Difference between revisions of "Simulation Recipes"

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(Nearby edge-on spiral)
(Nearby edge-on spiral)
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* model data: Milky Way 13CO from the [http://www.bu.edu/galacticring/ Galactic Ring Survey] on the 14m [http://www.astro.umass.edu/~fcrao/ FCRAO]
 
* model data: Milky Way 13CO from the [http://www.bu.edu/galacticring/ Galactic Ring Survey] on the 14m [http://www.astro.umass.edu/~fcrao/ FCRAO]
 
* units: K - first convert to flux surface brightness
 
* units: K - first convert to flux surface brightness
<math>\frac{Jy}{Sr} = \frac{4\times 10^{23} k T}{\pi D^2 4\pi\Omega}</math>, where <math>\Omega</math> is the beam solid angle.  At 110GHz the factor is <math>2x10^8</math>
+
<math>\frac{Jy}{Sr} = \frac{4\times 10^{23} k T}{\pi D^2 \Omega}</math>, where <math>\Omega</math> is the beam solid angle.  At 110GHz the factor is <math>2x10^8</math>
  
now we need to decide if this model data will work at the desired pixel scale and noise level
+
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".  [[File:Beamsummary.png]] indicates that for ALMA at 100GHz, configuration 20 is appropriate.
 
* 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".  [[File:Beamsummary.png]] indicates that for ALMA at 100GHz, configuration 20 is appropriate.
 
* if we intend to set <tt>cell=0.04arcsec</tt> in <tt>simdata</tt>, then the cube needs to be multiplied by  
 
* if we intend to set <tt>cell=0.04arcsec</tt> in <tt>simdata</tt>, then the cube needs to be multiplied by  
 
<math>2x10^8 * (.04/206265)^2 = 7.9x10^{-6}</math> to obtain Jy/pixel.  The cube peaks at ~3K, so we can perform the simulation with <tt>inbright=2.3e-5</tt>
 
<math>2x10^8 * (.04/206265)^2 = 7.9x10^{-6}</math> to obtain Jy/pixel.  The cube peaks at ~3K, so we can perform the simulation with <tt>inbright=2.3e-5</tt>
 +
 +
will we be dominated by the noise in the input model?
 +
* input noise ~150mK or S/N~20, so at our scaled intensity, a few mJy/bm. The exposure time calculator says that ALMA will achieve 1.3mJy/bm in an hour, so we should set this up as a half hour snapshot.

Revision as of 14:04, 16 December 2009

Massively Under Construction

(i.e. don't believe what you see here yet, or ask me when it doesn't make sense :)


Nearby edge-on spiral

Roughly modeled after NGC891

  • model data: Milky Way 13CO from the Galactic Ring Survey on the 14m FCRAO
  • units: K - first convert to flux surface brightness

[math]\frac{Jy}{Sr} = \frac{4\times 10^{23} k T}{\pi D^2 \Omega}[/math], where [math]\Omega[/math] is the beam solid angle. At 110GHz the factor is [math]2x10^8[/math]

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". Beamsummary.png 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

[math]2x10^8 * (.04/206265)^2 = 7.9x10^{-6}[/math] to obtain Jy/pixel. The cube peaks at ~3K, so we can perform the simulation with inbright=2.3e-5

will we be dominated by the noise in the input model?

  • input noise ~150mK or S/N~20, so at our scaled intensity, a few mJy/bm. The exposure time calculator says that ALMA will achieve 1.3mJy/bm in an hour, so we should set this up as a half hour snapshot.