Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/people/Matthew.Whiting/ASKAPsimAbs1/README Дата изменения: Tue May 3 05:32:18 2011 Дата индексирования: Tue Oct 2 17:22:06 2012 Кодировка: Поисковые слова: п п п п п п п п п п п п п п п п п п п п п п

This ASKAP data release consists of simulated observations typical of the FLASH
project. The simulation features both continuum and spectral-line data for a
low-frequency observation, with the sky consisting of the SKADS continuum sky
plus absorption-line components.

The input sky model consisted of:
* Continuum sources from the SKADS S3-SEX simulation (Wilman et al 2008), with
fluxes at 850MHz interpolated between the catalogue fluxes at 610MHz and 1400MHz.
* Absorption-line components:
* All components are single Gaussians
* All continuum sources with S_850>10mJy were selected, and from these the
brightest component of each galaxy in the SKADS model was kept (to avoid
having too-closely-resolved components).
* The components were distributed over ranges of:
* z = [0.76, 0.765, 0.77, 0.773, 0.775, 0.78, 0.785, 0.787, 0.79, 0.792]
* peak optical depth = [0.01, 0.02, 0.05, 0.10, 0.20, 0.30]
* velocity width = [5, 10, 15, 20, 25, 30, 40, 50, 60, 80] km/s
* The continuum and spectral-line datasets were kept separate. This is to mimic
continuum subtraction (the capability to do so in the ASKAP pipeline is not yet
fully developed). This means the spectral-line cube consists solely of negative
absorption components.

Using the sky model, simulated observations were made. In both cases:
* A 2hr observation was made, sampled with 20s integrations
* The effect of the phased-array feed was simulated with 21 beams separated by
1.1 degrees. This gives, at 850MHz, a field of view similar to the 32-beam array
at 1400MHz, but with uniform sensitivity over the large part of the field.
* Thermal noise was added to the visibilities such that the resulting noise in
the image/cube is according to ASKAP specs given the weighting/tapering.

For the continuum data:
* 256x1MHz channels were used in a band centred on 850MHz
* The data was imaged onto a 7.5-arcsec/pix image, with Wiener filtering of
robustness=0.25, and Gaussian Tapering of 20", resulting in a beam of 35x31arcsec
* The image was cleaned with multi-scale clean, scales of 0,3,10,20 pix
* The noise in the image is ~23uJy/beam

For the spectral-line data
* 1024x18.311kHz channels, centred on 800MHz (or HI redshift of 0.7755)
* The images created have 8.5 arcsec/pix
* Wiener filtering of robustness=0.25, and Gaussian Tapering of 20" were used,
resulting in a beam of approx 38x30 arcsec.
* The restoration was done with a 38x30 arcsec beam for all channels, with no cleaning.
* The noise in the image is ~3mJy/beam

Known issues:

* The continuum image shows horizontal features above and below a number of the
brighter sources. We believe this is related to the pixelisation of the model,
but investigations are ongoing.

The following data products are provided (images are all FITS unless stated otherwise):
* Catalogues:
* The SKADS S3-SEX catalogue as used to create the continuum model
* The input catalogue used for the absorption-line cube
* Models:
* The continuum model used as input for the simulations (5760x5760 pix, 127MB)
* The same, with the same pixel grid and smoothed to the same resolution as
the continuum image (3600x3600 pix, 50MB)
* The spectral-line model used as input for the simulations (tar-gzipped CASA
image only, 5760x5760x1024 pix, 131MB, inflates to 127GB!)
* The same, with the same pixel grid and resolution as the final spectral-line
cube (3000x3000x1024 pix, 35GB)
* Continuum data (all 3600x3600 pix, 50MB):
* The restored image, clean model image and the residual.
* The PSF image (after tapering/weighting) and weights image.
* Spectral-line data (all 3000x3000x1024 pix, 35GB):
* The restored cube, plus a 3000x3000x50 subcube centred on z=0.79 (1.7GB)
* The PSF image (after tapering/weighting), plus two subcubes: on corresponding
to the image subcube above, and the other to the central 600x600 spatial
pixels (ASKAPsim.FLASH.sl.psf.sub2.fits, 600x600x1024, 1.4GB)
* The weights image, plus the matching subcube centred on z=0.79


Processing was done on the NCI National Facility machine vayu - see http://nf.nci.org.au

The data are located in the directory giant:/DATA/DELPHINUS_2/whi550/ASKAPsimulations/Absorption/Dec2010
which can be accessed from most machines on the ATNF network.

Note 2011-1-11: The rest-frequency had not been included in the original
spectral-line cubes (this was an error in the conversion to FITS
format). These have been updated to include this figure.

Directory listing:

total 145G
-rw-r--r-- 1 whi550 at-astro 534M 2010-12-11 23:22 ASKAPsim.FLASH.cont.catalogue.dat
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-10 15:10 ASKAPsim.FLASH.cont.image.restored.fits
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-10 15:10 ASKAPsim.FLASH.cont.imagemodel.fits
-rw-rw-r-- 1 whi550 at-astro 127M 2010-12-14 10:15 ASKAPsim.FLASH.cont.model.input.fits
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-14 10:02 ASKAPsim.FLASH.cont.model.smoothed.fits
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-10 15:10 ASKAPsim.FLASH.cont.psf.fits
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-10 15:10 ASKAPsim.FLASH.cont.residual.fits
-rw-rw-r-- 1 whi550 at-astro 50M 2010-12-10 15:10 ASKAPsim.FLASH.cont.weights.fits
-rw-r--r-- 1 whi550 at-astro 50K 2010-12-12 22:35 ASKAPsim.FLASH.sl.catalogue.dat
-rw-r--r-- 1 whi550 at-astro 29K 2010-12-11 23:21 ASKAPsim.FLASH.sl.continuumCatalogue.dat
-rw-rw-r-- 1 whi550 at-astro 35G 2011-01-11 12:26 ASKAPsim.FLASH.sl.image.restored.fits
-rw-rw-r-- 1 whi550 at-astro 1.7G 2011-01-11 12:27 ASKAPsim.FLASH.sl.image.restored.sub.fits
-rw-rw-r-- 1 whi550 at-astro 131M 2010-12-13 11:47 ASKAPsim.FLASH.sl.model.input.tgz
-rw-r--r-- 1 whi550 at-astro 35G 2010-12-13 15:52 ASKAPsim.FLASH.sl.model.smoothed.fits
-rw-rw-r-- 1 whi550 at-astro 35G 2011-01-11 12:41 ASKAPsim.FLASH.sl.psf.fits
-rw-rw-r-- 1 whi550 at-astro 1.7G 2011-01-11 12:42 ASKAPsim.FLASH.sl.psf.sub.fits
-rw-rw-r-- 1 whi550 at-astro 1.4G 2011-01-11 12:42 ASKAPsim.FLASH.sl.psf.sub2.fits
-rw-rw-r-- 1 whi550 at-astro 35G 2011-01-11 12:55 ASKAPsim.FLASH.sl.weights.fits
-rw-rw-r-- 1 whi550 at-astro 1.7G 2011-01-11 12:56 ASKAPsim.FLASH.sl.weights.sub.fits
-rw-rw-r-- 1 whi550 at-astro 6.3K 2011-01-11 13:18 README