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2007-2008:reasearch

Cosmology and deep VLBI surveys

The first radio-loud quasar at redshift higher than six was observed with the EVN at 1.6 and 5 GHz by Sándor Frey (FÖMI SGO), Leonid Gurvits, Zsolt Paragi and Krisztina Gabányi (FÖMI SGO). Extremely high redshift quasars are interesting

The EVN data showed a double structure at 1.6 GHz, while at 5 GHz only the brighter feature was detected. Both components were resolved, and apparently steep spectrum. This is unlike the brightest radio quasars at a redshift ~2, which are flat spectrum core dominated sources. The double structure, resolved components and the steep spectrum in fact resembles to the compact symmetric objects (CSO) that are more frequent in the low-redshift Universe. CSO sources are believed to be young, or in some cases they may be small because they are confined by the dense interstellar medium. If J1427+3312 is indeed young, one could detect the expansion of the source by VLBI monitoring. The second highest redshift radio-loud quasar (J0836+0054, z=5.77) has a steep spectrum as well, but it has a single compact component. A deep, dedicated VLBI survey of the highest redshift quasars will show how frequent are CSO like structures in the early Universe.

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EVN images of the highest redshift radio quasar J1427+3312 at 18cm (left) and 6cm (right). The double morphology, steep spectrum and resolved components resemble the structure of CSO sources at much lower redshifts.

The Deep Extragalactic VLBI-Optical Survey (DEVOS), led by Sándor Frey (FÖMI SGO, Hungary) aims at constructing a sample of compact radio sources up to two orders of magnitude fainter than those usually studied with VLBI. The group involves Leonid Gurvits and Zsolt Paragi, László Mosoni (MPA, Heidelberg), Mike Garrett (Astron) and Simon Garrington (JBO, Univ. Manchester). Recent 5 GHz phase-referencing observations with the EVN 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. The results were published in Astronomy and Astrophysics.

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Four example sources observed in the Deep Extragalactic VLBI-Optical Survey (DEVOS). Almost 90% of all faint FIRST sources that had pointlike optical counterparts in SDSS were detected.

Gamma ray bursts and supernovae

On 19 March 2008 NASA's Swift GRB Explorer mission discovered a record breaking gamma ray burst, GRB 080319B. Our current understanding is that GRBs produce highly relativistic, collimated outflows, powered by a newly formed black hole. This jet decelerates, expands and interacts with the ISM. The primary emission is due to internal shocks within the jet, while the X-ray/optical/radio afterglow is produced by external shocks due to jet-ISM interaction. Multi-frequency observational campaigns are necessary to distinguish in between various physical scenarios. At its peak, GRB 080319B was the brightest optical and X-ray source measured for a GRB, and one of the highest gamma ray fluences recorded. The optical emission could have been observed by naked eye, without the aid of an astronomical telescope.

A group led by Alexander van der Horst (then Univ. Amsterdam) including Zsolt Paragi observed the source with the WSRT at several epochs. These data put strong constraints on the origin of the afterglow emission. In a broader collaboration, the richest multi-frequency information ever was gathered for this spectacular burst. It was shown that the prompt emission originated in a single physical region implying an extremely relativistic outflow that propagated within the narrow core of a two-component jet. The results were published in Nature.

The multi-frequency lightcurve of the “naked eye” GRB and the two component jet model that can explain the observed spectral behaviour of this powerful burst.

Gamma ray bursts have been shown to be occasionally associated with type Ib/c supernovae, which are thought to arise from the core collapse of a massive Wolf-Rayet star. This core collapse generates ultra-relativistic jets, which beam gamma rays and all other early emission into a narrow cone. Thus, most of these stars will not have detectable gamma-ray emission although they may still be detectable in optical wavelengths as SNe Ib/c. Direct evidence for the existence of (mildly) relativistic, collimated outflows in these sources may come from VLBI imaging. Making these measurements is extremely difficult because of the large distance and faint emission in the radio regime. So far only one SN Ib/c have been detected with VLBI, SN2001em.

