The AGN fuelling/feedback cycle in nearby radio galaxies - IV. Molecular gas conditions and jet-ISM interaction in NGC 3100

This is the fourth paper of a series investigating the AGN fuelling/feedback processes in a sample of eleven nearby low-excitation radio galaxies (LERGs). In this paper we present follow-up Atacama Large Millimeter/submillimeter Array (ALMA) observations of one source, NGC 3100, targeting the 12CO(1-0), 12CO(3-2), HCO+(4-3), SiO(3-2) and HNCO(6-5) molecular transitions. 12CO(1-0) and 12CO(3-2) lines are nicely detected and complement our previous 12CO(2-1) data. By comparing the relative strength of these three CO transitions, we find extreme gas excitation conditions (i.e. Tex ≳ 50 K) in regions that are spatially correlated with the radio lobes, supporting the case for a jet-ISM interaction. An accurate study of the CO kinematics demonstrates that, although the bulk of the gas is regularly rotating, two distinct non-rotational kinematic components can be identified in the inner gas regions: one can be associated to inflow/outflow streaming motions induced by a two-armed spiral perturbation; the second one is consistent with a jet-induced outflow with vmax ≈ 200 km s−1 and $\dot{M}\lesssim 0.12$ M⊙ yr−1. These values indicate that the jet-CO coupling ongoing in NGC 3100 is only mildly affecting the gas kinematics, as opposed to what expected from existing simulations and other observational studies of (sub-)kpc scale jet-cold gas interactions. HCO+(4-3) emission is tentatively detected in a small area adjacent to the base of the northern radio lobe, possibly tracing a region of jet-induced gas compression. The SiO(3-2) and HNCO(6-5) shock tracers are undetected: this - along with the tentative HCO+(4-3) detection - may be consistent with a deficiency of very dense (i.e. ncrit > 106 cm−3) cold gas in the central regions of NGC 3100.

A population of galaxy-scale jets discovered using LOFAR

ABSTRACT The effects of feedback from high luminosity radio-loud active galactic nuclei (AGN) have been extensively discussed in the literature, but feedback from low-luminosity radio-loud AGN is less well understood. The advent of high sensitivity, high angular resolution, large field-of-view telescopes such as LOFAR is now allowing wide-area studies of such faint sources for the first time. Using the first data release of the LOFAR Two Metre Sky Survey (LoTSS) we report on our discovery of a population of 195 radio galaxies with 150-MHz luminosities between 3 × 1022 and 1.5 × 1025 WHz−1 and total radio emission no larger than 80 kpc. These objects, which we term galaxy-scale jets (GSJ), are small enough to be directly influencing the evolution of the host on galaxy scales. We report upon the typical host properties of our sample, finding that 9 per cent are hosted by spirals with the remainder being hosted by elliptical galaxies. Two of the spiral-hosted GSJ are highly unusual with low radio luminosities and FRII-like morphology. The host properties of our GSJ show that they are ordinary AGN observed at a stage in their life shortly after the radio emission has expanded beyond the central regions of the host. Based on our estimates, we find that about half of our GSJ have internal radio lobe energy within an order of magnitude of the ISM energy so that, even ignoring any possible shocks, GSJ are energetically capable of affecting the evolution of the host. The current sample of GSJ will grow in size with future releases of LoTSS and can also form the basis for further studies of feedback from low-luminosity radio sources.

A rare case of FR I interaction with a hot X-ray bridge in the A2384 galaxy cluster

Clusters of varying mass ratios can merge and the process significantly disturbs the cluster environments and alters their global properties. Active radio galaxies are another phenomenon that can also affect cluster environments. Radio jets can interact with the intra-cluster medium (ICM) and locally affect its properties. Abell 2384 (hereafter A2384) is a unique system that has a dense, hot X-ray filament or bridge connecting the two unequal mass clusters A2384(N) and A2384(S). The analysis of its morphology suggests that A2384 is a post-merger system where A2384(S) has already interacted with the A2384(N), and as a result hot gas has been stripped over a ∼1 Mpc region between the two bodies. We have obtained its 325 MHz GMRT data, and we detected a peculiar FR I type radio galaxy which is a part of the A2384(S). One of its radio lobes interacts with the hot X-ray bridge and pushes the hot gas in the opposite direction. This results in displacement in the bridge close to A2384(S). Based on Chandra and XMM-Newton X-ray observations, we notice a temperature and entropy enhancement at the radio lobe-X-ray plasma interaction site, which further suggests that the radio lobe is changing thermal plasma properties. We have also studied the radio properties of the FR I radio galaxy, and found that the size and radio luminosity of the interacting north lobe of the FR I galaxy are lower than those of the accompanying south lobe.

