Netherlands Foundation for Research in Astronomy ASTRON

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Netherlands Foundation for Research in Astronomy ASTRON

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Gurkan G.,University of Manchester | Gurkan G.,University of Hertfordshire | Jackson N.,University of Manchester | Koopmans L.V.E.,University of Groningen | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Obtaining lensing time-delay measurements requires long-term monitoring campaigns with a high enough resolution (<1 arcsec) to separate the multiple images. In the radio, a limited number of high-resolution interferometer arrays make these observations difficult to schedule. To overcome this problem, we propose a technique for measuring gravitational time delays which relies on monitoring the total flux density with low-resolution but high-sensitivity radio telescopes to follow the variation of the brighter image. This is then used to trigger high-resolution observations in optimal numbers which then reveal the variation in the fainter image. We present simulations to assess the efficiency of this method together with a pilot project observing radio lens systems with the Westerbork Synthesis Radio Telescope to trigger Very Large Array observations. This new method is promising for measuring time delays because it uses relatively small amounts of time on high-resolution telescopes. This will be important because instruments that have high sensitivity but limited resolution, together with an optimum usage of follow-up high-resolution observations from appropriate radio telescopes may in the future be useful for gravitational lensing time-delay measurements by means of this new method. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bois M.,University of Lyon | Bois M.,European Southern Observatory | Bournaud F.,University Paris Diderot | Emsellem E.,University of Lyon | And 24 more authors.
AIP Conference Proceedings | Year: 2010

We study resolution effects in numerical simulations of gas-rich (20% of the total baryonic mass) major mergers, and show that the formation of slowly-rotating elliptical galaxies requires a resolution that is beyond the present-day standards to be properly modelled. Our findings show that a high-enough resolution is required to accurately model the global properties of merger remnants and the evolution of their angular momentum. The role of wet mergers of spiral galaxies in the formation of slow-rotating ellipticals may therefore have been underestimated. © 2010 American Institute of Physics.


Chi S.,University of Groningen | Chi S.,Joint Institute for VLBI in Europe JIVE | Chi S.,Netherlands Foundation for Research in Astronomy ASTRON | Barthel P.D.,University of Groningen | And 3 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Dust is commonly present in weakly radio emitting star-forming galaxies and this dust may obscure the signatures of accreting black holes in these objects. Aims. We aim to uncover weak active galactic nuclei, AGN, in the faint radio source population by means of deep high-resolution radio observations. Methods. VLBI observations with a world-wide array at unparallelled sensitivity are carried out to assess the nature of the faint radio source population in the Hubble deep field north and its flanking fields. Results. Images of twelve compact, AGN-driven radio sources are presented. These represent roughly one quarter of the detectable faint radio source sample. Most, but not all of these low power AGN have X-ray detections. Conclusions. The majority of the faint radio source population must be star-forming galaxies. Faint AGN occur in a variety of (distant) host galaxies, and these are often accompanied by a dust-obscured starburst. Deep, high-resolution VLBI is a unique, powerful technique to assess the occurrence of faint AGN. © 2013 ESO.


Bois M.,University of Lyon | Bois M.,European Southern Observatory | Bournaud F.,University Paris Diderot | Emsellem E.,University of Lyon | And 24 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We study resolution effects in numerical simulations of gas-rich and gas-poor major mergers, and show that the formation of slowly rotating elliptical galaxies often requires a resolution that is beyond the present-day standards to be properly modelled. Our sample of equal-mass merger models encompasses various masses and spatial resolutions, ranging from about 200 pc and 105 particles per component (stars, gas and dark matter), i.e. a gas mass resolution of ∼105 M⊙, typical of some recently published major merger simulations, to up to 32 pc and ∼103 M⊙ in simulations using 2.4 × 107 collisionless particles and 1.2 × 107 gas particles, among the highest resolutions reached so far for gas-rich major merger of massive disc galaxies. We find that the formation of fast-rotating early-type galaxies, that are flattened by a significant residual rotation, is overall correctly reproduced at all such resolutions. However, the formation of slow-rotating early-type galaxies, which have a low-residual angular momentum and are supported mostly by anisotropic velocity dispersions, is strongly resolution-dependent. The evacuation of angular momentum from the main stellar body is largely missed at standard resolution, and systems that should be slow rotators are then found to be fast rotators. The effect is most important for gas-rich mergers, but is also witnessed in mergers with an absent or modest gas component (0-10 per cent in mass). The effect is robust with respect to our initial conditions and interaction orbits, and originates in the physical treatment of the relaxation process during the coalescence of the galaxies. Our findings show that a high-enough resolution is required to accurately model the global properties of merger remnants and the evolution of their angular momentum. The role of gas-rich mergers of spiral galaxies in the formation of slow-rotating ellipticals may therefore have been underestimated. Moreover, the effect of gas in a galaxy merger is not limited to helping the survival/rebuilding of rotating disc components: at high resolution, gas actively participates in the relaxation process and the formation of slowly rotating stellar systems. © 2010 The Authors. Journal compilation © 2010 RAS.


