Double-lobed Structure Research Articles

Spatial distribution modulation of laser-accelerated charged particles with micro-tube structures

We present experimental studies on the spatial distribution of charged particles using a linearly polarized femtosecond laser interacting with a micro-structure target composed of micro-tube structure and planar foil. For protons, a six-lobed structure was observed in the low-energy region, while a smaller angular divergence was measured in the high-energy region. Electron distribution exhibits a circular distribution at low energies and double-lobed structure at high energies. These results are well reproduced by 3D particle-in-cell simulations, showing that the profile of electrons driven by a laser pulse is manipulated by the micro-tube structure, which maps into the spatial distribution of protons via a strong charge separation field. These results demonstrate the effect of micro-structures on laser-driven particle sources and provide a possible approach for spatial manipulation of the particle beams.

J1110+4817 – a compact symmetric object candidate revisited

ABSTRACT Compact symmetric objects (CSOs) are radio-emitting active galactic nuclei (AGNs) typically with a double-lobed radio structure confined to within 1 kpc. CSOs represent the earliest evolutionary phase of jetted AGNs. Some of them may eventually evolve into large-scale extended double sources, while others stall within the host galaxy and die out, depending on the longevity of nuclear activity, the jet power, and parameters of the surrounding galactic environment. Studying CSOs is a useful tool for understanding the evolution of the galaxies and the interactions between the jets and the medium of the host galaxy. Based on milliarcsec-resolution imaging observations using very long baseline interferometry (VLBI), it is not always straightforward to distinguish between a compact double-lobed or a core–jet structure. The quasar J1110+4817 was considered a CSO candidate in the literature earlier, but because of the lack of clear evidence, it could not be securely classified as a CSO. Here we present a comprehensive analysis of archival multifrequency VLBI observations combined with accurate Gaia optical astrometric information. Lower frequency VLBI images reveal an extended radio feature nearly perpendicular to the main structural axis of the source, apparently emanating from the brighter northern feature, which is rare among the known CSOs. While the presence of a binary AGN system cannot be fully excluded, the most plausible explanation is that J1110+4817 is a CSO.

Extended Radio Structures and a Compact X-Ray Cool-core in the Cluster Source PKS 1353–341

We present a radio and X-ray study of PKS 1353-341, the brightest cluster galaxy radio source at the center of a recent Chandra-discovered X-ray cluster. Our multi-frequency VLA images reveal an edge-brightened (FR-II), double-lobed structure with total ~50 kpc extent and 1.5 GHz power of $1.2\times10^{25}$ W Hz$^{-1}$, separated from the bright, arcsecond-scale core. We reanalyzed the Chandra data and found the X-ray emitting AGN is offset by ~9 kpc from a compact X-ray cool-core with temperature, $kT=3.1\pm0.5$ keV, and a radius of ~22 kpc, surrounded by a hotter $kT=6.3\pm0.7$ keV gas out to ~50 kpc. The offset suggests sloshing inside the cool-core induced by a minor merger or a past outburst of the AGN that produced the large-scale radio lobes. The comparable spatial scales of the lobes with the interface between the different temperature X-ray plasma indicate the lobes are actively heating the outer layers of what is now a remnant compact cool-core. Our dual-frequency VLBA images reveal substructure in the central radio source, consisting of a radio core with double-sided pc-scale jets pointing toward the kpc-scale structures. The northern jet is detected only at 8.4 GHz, indicating its emission is behind an absorbing torus or disk. We also measured faster apparent motions in the southern jet up to $1.9\pm1.1c$ than in the northern jet ($0.8\pm0.5c$). While the VLBA observations indicate the southern jet is aligned slightly closer to our line of sight, the asymmetries are overall modest and imply minimal projection effects in the large-scale radio structures.

