Radio Galaxy 3C Research Articles

Structure and environment of the giant radio galaxy 4C 73.08

The giant radio galaxy 4C 73.08 has been observed with the Westerbork Telescope at a wavelength of 21 cm. The radio map obtained is a significant improvement upon previous maps in terms of the combination of high dynamic range, sensitivity and angular resolution. The new map shows that the jet, previously thought to be one-sided, is probably symmetrical with one arm almost lost in the background of extended lobe emission. The brighter, more compact lobe also displays more intense emission from its hotspot and jet. The jets line up well with the nucleus and hotspots, although the hotspot on one side deviates from the lobe major axis. The unusual feature of the radio source's morphology is the existence of curved ridges running transverse to the source major axis. Three of the other galaxies in the 4C 73.08 group are also weak radio sources. We further detect radio emission from the foreground galaxies NGC 2957 and 2963, which form a small group. A background galaxy has double radio components of moderate size which we have mapped; there is an optical companion at the same redshift. Another extended source may be associated with a Two Micron All Sky Survey galaxy.

GAS SLOSHING AND RADIO GALAXY DYNAMICS IN THE CORE OF THE 3C 449 GROUP

We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last ~1.3-1.6 Gyrs. Both the northern and the southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge. We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. (1995) and are confirmed in our deep observation.

Single-Dish Radio Polarimetry in the F-GAMMA Program with the Effelsberg 100-m Radio Telescope

Studying the variability of polarized AGN jet emission in the radio band is crucial for understanding the dynamics of moving shocks as well as the structure of the underlying magnetic field. The 100-m Effelsberg Telescope is a high-quality instrument for studying the long-term variability of both total and polarized intensity as well as the electric-vector position angle. Since 2007, the F-GAMMA program has been monitoring the linear polarized emission of roughly 60 blazars at 11 frequencies between 2.7 and 43 GHz. Here, we describe the calibration of the polarimetric data at 5 and 10 GHz and the resulting F-GAMMA full-Stokes light curves for the exemplary case of the radio galaxy 3C 111.

Associated 21-cm absorption towards the cores of radio galaxies

We present the results of Giant Metrewave Radio Telescope observations to detect H i in absorption towards the cores of a sample of radio galaxies. From observations of a sample of 16 sources, we detect H i in absorption towards the core of only one source, the Fanaroff–Riley type II (FR II) radio galaxy 3C 452 which has been reported earlier by Gupta & Saikia. In this paper we present the results for the remaining sources which have been observed to a similar optical depth as for a comparison sample of compact steep-spectrum (CSS) and gigahertz peaked-spectrum (GPS) sources. We also compile available information on H i absorption towards the cores of extended radio sources observed with angular resolutions of a few arcsec or better. The fraction of extended sources with detection of H i absorption towards their cores is significantly smaller (7/47) than the fraction of H i detection towards CSS and GPS objects (28/49). For the cores of extended sources, there is no evidence of a significant correlation between H i column density towards the cores and the largest linear size of the sources. The distribution of the relative velocity of the principal absorbing component towards the cores of extended sources is not significantly different from that of the CSS and GPS objects. However, a few of the CSS and GPS objects have blueshifted components ≳1000 km s−1, possibly due to jet–cloud interactions. With the small number of detections towards cores, the difference in the detection rate between FR I (4/32) and FR II (3/15) sources is within the statistical uncertainties.

The Herschel★ view of the environment of the radio galaxy 4C+41.17 at z = 3.8

We present Herschel observations at 70, 160, 250, 350 and 500 micron of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65% of the extracted sources are securely identified with mid-IR sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 micron. We derive simple photometric redshifts, also including existing 850 micron and 1200 micron data, using templates of AGN, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the SED of the closest (~ 25" offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multi-wavelength data, in particular on the Rayleigh-Jeans side of the spectral energy distribution, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data sets.

