambda 15.56 is more symmetric about the nucleus. We show that most of the gas (with the exception of NeIII lambda 15.56) is predominantly heated by shocks driven by the radio jets into the gas, both for the ro-vibrational and rotational H$_2$ lines. In addition, the accompanying line broadening is sufficient to suppress star formation in the molecular gas. We also compared the morphology and kinematics of the rotational and ro-vibrational lines, finding the latter to be a good proxy to the global morphology and kinematic properties of the former in strongly turbulent environments. This demonstrates the potential of using the higher frequency ro-vibrational lines in studying turbulent molecular gas. Provided they are bright enough, they would allow us to examine turbulence in galaxies during the early phases of cosmic history, while most rotational lines are red-shifted out of the MIRI bandpass for $z ge1.5$

Astrophysical and relativistic modeling of the recoiling black hole candidate in quasar 3C 186

The compact object in quasar 3C 186 is one of the most promising recoiling black hole candidates, exhibiting both an astrometric displacement between the quasar and the host galaxy as well as a spectroscopic shift between broad and narrow lines. 3C 186 also presents a radio jet that, when projected onto the plane of the sky, appears to be perpendicular to the quasar-galaxy displacement. Assuming a gravitational-wave kick is indeed responsible for the properties of 3C 186 and using state-of-the-art relativistic modeling, we show that current observations allow for exquisite modeling of the recoiling black hole. Most notably, we find that the kick velocity and the black hole spin are almost collinear with the line of sight and the two former vectors appear perpendicular to each other only because of a strong projection effect. The targeted configuration requires substantial fine-tuning: while there is a region in the black hole binary parameter space that is compatible with 3C 186, the observed system appears to be a rare occurrence. Using archival radio observations, we explored different strategies that could potentially confirm or rule out our interpretation. In particular, we developed two observational tests that rely on the brightness ratio between the approaching and receding jet as well as the asymmetry of the jet lobes. While the available radio data provide loose constraints, deeper observations have the unique potential of unveiling the nature of 3C 186.

The LOFAR – eFEDS survey: The incidence of radio and X-ray AGN and the disk–jet connection

Context. Radio jets are present in a diverse sample of AGN. However, the mechanisms of jet powering are not fully understood, and it remains unclear to what extent they obey mass-invariant scaling relations similar to those found for the triggering and fuelling of X-ray-selected AGN. Aims. We use the multi-wavelength data in the eFEDS field observed by eROSITA/Spectrum-Roentgen-Gamma (SRG) and LOFAR to study the incidence of X-ray and radio AGN as a function of several stellar mass (M*)-normalised AGN power indicators. Methods. From the LOFAR – eFEDS survey, we defined a new sample of radio AGN, with optical counterparts from Legacy Survey DR9, according to a radio-excess relative to their host star formation rate. We further divided the sample into compact and complex radio morphologies. In this work, we used the subset matching to the well-characterised, highly complete spectroscopic GAMA09 galaxies (0 < z < 0.4). We release this value-added LOFAR – eFEDS catalogue*. We calculated the fraction of GAMA09 galaxies hosting radio, X-ray, and both radio and X-ray AGN as functions of the specific black hole kinetic (λJet) and radiative (λEdd) power. Results. Despite the soft-X-ray eROSITA-selected sample, the incidence of X-ray AGN as a function of λEdd shows the same mass-invariance and power law slope (−0.65) as that found in previous studies once corrected for completeness. Across the M* range probed, the incidence of compact radio AGN as a function of λJet is described by a power law with constant slope, showing that it is not only high mass galaxies hosting high power jets and vice versa. This slope is steeper than that of the X-ray incidence, which has a value of around −1.5. Furthermore, higher-mass galaxies are more likely to host radio AGN across the λJet range, indicating some residual mass dependence of jet powering. Upon adding complex radio morphologies, including 34 FRIIs, three of which are giant radio galaxies, the incidence not only shows a larger mass dependence but also a jet power dependence, being clearly boosted at high λJet values. Importantly, the latter effect cannot be explained by such radio AGN residing in more dense environments (or more massive dark matter haloes). The similarity in the incidence of quiescent and star-forming radio AGN reveals that radio AGN are not only found in “red and dead” galaxies. Overall, our incidence analysis reveals some fundamental statistical properties of radio AGN samples, but highlights open questions regarding the use of a single radio luminosity–jet power conversion. We explore how different mass and accretion rate dependencies of the incidence can explain the observed results for varying disk–jet coupling models.

