[AstroPy] Image reprojection and counts

Adam Ginsburg adam.g.ginsburg at gmail.com
Fri Jan 8 08:57:33 EST 2021

Hi Dominik,
     You will need to rescale when you change the pixel size, since
changing the pixel size is changing the (implicit) unit.  This is a tricky
problem that always gets me when I work with Jy/pixel (when interpolating)
or Jy/beam (when smoothing) units.  If you convert to Jy/arcsec^2 or
MJy/sr, making the unit explicit, then no additional scaling should be

On Fri, Jan 8, 2021 at 3:58 AM Ivan Valtchanov <ivvv68 at gmail.com> wrote:

> Hi Dominik,
> I would suggest you to do generate some toy models and test the
> behaviour. You can generate images with e.g. Gaussian clusters and
> then reproject and check the counts after reprojection. Additionally
> you could also check the radial profile, just to be sure the
> reprojection does not introduce any undesired side effects. Just an
> idea.
> Cheers,
> Ivan V
> On Thu, 7 Jan 2021 at 19:34, Dominik Rhiem <hg.dude.hg at gmail.com> wrote:
> >
> > Dear all,
> >
> > I am planning to use the reproject_interp function to rescale several
> fits images of different clusters in such a way that after the
> reprojection, the maps have the same number of pixels and the same size in
> terms of R500/Theta500 for the specific cluster; this means that the pixel
> size in arcsec will depend on the cluster after the rescaling.
> > However, the flux information contained in the maps is scaled by the
> pixel size; before the rescaling, each pixel contains counts with the units
> mJy per pixel area [arcsec**2]. Does the function reproject_interp take
> this into account or should I multiply the maps with the pixel area before
> rescaling?
> > If anything about this is unclear, please let me know.
> >
> > Sincerely,
> > Dominik Rhiem
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Adam Ginsburg
Assistant Professor, Department of Astronomy
University of Florida, Gainesville
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