On the 15th of August 2007 SN 2007gr was discovered in the nearby (~7.3 Mpc) spiral galaxy NGC 1058. A group led by Zsolt Paragi observed SN 2007gr at 5 GHz with the e-EVN just a few weeks after its discovery. Collaborators on this project were - amongst others - Huib van Langevelde, Arpad Szomoru, Yurii Pidopryhora, Chryssa Kouveliotou (NASA/MFSC), Mike Garrett (Astron), Enrico Ramirez-Ruiz (Univ. Santa Cruz), Michael Bietenholz (Hartebeesthoek) and Megan Argo (JBO). The supernova was detected at a 5.6 sigma level (420 microJy/beam), in agreement with the VLA position. The good sensitivity and the availability of the e-EVN (then still without the Effelsberg telescope) was very important for this result. More sensitive follow-up observations with a global array in November 2007 resulted in a non-detection, while the source was still about 280 microJy at 5 GHz. The initial e-EVN results exclude highly relativistic ejecta because the source appeared unresolved, but the global observations can only be explained if the source expanded with at least mildly relativistic speeds. This clearly demonstrates the importance of early VLBI observations of Type Ib/c SNe. The e-EVN results were quickly published in ATEL #1215.

The second type Ib/c supernova that was detected with the VLBI technique ever was SN2007gr, observed with the e-EVN shortly after its discovery.

Scintillation and propagation effects

The refractive medium in the interstellar medium acts like the agitated surface of a swimming pool, that bends sunlight to cause an irregular pattern of light and dark bands on the bottom of the pool. In the astronomical case, the Earth moves through an immense pattern of light and dark bands, which causes the variability of the compact radio sources. From the observed scintillation properties one may constrain the structure of high redshift sources, thus using the interstellar medium (ISM) as a magnifying lens to study quasars at resolutions otherwise not available with our astronomical instruments. On the other hand, compact radio sources are ideal tools to investigate the physics of the interstellar medium. In the course of his work about scintillation, interstellar medium and extragalactic compact sources, Giuseppe Cimò (in a collaboration led by Cliff Senkbeil, Univ. Tasmania) observed an extreme scattering event (ESE) towards the compact BL Lac object AO 0235+164. The scattering material was apparently compact, between 0.09 and 0.9 AU, and it was located at a distance less then 3.6 kpc from the Sun. The density of the cloud was minimum 4 x 10^{13} cm^{-3}. It was suggested that ESE events may be responsible for at least one transient discovered earlier by Bower et al. using VLA archive data.

The rapid flux variation of AO 0235+164 at 6.65 GHz in 2005. Crosses indicate independent measurements at 8 GHz by Uwe Bach et al.

AO 0235+164 was just one of the sources included in the Continuous Single-Dish Monitoring of Intraday Variability at Ceduna (COSMIC) program, in which Giuseppe Cimò actively participates. The observed modulation of the variability characteristics of compact extragalactic radio sources can be explained by seasonal effects due to changes on the relative velocity between the Earth and the interstellar clouds. Such modulation has been tentatively detected in the source PMN J1326-5256 (see below).

Intraday flux variations of PMN J1326-5256 (red) at 6.7 GHz. There was a dramatic change in the temporal behaviour after MJD 52744. The data were normalized for the target and the calibrator (B1934-638, black dots) as well.

Besides the single dish observations and data analysis, Giuseppe Cimò initiated a new VLBI project using the EVN in an innovative way, in order to study the ISM. In particular, the aim of the experiment is to measure the distance of the scattering material causing the rapid scintillation of the flat spectrum radio sources. In a pilot experiment the source 1819-3845 has been observed with the EVN array. This quasar has been known as the most extreme scintillator (600% variability within a few hours). The unexpected outcome of this experiment has shown that the extreme variability of J1819+3845 has stopped. Taking into account previous scintillation measurments of this quasar, it has been possible to put a lower limit of 34 A.U. to the size of the electron cloud responsible of the previously observed extreme variations.

Hayley Bignall analysed the first optical spectrum, taken earlier during AAT service observations, for the southern extreme intraday variable radio source PMN J1326-5256. In a poster paper presented at the 'Modern Radio Universe' conference in Manchester, Hayley Bignall, Giuseppe Cimò , Dave Jauncey (ATNF) and co-authors suggested that this object may be associated with an unidentified source in the 3rd EGRET catalogue, based on its multiwavelength properties. The Fermi Gamma-ray Space Telescope (formerly GLAST), will be able to confirm the gamma-ray source association. The optical spectrum is featureless between ~5000 and 9000 Å, with a signal-to-noise ratio of ~15 in the continuum, indicating that the source is mostly likely a BL Lac object. The object was noted to be much brighter than on historical optical plates, indicating that it is highly optically variable. In addition, the sub-arcsecond accurate radio position from ATCA data is coincident with an object in the 2MASS catalogue which has near-infrared colours typical of BL Lac objects.

