Western Radio Lobe Research Articles

Jet acceleration of the fast molecular outflows in the Seyfert galaxy IC5063.

Massive outflows driven by active galactic nuclei are widely recognized to have a key role in the evolution of galaxies, by heating the ambient gas, expelling it from the nuclear regions, and thereby affecting the star-formation histories of the galaxy bulges. It has been proposed that the powerful jets of relativistic particles (such as electrons) launched by some active nuclei can both accelerate and heat the molecular gas, which often dominates the mass budgets of the outflows. Clear evidence for this mechanism, in the form of detailed associations between the molecular gas kinematics and features in the radio-emitting jets, has however been lacking. Here we report that the warm molecular hydrogen gas in the western radio lobe of the Seyfert galaxy IC5063 is moving at high velocities-up to about 600kilometres per second-relative to the galaxy disk. This suggests that the molecules have been accelerated by fast shocks driven into the interstellar medium by the expanding radio jets. These results demonstrate the general feasibility of accelerating molecular outflows in fast shocks driven by active nuclei.

Suzaku Detection of Thermal X-Ray Emission Associated with the Western Radio Lobe of Fornax A

We present the results of X-ray mapping observations of the western radio lobe of the FornaxA galaxy, using the X-ray Imaging Spectrometer (XIS) onboard the Suzaku satellite with a total exposure time of 327 ks. The purpose of this study is to investigate the nature and spatial extent of the diffuse thermal emission around the lobe by exploiting the low and stable background of XIS. The diffuse thermal emission had been consistently reported in all previous studies of this region, but its physical nature and relation to the radio lobe had not been examined in detail. Using a data set covering the entire western lobe and the central galaxy NGC1316, as well as comparison sets in the vicinity, we find convincingly the presence of thermal plasma emission with a temperature of ∼1 keV in excess of conceivable background and contaminating emission (cosmic X-ray background, Galactic halo, intra-cluster gas of Fornax, interstellar gas of NGC1316, and the ensemble of point-like sources). Its surface brightness is consistent with having a spherical distribution peaking at the center of the western lobe with a projected radius of ∼12′. If the volume filling factor of the thermal gas is assumed to be unity, its estimated total mass amounts to ∼1010M⊙, which would be ∼102 times that of the central black hole, and comparable to that of the current gas mass of the host galaxy. Its energy density is comparable to or larger than those in the magnetic field and non-thermal electrons responsible for the observed radio and X-ray emission.

Discovery of γ-ray emission from the broad-line radio galaxy Pictor A

We report the discovery of high-energy \gamma-ray emission from the Broad Line Radio Galaxy (BLRG) Pictor A with a significance of ~5.8\sigma (TS=33.4), based on three years of observations with the Fermi Large Area Telescope (LAT) detector. The three-year averaged E>0.2 GeV \gamma-ray spectrum is adequately described by a power-law, with a photon index, \Gamma, of $2.93 \pm 0.03$ and a resultant integrated flux of $F_{\gamma}=(5.8\pm0.7) \times 10^{-9}$ ph cm$^{-2}$s$^{-1}$. A temporal investigation of the observed \gamma-ray flux, which binned the flux into year long intervals, reveals that the flux in the third year was 50% higher than the three-year average flux. This observation, coupled with the fact that this source was not detected in the first two years of {Fermi-LAT observations, suggests variability on timescales of a year or less. Synchrotron Self-Compton modelling of the spectral energy distribution of a prominent hot-spot in Pictor A's western radio lobe is performed. It is found that the models in which the \gamma-ray emission originates within the lobes, predicts an X-ray flux larger than that observed. Given that the X-ray emission in the radio lobe hot-spots has been resolved with the current suite of X-ray detectors, we suggest that the \gamma-ray emission from Pictor A originates from within its jet, which is in agreement with other \gamma-ray loud BLRGs. This suggestion is consistent with the evidence that the \gamma-ray flux is variable on timescales of a year or less.

