EVN and Global VLBI results and images

The European VLBI Network (EVN) is an interferometric array of radio telescopes spread throughout Europe and beyond. The figure color-codes existing operational stations (yellow/red), new stations not yet fully participating (blue), non-EVN stations that sometimes participate (purple), and non-EVN stations with whom initial EVN-tests have been carried out (green/brown). Observations are also often conducted in conjuction with the VLBA, GBT, and/or VLA telescopes in the U.S. (not shown).

The Deep Extragalactic VLBI-Optical Survey (DEVOS) aims at constructing a sample of compact radio sources up to two orders of magnitude fainter than those usually studied with VLBI. Recent 5-GHz phase-referencing observations with the EVN (EF016, 2 March 2007) targeted 26 radio sources around two compact calibrators. Optical identifications were ensured by selecting objects from the Sloan Digital Sky Survey (SDSS). An efficient way to identify potential VLBI targets with mas-scale compact radio structures at >1 mJy flux density level was found. Nearly 90% of the sources that are unresolved both in SDSS (i.e. optical quasars) and in the VLA Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey (<5", >20 mJy) have been successfully detected with the EVN. Images of four such quasars in a wide range of redshifts are shown here as an example. Peak brightnesses (from the top left corner) are 83.5, 13.5, 27.5 and 8.6 mJy/beam. Typical 3-sigma lowest image contours were 0.3 mJy/beam in the survey.

Cygnus X-3 is an X-ray binary system containing an unknown compact object (black hole or neutron star) accreting matter from a Wolf-Rayet star. In some particular states, matter is ejected from a region close to the compact object in the form of two opposite, relativistic jets in a plane nearly perpendicular to the accretion disk. Evidence shows that when present, the jets are oriented very close to the line of sight, so we are actually looking more or less into the approaching jet. Taking advantage of state of the art e-VLBI techniques, we have observed Cygnus X-3 at 5 GHz on 2006 April 20, when the system was in a quasi-quiescent state (relatively low flux at radio wavelengths), and 2006 May 18, a few days after a major flare. On the first epoch we detected faint emission probably associated with a fading jet. The second epoch, in contrast, reveals a bright, curved, relativistic jet more than 40 mas in extent. These results were obtained within the framework of the first open call for e-EVN observations (see also Rushton et al., 2007, MNRAS, 374, L47).

The methanol maser transition at 5 cm was observed on 2004 November 11 towards the Galactic source G23.657-0.127, using eight antennas of the EVN (Cambridge, Darnhalll, Effelsberg, Medicina, Noto, Onsala, Torun and Westerbork). The unique circular ring-like structure has a mean radius of 127 milliarcseconds. Assuming the near kinematic distance of 5.1 kpc, the radius of the maser ring is 650 AU (about 16 times larger than the Solar System). In principle there are two three-dimensional structures that project onto the sky as a ring structure like the one observed. These are a circumstellar disk seen face-on or a spherical bubble which may be the shock front originating from the central star and propagating into the circumstellar gas. Proper motions studies of maser clouds are undertaken to reveal the origin of the structure, by measuring expansion or rotation.

The e-VLBI technique has made it possible to transfer the data from a number of European VLBI Network (EVN) telescopes to the central data processor at JIVE through optical fibres, and correlate them in real time. This image shows SN2001em, a Type Ib/c supernova observed with e-EVN+MERLIN. The source is marginally detected in the radio observations. The data show that SN2001em either started fading in the last couple of months, or its radio spectrum is inverted at low frequencies,indicating free-free or synchrotron self-absorption. This is quite unusual, but not unprecedented in radio SNe.

Wednesday 28 April 2004 saw the production of the first ever real-time EVN image. Data from three telescopes of the European VLBI Network (EVN) were sent directly into the EVN MkIV Data Processor at JIVE and correlated, without the data at any time having been stored on disk. The experiment used telescopes located in Onsala (Sweden), Jodrell Bank (UK) and a single antenna of the Westerbork Synthesis Radio Telescope (the Netherlands). The source observed is a gravitational lens system, JVAS B0218+357. A lens system arises when the light from a distant object is deflected by an intervening massive galaxy. This causes the distant object to be distorted and can result in it being split into multiple images. In the case of 0218+357, we see two images of a bright radio quasar, separated by 334mas.