Hayley Bignall used the Effelsberg radio telescope to measure the rapid 22 GHz maser variability in NGC 3079. Preliminary analysis indicates that while Effelsberg has the sensitivity and stability for the rapid variations to be detected in at least the brightest maser feature, it may not be feasible to measure a time delay in the variability pattern arrival times between Effelsberg and the GBT, which could be used to determine the velocity and other properties of the scattering screen. The very bright, narrow blue-shifted feature observed by Wouter Vlemmings (University of Bonn), which was not seen in earlier data, has continued to fade and was very weak or absent during the observations at Effelsberg.

Hayley Bignall has contributed to some of the analysis of the first four epochs of VLA data from the MASIV Survey, led by Jim Lovell (ATNF), Barney Rickett (UCSD), Jean-Pierre Macquart (Caltech) and Dave Jauncey (ATNF). One of the most far-reaching results to come out of the MASIV Survey is an observed decrease in scintillation at high redshifts, greater than that expected from a cosmological decrease in brightness, implying that the high redshift sources have larger apparent angular sizes, suppressing scintillation in the local Galactic interstellar medium. This effect may be due to scatter-broadening in the ionized intergalactic medium, or a redshift dependence of the intrinsic source sizes. Redshifts for the whole MASIV sample are needed in order to separate the various observed effects. An observational programme to measure redshifts of MASIV Survey sources is being led by Tapio Pursimo (NOT). Hayley Bignall assisted with NOT observations during a six-night observing run in September 2007. In addition, the project was allocated two nights on the Palomar 200 inch telescope in the second half of 2007, and has been allocated two more nights on the 200” and three nights on the Keck telescope in the first half of 2008, with J-P. Macquart the PI for 200“ and Keck proposals, to obtain spectra for the remaining optically faint sources.

Active galactic nuclei

Hayley Bignall and Cormac Reynolds worked with summer student Gabriele Surcis on analysis of EVN+MERLIN data on BL Lac objects identified in the 'Deep X-ray Radio Blazar Survey' (DXRBS). These objects have properties spanning the range between classical X-ray- and radio-selected BL Lac samples. The results show that many of the sources have complex structures between milliarcsecond and arcsecond scales. Lower resolution images obtained with the VLA (by Hermine Landt, CfA) and ATCA (Hayley Bignall) suggest that these sources do not belong to a single parent population viewed at different angles, in accordance with the AGN unification scheme, but there are differences in the intrinsic source properties as well. The VLBI data will reveal similarities and differences in the mas-scale structure of these sources.

High-resolution 18cm images of the BL Lac object thought to be associated with X-ray source WGA J1231+2848. The top right-hand image is from observations using 10 antennas of the EVN. A lower resolution image from simultaneous MERLIN data is shown in the top left panel. An intermediate-resolution image made after carefully combining the data from both arrays is shown in the lower left panel, while the lower right panel shows the combined (u,v) coverage.

Hayden Rampadarath and Antonis Polatidis worked together with Mike Garrett (Astron) to obtain a list of potential calibrators and targets for LOFAR and RadioAstron. They analysed VLBA 92cm archival data of 43 extragalactic sources in order to identify early targets and potential calibrator sources for the LOFAR radio telescope and the RadioAstron space VLBI mission. Some of these sources could also be suitable as “in-beam” calibrators for low-requency VLBI experiments, permitting deep, wide-field studies of other faint sources in the same field of view. All publicly available VLBA 92cm data observed between 1 January 2003 and 31 December 2006 were analysed using an automatic pipeline, implemented within AIPS. The vast majority of the data were still unpublished. Of the 43 sources, 40 were detected on at least one VLBA baseline of which 29 had sufficient data to be successfully imaged. Most of the sources were compact, with a few showing extended structures. Of the 29 sources imaged, 13 were detected on the longest VLBA baselines (~9 Mλ), while all were detected on baselines greater than 2 Mλ (the maximum baseline of LOFAR including the current international baselines). A paper describing the results have been accepted for publication in Astronomy and Astrophysics.

With Silke Britzen (MPIfR) and Rene Vermuelen (ASTRON), Bob Campbell completed the statistical studies of the jet-component kinematics of CJF sources. This project had three basic thrusts. First, fitting elliptical Gaussian models to the 3-4 epochs of snapshot observations of the 293 sources, using a Difmap variant he made to output the statistical uncertainties associated with the elliptical Gaussian component parameters as well as the correlation matrix among them. Second, estimating kinematic models from these results for 779 jet components in 266 of the CJF sources, (237 of sources with measured redshifts, comprising 699 components). This large sample provides the basis for correlation analysis of apparent component velocity against other source properties (class, luminosity, etc.), direct comparison with the VLBA 2cm survey, and also compilation of intra-source statistics of acceleration and bending as a function of distance along the jets. Third, investigating the correlations among the radio and ROSAT soft X-ray properties of the sources, such as radio core-dominance and pc/kpc-scale misalignments versus ROSAT detections, as well as computation of both inverse-Compton and equipartition Doppler factors to investigate aspects of the beaming.