PKS2250−41: a case study for triggering

We present the results of a multiwavelength study of the z= 0.31 radio source PKS2250−41. Integral field unit and long-slit spectroscopy obtained using VIMOS and FORS1 on the VLT, and archival Hubble Space Telescope optical imaging observations are used to study the morphology, kinematics and ionization state of the extended emission-line region (EELR) surrounding this source, and also a companion galaxy at a similar redshift. Near-infrared imaging observations obtained using the New Technology Telescope are used to analyse the underlying galaxy morphologies. The EELR displays a complex variety of different gas kinematics and ionization states, consistent with a mixture of radio source shocks and active galactic nucleus (AGN) photoionization. The radio galaxy is likely to lie within a group environment, and is plausibly undergoing interactions with one or more other objects. The disc-like galaxy to the north-east of the radio source lies at a similar redshift to the radio galaxy itself, and has its major axis position angle aligned with the filamentary continuum and line emission extending outwards from the radio galaxy. This filamentary structure is most plausibly interpreted as a tidal structure associated with an interaction involving the radio source host galaxy and the aligned companion galaxy to the north-east; this encounter may have potentially triggered the current epoch of radio source activity. Overall, PKS2250−41 displays some of the best evidence that radio source activity can be triggered in this manner. While the environment and recent interactions of a radio galaxy can have some bearing on its subsequent evolution, our data also highlight the varied means by which the radio source can effect changes in adjacent objects. Our IFU and long-slit spectroscopy confirm the presence of radio source shocks within the western radio lobe, and, together with our continuum observations, add further weight to the presence of a faint continuum source coincident with the secondary hotspot in the western radio lobe. On the basis of our multiwavelength observations of this object, we suggest that the radio source has indeed triggered recent star formation within this faint companion.

X‐Ray Constraints on Galaxy‐Gas‐Jet Interactions in the Dumbbell Galaxies NGC 4782 and NGC 4783 in the LGG 316 Galaxy Group

We present results from a 49.3 ks Chandra X-ray observation of the strongly interacting dumbbell galaxies NGC4782(3C278) and NGC4783 that constrain the kinematics of the interaction and models for bending the radio jets associated with NGC4782. The galaxies are embedded in an approximately spherical distribution of group gas, centered on NGC4782,that is nearly isothermal with mean kT ~ 1.4+/- 0.4 keV. The X-ray morphology suggests that NGC4783 is infalling into a single, massive galaxy group (LGG316) with NGC4782 nearly at rest at the center of the group potential.NGC4783 shows a sharp X-ray surface brightness edge (cold front) to the east and a ~15 kpc ram-pressure-stripped tail to the west. Analysis of this cold front indicates NGC4783 is moving east with a total velocity ~870+270-400 km/s (Mach ~1.4+0.5-0.7) at an inclination angle ~46 deg.(>33 deg.)towards us with respect to theplane of the sky. A ~45Myr old X-ray cavity, with enthalpy of 4.4 x 10^{57}ergs, coincides with the eastern radio lobe of 3C278. X-ray knots are found on both the radio jet and counter-jet, coincident with peaks in the radio emission. Assuming a light, mildly relativistic jet in 3C278, ram pressure velocities of 100-200 km/s impacting the eastern jet and ~170 km/s acting on the western radio lobe are sufficient to produce their observed bending. These velocities may be caused by bulk motions established in the IGM by the high velocity interaction between the galaxies, by the motion of NGC4782 relative to the IGM, or both.