Observations with the EVN of powerful Hydroxyl (OH) emissions from the active galaxy Mrk231 (the most luminous galaxy in the local universe) reveal an emission structure consistent with a rotating, dusty, molecular torus. The images shown here (from left to right) are of the OH line velocity field, the velocity dispersion structure and finally a model of the nuclear torus. These observations strongly support the unification schemes that have been proposed for active galaxies.

LS 5039/RX J1826.2-1450 is a high-mass X-ray binary in our Galaxy, previous VLBI images of which revealed the presence of relativistic radio jets, indicating that LS 5039 was a microquasar. The EVN (right) and MERLIN (left) 5-GHz images shown here detect the jets, confirming their long-lived nature, and demonstrate that they are slightly asymmetric and extend to a distance of ~1000AU from the core. Therefore, this source appears to be a rather good natural laboratory to explore the accretion/ejection processes taking place near compact objects. Finally, LS 5039 may be associated with the high-energy gamma-ray source 3EG J1824-1514. There are still 170 unidentified EGRET sources, and some of them could be associated with microquasars.

The object SDSS 0836+0054 at z=5.82 is the highest redshift radio-detected quasar known to date and was discovered during the Sloan Digital Sky Survey. The detected radiation was emitted at a time when the Universe was ~7% of its present age placing SDSS 0836+0054 close to the edge of the Universe. The target source was clearly detected by the EVN with a dynamic range of ~10. The noise of the target image is about 34 microJy/beam and the peak flux density of the image 770 microJy/beam. This EVN image is one of the most sensitive VLBI images ever obtained and allows us to rule out strong gravitational lensing of this object predicted in recent theoretical works.

SN 1986J in the galaxy NGC 891 is one of the most radio luminous supernovae ever discovered. Left: VLA image of NGC 891 at 5 GHz. The brightest spot in the galaxy is SN1986J. Right: Global VLBI image of SN1986J at the same epoch and observing frequency. This high-resolution image shows a distorted shell of radio emission, indicative of a strong deformation of the shock front. There are several bright knots that delineate a shell-like structure, and an absolute minimum of emission, which could be tentatively identified with the centre of the supernova explosion. If this is the case, SN1986J has then suffered an asymmetric expansion which is likely due to collision of the ejecta with an anisotropic, clumpy (or filamentary) medium.

Shown here are EVN and EVN+VLBA images of several sources observed from a complete sample of young radio-loud AGN at low redshift (z<0.2). This new sample is used for statistical studies of the early evolution of young radio sources, free of cosmological evolution effects. The morphologies of these sources are consistent with them being compact doubles, as expected for these objects. Future multi-epoch VLBI observations will enable the determination of their dynamical ages. The dependence of age on radio luminosity and linear size, in combination with their overall luminosity function and source size distribution will put strong constraints on possible evolution scenarios.

JVAS B0218+357 is one of the most intriguing of gravitational lens systems and an excellent tool for the determination of the Hubble parameter. The figure here shows the two images (A - top, B - bottom) at 8.4 GHz with a resolution of ~1-mas. Both are dominated by two bright core components, but these observations show, for the first time, the extended emission of the radio jet. Image A is tangentially stretched compared to B and various instances of parity reversal can be seen - a textbook case of gravitational lensing.

In the movie, the EVN images come from the time range 18:00 to 01:00 on two days. The ejection of the component occurs mostly during the EVN session, and the second flare in the core is also mostly EVN images.

Top: The faintest radio sources ever detected using high resolution Very Long Baseline Interferometric techniques - EVN images of radio sources detected in the Hubble Deep Field. These images are overlayed upon a radio contour map of the region produced by the Westerbork Radio Telescope (yellow contours), which is itself superimposed upon a deep optical image of the HDF region made by the Canada-France-Hawaii telescope (courtesy Amy Barger, et al.). Bottom: an alernative image showing the optical image in colour with the EVN images again shown as insets. Also see PR.