An Old Fogey’s History of Radio Jets

This paper describes a personal view of the discovery of radio jets in celestial radio sources. The existence of narrow, collimated optical features in distant objects has been known about since the early 20th century; however, the advent of radio astronomy in the 1940s and 1950s revealed the existence of a large number of discrete radio sources. The realization that many of these objects were not primarily stellar or local to our own galaxy, but rather extragalactic, followed the determination of accurate radio positions, enabling identifications with optical objects. High-resolution radio interferometers found that they were often compact, and with a double lobed structure, implying outflow from a central object. Shortly afterwards, accurate techniques for the measurement of polarization were developed. However it was not until the advent of synthesis instruments in the 1970s that radio images of the sources were produced, and the existence of radio jets firmly established and their polarization characteristics found.

3D relativistic MHD numerical simulations of X-shaped radio sources

A significant fraction of extended radio sources presents a peculiar X-shaped radio morphology: in addition to the classical double lobed structure, radio emission is also observed along a second axis of simmetry in the form of diffuse wings or tails. In a previous investigation we showed the existence of a connection between the radio morphology and the properties of the host galaxies. Motivated by this connection we performed two-dimensional numerical simulations showing that X-shaped radio sources may naturally form as a jet propagates along the major axis a highly elliptical density distribution, because of the fast expansion of the cocoon along the minor axis of the distribution. We intend to extend our analysis by performing three-dimensional numerical simulations and investigating the role of different parameters is determining the formation of the X-shaped morphology. The problem is addressed by numerical means, carrying out three-dimensional relativistic magnetohydrodynamic simulations of bidirectional jets propagating in a triaxial density distribution. We show that only jets with power $\lesssim 10^{44}$ erg s$^{-1}$ can give origin to an X-shaped morphology and that a misalignment of $30^o$ between the jet axis and the major axis of the density distribution is still favourable to the formation of this kind of morphology. In addition we compute synthetic radio emission maps and polarization maps. In our scenario for the formation of X-shaped radio sources only low power FRII can give origin to such kind of morphology. Our synthetic emission maps show that the different observed morphologies of X-shaped sources can be the result of similar structures viewed under different perspectives.

ALMA IMAGING OF THE CO (6-5) LINE EMISSION IN NGC 7130*

ABSTRACT In this paper, we report our high-resolution (0.″20 × 0.″14 or ∼70 × 49 pc) observations of the CO(6-5) line emission, which probes warm and dense molecular gas, and the 434 μm dust continuum in the nuclear region of NGC 7130, obtained with the Atacama Large Millimeter Array (ALMA). The CO line and dust continuum fluxes detected in our ALMA observations are 1230 ± 74 Jy km s−1 and 814 ± 52 mJy, respectively, which account for 100% and 51% of their total fluxes. We find that the CO(6-5) and dust emissions are generally spatially correlated, but their brightest peaks show an offset of ∼70 pc, suggesting that the gas and dust emissions may start decoupling at this physical scale. The brightest peak of the CO(6-5) emission does not spatially correspond to the radio continuum peak, which is likely dominated by an active galactic nucleus (AGN). This, together with our additional quantitative analysis, suggests that the heating contribution of the AGN to the CO(6-5) emission in NGC 7130 is negligible. The CO(6-5) and the extinction-corrected Pa-α maps display striking differences, suggestive of either a breakdown of the correlation between warm dense gas and star formation at linear scales of <100 pc or a large uncertainty in our extinction correction to the observed Pa-α image. Over a larger scale of ∼2.1 kpc, the double-lobed structure found in the CO(6-5) emission agrees well with the dust lanes in the optical/near-infrared images.

