N891 simdata (CASA 3.3): Difference between revisions
No edit summary |
No edit summary |
||
Line 9: | Line 9: | ||
Roughly modeled after NGC891 | Roughly modeled after NGC891 | ||
{{Under Construction}} - mostly correct, but probably not very thoroughly explained. Updated for CASA 3. | {{Under Construction}} - mostly correct, but probably not very thoroughly explained. Updated for CASA 3.3 | ||
* model origin: Milky Way 13CO from the [http://www.bu.edu/galacticring/ Galactic Ring Survey] on the 14m [http://www.astro.umass.edu/~fcrao/ FCRAO] | * model origin: Milky Way 13CO from the [http://www.bu.edu/galacticring/ Galactic Ring Survey] on the 14m [http://www.astro.umass.edu/~fcrao/ FCRAO] | ||
Line 35: | Line 35: | ||
here are the simdata inputs : | here are the simdata inputs : | ||
<source lang="python"> | |||
default("simdata") | |||
project = "n891d" | project = "n891d" | ||
skymodel = "grs-12kms.fits" | skymodel = "grs-12kms.fits" | ||
incenter = "110.1777GHz" | incenter = "110.1777GHz" | ||
inwidth = "-.468MHz" | inwidth = "-.468MHz" | ||
inbright = "1.4e-4" | inbright = "1.4e-4" | ||
indirection = 'J2000 7h00m34 -23d03m00' | indirection = 'J2000 7h00m34 -23d03m00' | ||
incell = "0.2arcsec" | incell = "0.2arcsec" | ||
setpointings = True | |||
setpointings = | |||
integration = "300s" | integration = "300s" | ||
pointingspacing = "25arcsec" | pointingspacing = "25arcsec" | ||
mapsize = '60arcsec' | mapsize = '60arcsec' | ||
graphics = "both" | graphics = "both" | ||
verbose = True | verbose = True | ||
overwrite = True | overwrite = True | ||
observe = True | |||
antennalist = "alma;0.5arcsec" | antennalist = "alma;0.5arcsec" | ||
totaltime = "3600s" | totaltime = "3600s" | ||
image=T | image=T | ||
simdata() | |||
</source> | |||
Revision as of 19:54, 30 September 2011
↵ Simulating Observations in CASA
Old version: N891 simdata2.
To create a script of the Python code on this page see Extracting scripts from these tutorials.
Nearby edge-on spiral
Roughly modeled after NGC891
This article is under construction. Watch this space!
- mostly correct, but probably not very thoroughly explained. Updated for CASA 3.3
- model origin: Milky Way 13CO from the Galactic Ring Survey on the 14m FCRAO
- I binned the cube to coarser velocity resolution in order to speed the simulation. the fits file is grs-12kms.fits
- units: K - first convert to flux surface brightness
Jy/Sr = 2x1023 k T / λ2, = 4x108T at 110GHz.
now we need to decide if this model data will work at the desired pixel scale
- the GRS resolution of 40" at ~10kpc is 0.04" at 10Mpc, so we should be able to do a simulation of observing at ~0.1-0.2". The resolution plot () indicates that for ALMA at 100GHz, configuration 20 is appropriate.
- if we intend to set cell=0.04arcsec in simdata, then the cube needs to be multiplied by
4x108 * (.04/206265)2 = 1.4x10-5 to obtain Jy/pixel. The cube peaks at ~20K, so we can perform the simulation with inbright=3e-4, which should yield a peak of ~1mJy/bm.
will we be dominated by the noise in the input model?
- input noise ~150mK or S/N~20, so at our scaled intensity, ~0.05 mJy/bm. The exposure time calculator says that ALMA will achieve 2.5mJy/bm in 2 hours for the input 212m/s channel width (0.075MHz), so the noise in the input model should not affect our results.
- We do have a sensitivity issue though - if we decrease the spectral resolution by a factor of 6 (bin the input channels in some other program - simdata will know how to do that in the future but not yet), and plan for 3 8-hr tracks, then the sensitivity calculator suggests that we'll get <0.25mJy rms, or S/N>10 per beam. Rather than simulate 3 days of observing, I'll increase inbright by sqrt(3) and simulate one 8 hour track.
setup:
- the ALMA 12m primary beam is 50" so we'd space a mosaic by 25", but the model cube has 326x357 pixels, or 13 arcsec with our small pixels. That's a lot smaller than the primary beam, so it doesn't matter much what output image size we ask for.
- there are 659 channels in the input cube, but as noted above we want to bin those to 109 channels of 1.2 km/s each.
here are the simdata inputs :
default("simdata")
project = "n891d"
skymodel = "grs-12kms.fits"
incenter = "110.1777GHz"
inwidth = "-.468MHz"
inbright = "1.4e-4"
indirection = 'J2000 7h00m34 -23d03m00'
incell = "0.2arcsec"
setpointings = True
integration = "300s"
pointingspacing = "25arcsec"
mapsize = '60arcsec'
graphics = "both"
verbose = True
overwrite = True
observe = True
antennalist = "alma;0.5arcsec"
totaltime = "3600s"
image=T
simdata()
here's the cube with the simdata's scaling and World Coordinate System:
and a spectral profile in the box marked in green
Sample results:
Input: |
Predict: |
Image: |
Analyze: |