At a redshift of 3.366, 0014+813 is one of the most luminous quasars in the Universe, lying at a distance of 13.6 billion light years. The figure shows 1.6 GHz images of the quasar 0014+813, obtained with the EVN (left panel) and VSOP (right panel), the first dedicated Space VLBI mission. The VSOP observation was made with the Japanese Space Radio Telescope HALCA, six telescopes of the European VLBI Network and the NRAO Green Bank 43 m telescope. Space-ground baselines (right panel) make it possible to zoom in the source radio structure with the magnification factor of ~3. The synthesized beam of the Space VLBI image is 2x1 mas (FWHM).

Global VLBI image at 8.4 GHz of 1144+35. The HPBW is 1.45 x 0.66 mas in PA -13. The nuclear source is the strong component located at about -10 (RA) and +10 (Dec) mas from the image center. The NW component is a short counter-jet, while the extended and complex structure SE to the core is the main jet component. Multi epoch images show that the main jet is moving with respect to the core with an apparent velocity of 2.7c.

Top: Compact 1667 MHz OH masers around IK Tau detected by the EVN with sufficient resolution to measure proper motions, superimposed on a MERLIN map.

Bottom: EVN/Global VLBI map of Stokes V OH 1667 MHz maser emission from VX Sgr, showing the proposed direction of the magnetic field axis.

Top: Global 6cm VLBI image of 0820+225. Bottom: Lower resolution 6 cm VLBA image of 0820+225 with distributions of the spectral index (left) and rotation measure (right) superposed. All images from Gabuzda, Pushkarev and Garnich.

The distribution of the neutral hydrogen in the central ~50 parsecs of compact radio galaxies can be traced by observing the 21 cm line in absorption. The profiles shown here toward the Compact Symmetric Object 1946+708 indicate a circumnuclear torus comprised of predominantly neutral gas. Evidence of this torus is also detected in the ionized gas by imaging free-free absorption.

The LH picture shows the MERLIN+VLA 20cm image of M82 with an inset showing one of the supernova remnants imaged by EVN at two epochs - 1986 and 1997. By comparing the shell sizes an average expansion velocity of 9500km/s can be estimated - consistent with an age of ~30-40 years (Pedlar et al. 1999). The RH picture shows the same supernova imaged with global VLBI at 20cm with 3mas (0.05 pc) resolution.

Hubble telescope image of the accretion disk in NGC4261, and a VLBI map of its nucleus. The spectrum of atomic Hydrogen gas at the location where the inner part of the disk covers the radio source. This result is the first scientific outcome of the EVN MkIV data processor at JIVE.

The lens system MG J0414+0534 comprises four images of a z=2.64 QSO. These images illustrate how the gravitational potential of the lensing galaxy distorts the structure of the background object - rotating, translating and "flipping". Image A1 in this system is particularly distorted.

VLBI observations of SN1993J at wavelengths of 3.6, 6, 13 and 18cm since 1993 have shown that the expansion of the shell-like radio structure, discovered in 1995, is self-similar and is decelerating, yielding support to a binary scenario for the progenitor. An avi movie (gzipped) of the expansion can be found here.

These observations of supernova SN1993J used the technique of phase referencing that has enabled extremely accurate positions for the radio emission to be determined. The phase-reference source was the nucleus of M81, the host galaxy of the supernova.

In the figure the color scale represents the velocity whilst the spot size scales with the flux density.

Mkn 421 was observed at a number of epochs and frequencies with the EVN, VLBA, and VSOP. The images show subluminal, mildly relativistic, motion on the parsec-scale. Since highly relativistic motion in the core is required to explain the TeV gamma-ray variability, this suggests deceleration of the jet between the TeV emitting region and parsec-scales.

Global VLBI and MERLIN observations of the precessing beams of the Galactic radio-jet X-ray binary ("microquasar") system SS433 at 1.6 GHz are shown in the top figure. Focusing on the central parts of the source (bottom) reveals the Equatorial Emission Region (discovered by Paragi et al., 1999, A&A 348, 910), quasi-perpendicular to the normal jets. This region changes with the precession cycle. It is most probably related to an equatorial outflow from the binary system.