Evidence of a toroidal magnetic field in the core of 3C 84

The spatial scales of relativistic radio jets, probed by relativistic magneto-hydrodynamic (RMHD) jet launching simulations and by most very long baseline interferometry (VLBI) observations differ by an order of magnitude. Bridging the gap between these RMHD simulations and VLBI observations requires selecting nearby active galactic nuclei (AGN), the parsec-scale region of which can be resolved. The radio source 3C 84 is a nearby bright AGN fulfilling the necessary requirements: it is launching a powerful, relativistic jet powered by a central supermassive black hole, while also being very bright. Using 22 GHz globe-spanning VLBI measurements of 3C 84 we studied its sub-parsec region in both total intensity and linear polarisation to explore the properties of this jet, with a linear resolution of ∼0.1 parsec. We tested different simulation set-ups by altering the bulk Lorentz factor Γ of the jet, as well as the magnetic field configuration (toroidal, poloidal, helical). We confirm the persistence of a limb brightened structure, which reaches deep into the sub-parsec region. The corresponding electric vector position angles (EVPAs) follow the bulk jet flow inside but tend to be orthogonal to it near the edges. Our state-of-the-art RMHD simulations show that this geometry is consistent with a spine-sheath model, associated with a mildly relativistic flow and a toroidal magnetic field configuration.

Faraday rotation as a probe of radio galaxy environment in RMHD AGN jet simulations

Abstract Active galactic nuclei (AGN) play an integral role in galaxy formation and evolution by influencing galaxies and their environments through radio jet feedback. Historically, interpreting observations of radio galaxies and quantifying radio jet feedback has been challenging due to degeneracies between their physical parameters. In particular, it is well-established that different combinations of jet kinetic power and environment density can yield indistinguishable radio continuum properties, including apparent size and Stokes I luminosity. We present an approach to breaking this degeneracy by probing the line-of-sight environment with Faraday rotation. We study this effect in simulations of three-dimensional relativistic magnetohydrodynamic AGN jets in idealised environments with turbulent magnetic fields. We generate synthetic Stokes I emission and Faraday rotation measure (RM) maps, which enable us to distinguish between our simulated sources. We find enhanced RMs near the jet head and lobe edges. We show that increasing the environment density and the average cluster magnetic field strength broadens the distribution of Faraday rotation measure values. We study the depolarisation properties of our sources, finding that the hotspot regions depolarise at lower frequencies than the lobes. We quantify the effect of depolarisation on the RM distribution, finding that the frequency at which the source is too depolarised to measure the RM distribution accurately is a probe of environmental properties. This technique offers a range of new opportunities for upcoming surveys, including probing radio galaxy environments and determining more accurate estimates of the AGN feedback budget.

Possible jet contribution to the gamma-ray luminosity in NGC 1068

NGC\,1068 is a nearby, widely studied Seyfert II galaxy presenting radio, infrared, X-ray, and gamma -ray emission, along with strong evidence for high-energy neutrino emission. Recently, the evidence for neutrino emission was explained in a multimessenger model, whereby the neutrinos originate from the corona of the active galactic nucleus (AGN). In this environment, gamma -rays are strongly absorbed, so that an additional contribution is necessar, for instance, from the circumnuclear starburst ring. In this work, we discuss whether the radio jet can be an alternative source of the gamma -rays between about $0.1$ and $100$ GeV, as observed by Fermi-LAT. In particular, we include both leptonic and hadronic processes, namely,\ accounting for inverse Compton emission and signatures from $pp$ as well as $p interactions. In order to constrain our calculations, we used VLBA and ALMA observations of the radio knot structures, which are spatially resolved at different distances from the supermassive black hole (SMBH). Our results show that the best leptonic scenario for the prediction of the Fermi-LAT data is provided by the radio knot closest to the central engine. For that to be the case, a magnetic field strength of $ mG $ is needed as well as a strong spectral softening of the relativistic electron distribution at $(1-10)\ GeV $. However, we show that neither such a weak magnetic field strength, nor such a strong softening is expected for that knot. A possible explanation for the sim 10 GeV gamma -rays could potentially be provided by hadronic pion production in case of a gas density $ cm $. Nonetheless, this process is not found to contribute significantly to the low-energy end of the Fermi-LAT range. We conclude that the emission sites in the jet are not sufficient to explain the gamma -rays across the whole Fermi-LAT energy band.

