| 1. |
- Backes, M., et al.
(författare)
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The Africa Millimetre Telescope
- 2016
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- It is believed that supermassive black holes are found in the centres of galaxies, including the Milky Way. Still, only indirect evidence has been gathered for the existence of these enigmatic objects that are predicted by the general theory of relativity. With the Event Horizon Telescope, a Very Long Baseline Interferometry network of millimetre-wave (radio) telescopes, it will be possible to directly image the 'shadow' of the event horizon of the black hole at the centre of the Milky Way, Sgr A∗. Although the Event Horizon Telescope utilises an extensive network of telescopes, there is a huge gap in the coverage of the u-v-plane for these observations across Africa. We discuss the benefits of adding the Africa Millimetre Telescope to the Event Horizon Telescope and present Mt. Gamsberg in Namibia as the best site for this new and first mm-wave telescope in Africa.
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| 2. |
- Beswick, R. J., et al.
(författare)
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SKA studies of nearby galaxies: Star-formation, accretion processes and molecular gas across all environments
- 2014
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with mJy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact.
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| 3. |
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| 4. |
- Conway, John, 1963, et al.
(författare)
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Modelling OH Megamasers in by Clumpy Starburst Rings
- 2004
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Ingår i: in Proceedings of "The Neutral ISM in Starburst Galaxies", Marstrand, June 2003, eds. Aalto S., Huettemeister S., Pedlar A., Astronomical Society of the Pacific Conf. Series, San Francisco. - 1583811826 ; , s. 191-194
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Konferensbidrag (refereegranskat)
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| 5. |
- Conway, John, 1963, et al.
(författare)
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Radio properties of young SNe/SNRs in Arp220
- 2007
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Ingår i: Proceedings of Science. - 1824-8039. ; 52
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Konferensbidrag (refereegranskat)abstract
- Radio observations of young radio supernovae (SNe) and supernova remnants (SNRs) can provide a unique window on the stellar/ISM properties of starburst galaxies. Such observations can potentially constrain issues of cosmological importance such as whether stellar IMFs are radically different in extreme star-forming environments. Recently published observations of the nearest ultra-luminous infra-red galaxy Arp 220 have revealed the radio spectra of a group of SNe/SNR. About half of the sources detected at high frequency have spectral and variability properties consistent with young Type IIn supernovae interacting with their pre-explosion stellar winds. However the high rate of appearance of these sources implies that an unusually large fraction of core-collapse supernovae are highly luminous, which might be at least partly explained by a top heavy IMF. The other half of the compact sources found in Arp 220 were interpreted as SNRs interacting with a dense (104 to 105 cm−3) ISM. In this paper we report on new more sensitive VLBI observations at wavelengths of 2 cm and 3.6 cm. We find that the spectral evolution of most of the suspected SNe sources is consistent with them being of Type IIn. However two rapidly dimming objects may instead be of Type Ib/c or IIb. Most of the long-lived candidate SNR sources show small or undetectable flux density variations, however one almost doubled its 3.6 cm intensity in 11 months. Another source also shows some variability and a complex spectrum. These two objects plus another with a flat spectrum up to 2 cm are the best candidates for an AGN core, though the data does not yet require this interpretation. At least three sources show signs of resolution with diameters in the range 0.1 to 0.2 pc. These sizes put them sightly above, but still consistent with, the size-luminosity correlation for SNRs. The SKA will have sufficient sensitivity to detect the emission from Arp220-like compact sources out to cosmological distances (i.e. up to z≈ 0.5). However the SKA needs global baselines both to separate out the discrete sources from more extended radio emission and to resolve them apart.