With Silke Britzen (MPIfR), Nadia Kudryavtseva (MPIfR), and others, Bob Campbell investigated the kinematics of the pc-scale jet components of the blazar S5 1803+784. Many of the jet components remain at roughly constant radius from the core, but the jet ridge-line itself shows quasi-periodic oscillations in position angle on the order of 10 degrees over the inner 4 mas, with a time-scale on the order of 8-9 years.

Atomic gas in galaxies

Arpad Szomoru worked on a pilot study of two galaxy clusters at z=0.2, in collaboration with Marc Verheijen (Kapteyn Institute, Groningen), Jacqueline van Gorkom (Columbia University), K.S. Dwarakanath (Raman Research Institute), Bianca Poggianti (INAF) and David Schiminovich (Columbia University). Observations with the powerful new backend of the Westerbork Synthesis Radio Telescope revealed neutral hydrogen emission in 42 galaxies. In Abell 963 most of the gas-rich galaxies are located between 1 and 3 Mpc in projection, northeast from the cluster core. The velocities are slightly redshifted with respect to the cluster, indicating that this is largely a background group. None of the blue galaxies in the core of Abell 963 are detected in HI, although they have colors and luminosities similar to those of the HI detected galaxies in the cluster outskirts and field. Abell 2192 is less massive and more diffuse. Here the gas-rich galaxies are more uniformly distributed. The detected HI masses range from 5×10^{9} to 4×10^{10} Msun. Some galaxies are spatially resolved, providing rudimentary rotation curves useful for detailed kinematic studies of galaxies in various environments. On the long term, the project is aiming at ultradeep integrations down to HI masses 8×10^8 Msun, that will provide a complete survey of the gas content of galaxies at z=0.2, probing environments ranging from cluster cores to voids.

An example HI detection: a spatially resolves galaxy at the same redhsift as Abell 963. The HI spectrum is shown top left, the position-velocity diagram, indicating the systemic velocity and the spatial center of the galaxy is shown bottom left. The integrated HI emission is overlaid on optical R-band image on top right, and a zoomed in version of the optical image showing the morphology of the normal spiral galaxy is shown bottom right.

Yurii Pidopryhora continued his work on the large project to study the extra-planar hydrogen in the inner Milky Way based on the observations of 21 cm HI line with the Green Bank Telescope (GBT), Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) performed earlier in 2003-2006 as a part of his PhD thesis work in the USA. The project is done in collaboration with Felix Lockman (NRAO) and, in parts, with K.S. Dwarakanath (RRI), Harvey Liszt (NRAO), Joseph Shields (Ohio University) and Michael Rupen (NRAO).

Within the framework of this project additional 25 hours of observations with the GBT (proposal GBT06C-038) were performed in 2007. The purpose of these observations was to make high-quality HI maps around clouds in the disk-halo interface of the Galaxy for which there were available VLA HI maps at high angular resolution. The GBT data supply zero-spacing information, constrain the deconvolution of the interferometric data, and detect extended, low surface brightness emission which might not have been detected by the VLA observations. Successful recipes (using procedures of both AIPS and MIRIAD packages) for the combined interferometry - single dish data reduction were developed and employed to make high-resolution maps of two HI halo clouds (G19.4+6.3 and G27.0+6.3) observed with the VLA in both C and D configurations. This has allowed to make unique measurements of the properties of Galactic halo HI; this result was presented at the conference “The Role of Disk-Halo Interaction in Galaxy Evolution: Outflow vs. Infall?” in Espinho, Portugal. The work of making high-resolution maps of more halo clouds is in progress. An earlier project on the Ophiuchus Superbubble, discovered in the course of a different vein of the same Galactic halo HI project, was finalized. A detailed paper describing the properties of this object was published in the Astrophysical Journal and were presented at several meetings.

The Ophiucus superbubble in HI (purple) an Hα (green). HI spectra (mostly as observed by the Green Bank Telescope (GBT) during a dedicated survey, but data from the lower resolution Leiden-Dwingeloo survey were used around the edges) were integrated over 60-160 km/s LSR (the integration covers all the tangent point velocities at these longitudes), Hα (as observed with the Wisconsin H-Alpha Mapper (WHAM)) integrated over 55-95 km/s LSR (limited by the spectral range of the WHAM Halpha survey) The superbubble is a major feature in ionized hydrogen as well as HI, but unlike the neutral hydrogen, the ionized hydrogen fills the area and is not concentrated at its edges. There is detailed correspondence between HI and Hα for many features. The diagonal purple stripe at the bottom results from extinction of the Hα by dust in the Great Rift.

