Trouble with "Constructing the Spatially-resolved Mass-Metallicity Relation" exercise

[TheRealEKL]

Hello,

in the "Constructing the Spatially-resolved Mass-Metallicity Relation" exercise, I am having trouble understanding how the CSV file was created. I have been looking through the FIREFLY FITS file here:

And I am confused as to how the CSV file for the galaxy with the MaNGA plateIFU 8077-6104 was created. I have tried creating CSV's of the photometric mass as seen in the first extension of the HDU, but that seems to only be a single value as opposed to the array of values in the CSV that is needed. If I try to access the "STELLAR_MASS_VORONOI" in extension 11, I retrieve a large amount of data that can't be turned into a CSV (due to >1 dimensions), and even if I could create a CSV of that I am unsure of how to line it up with the PLATEIFU. So basically: How do you create the CSV containing the stellar mass of a particular galaxy using the PLATEIFU?

[havok2063]

Hi @TheRealEKL I wasn't the original author of that tutorial so I can't say for sure how that CSV file was made. The author probably extracted the data from the FIREFLY VAC, reshaped it in the format of a 2d map slice, and saved it out to a CSV file. That tutorial was also written using an older version of the FIREFLY VAC, so the file structure may have changed. If so, then it may not be transparent how the CSV comes from the new FITS file. I'm not intimately familiar with the FIREFLY VAC.

I would download and use the latest DR17 version of the FIREFLY VAC. You can find the latest FIREFLY datamodel description at https://data.sdss.org/datamodel/files/MANGA_FIREFLY/FIREFLY_VER/manga_firefly.html. You can also read more about the FIREFLY VAC at https://www.sdss.org/dr17/data_access/value-added-catalogs/?vac_id=manga-firefly-stellar-populations and https://www.sdss.org/dr17/manga/manga-data/manga-firefly-value-added-catalog//.

Skimming the FITS file, it looks like the galaxy id info, e.g. plate-ifu, manga-id are in the GALAXY_INFO extension, and the rest of extensions are organized by galaxy id, then spaxel row, then data value. For stellar mass, the shape of the data is [10735, 2800, 4]. The 1st dimension is the galaxy row from extension 1 , the 2nd dimension are the values per spaxel stored as 1d arrays, and the 3rd dimension contains the differement mass measurements, e.g. index 0 gives stellar mass per spaxel. You need to select the galaxy of interest from ext 1, and use that reference to select the correct data from the other extensions. If you're interested in re-making it back into a 2d map slice, you'll need to reshape the spaxel array info from a 1d array back into a 2d array.