The circumnuclear cold gas environments of the powerful radio galaxies 3C 236 and 4C 31.04

We present Very Long Baseline Array (VLBA) H i absorption observations of the core regions of the powerful radio galaxies 3C 236 and 4C 31.04. Broad absorption (Δv ≈ 350 km s-1) straddling the systemic velocity is detected in both sources, in each case concentrated on one side of the radio core. We argue that the observations are consistent with the presence of H i absorbing disks with r ≈ 900 pc and r ≥ 200 pc in 3C 236 and 4C 31.04 respectively - although given the limited spatial coverage of the HI absorption other interpretations cannot be ruled out. The spatially resolved absorption detected against the counter-jet of 3C 236 shows a velocity gradient with an amplitude and direction supporting a rotating disk model; in contrast only a tentative velocity gradient is seen in the 4C 31.04 data set. While on larger scales both radio galaxies show evidence for interaction and merging we find no direct evidence in either source that cold gas is in-falling onto the radio core. In 3C 236 we instead find against the core blue-shifted absorption that might be part of the fast outflow of neutral gas detected in more sensitive (but lower spatial resolution) observations. Along the main jet of 3C 236 we find clumps of high opacity H i absorption concentrated to one side of the jet. We speculate that these H i clumps may be interacting with the jet, potentially even being the cause of the misalignment of the eastern jet between kiloparsec and megaparsec scales. In addition to its broad absorption 4C 31.04 shows a narrow absorption component (FWHM = 23 km s-1) redshifted relative to the galaxy systemic velocity by 115 km s-1. This feature may be a residual sign of a recent accretion/merging event, however the absorbing gas cloud must be located ≫ 100 pc from the core.

EXTREME HOST GALAXY GROWTH IN POWERFUL EARLY-EPOCH RADIO GALAXIES

During the first half of the universe's age, a heyday of star-formation must have occurred because many massive galaxies are in place after that epoch in cosmic history. Our observations with the revolutionary Herschel Space Observatory reveal vigorous optically obscured star-formation in the ultra-massive hosts of many powerful high-redshift 3C quasars and radio galaxies. This symbiotic occurrence of star-formation and black hole driven activity is in marked contrast to recent results dealing with Herschel observations of X-ray selected active galaxies. Three archetypal radio galaxies, at redshifts 1.132,1.575, and 2.474 are presented here, with inferred star-formation rates of hundreds of solar masses per year. A series of spectacular coeval AGN/starburst events may have formed these ultra-massive galaxies and their massive central black holes during their relatively short lifetimes.

The nature of the multi-wavelength emission of 3C 111

We attempt to determine the nature of the high energy emission of the radio galaxy 3C 111, by distinguishing between the effects of the thermal and non-thermal processes. We study the X-ray spectrum of 3C 111 between 0.4 keV and 200 keV, and its spectral energy distribution, using data from the Suzaku satellite combined with INTEGRAL, Swift/BAT data, and Fermi/LAT data. We then model the overall spectral energy distribution including radio and infrared data. The combined Suzaku, Swift and INTEGRAL data are represented by an absorbed exponentially cut-off power-law with reflection from neutral material with a photon index Gamma = 1.68+-0.03, a high-energy cut-off Ecut = 227+143-67 keV, a reflection component with R = 0.7+-0.3 and a Gaussian component to account for the iron emission-line at 6.4 keV with an equivalent width of EW = 85+-11 eV. The X-ray spectrum appears dominated by thermal, Seyfert-like processes, but there are also indications of non-thermal processes. The radio to gamma-ray spectral energy distribution can be fit with a single-zone synchrotron-self Compton model, with no need for an additional thermal component. We suggest a hybrid scenario to explain the broad-band emission, including a thermal component (iron line, reflection) that dominates in the X-ray regime and a non-thermal one to explain the spectral energy distribution.

The broad line emission from the AGN 3C 390.3: complex broad-line region and perturbation in accretion disk

AbstractFrom 13-years of the spectral optical monitoring of a well-known broad-line radio galaxy 3C 390.3 we concluded that the geometry of the broad emission-line region is complex, while still the main part of the emission is coming from the accretion disk. Here we present part of the analysis of the broad Hα and Hβ emission lines, which are showing highly variable double-peaked profiles during the monitoring period (1995-2007), with the aim to probe the accretion disk properties. The disk-like geometry plays a dominant role, but the variability of Hα and Hβ line profiles and intensities shows a presence of an additional emission-line region, that has a different nature for different periods, e.g. in one period the observed variation can be well modeled if one assumes changes in position and size of the emitting disk along the accretion disk.