Hayden Rampadarath was involved in a project led by Mike Garrett (Astron) to investigate Hanny's Voorwerp. This is a hot, irregular gas cloud located about 60000 light years from the galaxy IC 2497 which apparently does not contain any heating source. WSRT observations of the neutral hydrogen show that Hanny's Voorwerp is embedded in a gas cloud of 5000 million solar masses, which has an extension stretching out to the position of a galaxy group. Hydrogen spectra reveal the connection between the gas around IC 2497 and the galaxy group. The Voorwerp is part of a much bigger gas cloud, the remnant of an interaction between IC 2497 and a galaxy group. The WSRT radio continuum observations show a source at the centre of IC 2497 with a jet-like extension in the direction of the Voorwerp. Short e-EVN observations reveal a very small source at the centre of the galaxy, less than 0.1 light years across. This suggests that IC 2497 contains a supermassive black hole at its centre. The plasma jet emanating from the central engine clears a channel through the thick dust and gas that surrounds the black hole, permitting the intense radiation to reach Hanny's Voorwerp. Hayden Rampadarath was leading the e-VLBI observations, that included Paragi as well.

WSRT radio continuum observations (white contours) of IC 2497 show a jet-like extension in the direction of Hanny's Voorwerp. The e-VLBI observations reveal a very small source at the centre of the galaxy (top-right image). The WSRT neutral hydrogen show that Hanny's Voorwerp is embedded in a gas cloud of 5000 million solar masses (red in the image), which has an extension stretching out to the position of a galaxy group (to the right). Hydrogen spectra reveal the connection between the gas around IC 2497 and the galaxy group (bottom picture).

Starburst galaxies

The central regions of many Luminous Infra-red Galaxies (LIRG) are known to host intense bursts of massive star formation, resulting in copious explosions of supernovae. However, the dust-enshrouded ambients where those supernovae explode prevent their detection at optical and near-infrared wavelengths, and the only way to discover them is by means of radio observations. Antonis Polatidis worked together with Miguel Angel Pėrez-Torres (IAA, Granada, Spain) and others on the famous LIRG Arp299. e-EVN observations were carried out on 8-9 April 2008 with Cambridge, Medicina, Jodrell Bank (Lovell Telescope), Onsala, Torun and Westerbork at 5 GHz. During the second observing epoch the array included Effelsberg, Knockin and Shanghai as well. There were 25 compact radio sources detected (above 5 sigma) in the central 500 light years of the galaxy. The only viable explanation for many of the newly discovered sources is that they correspond to recently exploded core-collapse supernovae, and the rest are most likely super star clusters and supernova remnants. This result rules out starburst scenarios with constant star forming rates of massive stars in Arp 299, and yields support for either recent (few Myr), instantaneous starbursts or, alternatively, a top-heavy initial mass function of the stars in Arp 299.

Top: 5 GHz VLA archival observations of Arp 299 on 24 October 2000, displaying the four brightest knots of radio emission in this merging galaxy. At this frequency, region A accounts for ~70% of the total VLA emission from Arp 299, and for ~50% of its far infrared emission. Middle and bottom: 5 GHz e-EVN observations of the central 500 light years of the Luminous Infrared galaxy Arp 299 on 8 April 2008 and 5 December 2008. The off-source rms noise is of 39 μJy/beam and 25 μJy/beam for the middle and bottom images, respectively. The appearance and disappearance of several (at least eight) new compact sources between April and December 2008 is evident. The only viable explanation for those components is that we are witnessing the fading away of several radio supernovae, along with the rising phase of radio emission of core-collapse SNe that exploded very recently. The rest of the compact sources are most likely either supernova remnants, or super star clusters. North is up and East is left in the image.