Feedback and ionized gas outflows in four low-radio power AGN at z ∼ 0.15

An increasing number of observations and simulations suggests that low-power (< 1044 erg s−1) jets may be a significant channel of feedback produced by active galactic nuclei (AGN), but little is known about their actual effect on their host galaxies from the observational point of view. We targeted four luminous type 2 AGN hosting moderately powerful radio emission (∼1044 erg s−1), two of which and possibly a third are associated with jets, with optical integral field spectroscopy observations from the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) to analyze the properties of their ionized gas as well as the properties and effects of ionized outflows. We combined these observations with Very Large Array (VLA) and e-MERLIN data to investigate the relations and interactions between the radio jets and host galaxies. We detected ionized outflows as traced by the fast bulk motion of the gas. The outflows extended over kiloparsec scales in the direction of the jet, when present. In the two sources with resolved radio jets, we detected a strong enhancement in the emission-line velocity dispersion (up to 1000 km s−1) perpendicular to the direction of the radio jets. We also found a correlation between the mass and the energetics of this high-velocity dispersion gas and the radio power, which supports the idea that the radio emission may cause the enhanced turbulence. This phenomenon, which is now being observed in an increasing number of objects, might represent an important channel for AGN feedback on galaxies

The Intrinsic Sizes of Odd Radio Circles

A new class of sources, the so-called odd radio circles (ORCs), have been discovered by recent sensitive, large-area radio continuum surveys. The distances of these sources have so far relied on photometric redshifts of optical galaxies found at the centers of or near ORCs. Here we present Gemini rest-frame optical spectroscopy of six galaxies at the centers of, or potentially associated with, the first five ORC discoveries. We supplement this with Legacy Survey imaging and Prospector fits to their griz+W1/W2 photometry. Of the three ORCs with central galaxies, all lie at distances (z = 0.27–0.55) that confirm the large intrinsic diameters of the radio circles (300–500 kpc). The central galaxies are massive (M * ∼ 1011 M ☉), red, unobscured ellipticals with old (≳1 Gyr) stellar populations. They have LINER spectral types that are shock-powered or active galactic nucleus (AGN)-powered. All three host low-luminosity, radio-quiet AGN. The similarity of their central galaxies is consistent with a common origin, perhaps as a blast wave from an ancient starburst. The other two ORCs are adjacent and have no prominent central galaxies. However, the z = 0.25 disk galaxy that lies between them hosts a Type 2, moderate-luminosity AGN. They may instead be the lobes of a radio jet from this AGN.

On the Origin of the X-Ray Emission in Heavily Obscured Compact Radio Sources

X-ray continuum emission of active galactic nuclei (AGNs) may be reflected by circumnuclear dusty tori, producing prominent fluorescence iron lines at X-ray frequencies. Here, we discuss the broadband emission of three radio-loud AGNs belonging to the class of compact symmetric objects (CSOs), with detected narrow Fe Kα lines. CSOs have newly born radio jets, forming compact radio lobes with projected linear sizes of the order of a few to hundreds of parsecs. We model the radio-to-γ-ray spectra of compact lobes in J1407+2827, J1511+0518, and J2022+6137, which are among the nearest and the youngest CSOs known to date, and are characterized by an intrinsic X-ray absorbing column density of N H > 1023 cm−2. In addition to the archival data, we analyze the newly acquired Chandra X-ray Observatory and Submillimeter Array (SMA) observations, and also refine the γ-ray upper limits from Fermi Large Area Telescope monitoring. The new Chandra data exclude the presence of the extended X-ray emission components on scales larger than 1.″5. The SMA data unveil a correlation between the spectral index of the electron distribution in the lobes and N H, which can explain the γ-ray quietness of heavily obscured CSOs. Based on our modeling, we argue that the inverse-Compton emission of compact radio lobes may account for the intrinsic X-ray continuum in all these sources. Furthermore, we propose that the observed iron lines may be produced by a reflection of the lobes’ continuum from the surrounding cold dust.

