296 research outputs found
Neutral hydrogen absorption towards Fast Radio Bursts
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
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
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
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
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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