Late time X-ray, IR and radio observations of the tidal disruption event galaxy NGC 5905

NGC 5905 is one of the few galaxies with no prior evidence for an active galactic nucleus (AGN) in which an X-ray flare was detected by the ROSAT All Sky Survey (RASS) in 1990–1991. Follow-up studies showed that the X-ray flare was due to the tidal disruption of a star by the massive black hole in the center of the galaxy. In this study we present analysis of late-time follow-up observations of NGC 5905 using Chandra archival data, Spitzer archival data, GMRT 1.28 GHz radio observations and VLA 3 GHz and 8 GHz archival data. The X-ray image shows no compact source that could be associated with an AGN. Instead, the emission is extended—likely due to nuclear star formation. The total measured X-ray luminosity from this extended emission region is comparable to the X-ray luminosity determined from the 2002 Chandra observations and is a factor of 200 less than the peak of the X-ray flare observed in 1990. Diffuse X-ray emission was detected close to the circum-nuclear star forming ring. The Spitzer 2006 mid-infrared spectrum also shows strong evidence of nuclear star formation but no clear AGN signatures. The semi-analytical models of Tommasin et al. (Astrophys. J. 709:1257, 2010) together with the measured [OIV]/[NeII] line ratio suggest that at most only 5.6 % of the total IR Flux at 19 μm is being contributed by the AGN. The GMRT 1.28 GHz observations reveal a nuclear source. In the much higher resolution VLA 3 GHz map, the emission has a double lobed structure of size 2.7′′ due to the circumnuclear star forming ring. The GMRT 1.28 GHz peak emission coincides with the center of the circumnuclear ring. We did not detect any emission in the VLA 8 GHz (1996) archival data. Instead we give upper limits to the radio afterglow of the tidal disruption event (TDE) using 3 σ upper limits where σ is the map noise. The 3 σ limits at 1.28 GHz, 3 GHz and 8 GHz are 0.17 mJy, 0.09 mJy and 0.09 mJy, respectively. Our studies thus show that (i) NGC 5905 has a declining X-ray flux consistent with a TDE, (ii) the IR flux is dominated by nuclear star formation, (iii) the nuclear radio emission observed from the galaxy is due to circumnuclear star formation, (iv) no compact radio emission associated with a radio afterglow from the TDE is detected.

Azimuthal asymmetry in collective electron dynamics in relativistically transparent laser–foil interactions

Asymmetry in the collective dynamics of ponderomotively-driven electrons in the interaction of an ultraintense laser pulse with a relativistically transparent target is demonstrated experimentally. The 2D profile of the beam of accelerated electrons is shown to change from an ellipse aligned along the laser polarization direction in the case of limited transparency, to a double-lobe structure aligned perpendicular to it when a significant fraction of the laser pulse co-propagates with the electrons. The temporally-resolved dynamics of the interaction are investigated via particle-in-cell simulations. The results provide new insight into the collective response of charged particles to intense laser fields over an extended interaction volume, which is important for a wide range of applications, and in particular for the development of promising new ultraintense laser-driven ion acceleration mechanisms involving ultrathin target foils.

Precision astrometry of pulsars and other compact radio sources in the globular cluster M15

The globular cluster (GC) M15 (NGC 7078) is host to at least eight pulsars and two low mass X-ray binaries (LMXBs) one of which is also visible in the radio regime. Here we present the results of a multi-epoch global very long baseline interferometry (VLBI) campaign aiming at i) measuring the proper motion of the known compact radio sources, ii) finding and classifying thus far undetected compact radio sources in the GC, and iii) detecting a signature of the putative intermediate mass black hole (IMBH) proposed to reside at the core of M15. We measure the sky motion in right ascension ($\mu_{\alpha}$) and declination ($\mu_{\delta}$) of the pulsars M15A and M15C and of the LMXB AC211 to be $(\mu_{\alpha},\,\mu_{\delta})_{\text{M15A}}=(-0.54\pm0.14,\,-4.33\pm0.25)\,$mas$\,$yr$^{-1}$, $(\mu_{\alpha},\,\mu_{\delta})_{\text{M15C}}=(-0.75\pm0.09,\,-3.52\pm0.13)\,$mas$\,$yr$^{-1}$, and $(\mu_{\alpha},\,\mu_{\delta})_{\text{AC211}}=(-0.46\pm0.08,\,-4.31\pm0.20)\,$mas$\,$yr$^{-1}$, respectively. Based on these measurements we estimate the global proper motion of M15 to be $(\mu_{\alpha},\,\mu_{\delta})=(-0.58\pm0.18,\,-4.05\pm0.34)\,$mas$\,$yr$^{-1}$. We detect two previously known but unclassified compact sources within our field of view. Our observations indicate that one them is of extragalactic origin while the other one is a foreground source, quite likely an LMXB. The double neutron star system M15C became fainter during the observations, disappeared for one year and is now observable again---an effect possibly caused by geodetic precession. The LMXB AC211 shows a double lobed structure in one of the observations indicative of an outburst during this campaign. With the inclusion of the last two of a total of seven observations we confirm the upper mass limit for a putative IMBH to be M$_{\bullet}<500$ M$_{\odot}$.

