Based on images from the FIRST survey of the radio sky at 1.4 GHz, the positions of $\sim$5200 hotspots in $\sim$2870 radio galaxies and quasars were compiled, and linear sizes and radio luminosities were derived from the hosts redshifts. For a subsample of $\sim$2100 radio sources with exactly one hotspot in each of the two opposite lobes, their geometry in terms of asymmetry and bending was studied. The known (weak) tendency for the brighter lobe (here hotspot) to lie closer to the host than the fainter one, is confirmed. The median bending angle between the two arms of radio sources is 4.8$^{\circ}$ with a significant difference in the distribution between the 627 quasar hosts and the 1501 galaxies.
Hotspots of radio galaxies are regions of shock-driven particle acceleration. Multiple hotspots have long been identified as potential indicators of jet movement or precession. Two frequent explanations describe a secondary hotspot as either the location of a prior jet termination point, or a deflected backflow-driven shock: the so-called Dentist's Drill and Splatter Spot models. We created high-resolution simulations of precessing jets with a range of parameters. In addition to the existing mechanisms, our results show three additional mechanisms for multiple hotspot formation: (1) the splitt…
The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ~3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepe…
In an effort to understand the cause of the apparent depletion in the number density of radio-loud AGNs at $z>3$, this work investigates the viability of the so-called Cosmic Microwave Background (CMB) quenching mechanism of intrinsically jetted, high-z AGNs, whereby Inverse Compton scattering of CMB photons off electrons within the extended lobes results in a substantial dimming of the lobe synchrotron emission at GHz frequencies, while simultaneously boosting their diffuse X-ray signal. We focus on five $z>3.5$ radio galaxies that have sufficiently deep Chandra exposure (> 50 ks) to warrant …
We present JWST/MIRI MRS spectroscopy of NGC7319, the largest galaxy in the Stephan's Quintet, observed as part of the Early Release Observations (ERO). NGC7319 hosts a type 2 active galactic nucleus (AGN) and a low-power radio jet (L_1.4GHz=3.3x10^22 W Hz^-1) with two asymmetric radio hotspots at 430 pc (N2) and 1.5 kpc (S2) projected distances from the unresolved radio core. The MRS data suggest that the molecular material in the disk of the galaxy decelerates the jet and causes this length asymmetry. We find enhanced emission from warm and hot H_2 (T_w=330+-40 K, T_h=900+-60 K) and ionized …
We have examined the giant radio galaxy 3C~236 using LOFAR at 143 MHz down to an angular resolution of 7", in combination with observations at higher frequencies. We have used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region…
Our goal is to study the termination of an AGN jet in the young universe and to deduce physical parameters of the jet and the intergalactic medium. We use LOFAR to image the long-wavelength radio emission of the high-redshift blazar S5 0836+710 on arcsecond scales between 120 MHz and 160 MHz. The LOFAR image shows a compact unresolved core and a resolved emission region about 1.5 arcsec to the southwest of the radio core. This structure is in general agreement with previous higher-frequency radio observations with MERLIN and the VLA. The southern component shows a moderately steep spectrum wit…
The diverse morphologies and evolution of low-luminosity edge-brightened radio galaxies
University of Hertfordshire（赫特福德大学）；The Open University（开放大学）；University of Cambridge（剑桥大学）；CSIRO Space and Astronomy, ATNF（澳大利亚联邦科学与工业研究组织空间与天文台，ATNF）
We present polarization images of 9 radio-loud (RL) quasars from the VLA B-array at 6 GHz. These quasars belong to the Palomar-Green (PG) "blazar" sample comprising 16 RL quasars and 8 BL Lac objects. Extensive polarization is detected in the cores, jets and lobes of all the quasars, with cores primarily displaying magnetic (B-) fields transverse to, and jets displaying fields aligned with the jet direction. Hotspots display either transverse B-fields signifying B- field compression at terminal shocks or more complex structures. The fractional polarization in the cores ranges from 1-10% and je…
We present a low-frequency, broadband polarization study of the FRII radio galaxy PKS J0636-2036 (z = 0.0551), using the Murchison Widefield Array (MWA) from 70 to 230 MHz. The northern and southern hotspots (separated by ~14.5' on the sky) are resolved by the MWA (3'.3 resolution) and both are detected in linear polarization across the full frequency range. A combination of Faraday rotation measure (RM) synthesis and broadband polarization model-fitting are used to constrain the Faraday depolarization properties of the source. For the integrated southern hotspot emission, two RM component mod…