There is growing evidence that the properties of the molecular gas in the nuclei of starburst galaxies may be very different from those seen in Galactic star forming regions. Unfortunately, among the fundamental parameters derived from molecular line observations, the kinetic temperature of the molecular gas in external galaxies is often not well determined. Stefanie Mühle has developed a diagnostic method to derive the physical properties of the molecular gas in external galaxies, in particular its kinetic temperature, using a set of para-formaldehyde lines and a non-LTE radiative transfer model. As a proof of concept, she in collaboration with Ernest R. Seaquist (Toronto) and Christian Henkel (Bonn) tightly constrained the physical properties of the prototypical nearby starburst galaxy M82. This result was published in the Astrophysical Journal. The analysis, which is completely independent of observations of other molecular tracers like ammonia, suggests the presence of an unusually warm, moderately dense molecular gas component in the circumnuclear ring of the starburst galaxy. These findings agree very well with the properties of the high-excitation molecular gas component found in the most comprehensive CO-line studies and further support the emerging picture of molecular gas in active galaxies being very different from that in more quiet environments. The observations also indicate the presence of methanol in at least one of the molecular lobes of M82. Investigations of the properties of the molecular gas in other starburst galaxies and AGN using this new diagnostic tool are underway. Having thus demonstrated the diagnostic power of para-formaldehyde lines, Stefanie Mühle now investigates the diagnostic properties of ortho-formaldehyde lines using VLA data taken at 4.8 GHz and 14.5 GHz.

Para-formaldehyde lines detected towards the prototypical starburst galaxy M82. The Gaussian fits correspond to the following transitions: a = H_2CO(2_{02}-1_{01}), b = HC_3N(16-15), c = H_2CO(3_{21}-2_{20}), d = H_2CO(3_{22}-2_{21}), e = H_2CO(3_{03}-2_{02}).

Stefanie Mühle has participated in a multi-species multi-transition survey of the properties of the molecular gas in a sample of Luminous Infrared Galaxies (LIRGs) with Padelis P. Papadopoulos (Zurich), Thomas R. Greve (Pasadena), Paul van der Werf (Leiden), Kate Isaak (Cardiff), and Yu Gao (Nanjing). For this survey, she analyzed data taken with the recently commissioned ACSIS spectrometer at the JCMT in combination with older JCMT data. First results suggest that the HCN(1-0) and HCO+(1-0) line luminosities alone can be poor estimators of dense molecular gas unless the excitation conditions are accounted for. In Ultraluminous Infrared Galaxies (ULIRGs), the CO cooling of the _dense_ gas may be comparable to that of the CII line at 158 micron. At the same time, the global molecular gas reservoir may still be in a low excitation state.

As a member of the JCMT Nearby Galaxy Legacy Survey (NGLS) team, Stefanie Mühle investigates the molecular gas and dust content of galaxies within a distance of 25 Mpc using new observations at the JCMT and ancilliary data. The first phase of the NGLS consists of CO(3-2) observations for 21 galaxies from the SINGS sample as well as additional galaxies from the Virgo cluster. The subsequent phases, which will begin in 2009, will consist of SCUBA-2 observations of all sample galaxies and possibly CO(3-2) observations of the sample galaxies not yet observed in this transition. CO(3-2) emission has been detected in the Virgo galaxies NGC4254, NGC4321, NGC4569 and weakly in NGC4579. For the three CO-bright galaxies, the molecular gas masses are of the order of 10^9 solar masses and the instantaneous gas depletion times are about one Gigayear.

Lisa Harvey-Smith worked with Willem Baan (ASTRON) on observations of nearby galaxies at 6.7 GHz using the Effelsberg 100m, Radio Telescope. The aim was to search for methanol masers and thereby pinpoint sites of active massive star-formation in those galaxies.

Lisa Harvey-Smith and Willem Baan observing at the Effelsberg 100-m Telescope

Galactic transients

LSI +61 303 is a microquasar candidate that is active from radio wavelength to the gamma-ray regime. The exact nature of the binary system is however not clear, recent VLBA measurements suggested that the activity in fact comes from the interaction of a pulsar wind with its companion's. The MAGIC collaboration carried out an observing campaign with the MAGIC telescope, CHANDRA, VLBA, MERLIN and the e-EVN. The radio monitoring was coordinated by Miguel-Angel Perez-Torres (IAA, Granada, Spain), the e-EVN data were processed by Zsolt Paragi. At the epoch of e-EVN observations the source did not show extended emission from the 10-100 mas scales, which has been seen at earlier epochs. There was a hint of correlation seen between the X-ray and the TeV gamma-rays during the campaign suggesting that in these two high energy regimes the emission comes from the same electron population, which is different from the electron population producing the radio emission. The results were published in the Astrophysical Journal.

High resolution LSI +61 303 images during the MAGIC observational campaign. There was no apparent correlation between radio and X-rays/gamma rays, indicating that the emission is coming from different electron populations.