GOALS-JWST: Gas Dynamics and Excitation in NGC 7469 Revealed by NIRSpec

We present new JWST NIRSpec integral field spectroscopy (IFS) data for the luminous infrared galaxy NGC 7469, a nearby (70.6 Mpc) active galaxy with a Seyfert 1.5 nucleus that drives a highly ionized gas outflow and a prominent nuclear star-forming ring. Using the superb sensitivity and high spatial resolution of the JWST instrument NIRSpec IFS, we investigate the role of the Seyfert nucleus in the excitation and dynamics of the circumnuclear gas. Our analysis focuses on the [Fe ii], H2, and hydrogen recombination lines that trace the radiation/shocked-excited molecular and ionized interstellar medium around the active galactic nucleus (AGN). We investigate gas excitation through H2/Brγ and [Fe ii]/Paβ emission line ratios and find that photoionization by the AGN dominates within the central 300 pc of the galaxy except in a small region that shows signatures of shock-heated gas; these shock-heated regions are likely associated with a compact radio jet. In addition, the velocity field and velocity dispersion maps reveal complex gas kinematics. Rotation is the dominant feature, but we also identify noncircular motions consistent with gas inflows as traced by the velocity residuals and the spiral pattern in the Paα velocity dispersion map. The inflow is 2 orders of magnitude higher than the AGN accretion rate. The compact nuclear radio jet has enough power to drive the highly ionized outflow. This scenario suggests that the inflow and outflow are in a self-regulating feeding–feedback process, with a contribution from the radio jet helping to drive the outflow.

Identification of the optical emission detected by Gaia with radio structures in parsec-scale active galactic nucleus jets

Aims. We investigated the location of the optical emission with respect to the parsec-scale radio structure and attempted to identify whether the optical centroid is coincident with the radio core or a radio component of the jet. Methods. We used optical Gaia DR3 and 8 GHz ICRF3 positions and a model fitting of 15 GHz imaging by the MOJAVE VLBA survey for 422 sources, mostly blazars. We searched for possible associations between optical centroids and radio components. We also compared the astrometric and photometric properties of each category, looked for trends between the various source parameters, and discussed possible biases. Results. Sources can be separated into four categories based on whether their optical centroid (i) falls onto the radio core (category C), (ii) lies close to the base of the jet (category B), (iii) coincides with a radio component downstream in the jet (category J), or (iv) is not found to coincide with a detected radio component (category O). Due to a number of random and systematic errors, the number of sources falling into each category remains approximate but close to 32%, 36%, 22%, and 10%, respectively. The family of quasars, mostly flat spectrum radio quasars (FSRQs), clearly dominates the C and B categories, with their percentage decreasing from categories C to O. Conversely, the family of BL Lacs is spread over the four classes and dominates the category O. Radio galaxies are mainly in classes O and J, and the radio-loud narrow-line Seyfert 1 all belong to class C. An individual analysis of O sources shows that, despite the absence of a direct association with a specific radio component, the optical Gaia centroid is globally related to the radio VLBI jet structure. Conclusions. Our study shows that the spatial distribution of the optical counterparts seen by Gaia below the 0.2-arcsec scale around the radio cores appears in the vast majority of cases to be related to the AGN core or to its jet, with most of them located downstream in the jet. Those associated to the core also exhibit a bluer color index, suggesting a possible contribution of the accretion disk to the optical emission, while those associated to a radio knot in the jet appear redder and tend on average to be found in more polarized radio sources. Most BL Lacs have their optical emission coincident with the jet base or a knot in the jet, while sources with an optical emission on or close to the radio core are mostly FSRQs. Radio components associated with the optical centroid at the jet base or along the jet are mainly stationary or quasi-stationary features, with low apparent MOJAVE velocities. There are indications that the apparent proper motion of the Gaia centroids may be higher than the speed of the associated radio components, but the significance of this trend requires further investigation.