Chandradiscovery of extended non-thermal emission in 3C 207 and the spectrum of the relativistic electrons

We report on the Chandra discovery of large scale non–thermal emission features in the double lobed SSRL quasar 3C 207 (). These are: a diffuse emission well correlated with the western radio lobe, a bright one sided jet whose structure coincides with that of the eastern radio jet and an X-ray source at the tip of the jet coincident with the hot spot of the eastern lobe. The diffuse X-ray structure is best interpreted as inverse Compton (IC) scattering of the IR photons from the nuclear source and provides direct observational support to an earlier conjecture (Brunetti et al. [CITE]) that the spectrum of the relativistic electrons in the lobes of radio galaxies extends to much lower energies than those involved in the synchrotron radio emission. The X-ray luminous and spatially resolved knot along the jet is of particular interest: by combining VLA and Chandra data we show that a SSC model is ruled out, while the X-ray spectrum and flux can be accounted for by the IC scattering of the CMB photons (EIC) under the assumptions of a relatively strong boosting and of an energy distribution of the relativistic electrons as that expected from shock acceleration mechanisms. The X-ray properties of the hot spot are consistent with a SSC model. In all cases we find that the inferred magnetic field strength are lower, but close to the equipartition values. The constraints on the energy distribution of the relativistic electrons, imposed by the X-ray spectra of the observed features, are discussed. To this aim we derive in the Appendices precise semi–analytic formulae for the emissivities due to the SSC and EIC processes.

ChandraX‐Ray Observations of Pictor A: High‐Energy Cosmic Rays in a Radio Galaxy

We report X-ray observations of the nearby, powerful radio galaxy Pictor A with the Chandra Observatory and optical and near-UV observations of its western radio hot spot with the Hubble Space Telescope. X-ray emission is detected from the nucleus, a 19 (110 kpc) long jet to the west of the nucleus, the western radio hot spot some 42 (240 kpc) from the nucleus, and the eastern radio lobe. The morphology of the western hot spot is remarkably similar to that seen at radio and optical wavelengths, where the emission is known to be synchrotron radiation. The X-ray spectrum of the hot spot is well described by an absorbed power law with photon index Γ = 2.07 ± 0.11. The X-ray jet coincides with a weak radio jet and is laterally extended by 20 (1.9 kpc). The observed jet is up to 15 times brighter in X-rays than any counterjet, a difference ascribed to relativistic boosting since the western radio lobe is probably the closer. The jet's spectrum is well modeled by an absorbed power law with Γ = 1.94 and poorly fitted by a Raymond-Smith thermal plasma model. The emission processes responsible for the X-rays are discussed in detail. The radio-to-optical spectrum of the hot spot breaks or turns down at 1013-1014 Hz, and its X-ray spectrum is not a simple extension of the radio-to-optical spectrum to higher frequencies. Thermal models for the hot spot's X-ray emission are ruled out. Synchrotron self-Compton models involving scattering from the known population of electrons give the wrong spectral index for the hot spot's X-ray emission and are also excluded. A composite synchrotron plus synchrotron self-Compton model can match the X-ray observations but requires similar contributions from the two components in the Chandra band. We show that the hot spot's X-ray emission could be synchrotron self-Compton emission from a hitherto unobserved population of electrons emitting at low radio frequencies but do not favor this model in view of the very weak magnetic field required. An inverse Compton model of the jet, in which it scatters microwave background photons but moves nonrelativistically, requires a magnetic field a factor of 30 below equipartition and ad hoc conditions to explain why the radio lobes are fainter than the jet in X-rays but brighter in the radio. These problems are alleviated if the jet moves relativistically, but models with an equipartition field require an implausibly small angle (θ) between the jet and the line of sight. A model with θ 23° and a field a factor of 6 below equipartition seems viable. Synchrotron radiation is an alternative process for the X-ray emission. The expected synchrotron spectrum from relativistic electrons accelerated by strong shocks and subject to synchrotron radiation losses is in very good agreement with that observed for both the hot spot and jet. The possibility that the relativistic electrons result via photopion production by high-energy protons accelerated in shocks (a proton-induced cascade) is briefly discussed.