The optical spectra of X-shaped radio galaxies

X-shaped radio galaxies are defined by their peculiar large-scale radio morphology. In addition to the classical double-lobed structure they have a pair of low-luminosity wings that straddles the nucleus at almost right angles to the active lobes, thus giving the impression of an 'X'. In this paper we study for the first time the optical spectral properties of this object class using a large sample (~50 sources). We find that the X-shaped radio population is composed roughly equally of sources with weak and strong emission line spectra, which makes them, in combination with the well-known fact that they preferentially have radio powers intermediate between those of Fanaroff-Riley type I (FR I) and type II (FR II) radio galaxies, the archetypal transition population. We do not find evidence in support of the proposition that the X-shape is the result of a recent merger: X-shaped radio sources do not have unusually broad emission lines, their nuclear environments are in general not dusty, and their host galaxies do not show signs of enhanced star formation. Instead, we observe that the nuclear regions of X-shaped radio sources have relatively high temperatures. This finding favours models, which propose that the X-shape is the result of an overpressured environment.

The extended X-ray emission around HDF130 at z = 1.99: an inverse Compton ghost of a giant radio source in the Chandra Deep Field-North

Abstract One of the six extended X-ray sources found in the Chandra Deep Field-North is centred on Hubble Deep Field (HDF) 130, which has recently been shown to be a massive galaxy at z = 1.99 with a compact radio nucleus. The X-ray source has a roughly double-lobed structure with each lobe about 41-arcsec long, or 345 kpc at the redshift of HDF 130. We have analysed the 2 Ms X-ray image and spectrum of the source and find that it is well fit by a power-law continuum of photon index 2.65 and has a 2–10 keV luminosity of 5.4 × 1043 erg s−1 (if at z = 1.99). Any further extended emission within a radius of 60 arcsec has a luminosity less than half this value, which is contrary to what is expected from a cluster of galaxies. The source is best explained as an inverse Compton ghost of a giant radio source, which is no longer being powered, and for which Compton losses have downgraded the energetic electrons, γ &amp;gt; 104, required for high-frequency radio emission. The lower energy electrons, γ∼ 1000, produce X-rays by inverse Compton scattering on the cosmic microwave background. Depending on the magnetic field strength, some low-frequency radio emission may remain. Further inverse Compton ghosts may exist in the Chandra Deep Fields and beyond.

Discovery of Radio Jets in z ~ 2 Ultraluminous Infrared Galaxies with Deep 9.7 μm Silicate Absorption

Recent Spitzer observations have revealed a substantial population of z ~ 2 ultraluminous infrared galaxies (ULIRGs) with deep silicate absorption (τ_(9.7) > 1). This paper reports a 20 cm radio study of such a sample to elucidate their physical nature. We discover that a substantial fraction (40%) of deep silicate absorption ULIRGs at z ~ 2 are moderately radio-loud, with L_(1.4GHz) = 10^(25)-10^(26) W Hz^(-1). This is in strong contrast with z ≲ 1 radio galaxies and radio-loud quasars where none of the sources with available IRS spectra have τ_(9.7) > 1. In addition, we observe radio jets in two of our sources, with one having a double lobe structure ~200 kpc in extent and the other showing a one-sided jet extending ~90 kpc from the nucleus. The likely high inclination of the latter, coupled with its deep silicate absorption, implies the mid-IR obscuration does not share an axis with the radio jets. These sources are highly obscured quasars, observed in the transition stage after the birth of the radio source, but before feedback effects dispel the interstellar medium and halt the black hole accretion and starburst activity.