Miqroquasar Cyg X-3 has been active in recent years. The triggered e-EVN proposal by Valeriu Tudose (Univ. Amsterdam), Anthony Rushton (JBO), Zsolt Paragi, Rob Fender (Univ. Southampton), Ralph Spencer (JBO) and Mike Garrett (Astron) was activated on 9 April 2008 when the source showed signs of an accretion disk state change in the X-rays. This particular state has never been targeted at milliarcsecond resolution in the radio regime. A single radio component (earlier assumed to be a permanent jet-ISM interaction feature) was detected at a lower emission level than in 2007, consistent with the radio core quenching scenario in the soft X-ray state. The identification of the radio core allowed the group to estimate the proper motion of Cyg X-3. As expected following the state change, Cyg X-3 began a strong radio flare which was observed at three epochs separated by a few days. The group will use the e-EVN as well as archival VLBA data to separate the core flux from the occasional jet emission, that will allow a clearer classification of accretion disk states in the system and measure the proper motion of Cyg X-3.

e-EVN images of Cyg X-3 during different accretion disk states in the period 2006-2008. With these observations the core of the system was cleary identified.

Gloria Dubner (IASP, Argentina), Elsa Giacani (IASP, Argentina), Andrei Bykov (A.F. Ioffe Institute of Physics and Technology, Russia), Zsolt Paragi and Huib van Langevelde observed a radio source in the error box of the 27 May AGILE transient on 24 June 2008 with the e-EVN. The data were analysed by JIVE summer student Alfonso Trejo (UNAM, Mexico). In the AGILE error box there is the brightest, so far unidentified gamma-ray source from the EGRET catalog as well. Because the radio source observed is positionally consistent with the only hard X-ray source (IGR J20187+4041) in the close vicinity of the transient, it was assumed that they may be related. In the e-EVN observations the radio source was detected on 10-mas scales, but it did not show flaring activity. The results were published in ATel #1597. This was soon cited by ATel #1623, in which it was shown that IGR J2018+4041 is a low- luminosity type-2 Seyfert galaxy at a redshift of z=0.0144. One would not expect flaring gamma-ray activity from normal Seyfert galaxies, which questions the relation of the radio source to the gamma transient. The nature of the high energy source is still not clear.

The hard X-ray and radio source IGR J20187+4041 was in the error box of an AGILE flare on 27 May 2008. e-EVN observations showed a faint, compact structure, with apparently no flaring activity. Later AGILE observations and analysis showed that the flare was likely not related to IGR J20187+4041.

On 28 October 2008 RATAN-600 reported a major flare in the famous microquasar SS433. Valeriu Tudose (Univ. Amsterdam) and Zsolt Paragi organised e-EVN monitoring observations together with Paolo Soleri (Univ. Amsterdam), Rob Fender (Univ. Southampton), Sergei Trushkin (SAO, Russia), Mike Garrett (Astron), Ralph Spencer and Anthony Rushton (JBO). The first epoch data on 6 November showed three pairs of radio components located symmetrically on both sides of the presumed position of the core of the system, two of which were already resolved. Assuming that the radio ejecta were moving at a rate of about 8 mas/day, the furthest components at about 100 mas from the core were ejected at around 24 October and perhaps the RATAN-600 observations on 28 October caught the aftermath of this event. The two components at about 25 mas from the core could have been ejected around November 3, date which also corresponds to the rebrightening event witnessed by RATAN-600. The results were reported in ATel #1836. Continuing observations with RATAN-600 and the e-EVN (on 13 and 19 November) showed a long-lived flaring activity in the system.

e-EVN images of a long-lived SS433 flare.

Massive star forming regions

Kalle Torstensson and Huib van Langevelde continued their studies of methanol masers associated with high mass star formation. In collaboration with Floris van der Tak (SRON Groningen) and Wouter Vlemmings (Bonn University), interesting results were obtained on the nearest high mass star forming region Cep A, which is studied as the archetypical source in the sample. Analysis of Harp data taken with the JCMT allows the derivation of the rotation temperature and column density of the thermal methanol gas. The methanol is clearly associated with the central source in this famous HII region and the derived temperature peaks at the location where the maser is found. Combined with earlier dust maps, it is possible to get a handle on the abundance. Methanol is believed to be a short-lived species in the gas phase, requiring a shock process to be released from interstellar grains. The data shows a large scale outflow from the central source where also the masers reside, consistent with the masers arising close to the place where the methanol is released.


Thermal methanol in Cep A, from left to right the integrated flux, the velocity field and the line width of the methanol (7_1_7 - 6_1_6) E-type transition is shown. This is the strongest unblended line in the JCMT Harp spectra.

The direction of the outflow is also roughly consistent with the orientation of the methanol masers on a much smaller scale as observed with the EVN. The methanol masers that straddle the waist of Cep A are interpreted to outline a large scale ring structure perpendicular to the outflow axis of the central source. Remarkably, the velocity field does not show a rotation signature, but seems to be dominated by a radial motion. It could be hypothesised that the ring outlines an accretion shock, where in-falling gas hits the accretion disk.