Ringlike Structure in the Radio Lobe of MG 0248+0641

We present radio and optical observations of MG 0248+0641, which contains a kiloparsec-scale ringlike structure in one of its radio lobes. The radio observations show a typical core-double morphology: a central core between two lobes, each of which has a hot spot. The western radio lobe appears as a nearly continuous ring, with linear polarization electric field vectors that are oriented in a radial direction from the ring's center. We consider several different interpretations for the nature of this ring, including gravitational lensing of a normal jet by a foreground galaxy. Even though simple lensing models can describe the ring morphology reasonably well, the high linear polarization seen around the ring cannot be easily explained, and no lensing object has yet been found in deep optical and infrared searches within the extent of the ring. If the radio ring is indeed caused by gravitational lensing, the implied mass-to-light ratio is typical of the very high values seen in other candidate dark gravitational lenses. The chance interposition of a Galactic supernova remnant, nova, planetary nebula, or H II region has been ruled out. The highly polarized ring of MG 0248+0641 is much like the prominent ring seen in 3C 219 and the multiple ones in 3C 310 and Hercules A, suggesting that similar physical processes are producing shell structures in these radio galaxies. The ring in MG 0248+0641 may be caused by the formation of bubbles as a result of instabilities in the energy flow down the western radio jet. It may also be possible that the required instabilities are triggered by the infall of gas, via tidal interaction of the central source with a nearby galaxy. This scenario may be indicated by our marginal detection of an optical source close to the western hot spot.

The Morphology of the Narrow-Line Region of Markarian 3

view Abstract Citations (71) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Morphology of the Narrow-Line Region of Markarian 3 Capetti, A. ; Macchetto, F. ; Axon, D. J. ; Sparks, W. B. ; Boksenberg, A. Abstract We present the results of Hubble Space Telescope observations of the Seyfert 2 galaxy Mrk 3. Images were taken with the Faint Object Camera and Wide Field Planetary Camera with filters centered on the emission lines [O II] λ3727, [O III] λ5007, Hα, and Hγ. The narrow-line region (NLR) of Mrk 3 has a striking S-shaped morphology extending over more than 2" and comprising a large number of resolved knots. Its small-scale structure is remarkably well reproduced in all the emission lines observed, with a close knot-to-knot correspondence. The ratios between [O II] and [O III] and between [O III] and Hγ emission-line fluxes are constant. The photon budget confirms that the nucleus of Mrk 3 is heavily obscured along the line of sight. Radio maps of Mrk 3 shows two highly collimated radio jets and the optical line and radio emissions are very closely associated. We propose a scenario where the line-emitting gas is compressed by the shocks created by the passage of the supersonic jet. The increase in the density due to the shocks causes the line emission to be highly enhanced in the region where this interaction occurs. On each side of the S, the line emission is, on average, displaced in opposite directions with respect to the radio emission as expected from the finite cooling time of the shocked gas which follows the galaxy rotation. The Faint Object Spectrograph spectrum west of the nucleus shows that the line widths are very large, FWHM 1200 km s-1, and that the [O III] lines are clearly double-peaked as would be expected in this interpretation. The range of shock velocity obtained from the cooling length argument is consistent with the measured line widths. The prominent western radio lobe has a high-excitation emission-line core, surrounded by a diffuse halo of relatively lower ionization. We interpret this as a consequence of the sweeping up of gas by the expanding radio lobe. The narrow linear ridge of the S-shaped NLR is misaligned with respect to the symmetry axis of the larger scale biconical emission. If there is a wide angle ionization cone, as in NGC 1068, it must be partly filled by gas and its opening angle must be larger than 1100. It appears that, at least on the small scale, the dominant factors in determining the NLR morphology are either the gas distribution or the effects of the radio outflow rather than the geometry of the ionizing field. A small-scale bar (≍0".35 × 1") of continuum emission is also observed, possibly due to free-free emission from the hot shocked gas or scattered nuclear light. Publication: The Astrophysical Journal Pub Date: August 1995 DOI: 10.1086/175989 Bibcode: 1995ApJ...448..600C Keywords: GALAXIES: INDIVIDUAL NAME: MARKARIAN 3; GALAXIES: JETS; GALAXIES: NUCLEI; GALAXIES: SEYFERT; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (1) NED (1) MAST (1) ESA (1)