296 research outputs found

    Neutral hydrogen absorption towards Fast Radio Bursts

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    If Fast Radio Bursts (FRBs) are truly at astronomical, in particular cosmological, distances, they represent one of the most exciting discoveries in astrophysics of the past decade. However, the distance to FRBs has, to date, been estimated purely from their excess dispersion, and has not been corroborated by any independent means. In this paper we discuss the possibility of detecting neutral hydrogen absorption against FRBs both from spiral arms within our own galaxy, or from intervening extragalactic HI clouds. In either case a firm lower limit on the distance to the FRB would be established. Absorption against galactic spiral arms may already be detectable for bright low-latitude bursts with existing facilities, and should certainly be so by the Square Kilometre Array (SKA). Absorption against extragalactic HI clouds, which would confirm the cosmological distances of FRBs, should also be detectable with the SKA, and maybe also Arecibo. Quantitatively, we estimate that SKA1-MID should be able to detect extragalactic HI absorption against a few percent of FRBs at a redshift z~1.Comment: Accepted for publications as a Letter in MNRA

    HI Science with the Square Kilometre Array

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    The Square Kilometre Array (SKA) will be a formidable instrument for the detailed study of neutral hydrogen (HI) in external galaxies and in our own Galaxy and Local Group. The sensitivity of the SKA, its wide receiver bands, and the relative freedom from radio frequency interference at the SKA sites will allow the imaging of substantial number of high-redshift galaxies in HI for the first time. It will also allow imaging of galaxies throughout the Local Volume at resolutions of <100 pc and detailed investigations of galaxy disks and the transition between disks, halos and the intergalactic medium (IGM) in the Milky Way and external galaxies. Together with deep optical and millimetre/sub-mm imaging, this will have a profound effect on our understanding of the formation, growth and subsequent evolution of galaxies in different environments. This paper provides an introductory text to a series of nine science papers describing the impact of the SKA in the field of HI and galaxy evolution. We propose a nested set of surveys with phase 1 of the SKA which will help tackle much of the exciting science described. Longer commensal surveys are discussed, including an ultra-deep survey which should permit the detection of galaxies at z=2, when the Universe was a quarter of its current age. The full SKA will allow more detailed imaging of even more distant galaxies, and allow cosmological and evolutionary parameters to be measured with exquisite precision.Comment: 9 pages, 1 figure, accepted by Proceedings of Science as the HI Overview Chapter for "Advancing Astrophysics with the Square Kilometre Array

    Circumnuclear HI disks in radio galaxies: The case of Cen A and B2 0258+35

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    New HI observations of the nearby radio-loud galaxies Centaurus A and B2 0258+35 show broad absorption (Delta_v=400km/s) against the unresolved nuclei. Both sources belong to the cases where blue- and redshifted absorption is observed at the same time. In previous Cen A observations only a relative narrow range of redshifted absorption was detected. We show that the data suggest in both cases the existence of a circumnuclear disk. For Cen A the nuclear absorption might be the atomic counterpart of the molecular circumnuclear disk that is seen in CO and H_2. Higher resolution observations are now needed to locate the absorption and to further investigate the structure and kinematics of the central region of the AGN and the way the AGN are fueled.Comment: Talk given at "The Central Kiloparsec: Active Galactic Nuclei and Their Hosts", Ierapetra, Crete, 4-6 June, 2008. To appear in Volume 79 of the Memorie della Societa Astronomica Italiana. 4 pages, 2 figure

    Taking snapshots of the jet-ISM interplay with ALMA

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    We present an update of our on-going project to characterise the impact of radio jets on the ISM by tracing molecular gas at high spatial resolution using ALMA. The radio active galactic nuclei (AGN) studied show recently born radio jets. In this stage, the plasma jets can have the largest impact on the ISM, as also predicted by state-of-the-art simulations. The two targets have quite different ages, allowing us to get snapshots of the effects of radio jets as they grow. Interestingly, both also host powerful quasar emission. The largest mass outflow rate of molecular gas is found in a radio galaxy hosting a newly born radio jet emerging from an obscuring cocoon of gas and dust. Although the mass outflow rate is high (few hundred Msun/yr), the outflow is limited to the inner few hundred pc region. In a second object, the jet is larger (a few kpc) and is in a more advanced evolutionary phase. In this object, the distribution of the molecular gas is reminiscent of what is seen, on larger scales, in cool-core clusters hosting radio galaxies. Gas deviating from quiescent kinematics is not very prominent, limited only to the very inner region, and has a low mass outflow rate. Instead, on kpc scales, the radio lobes appear associated with depressions in the distribution of the molecular gas, suggesting they have broken out from the dense nuclear region. The AGN does not appear to be able at present to stop the star formation observed in this galaxy. These results suggest that the effects of the radio source start in the first phases by producing outflows which, however, tend to be limited to the kpc region. After that, the effects turn into producing large-scale bubbles which could, in the long term, prevent the surrounding gas from cooling. Our results characterise the effect of radio jets in different phases of their evolution, bridging the studies done for radio galaxies in clusters.Comment: 5 Pages 2 figures; Proceedings IAU Symposium No. 359, "Galaxy evolution and feedback across different environments", T. Storchi-Bergmann, R. Overzier, W. Forman & R. Riffel, ed

    The latest on Apertif

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    We describe a Phased Array Feed (PAF) system, called Apertif, which will be installed in the Westerbork Synthesis Radio Telescope (WSRT). The aim of Apertif is, at frequencies from 1.0 to 1.7 GHz, to increase the instantaneous field of view of the WSRT 8 deg^2 and its observing bandwidth to 300 MHz with high spectral resolution. This system will turn the WSRT into an effective survey telescope with scientific applications ranging from deep surveys of the northern sky of HI and OH emission and polarised continuum to efficient searches for pulsars and transients. We present results obtained with a prototype PAF installed in one of the WSRT dishes. These results demonstrate that at decimetre wavelengths PAFs have excellent performance and that even for a single beam on the sky they outperform single feed radio dishes. PAFs turn radio telescopes into very effective survey instruments. Apertif is now fully funded and the community is invited to express their interest in using Apertif (http://www.astron.nl/radio-observatory/call-expressions-interest-apertif-surveys )Comment: Talk presented at 'A New Golden Age for Radio Astronomy', International SKA Forum 2010, 10-14 June 2010, Hof van Saksen, N
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