16 research outputs found
Disks, Tori, and Cocoons: Emission and Absorption Diagnostics of AGN Environments
One of the most important problems in the study of active galaxies is
understanding the detailed geometry, physics, and evolution of the central
engines and their environments. The leading models involve an accretion disk
and torus structure around a central dense object, thought to be a supermassive
black hole. Gas found in the environment of AGN is associated with different
structures: molecular accretion disks, larger scale atomic tori, ionized and
neutral "cocoons" in which the nuclear regions can be embedded. All of them can
be studied at radio wavelengths by various means. Here, we summarize the work
that has been done to date in the radio band to characterize these structures.
Much has been learned about the central few parsecs of AGN in the last few
decades with contemporary instruments but the picture remains incomplete. In
order to be able to define a more accurate model of this region, significant
advances in sensitivity, spectral and angular resolution, and bandpass
stability are required. The necessary advances will only be provided by the
Square Kilometer Array and we discuss the possibilities that these dramatic
improvements will open for the study of the gas in the central region of AGN.Comment: To appear in "Science with the Square Kilometer Array," eds. C.
Carilli and S. Rawlings, New Astronomy Reviews (Elsevier: Amsterdam); 17
pages, 7 figures (four of them in separate gif/tif files) The full paper with
high resolution images can be downloaded from
http://www.astron.nl/~morganti/Papers/AGNenvironment.ps.g
Enabling a High Throughput Real Time Data Pipeline for a Large Radio Telescope Array with GPUs
The Murchison Widefield Array (MWA) is a next-generation radio telescope
currently under construction in the remote Western Australia Outback. Raw data
will be generated continuously at 5GiB/s, grouped into 8s cadences. This high
throughput motivates the development of on-site, real time processing and
reduction in preference to archiving, transport and off-line processing. Each
batch of 8s data must be completely reduced before the next batch arrives.
Maintaining real time operation will require a sustained performance of around
2.5TFLOP/s (including convolutions, FFTs, interpolations and matrix
multiplications). We describe a scalable heterogeneous computing pipeline
implementation, exploiting both the high computing density and FLOP-per-Watt
ratio of modern GPUs. The architecture is highly parallel within and across
nodes, with all major processing elements performed by GPUs. Necessary
scatter-gather operations along the pipeline are loosely synchronized between
the nodes hosting the GPUs. The MWA will be a frontier scientific instrument
and a pathfinder for planned peta- and exascale facilities.Comment: Version accepted by Comp. Phys. Com
Galaxy evolution, cosmology and dark energy with the Square Kilometer Array
The present-day Universe is seemingly dominated by dark energy and dark
matter, but mapping the normal (baryonic) content remains vital for both
astrophysics - understanding how galaxies form - and astro-particle physics -
inferring properties of the dark components. The Square Kilometre Array (SKA)
will provide the only means of studying the cosmic evolution of neutral
Hydrogen (HI) which, alongside information on star formation from the radio
continuum, is needed to understand how stars formed from gas within dark-matter
over-densities and the roles of gas accretion and galaxy merging. `All
hemisphere' HI redshift surveys to redshift 1.5 are feasible with
wide-field-of-view realizations of the SKA and, by measuring the galaxy power
spectrum in exquisite detail, will allow the first precise studies of the
equation-of-state of dark energy. The SKA will be capable of other uniquely
powerful cosmological studies including the measurement of the dark-matter
power spectrum using weak gravitational lensing, and the precise measurement of
H0 using extragalactic water masers. The SKA is likely to become the premier
dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those
likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST,
SNAP) and other early-21st-century datasets.Comment: 15 pages, 7 figures, to appear in "Science with the Square Kilometer
Array", eds.C. Carilli and S. Rawlings, New Astronomy Reviews (Elsevier:
Amsterdam
Orion Source I 3mm SiO maser emission
Item does not contain fulltextReduced spectral cube of the SiO v=1, J=2-1 maser transition near Orion Source I observed on Jan 24, 2011, in FITS format (with velocity as primary axis). VLBA project code BG205. (2 data files)