The nature of the jet-driven outflow in the radio galaxy 3C 305

We present Chandra X-ray and VLA radio observations of the radio galaxy 3C305. The X-ray observations reveal the details of the previously known extended X-ray halo around the radio galaxy. We show using X-ray spectroscopy that the X-ray emission is consistent with being shock-heated material and can be modelled with standard collisional-ionization models, rather than being photoionized by the active nucleus. On this basis, we can make a self-consistent model in which the X-ray-emitting plasma is responsible for the depolarization of some regions of the radio emission from the jets and hotspots, and to place lower and upper limits on the magnetic field strength in the depolarizing medium. On the assumption that the X-ray-emitting material, together with the previously-known extended emission-line region and the outflow in neutral hydrogen, are all being driven out of the centre of the galaxy by an interaction with the jets, we derive a detailed energy budget for the radio galaxy, showing that the X-ray-emitting gas dominates the other phases in terms of its energy content. The power supplied by the jets must be ~ 10^43 erg/s.

Comparison of ejection events in the jet and accretion disc outflows in 3C 111

We present a comparison of the parameters of accretion disc outflows and the jet of the broad-line radio galaxy 3C 111 on sub-pc scales. We make use of published X-ray observations of ultra-fast outflows (UFOs) and new 43GHz VLBA images to track the jet knots ejection. We find that the superluminal jet coexists with the mildly relativistic outflows on sub-pc scales, possibly indicating a transverse stratification of a global flow. The two are roughly in pressure equilibrium, with the UFOs potentially providing additional support for the initial jet collimation. The UFOs are much more massive than the jet, but their kinetic power is probably about an order of magnitude lower, at least for the observations considered here. However, their momentum flux is equivalent and both of them are powerful enough to exert a concurrent feedback impact on the surrounding environment. A link between these components is naturally predicted in the context of MHD models for jet/outflow formation. However, given the high radiation throughput of AGNs, radiation pressure should also be taken into account. From the comparison with the long-term 2-10keV RXTE light curve we find that the UFOs are preferentially detected during periods of increasing flux. We also find the possibility to place the UFOs within the known X-ray dips-jet ejection cycles, which has been shown to be a strong proof of the disc-jet connection, in analogue with stellar-mass black holes. However, given the limited number of observations presently available, these relations are only tentative and additional spectral monitoring is needed to test them conclusively.

VLBI and single-dish monitoring of 3C 84 for the period 2009–2011

ABSTRACT The radio galaxy 3C 84 is a representative of γ-ray-bright misaligned active galactic nuclei (AGNs) and one of the best laboratories to study the radio properties of the subparsec jet in connection with the γ-ray emission. In order to identify possible radio counterparts of γ-ray emissions in 3C 84, we study the change in structure within the central 1 pc and the light curve of subparsec-sized components C1, C2 and C3. We search for any correlation between changes in the radio components and the γ-ray flares by making use of the Very Long Baseline Interferometry (VLBI) and single-dish data. Throughout the radio monitoring spanning over two GeV γ-ray flares detected by the Fermi Large Area Telescope and the MAGIC Cherenkov Telescope during 2009 April–May and 2010 June–August, the total flux density in the radio band increases on average. This flux increase mostly originates in C3. Although γ-ray flares span the time-scale of days to weeks, no clear correlation with the radio light curve on this time-scale is found. No new prominent components and change in morphology associated with the γ-ray flares are found on VLBI images.