VLBI observations of nineteen GHz-peaked-spectrum radio sources at 1.6 GHz

. We present the results of VLBI observations of nineteen GHz-peaked-spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are selected from the Parkes half-jansky (PHJ) sample (Snellen et al. 2002, MNRAS, 337, 981), and 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for compact symmetric objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources. . We obtained total-intensity 1.6 GHz VLBI images of 17 sources for the first time. Of them, 80% show a mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112, and J2325-0344 are classified as CSOs with measured redshift, showing double-lobe structure with sizes of <1 kpc. Three sources J1057+0012, J1600-0037, and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.

3C 254: MERLIN observations of a highly asymmetric quasar

Multifrequency, high-resolution radio observations of the quasar 3C 254 using the Multi-Element Radio-linked Interferometer Network (MERLIN) are presented. The quasar has a highly asymmetric radio structure, with the eastern component of the double-lobed structure being much closer to the nucleus and significantly less polarized than the western one. However, the two lobes are more symmetric in their total flux densities. The observations show the detailed structure of the hotspots which are very different on opposite sides of the radio core, reveal no radio jet and suggest that the oppositely directed jets may be intrinsically asymmetric.

The Shaping of the Red Rectangle Proto-Planetary Nebula

I argue that the slowly expanding biconical structure of the Red Rectangle?a nebula around the post?asymptotic giant branch binary stellar system HD 44179?can be formed by intermittent jets blown by the accreting companion. The bright biconical structure of the Red Rectangle nebula can be understood to be composed of a multiple double-ring system. In the proposed shaping process, one among several processes through which a companion can shape the circumbinary gas, the companion accretes mass from the slow wind blown by the evolved mass-losing star. An accretion disk is formed, and if mass accretion is larger than a critical value, two jets, or a collimated fast wind, are blown. If the high mass loss rate duration is long, bipolar lobes are formed. If, on the other hand, the mass-loss rate is intermittent and during one orbital period the slow wind fills a region that does not extend much beyond the binary system, then only a fraction of the double-lobe structure is formed, namely, rings. This, I propose, was the case with the progenitor of the Red Rectangle, where intermittent episodes of enhanced mass-loss rate led to the formation of a multiple double-ring system.

Abundance constraints and direct redshift measurement of the diffuse X-ray emission from a distant cluster of galaxies

We report on the XMM-Newton (XMM) observation of RX J1053.7+5735, one of the most distant X-ray selected clusters of galaxies, which also shows an unusual double-lobed X-ray morphology, indicative of a possible equal-mass cluster merger. The cluster was discovered during the ROSAT pointings in the direction of the Lockman Hole. All XMM Lockman Hole observations (PV, AO-1 & AO-2 phases) with the European Photon Imaging Camera (EPIC) were combined for the analysis, totaling exposure times ∼648 ks, 738 ks, and 758 ks for pn, MOS1, and MOS2, respectively. With this deep dataset, we could detect the Fe K line and obtain a strong constraint on cluster metallicity, which is difficult to achieve for clusters at z > 1. The best-fit abundance is 0.46 +0.11 −0.07 times the solar value. The Fe line emission also allows us to directly estimate the redshift of diff use gas, with av aluez = 1.14 +0.01 −0.01 . This is one of the first clusters whose X-ray redshift is directly measured prior to the secure knowledge of cluster redshift by optical/NIR spectroscopy. We could also estimate the X-ray redshift separately for each of the two lobes in the double-lobed structure, and the result is consistent with the two lobes being part of one cluster system at the same redshift. Comparison with other metallicity measurements of nearby and distant clusters shows that there is little evolution in the ICM metallicity from z ∼ 1t o the present.