FAUST

Context. The origin of the chemical diversity observed around low-mass protostars probably resides in the earliest history of these systems. Aims. We aim to investigate the impact of protostellar feedback on the chemistry and grain growth in the circumstellar medium of multiple stellar systems. Methods. In the context of the ALMA Large Program FAUST, we present high-resolution (50 au) observations of CH3OH, H2CO, and SiO and continuum emission at 1.3 mm and 3 mm towards the Corona Australis star cluster. Results. Methanol emission reveals an arc-like structure at ∼1800 au from the protostellar system IRS7B along the direction perpendicular to the major axis of the disc. The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B. The region inside the cone is probed by H2CO, while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer. Taking into account the association with a previously detected radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process. For each cavity wall, we derive an average H2 column density of ∼7 × 1021 cm−2, a mass of ∼9 × 10−3 M⊙, and a lower limit on the dust spectral index of 1.4. Conclusions. These observations provide the first evidence of a shock and a conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar System analogues.

Formation of Limb-brightened Radio Jets by Angle-dependent Energy Extraction from Rapidly Rotating Black Holes

Using general relativistic magnetohydrodynamic simulations, it has been suggested that the rotational energy of a rapidly rotating black hole (BH) is preferentially extracted along the magnetic field lines threading the event horizon in the middle and lower latitudes. Applying this angle-dependent Poynting flux to the jet downstream, we demonstrate that the jets exhibit limb-brightened structures at various viewing angles, as observed from Mrk 501, M87, and Cyg A between 5° and 75°, and that the limb brightening is enhanced when the jet is collimated strongly. It is also found that the jet width perpendicular to the propagation direction shrinks at the projected distance of the altitude where the jet collimates from a conical shape (near the BH) to a parabolic one (in the jet). Comparing with Very Long Baseline Interferometry observations, we show that this collimation takes place within the deprojected altitude of 100 Schwarzschild radii from the BH in the case of the M87 jet.

Alignments in the orientation of radio jets from AGN and their host galaxies

It is well established that active galactic nuclei (AGNs) play an important role in the evolution of galaxies. These AGNs can be linked to the accretion processes onto massive black holes and past merger events in their host galaxies, which may lead to different alignments of the jets with respect to the host galaxies. This paper presents a study of the position angle (PA) differences between radio and optical images of radio-AGNs based on the second data release (DR2) of the Low Frequency Array (LOFAR) Two-Meter Sky Survey (LoTSS), the Karl G. Jansky Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters Survey (FIRST), the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys, and the Sloan Digital Sky Survey (SDSS). We assessed PA measurement biases in the data and classified the radio-AGNs based on the radio luminosity and infrared colour from the Wide-field Infrared Survey Explorer (WISE). This resulted in the largest sample of radio AGNs with reliable radio and optical PA measurements published to date, with a total of 3682 AGNs. The PA difference (dPA) distributions for the radio-AGN sample show a prominent minor-axis alignment tendency. Based on some simple assumptions, we simulated the projection effect to estimate the intrinsic jet--galaxy alignment. The observed dPA distribution can be well described by a two-component jet-alignment model in which one component is more aligned with the minor axis of the host galaxy than the other. The fitting results indicate that the jet alignment is dependent on radio luminosity and the shape of the host galaxies, with the jets being more likely to be aligned with the minor axis of the galaxy for lower radio luminosity and for optically more elongated radio-AGNs. The minor-axis alignment of the entire sample may suggest a coherent accretion model present in most AGN host galaxies, while a considerable number of luminous radio-AGNs with massive host galaxies might have undergone accretion ---according to the chaotic model--- or past merger events.