A RECOLLIMATION SHOCK 80 mas FROM THE CORE IN THE JET OF THE RADIO GALAXY 3C 120: OBSERVATIONAL EVIDENCE AND MODELING

We present Very Long Baseline Array observations of the radio galaxy 3C120 at 5, 8, 12, and 15 GHz designed to study a peculiar stationary jet feature (hereafter C80) located ~80 mas from the core, which was previously shown to display a brightness temperature ~600 times lager than expected at such distances. The high sensitivity of the images -- obtained between December 2009 and June 2010 -- has revealed that C80 corresponds to the eastern flux density peak of an arc of emission (hereafter A80), downstream of which extends a large (~20 mas in size) bubble-like structure that resembles an inverted bow shock. The linearly polarized emission closely follows that of the total intensity in A80, with the electric vector position angle distributed nearly perpendicular to the arc-shaped structure. Despite the stationary nature of C80/A80, superluminal components with speeds up to ~3 c have been detected downstream from its position, resembling the behavior observed in the HST-1 emission complex in M87. The total and polarized emission of the C80/A80 structure, its lack of motion, and brightness temperature excess are best reproduced by a model based on synchrotron emission from a conical shock with cone opening angle \eta=10 degrees, jet viewing angle \theta=16 degrees, a completely tangled upstream magnetic field, and upstream Lorentz factor \gamma=8.4. The good agreement between our observations and numerical modeling leads us to conclude that the peculiar feature associated with C80/A80 corresponds to a conical recollimation shock in the jet of 3C120 located at a de-projected distance of ~190 pc downstream from the nucleus.

THE CENTRAL ENGINE STRUCTURE OF 3C120: EVIDENCE FOR A RETROGRADE BLACK HOLE OR A REFILLING ACCRETION DISK

The broad-line radio galaxy 3C120 is a powerful source of both X-ray and radio emission including superluminal jet outflows. We report on our reanalysis of 160 ks of Suzaku data taken in 2006, previously examined by Kataoka et al. (2007). Spectral fits to the XIS and HXD/PIN data over a range of 0.7-45 keV reveal a well-defined iron K line complex with a narrow Ka core and relativistically broadened features consistent with emission from the inner regions of the accretion disk. Furthermore, the inner region of the disk appears to be truncated with an inner radius of r_in = 11.7^{+3.5}_{-5.2} r_g. If we assume that fluorescent iron line features terminate at the inner-most stable circular orbit (ISCO), we measure a black hole spin of a < -0.1 at a 90% confidence level. A rapidly spinning prograde black hole (a > 0.8) can be ruled out at the 99% confidence level. Alternatively, the disk may be truncated well outside of the ISCO of a rapid prograde hole. The most compelling scenario is the possibility that the inner regions of the disk were destroyed/ejected by catastrophic instabilities just prior to the time these observations were made.

Group of galaxies around the giant radio galaxy 4C 73.08

The optical field of the giant radio galaxy (GRG) 4C 73.08 has been spectroscopically investigated to look for companions to the host 7Zw 292. We have taken spectra of 12 candidates and have determined redshifts for all of them. When combined with the previously known redshift of 7Zw 292, we find that the radio source is accompanied by a small group of nine galaxies, of which the GRG host is the brightest. Seven members of the group lie within 350 kpc of 7Zw 292, gathered around the brighter, more compact component of the double radio source. The whole group has a velocity dispersion of similar to 270 km s-1. We discuss this result in the light of the X-ray emission which has been detected from the region. 4C 73.08 follows the pattern found in other GRGs of being associated with a small group, but not falling in a rich cluster.

Faraday rotation in jets of AGN: the case of 3C 120

The source of Faraday rotation in the jet of the radio galaxy 3C 120 is analyzed through Very Long Baseline Array observations carried out between 1999 and 2007 at 15, 22 and 43 GHz. Uncorrelated changes in the linear polarization of the underlying jet emission and the Faraday rotation screen indicate that the emitting jet and the source of Faraday rotation are not closely connected physically and have different configurations for the magnetic field and/or kinematical properties. Furthermore, the existence of a region of enhanced rotation measure whose properties remain constant over three years requires a localized source of Faraday rotation, favoring a model in which a significant fraction of the rotation measure originates in foreground clouds.