Euclid: Quick Data Release (Q1) -- Optical hotspots in powerful radio galaxies
University of Hertfordshire（赫特福德大学）；INAF-Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；INAF, Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）；INAF-Istituto di Astrofisica e Planetologia Spaziali（意大利国家天体物理研究所天体物理学与行星科学研究所）；Durham University（杜伦大学）；Leiden University（莱顿大学）；Roma Tre University（罗马三大）；INAF-Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）；University of Oslo（奥斯陆大学）
The remnant phase of a radio galaxy begins when the jets launched from an active galactic nucleus are switched off. To study the fraction of radio galaxies in a remnant phase, we take advantage of a $8.31$\,deg$^2$ sub-region of the GAMA~23~field which comprises of surveys covering the frequency range 0.1--9\,GHz. We present a sample of 104 radio galaxies compiled from observations conducted by the Murchison Wide-field Array (216\,MHz), the Australia Square Kilometer Array Pathfinder (887\,MHz), and the Australia Telescope Compact Array (5.5\,GHz). We adopt an `absent radio core' criterion to …
We present a polarization and Faraday rotation study of the hybrid morphology radio galaxy NGC 612 (PKS 0131-36), using Australian Telescope Compact Array observations from 1 to 3 GHz. In general, the results are consistent with an external Faraday screen close to the radio source. In the eastern FRII lobe, the RM of the hotspot increases in magnitude towards the leading edge, as well as changing sign (compared to the rest of the lobe). The Faraday depolarization is also ~3 times larger at the hotspot than elsewhere. A plausible explanation for this is significant compression of ambient magnet…
As a rule, both lobes of Fanaroff-Riley (FR) type-II radio sources are terminated with hotspots, but the 3C328 radio galaxy is a specimen of an FR II-like object with a hotspot in only one lobe. A conceivable reason for such asymmetry is that the nucleus of 3C328 was temporarily inactive. There was no energy transfer from it to the lobes during the period of quiescence, and so they began to fade out. However, under the assumption that the axis connecting the two lobes makes an appreciable angle with the sky plane, and hence one is considerably farther from the observer than the other, the lobe…
In this paper, the second in a series investigating FR II radio galaxies at low frequencies, we use LOFAR and VLA observations between 117 and 456 MHz in addition to archival data to determine the dynamics and energetics of two radio galaxies, 3C452 and 3C223, through fitting of spectral ageing models on small spatial scales. We provide improved measurements for the physical extent of the two sources, including a previously unknown low surface brightness extension to the northern lobe of 3C223, and revised energetics based on these values. We find spectral ages of $77.05^{+9.22}_{-8.74}$ and $…
Radio galaxies are linearly polarized -- an important property that allows us to infer the properties of the magnetic field of the source and its environment. However at low frequencies, Faraday rotation substantially depolarizes the emission, meaning that comparatively few polarized radio galaxies are known at low frequencies. Using the LOFAR Two Metre Sky Survey at 150 MHz and at 20 arcsec resolution, we select 342 radio galaxies brighter than 50 mJy and larger than 100 arcsec in angular size, of which 67 are polarized (18 per cent detection fraction). These are predominantly Fanaroff Riley …
Models of radio galaxy physics have been primarily based on high frequency ($\geqslant$1 GHz) observations of their jets, hotspots, and lobes. Without highly resolved low frequency observations, which provide information on older plasma, our understanding of the dynamics of radio galaxies and their interaction with their environment is limited. Here, we present the first sub-arcsecond (0.3") resolution images at 144 MHz of two powerful radio galaxies situated in rich cluster environments, namely 3C 34 and 3C 320, using the International Low Frequency Array Telescope. We detect for the first ti…
