search

dendrograms / astrodendro

Generate a dendrogram from a dataset
https://dendrograms.readthedocs.io/
Other
37 stars 36 forks source link

Work around for correctly calculating flux from an integrated emission (moment 0 - 2D) image and constraining min_npix? #160

Open AstroJLo opened 6 years ago

AstroJLo commented 6 years ago

Hi there,

Firstly, a big thank you to everyone that has worked on updating and maintaining the astrodendro package; i found the tutorial to be very useful and informative at allowing me to understand what dendrograms are and how they can be utilised. Now, onto my questions:

Is it possible to calculate the correct flux from a 2D moment 0 (integrated emission) image of a molecular cloud? The units of the 2D image for BUNIT are in K*km/s. I am aware that when i try to do this, i get an error message stating that it isn't possible, due to these units not being implemented yet. However, i am just wondering whether a work around exists for this issue?

If I use 3D data (i.e. a PPV molecular line cube), this issue doesn't occur and the flux can be correctly calculated when BUNIT is equal to 'K' (thanks to the efforts of @tomr-stargazer !).

The issue with using a data cube (for now) is that it becomes slightly more challenging to choose the correct min_value, min_npix (this one in particular) and min_delta values; which isn't an issue that occurs with the 2D data. Perhaps @keflavich may have some ideas here for constraining min_npix in a data cube? The cloud I'm looking at is 'small' with the x and y dimensions of the image having an area that won't exceed 870" x 870" (29 x 29 pixels, with each pixel increment being 30 arc seconds).

keflavich commented 6 years ago

Could you post the traceback you get when using BUNIT = K km/s ? I don't remember exactly where that is, but it sounds like it might be an equivalency issue that may have been solved.

AstroJLo commented 6 years ago

Hi @keflavich , thanks for getting back to me. As per your request, here is a screenshot of the code.

dendrograms_2d_units_issue_screengrab

AstroJLo commented 6 years ago

Hi @keflavich , i'm just wondering if there has been any update on this issue?

keflavich commented 6 years ago

No, I don't have anything. Could you post a minimum working example? That might help.

FYI, I'm not an official maintainer of this repository, so I'm not promising anything.