Monday, 29 April 2013

Milky Way stellar number density : is the stated equation in this paper incorrect?

The paper is :
http://www.astro.washington.edu/users/ivezic/Publications/tomographyI.pdf



The equation is equation #23 in the paper. It's a model for the density of stars in the Milky Way's disk. It has an exponential dependence on both R and Z. R is the distance from the center of the galaxy, and Z is the distance above/below the plane of the disk.



The relation is roughly this:



varrho=textconstanttimesefracRLfracZ+Z0H



The problem I'm seeing is the Z-dependence of the formula. R and Z here are standard cylindrical coordinates. Thus, Z can be positive or negative. The problem is that the formula blows up when Z is negative. This is unphysical, since the number density must generally decrease going further away from the disk.



Am I missing something? Or should the equation really have an absolute magnitude of |Z+Z0|?



[Added Later:]
I finished making a 3D demo of the stellar number density of the Milky Way. Note that your browser needs to support WebGL.

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