3C264 is an FR-I source that contains a jet that is clearly visible in both the radio and the optical. Seen with the VLA, MERLIN and the EVN, the different resolutions reveal radio emission on different scales, from the large extended lobes seen with the short baselines of the VLA to the collimated jets that are seen at the highest resolution with the EVN.

These observations reveal a change in the jet morphology that is coincident with an optical "ring" that has been imaged with the Hubble Space Telescope (HST).

The upper panel shows an EVN+MERLIN 18cm map of the Seyfert 2 Galaxy Markarian 3, showing two highly collimated radio jets and an isolated core component (situated ~0.3 arcsec east of the image centre). The western jet terminates in a bright hotspot containing complex substructure. The spatial scale of the image is 250 pc/arcsec. The lower panel shows the 18-cm radio map (contours) superimposed on the [OIII] emission line structure imaged with HST by Capetti et al. (1995, ApJ, 454, L85).

3C452 was observed with the EVN as part of an effort to observe a large sample of radio galaxies at milli-arcsecond resolution. This source has an FRII morphology on the largest scales and displays very symmetric structure in this high-resolution image.

1943+546 is a compact symmetric object (CSO), a class of radio sources that are believed to be relatively young. The age of this source has been estimated at ~1000 years from the detection of increasing separation between the two "hotspots" (brightest points in the image).

M87 (3C274) is a relatively nearby AGN containing a well-studied radio jet. These images show the core and jet when imaged using Global VLBI at 43 GHz (top) and at multiple epochs with a Global VLBI+VSOP (bottom) array at 5 GHz. One interesting aspect of this system is the very wide opening angle of the jet seen at 43 GHz, in stark contrast to the behaviour further along the jet which shows that the emitting plasma is well collimated. From this it is possible to estimate the distance along the jet that the collimation process begins (approximately 100 Schwarzschild radii in this case).

The increase in the separation of the two most prominent components of the GHz-Peaked Spectrum (GPS) radio galaxy 2021+614 has been determined by comparison with previous observations. The projected speed with which these two components recede from each other is 0.12/h c which, given a projected separation of 16.1/h pc, implies a kinematic age of 440 years. This result provides additional support for the contention that compact symmetric radio objects are young and the precursors of the extended radio sources.

EVN 18cm observations of the gravitational lens 0957+561. This wide-field image is able to detect for the first time compact features in the extended arcsecond scale jet structures. These data were used to refine wide-field VLBI imaging techniques that were later applied to the HDF (Garrett et al.) and M82 (Pedlar et al.).

Shown here is a 1.6-GHz image of the giant radio galaxy 3C236. With a linear extent of ~4 Mpc, this is the largest known radio source in the universe although this image only shows the inner part (~2kpc) of the source. Its size, as well as the presence of both large-scale (FRI/II) and small-scale (CSS) structures, make it an important object for radio source evolution studies.

3C380, a quasar, is one of the most powerful radio sources known and is a member of the Compact Steep Spectrum (CSS) class. On parsec scales the source consists of a one-sided jet which is shown here.

EVN+MERLIN 18cm observations of the luminous infrared galaxy IIIZw35 show the OH megamaser emission to have a ring-like distribution. Such a ring can account for both the compact as well as the diffuse masers observed. The same observations also show compact continuum sources that are consistent with being either radio supernovae or supernova remnants.

EVN 6-cm observations of the gravitational lens 2016+112 resolve all three images, A, B and C. In the region of image C the magnification may be a factor of 100 or more thus providing super-resolved maps of the lensed radio source.

The upper image was made with the VLA at 5 GHz and shows two faint jets feeding two extended radio lobes. The remaining VLBI images show the structure surrounding the nucleus. The bottom image shows the inner 3 milli-arcseconds with an angular resolution of 0.15 milli-arcseconds (or 130 light days!). Comparison of the brightness ratio between western and eastern jets at the different wavelengths yields strong evidence for a gaseous torus of absorbing material surrounding the core, which partially blocks the radiation from the counter-jet, but not from the jet.