Berciano Alba A.,Netherlands Foundation for Research in Astronomy ASTRON | Berciano Alba A.,University of Groningen | Koopmans L.V.E.,University of Groningen | Garrett M.A.,Netherlands Foundation for Research in Astronomy ASTRON | And 5 more authors.
Astronomy and Astrophysics | Year: 2010

Context: SMM J04542-0301 is an extended (∼1′) submm source located near the core of the cluster MS0451.6-0305. It has been suggested that part of its emission arises from the interaction between a LBG and two EROs at z ∼ 2.9 that are multiply-imaged in the optical/NIR observations. However, the dramatic resolution difference between the sub-mm map and the optical/NIR images make it difficult to confirm this hypothesis. Aims: In a previous paper, we reported the detection of 1.4 GHz continuum radio emission coincident with this sub-mm source using VLA archival data. To fully understand the relation between this radio emission, the sub-mm emission, and the optical/IR multiplyimaged sources, we have re-observed the cluster with the VLA at higher resolution. Methods: The previous archival data has been re-reduced and combined with the new observations to produced a deep (∼10 μJy beam -1), high resolution (∼2″) map centred on the cluster core. The strong lensing effect in the radio data has been quantified by constructing a new lens model of the cluster. Results: From the high resolution map we have robustly identified six radio sources located within SMM J 04542-0301. The brightest and most extended of these sources (RJ) is located in the middle of the sub-mm emission, and has no obvious counterpart in the optical/ NIR. Three other detections (E1, E2 and E3) seem to be associated with the images of one of the EROs (B), although the NIR and radio emission appear to originate at slightly different positions in the source plane. The last two detections (CR1 and CR2), for which no optical/NIR counterpart have been found, seem to constitute two relatively compact emitting regions embedded in a ∼5″ extended radio source located at the position of the sub-mm peak. The presence of this extended component (which contributes 38% of the total radio flux in this region) can only be explained if it is being produced by a lensed region of dust obscured star formation in the center of the merger. A comparison between the radio and sub-mm data at the same resolution suggests that E1, E2, E3, CR1 and CR2 are associated with the sub-mm emission. Conclusions: The radio observations presented in this paper provide strong observational evidence in favour of the merger hypothesis. However, the question if RJ is also contributing to the observed sub-mm emission remains open. These results illustrate the promising prospects for radio interferometry and strong gravitational lensing to study the internal structure of SMGs. © 2010 ESO.


Bruggen M.,Jacobs University Bremen | Bruggen M.,University of Hamburg | Van Weeren R.J.,Leiden University | Van Weeren R.J.,Netherlands Foundation for Research in Astronomy ASTRON | Rottgering H.J.A.,Leiden University
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

The newly discovered galaxy cluster 1RXS J0603.3+4214 hosts a 1.9 Mpc long, bright radio relic with a peculiar linear morphology. Using hydrodynamical N-body adaptive mesh refinement simulations of the merger between three initially hydrostatic clusters in an idealized set-up, we are able to reconstruct the morphology of the radio relic. Based on our simulation, we can constrain the merger geometry, predict lensing mass measurements and X-ray observations. Comparing such models to X-ray, redshift and lensing data will validate the geometry of this complex merger which helps in constraining the parameters for shock acceleration of electrons that produces the radio relic. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS.

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