AN ACTIVE GALACTIC NUCLEUS DRIVEN SHOCK IN THE INTRACLUSTER MEDIUM AROUND THE RADIO GALAXY 3C 310

We present results from a 57.6 ks Chandra observation of the cluster gas associated with the fat-double radio galaxy 3C 310. We find a surface brightness discontinuity in the gas outside the southern radio lobe that we attribute to a shock driven by the supersonic inflation of this lobe ~180 kpc from the nucleus. Modeling the surface brightness/density jump, the shock has Mach number 1.5-1.9, depending on the assumptions one makes about the density profile and the nature of the energy input. There are not sufficient counts in the image to detect conclusively the temperature jump associated with the shock. The total mechanical energy of the outburst is 5 × 1060 erg. Assuming a Mach 1.9 shock, the age of the outburst is ~100 million yrs, and the time-averaged power of the outburst is ~1.3 × 1045 erg s–1. The power input is 100 times greater than the radiative losses of the gas within the radius of the shock. Most importantly, the equivalent heat input due to the entropy increase is roughly 10% of the thermal energy of the gas to the radius of the shock. 3C 310 is another example where regular outbursts of the observed strength with a duty cycle of 0.1 could offset the radiative losses of the gas near the Bondi radius and regulate feedback. We also detect a cool filamentary X-ray arm along the eastern periphery of the southern radio lobe. This arm is probably composed of low-entropy gas dredged up in the inflation of the radio plasma, similar to features seen in M87.

HELICAL MAGNETIC FIELDS IN RELATIVISTIC JETS THROUGH FARADAY ROTATION AND JET STRATIFICATION STUDIES

Helical magnetic fields may play an important role in the formation, collimation, and acceleration of relativistic jets in active galactic nuclei. These may be searched for by looking for Faraday rotation measure (RM) gradients and emission stratification across the jet width. Multi-epoch polarimetric Very Long Baseline Array (VLBA) observations of the radio galaxy 3C 120 have revealed the existence of such a RM gradient across the jet, but the presence of a localized region of enhanced RM and uncorrelated changes in the polarization of the underlying jet emission and the Faraday rotation screen suggest that a significant fraction of the RM found in 3C 120 originates in foreground clouds. Thanks to the combination of 48 images spanning 14 years of 15 GHz VLBA observations of 3C 273 we have found a stratification in total intensity across the jet that flips sides with distance along the jet, supporting a model in which the jet of 3C 273 accelerates and is threaded by a helical magnetic field.

THE UNUSUAL EMISSION STRUCTURE 140 PC FROM THE CORE IN THE JET OF THE RADIO GALAXY 3C 120

We present Very Long Baseline Array observations of the radio galaxy 3C 120 during 2010, revealing the existence of a very unusual component (hereafter C80) located at 80 mas (deprojected to 140 pc) with a brightness temperature ≈ 600 times higher than expected at such distance from the core. No significant changes in the position and flux density of C80 has been observed from its discovered up to these new observations suggesting that it may be associated with a strong recollimation shock. Components downstream of C80 move at superluminal velocities, resembling the situation near the HST-1 component in M87.

Evidence that the bursting component of the X-ray radiation from 3C 111 originates in the PC-scale jet

Evidence is presented indicating that the bursting component of the X-ray radiation detected in the nuclear region of the active radio galaxy 3C 111 comes from the blobs ejected in the pc-scale jet and not from the accretion disc. After each new outburst the radio flux density associated with it increases to a peak in ∼1 year and then subsides over a period of 1–2 years with the flux falling off exponentially as the blob moves outward and dissipates. Similar peaks (bursts) are seen in the X-ray light curve and a cross-correlation between the two shows a very high correlation with the X-ray peaks leading the radio peaks by ∼100 days. A second cross-correlation, this time between the radio event start times and the X-ray light curve, also shows a significant correlation. When this is taken together with the long (∼1 yr) delay between the start of each ejection event and its associated X-ray peak it indicates that this bursting component of the X-ray flux must be associated with the ejected blobs in the pc-scale jet and not with the accretion disc. Because X-ray telescopes do not have the resolution required to resolve the accretion disc area from the pc-scale jet, this paper is the first to present observational evidence that can pinpoint the point of origin of at least those long-timescale X-ray bursts with durations of 1–3 yrs.