<p>If the 3D data cube is sufficiently highly resolved, try to find <a href="http://en.wikipedia.org/wiki/Relativistic_Doppler_effect" rel="nofollow">Doppler shifts</a> in the <a href="http://astronomy.nmsu.edu/nicole/teaching/ASTR505/lectures/lecture26/slide01.html" rel="nofollow">spectra</a> by looking for <a href="http://en.wikipedia.org/wiki/H-alpha" rel="nofollow">typical absorption/emission lines</a>. Doppler shifts correspond to <a href="http://en.wikipedia.org/wiki/Radial_velocity" rel="nofollow">radial velocities</a>. Calculate the mean radial velocity, and e.g. the <a href="http://en.wikipedia.org/wiki/Standard_deviation" rel="nofollow">standard deviation</a> of the radial velocities, as velocity dispersion.</p>

<p>The velocity dispersion of galaxies leads to a widening of spectral lines in comparison to a reference star. A couple of methods are discussed in <a href="http://mnras.oxfordjournals.org/content/339/1/215.full.pdf" rel="nofollow">this paper</a>, mostly some kind of <a href="http://cas.sdss.org/stripe82/en/help/docs/algorithm.asp?key=veldisp" rel="nofollow">Fourier fitting, but direct fitting is used, too</a>.</p>

<p><a href="http://en.wikipedia.org/wiki/Redshift" rel="nofollow">Redshifts</a> may contain a <a href="http://en.wikipedia.org/wiki/Gravitational_redshift" rel="nofollow">gravitational</a> component.</p>

<p><a href="http://p3d.sourceforge.net/" rel="nofollow">There exist data reduction software tools</a>.</p>

<p><a href="http://www.eso.org/~hkuntsch/papers/MNRAS_373_906.pdf" rel="nofollow">A paper</a> describing data reduction and velocity analysis using the <a href="http://cral.univ-lyon1.fr/labo/oasis/download/" rel="nofollow">XOASIS tool</a>.</p>

CC BY-SA 3.0
2014-03-06T12:43:40.133Z
2014-03-06T14:16:09.117Z
2014-03-06T14:16:09.117Z
Gerald
<p>I couldn't find on the web how to get the velocity dispersion and velocity maps of galaxies from the 3D data cube that I get from the integral field spectrograph.</p>

CC BY-SA 3.0
2014-03-06T05:59:11.283Z
Could you please add some more detail? what is 3D data cube? For "integral field spectrograph" you mean the observation of the whole field of view of the instrument/satellite?
Py-ser
<spectroscopy><data-analysis><observatory>
How do I calculate the velocity dispersion of a galaxy given an integral field spectrograph?
lital
# How do I calculate the velocity dispersion of a galaxy given an integral field spectrograph?

(Asked by: username_0 on 2014-03-05)

I couldn't find on the web how to get the velocity dispersion and velocity maps of galaxies from the 3D data cube that I get from the integral field spectrograph.

**Tags:** spectroscopy, data-analysis, observatory

> **Comments:**
> **username_1**: Could you please add some more detail? what is 3D data cube? For "integral field spectrograph" you mean the observation of the whole field of view of the instrument/satellite?  

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## 1 answers

### Answer by username_2 on 2014-03-06. Score: 3

If the 3D data cube is sufficiently highly resolved, try to find [Doppler shifts](http://en.wikipedia.org/wiki/Relativistic_Doppler_effect) in the [spectra](http://astronomy.nmsu.edu/nicole/teaching/ASTR505/lectures/lecture26/slide01.html) by looking for [typical absorption/emission lines](http://en.wikipedia.org/wiki/H-alpha). Doppler shifts correspond to [radial velocities](http://en.wikipedia.org/wiki/Radial_velocity). Calculate the mean radial velocity, and e.g. the [standard deviation](http://en.wikipedia.org/wiki/Standard_deviation) of the radial velocities, as velocity dispersion.

The velocity dispersion of galaxies leads to a widening of spectral lines in comparison to a reference star. A couple of methods are discussed in [this paper](http://mnras.oxfordjournals.org/content/339/1/215.full.pdf), mostly some kind of [Fourier fitting, but direct fitting is used, too](http://cas.sdss.org/stripe82/en/help/docs/algorithm.asp?key=veldisp).

[Redshifts](http://en.wikipedia.org/wiki/Redshift) may contain a [gravitational](http://en.wikipedia.org/wiki/Gravitational_redshift) component.

[There exist data reduction software tools](http://p3d.sourceforge.net/).

[A paper](http://www.eso.org/~hkuntsch/papers/MNRAS_373_906.pdf) describing data reduction and velocity analysis using the [XOASIS tool](http://cral.univ-lyon1.fr/labo/oasis/download/).


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