Spectroscopic properties of radio-loud and radio-quiet quasars

Surveys have shown radio-loud (RL) quasars constitute 10%-15% of the total quasar population and rest are radio-quiet (RQ). However, it is unknown if this radio-loud fraction (RLF) remains consistent among different parameter spaces. This study shows that RLF increases for increasing full width half maximum (FWHM) velocity of the Hβ broad emission line (z < 0.75). To analyse the reason, we compared bolometric luminosity of RL and RQ quasars sample which have FWHM of Hβ broad emission line greater than 15000km/s (High Broad Line or HBL) with which have FWHM of Hβ emission line less than 2500km/s (Low Broad Line or LBL). From the distributions we can conclude for the HBL, RQ and RL quasars are peaking separately and RL quasars are having higher values whereas for the LBL the peaks are almost indistinguishable. We predicted selection effects could be the possible reason but to conclude anything more analysis is needed. Then we compared our result with Wills & Brotherton (1995) and have shown that some objects from our sample do not follow the pattern of the logR vs FWHM plot where R is the ratio of 5 GHz radio core flux density with the extended radio lobe flux density.

The morphological classification of distant radio galaxies explored with three-dimensional simulations

ABSTRACT We explore the observational implications of a large systematic study of high-resolution three-dimensional simulations of radio galaxies driven by supersonic jets. For this fiducial study, we employ non-relativistic hydrodynamic adiabatic flows from nozzles into a constant pressure-matched environment. Synchrotron emissivity is approximated via the thermal pressure of injected material. We find that the morphological classification of a simulated radio galaxy depends significantly on several factors with increasing distance (i.e. decreasing observed resolution) and decreasing orientation often causing reclassification from FR II (limb-brightened) to FR I (limb-darkened) type. We introduce the Lobe or Limb Brightening Index (LBI) to measure the radio lobe type more precisely. The jet density also has an influence as expected with lower density leading to broader and bridged lobe morphologies as well as brighter radio jets. Hence, relating observed source type to the intrinsic jet dynamics is not straightforward. Precession of the jet direction may also be responsible for wide relaxed sources with lower LBI and FR class as well as for X-shaped and double–double structures. Helical structures are not generated because the precession is usually too slow. We conclude that distant radio galaxies could appear systematically more limb darkened due to merger-related redirection and precession as well as due to the resolution limitation.

Radio jet structures at ∼100 pc and larger scales of the γ-ray-emitting narrow-line Seyfert 1 galaxy PMN J0948+0022

The narrow-line Seyfert 1 (NLS1) galaxy PMN J0948+0022 is an archetype of γ-ray-emitting NLS1s in active galactic nuclei (AGNs). In this study, we investigate its radio structures using archival data obtained using the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA). The new VLA images reveal an outermost radio emission separated by 9.1 arcsec. Its resolved structure and steep spectrum suggest a terminal shock in a radio lobe energized by the jet from the PMN J0948+0022 nucleus. This large-scale radio component is found at almost the same position angle as that of the pc-scale jet, indicating a stable jet direction up to ∼1 Mpc. Its apparent one-sidedness implies a moderate advancing speed (β &gt; 0.27). The kinematic age of &lt;1× 107 yr of the jet activity is consistent with the expected NLS1 phase of ∼107 yr in the AGN lifetime. The VLBA image reveals the jet structure at distances ranging from r = 0.82 milliarcsec to 3.5 milliarcsec, corresponding to approximately 100 pc, where superluminal motions were found. The jet width profile (∝ r1.12) and flux-density profile (∝ r−1.44) depending on the distance r along the jet suggest that the jet kinetic energy is converted to internal energy in this region. The jet is causally connected in a nearly conical streamline, which is supported by ambient pressure at 100 pc scales in the host galaxy of PMN J0948+0022.

The Extraordinary Linear Polarisation Structure of the Southern Centaurus A Lobe Revealed by ASKAP

We present observations of linear polarisation in the southern radio lobe of Centaurus A, conducted during commissioning of the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. We used 16 antennas to observe a 30 square degree region in a single 12-h pointing over a 240 MHz band centred on 913 MHz. Our observations achieve an angular resolution of 26 × 33 arcseconds (480 parsecs), a maximum recoverable angular scale of 30 arcminutes, and a full-band sensitivity of 85 μ Jy beam − 1 . The resulting maps of polarisation and Faraday rotation are amongst the most detailed ever made for radio lobes, with order 10 5 resolution elements covering the source. We describe several as-yet unreported observational features of the lobe, including its detailed peak Faraday depth structure, and intricate networks of depolarised filaments. These results demonstrate the exciting capabilities of ASKAP for widefield radio polarimetry.