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| 6. |
- Conway, John, 1963
(författare)
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Scientific applications of e-VLBI
- 2009
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Ingår i: Proceedings of Science. - Trieste, Italy : Sissa Medialab. - 1824-8039. ; 82
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Konferensbidrag (refereegranskat)abstract
- The advantages of e-VLBI over traditional media-recorded VLBI are briefly discussed. These advantages lie in two broad areas, those which reduce the operational burden of VLBI and those which enable wholly new kinds of observations to be made. In the first category, e-VLBI contributes to increases in reliability, to a more convenient way to use the instrument, reduced manpower effort and an easing of scheduling constraints. It also allows us to more easily expand bandwidth without building new recording equipment. In the second area the obvious advantage is in the increased speed of results from e-VLBI, which allows rapidly evolving sources to be observed and the next observations planned. A less appreciated, and yet to be fully realised e-VLBI advantage, especially when married to real time software correlation, is that of automation. Automated media-less operations will allow new types of long duration survey VLBI observations to be made lasting weeks to months. Potentially such a system could be used to create an always-on few telescope VLBI network which would follow up all suitable transient detections for accurate radio position and structure determination. An important and continuing benefit of the e-VLBI developments of recent years has been the closer integration and merging of connected element and long baseline interferometry via the e-MERLIN and e-LOFAR projects. The long term prospects for this synergy and the implications for long baseline centimetre wavelength interferometry in the era of the SKA are briefly mentioned.
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| 7. |
- de Blok, W.J.G., et al.
(författare)
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an overview of the MHONGOOSE survey: Observing nearby galaxies with MeerKAT
- 2016
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Ingår i: Proceedings of Science. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with H I masses from ∼ 106 to ∼ 1011 M, and luminosities from MR ∼ 12 to MR ∼ −22. The sample is selected to uniformly cover the available range in log(MHI). Our extremely deep observations, down to H I column density limits of well below 1018 cm−2 — or a few hundred times fainter than the typical H I disks in galaxies — will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modeling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT’s capabilities.
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| 8. |
- Elgered, Gunnar, 1955, et al.
(författare)
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The Onsala Twin Telescopes Project
- 2017
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Ingår i: The 23rd Working Meeting of the European VLBI Group for Geodesy and Astrometry (EVGA), Gothenburg, May 14–18, 2017.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Onsala Space Observatory is the European site in the International VLBI Service for Geodesy and Astrometry (IVS) that has the longest history in VLBI. First geodetic VLBI measurements were performed already in 1968 with the 25 m radio telescope. Onsala is today one of the sites with thelongest time series in the IVS data base. The observatory is one of the unique fundamental space geodetic sites that have a direct access to the coast line and co-locate VLBI, GNSS, gravimetry, and sea-level monitoring. Onsala is thus an important co-location site for the GlobalGeodetic Observing System (GGOS). Being well aware of the VGOS standard it was clear around 2010 that Onsala was in need for a telescope with significantly faster slew rates than the existing radome-enclosed 20 m telescope.
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| 9. |
- Elgered, Gunnar, 1955, et al.
(författare)
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The Onsala Twin Telescopes: the Status at the Time for the Inauguration
- 2017
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Ingår i: Proceedings of the 23rd European VLBI Group for Geodesy and Astrometry Working Meeting. - 9789188041098 ; , s. 136-139
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We summarise the activities related to the Onsala Twin Telescopes (OTT), from the time when the decision was taken to fund the proposal, to the inauguration on 18 May 2017.
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| 10. |
- Flygare, Jonas, 1988, et al.
(författare)
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Design trade-offs in feed systems for ultra-wideband VLBI observations
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to the advanced capability of today’s ultra-wideband feed systems and low-noise amplifiers, interesting upgrades for future VLBI receiver and tele- scope design should be considered. Multiple input pa- rameters need to be taken into account for optimal sensitivity and applications of the future astronomical and geodetic observational systems. In this paper we present an overview of some trade-offs for wideband systems between SEFD, bandwidth and telescope re- flector optics. We evaluate receiver bandwidths from 3.5:1 to 10.3:1 bandwidth within the frequency range 1.5-24 GHz in different configurations. Due to poten- tial RFI-pollution of the lower frequencies we present potential feed upgrades for the most common reflector geometries ofVGOS and EVN telescopes that mitigate this problem. The results of this work is relevant for fu- ture VLBI stations and telescope design in general. Keywords
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