Similar ring structures have now also been found in a larger scale sample studied by Huib van Langevelde and Kalle Torstensson in collaboration with the group in Torun (Anna Bartkiwiecz and Marian Szcymcak). Following up a blind survey along the Galactic plane with sensitive observations using the European VLBI Network, a substantial fraction of elliptical sources have been revealed. Also in these sources there is a tendency for the methanol maser structures to be dominated by radial motions, rather than rotation. For both samples of methanol masers, attempts were made to detect Ultra Compact or Hyper Compact HII regions, for example by using the VLA. Some detections were obtained but generally the detection statistics were lower than expected.

In a collaboration with Gary Fuller (University of Manchester), Kalle Torstensson and Huib van Langevelde got involved in the MERLIN follow-up of the methanol multibeam survey. This will allow the study of more complete samples, especially when the current Parkes results will be augmented by a Northern hemisphere survey.

Huib Van Langevelde worked with Andreas Brunthaler and Kazi Rygl (MPIfR Bonn) on the use of methanol masers to obtain distances to high mass star formation regions and indeed the overall scale of the Milky Way. In this programme the first EVN parallax measurements were obtained.

figure Kazi
The preliminary parallax results for the dark cloud L1287 measured using the 6.7 GHz methanol maser emission. The Right Ascension (solid line) and declination (dashed line) signatures of the parallax are shown. Each maser channel which was used for the parallax fitting is indicated by a different color.

Lisa Harvey-Smith worked closely with Rebeca Soria-Ruiz on projects to study the structure of masers in regions of massive star-formation at high angular resolution. Their work included discovering several new masers in the DR21 giant molecular clouds and measuring their polarization. They also found a candidate circumstellar disc with a well-sampled Keplerian rotation curve.

The velocity gradient of methanol masers in DR21(OH)N, showing evidence of Keplerian rotation around the massive protostar ERO3

Evolved stars

Nikta Amiri worked with Huib van Langevelde and Wouter Vlemmings (Bonn University) on the role of magnetic fields in structuring the outflow of evolved stars that are in transition to become a planetary nebula. MERLIN observations of the OH maser in the water fountain source W43A reveal circular polarization. When interpreted as the Zeeman effect, the measured magnetic field is 100 micro gauss. This is consistent with the previous estimate of the magnetic field of 70 micro gauss extrapolated from water maser polarization observations. Together these measurements seem to confirm that magnetic fields play an important role in shaping the circumstellar material in the transition to Planetary Nebulae.

figure Nikta
Spatial distribution of OH and H2O maser features in W43A. The offset positions are with respect to the reference feature. H2O features are indicated by filled circles and OH components are shown as triangles. Red and blue show the redshifted and blueshifted features.

The same team also started a VLBI campaign of OH/IR stars that have a previous distance determination with the so-called phase lag method. The goal is to determine whether these stars have enough compact maser emission to allow a parallax measurement with VLBI. This would be an independent check of the phase lag distance and its underlying assumption. In particular it is interesting to check whether the OH maser shells are spherical. Processing of the data from the first campaign revealed that the masers show dominant structure on the shortest EVN baselines, and the observations were repeated in 2008 using a special mode that combines the EVN with four of the UK based telescopes that participate in MERLIN.

Other

Algol is an eclipsing binary stellar system in which the cool K2 IV sub-giant looses matter through Roche-lobe overflow to the more massive B8 V star. A third star is orbiting around the close binary in a long period orbit. The system is the nearest and one of the most active of its kind. A group led by Szilárd Csizmadia (Konkoly Observatory, Budapest, Hungary) monitored the system with the CHARA optical interferometer, while Zsolt Paragi organised e-EVN observations. During the e-EVN run there was a radio flare. The observed position offset between the total intensity and the circular polarization image indicated that the flare either did not occur in the well-known gyrosycnhrotron radio lobes, or only one of the lobes flared. The results were published in the proceedings of the Modern Radio Universe conference, held in Manchester in October 2007. The optical interferometer data provided the most accurate measurement of the mutual inclination between the close and wide pair orbits. The role of the e-EVN data was to resolve the 180 degrees ambiguity in the longitude of the ascending node of the close pair. Using these latest results for the orbital parameters, Csizmadia et al. investigated the dynamics of Algol with numerical integration of the equation of motions. It was found that the change in inclination of the close pair has a very long period, about 20.000 years. This is in good agreement with the observed small change in the eclipse depth during primary minima. The results were submitted for publication in the Astrophysical Journal.

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