The Fanaroff-Riley class II radio galaxy Cygnus A hosts jets which produce radio emission, X-ray cavities, cocoon shocks, and X-ray hotspots where the jet interacts with the ICM. Surrounding one hotspot is a peculiar "hole" feature which appears as a deficit in X-ray emission. We use relativistic hydrodynamic simulations of a collimated jet interacting with an inclined interface between lobe and cluster plasma to model the basic processes which may lead to such a feature. We find that the jet reflects off of the interface into a broad, turbulent flow back out into the lobe, which is dominated …
J023721.13$-$010528.5: A Giant $S$-shaped Radio Galaxy Showing Four Episodes of Jet Activity
Indian Institute of Science Education and Research（印度科学教育研究所）；National Centre for Radio Astrophysics - Tata Institute of Fundamental Research（塔塔基础研究院国家射电天文中心）
We report the systematic analysis of knots, hotspots, and lobes in 57 active galactic nuclei (AGNs) to investigate the variation of the magnetic field along with the jet from the sub-pc base to the terminus in kpc-to-Mpc scales. Expanding the number of radio/X-ray samples in Kataoka & Stawarz (2005), we analyzed the data in 12 FR I and 30 FR II radio galaxies, 12 quasars, and 3 BL Lacs that contained 76 knots, 42 hotspots, and 29 radio lobes. We first derived the equipartition magnetic fields in the cores and then estimated those in various jet components by assuming $B_{\rm est}$ $\propto$ $d…
Observations using the Fermi Large Area Telescope (Fermi-LAT) have found a significant gamma-ray excess surrounding the center of the Milky Way (GC). One possible interpretation of this excess invokes gamma-ray emission from an undiscovered population of either young or recycled pulsars densely clustered throughout the inner kiloparsec of the Milky Way. While these systems, by construction, have individual fluxes that lie below the point source sensitivity of the Fermi-LAT, they may already be observed in multiwavelength observations. Notably the Australia Telescope National Facility (ATNF) ca…
The aim of this paper is to present an analysis of newly acquired X-ray observations of 16 extragalactic radio sources, listed in the Third Cambridge Revised (3CR) catalog, and not previously observed by Chandra. Observations were performed during Chandra Cycle 17, extending X-ray coverage for the 3CR extragalactic catalog up to $z$=1.5. Among the 16 targets, two lie at $z<$0.5 (i.e., 3CR27, at $z$=0.184 and 3CR69, at $z$=0.458), all the remaining 14 have redshifts between 1.0 and 1.5. In the current sample there are three compact steep spectrum (CSS) sources, three quasars and an FRI radio ga…
From compact jets to extended lobes: radio morphologies of distant quasars at z > 4
Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，HUN-REN 地球与天文学研究中心）；ELTE Eötvös Loránd University（布达佩斯罗兰大学）；Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, NCU（托伦大学物理、天文与信息学院天体物理研究所）；Joint Institute for VLBI ERIC（甚长基线干涉测量联合研究所）；Shangqiu Normal University（商丘师范学院）；University of Science and Technology of China（中国科学技术大学）
We have undertaken a Spitzer campaign to measure the IR structures and spectra of low-redshift 3CRR radio galaxies. The results show that the 3.6 - 160 micron infrared properties vary systematically with integrated source power, and so demonstrate that contemporary core activity is characteristic of the behaviour of sources over their lifetimes. IR synchrotron emission is seen from jets and hotspots in some cases. Thermal emission is found from a jet/gas interaction in NGC 7385. Most of the near-IR integrated colours of the low-redshift 3CRR radio galaxies are similar to those of passive galax…
This paper presents the analysis of Chandra X-ray snapshot observations of a subsample of the extragalactic sources listed in the revised Third Cambridge radio catalog (3CR), previously lacking X-ray observations and thus observed during Chandra Cycle 15. This data set extends the current Chandra coverage of the 3CR extragalactic catalog up to redshift $z$=1.0. Our sample includes 22 sources consisting of one compact steep spectrum (CSS) source, three quasars (QSOs), and 18 FR\,II radio galaxies. As in our previous analyses, here we report the X-ray detections of radio cores and extended struc…
We have carried out numerical hydrodynamic simulations of radio jets from active galactic nuclei using the PLUTO simulation code, with the aim of investigating the effect of different environments and intermittency of energy injection on the resulting dynamics and observable properties of the jet-inflated lobes. Initially conical jets are simulated in poor group and cluster environments. We show that the environment into which a radio jet is propagating plays a large role in the resulting morphology, dynamics and observable properties of the radio source. The same jet collimates much later in …