Absorption and Emission in the Four Ground-State OH Lines Observed at 18 cm with the VLA Towards the Galactic Centre

The OH distribution in the Sgr A Complex has been observed in the 1612, 1665, 1667, and 1720 MHz OH transitions with the Very Large Array (VLA), in the BnA and DnC configurations. Spectral line maps have been produced with a channel velocity resolution of about 9 km s–1 and with angular resolutions of 4″ × 3″, and 24″ × 22″, respectively. Some clear results are highlighted here: i) the existence of an OH streamer inside the Circumnuclear Disk (CND) near Sgr A*, ii) absorption from the CND, iii) strong absorption towards the eastern and most of the western parts of the Sgr A East shell, iv) lack of absorption towards both Sgr A West and the compact H II-regions to the east of Sgr A East, v) a double-lobed structure of the High Negative Velocity Gas (HNVG) oriented to the northeast and southwest of Sgr A*, and vi) compact point-like maser emission in all four transitions. In particular, a 1720 MHz maser at –132 km s–1 in the CND as counterpart to a 1720 MHz maser at +132 km s–1 in the CND, was observed.

3C 459: a highly asymmetric radio galaxy with a starburst

Multifrequency radio observations of the radio galaxy 3C 459 using MERLIN, VLA and the EVN and an optical Hubble Space Telescope (HST) image using the F702W filter are presented. The galaxy has a very asymmetric radio structure, a high infrared luminosity and a young stellar population. The eastern component of the double-lobed structure is brighter, much closer to the nucleus and is significantly less polarized than the western one. This is consistent with the jet on the eastern side interacting with dense gas, which could be due to a merged companion or dense cloud of gas. The HST image of the galaxy presented here exhibits filamentary structures and is compared with the MERLIN 5-GHz radio map. EVN observations of the prominent central component, which has a steep radio spectrum, show a strongly curved structure suggesting a bent or helical radio jet. The radio structure of 3C 459 is compared with other highly asymmetric, Fanaroff‐Riley II radio sources, which are also good candidates for studying jet‐cloud interactions. Such sources are usually of small linear size and it is possible that the jets are interacting with clouds of infalling gas that fuel the radio source.

On the origin of X-shaped radio-sources: New insights from the properties of their host galaxies

A significant fraction of extended radio sources presents a peculiar X-shaped radio morphology: in addition to the classical double lobed structure, radio emission is also observed along a second axis of symmetry in the form of diffuse wings or tails. We re-examine the origin of these extensions relating the radio morphology to the properties of their host galaxies. The orientation of the wings shows a striking connection with the structure of the host galaxy as they are preferentially aligned with its minor axis. Furthermore, wings are only observed in galaxies of high projected ellipticity. Hydrodynamical simulations of the radio-source evolution show that X-shaped radio-sources naturally form in this geometrical situation: as a jet propagates in a non-spherical gas distribution, the cocoon surrounding the radio-jets expands laterally at a high rate producing wings of radio emission, in a way that is reminiscent of the twin-exhaust model for radio-sources.

Magnetic character of the empty density of states in uranium compounds from X-ray magnetic circular dichroism

We present a discussion of published X-ray magnetic circular dichroism (XMCD) measurements performed at the uranium M 4,5 edges of metallic uranium compounds, focusing on the shape of the dichroic signal at the M 5 edge. A well-resolved double-lobe structure, comprised of a positive and negative peak, is sometimes observed. Out of the 12 metallic uranium compounds so far investigated by XMCD, six exhibit an intense double-lobe structure at the M 5 edge. This line shape gives information on the empty 5f magnetic density of states with angular quantum number j=7/2. Conclusions about the difference between these two families of compounds are given regarding the splitting of the j=7/2 band and the occupation among the different m 7/2 sublevels.