FUV line emission, gas kinematics, and discovery of [Fe XXI] λ1354.1 in the sightline toward a filament in M87

We present new Hubble Space Telescope – Cosmic Origins Spectrograph (HST-COS) G130M spectroscopy which we have obtained for a sightline toward a filament projected 1.9 kpc from the nucleus of M87, near the edge of the inner radio lobe to the east of the nucleus. The combination of the sensitivity of COS and the proximity of M87 allows us to study the structure of this filament in unparalleled detail. We propose that the filament is composed of many cold clumps, each surrounded by an FUV-emitting boundary layer, with the filament having a radius rc ~ 10 pc and the clumps filling the cylinder with a low volume filling factor. The observed velocity dispersion in emission lines from the filament results from the random motions of these clumps within the filament. We have measured fluxes and kinematics for emission lines of Lyα, C II λ1335, and N V λ1238, finding vr = 147 ± 2 km s−1, 138 ± 18 km s−1, and 148−16+14 km s−1 relative to M87, and line broadenings σr = 171 ± 2 km s−1, 189−11+12 km s−1, and 128−17+23 km s−1 respectively. We associate these three lines, as well as archival measurements of Hα, C IV λ1549, and He II λ1640, with a multitemperature boundary layer around clumps which are moving with supersonic random motions in the filament. This boundary layer is a significant coolant of the hot gas. We show that the [C II] λ158 μm flux observed by Herschel-PACS from this region implies the existence of a massive cold (T ~ 103 K) component in the filament which contains significantly more mass (M ~ 8000 M⊙ within our r ≈ 100 pc sightline) than the FUV-emitting boundary layer. It has about the same bulk velocity and velocity dispersion as the boundary layer. We also detect [Fe XXI] λ1354 in emission at 4−5σ. This line is emitted from 1 keV (T ≈ 107 K) plasma, and we use it to measure the bulk radial velocity vr = −92−22+34 km s−1 and velocity dispersion σr = 69−27+79 km s−1 of the plasma at this temperature. In contrast to the intermediate-temperature FUV lines, [Fe XXI] is blueshifted relative to M87 and matches the bulk velocity of a nearby filament to the south. We hypothesize that this line arises from the approaching face of the radio bubble expanding through this sightline, while the filament lies on the receding side of the bubble. A byproduct of our observations is the detection of absorption from interstellar gas in our Galaxy, observed in C II λ1335 and Lyα.

The 500 ks Chandra observation of the z = 6.31 QSO SDSS J1030 + 0524

We present the results from a ~ 500 ks Chandra observation of the z = 6.31 QSO SDSS J1030 + 0524. This is the deepest X-ray observation to date of a z ~ 6 QSO. The QSO is detected with a total of 125 net counts in the full (0.500A0–7 keV) band and its spectrum can be modeled by a single power-law model with photon index of Γ = 1.81 ± 0.18 and full band flux of f = 3.95 × 10−15 erg s−1 cm−2. When compared with the data obtained by XMM-Newton in 2003, our Chandra observation in 2017 shows a harder (ΔΓ ≈ −0.6) spectrum and a 2.5 times fainter flux. Such a variation, in a timespan of ~ 2 yr rest-frame, is unexpected for such a luminous QSO powered by a > 109M⨀ black hole. The observed source hardening and weakening could be related to an intrinsic variation in the accretion rate. However, the limited photon statistics does not allow us to discriminate between an intrinsic luminosity and spectral change, and an absorption event produced by an intervening gas cloud along the line of sight. We also report the discovery of diffuse X-ray emission that extends for 30″ × 20″ southward of the QSO with a signal-to-noise ratio (S/N) of approximately six, hardness ratio of HR = 0.03+0.20−0.25, and soft band flux of f0.5– keV = 1.1+0.3−0.3 × 10−15 erg s−1 cm−2 , that is not associated to a group or cluster of galaxies. We discuss two possible explanations for the extended emission, which may be either associated with the radio lobe of a nearby, foreground radio galaxy (at z ≈ 1 – 2), or ascribed to the feedback from the QSO itself acting on its surrounding environment, as proposed by simulations of early black hole formation.