Creating metallicity and stellar age maps

Pablo Galan de Anta
  • 28 Apr

Hi,

I would like to know how can I reproduce a 2D map of metallicity (Z/Z_sun) for the stars for a given snapshot. I was looking for the quantity on the Data Access webpage and the only quatity I found is GFM_Metallicity for the PartType4, and it specifies to adopt this amount divided by 0.0127 to convert to solar metallity, but when I compare with the maps on the visualization tool for the same subhalo, the number I get are completely different.

Also, how coud I produce a map of stellar age for the PartType4? Is it just simply the entry GFM_StellarFormationTime?

Thanks in advance,
Pablo

Dylan Nelson
  • 28 Apr

Hi Pablo,

I'd suggest to also look at Hemler+ (2020) e.g. Fig 2 for some examples, and some text about how to create such maps.

The procedure you describe should work for metallicity and should match the visualization tool images (roughly). If it doesn't, either a units issue, or in the details of how you are doing weighting, or projection.

For stellar age (e.g. in Gyr), you should calculate this from the GFM_StellarFormationTime (which is the scale factor).

Pablo Galan de Anta
  • 28 Apr

Ah I see, yeah so probably is the way I'm weighting. I'm using the function binned_statistic_2d from scipy and for metallicity I'm using the 'mean', as it makes 0 sense to sum up the metallicity if it is stellar weighted.

Alright so for GFM_StellarFormationTime, should I apply the typical relation between scale factor and time for a Lambda-CDM cosmology, right?

Dylan Nelson
  • 28 Apr

If you change "render method" to histo, then the visualization tool is doing essentially binned_statistic_2d (mass weighted). So you should be able to produce a very similar image.

As for stellar age, yes you can use e.g. astropy or else just copy this equation from a textbook.

Pablo Galan de Anta
  • 28 Apr

Alright, much clearer, thanks a lot Dylan :-)

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