SIMBA discrepancies - Githubissues

IQcollaboratory / galpopFM

forward modeling galaxy populations

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SIMBA discrepancies #48

Open changhoonhahn opened 3 years ago

changhoonhahn commented 3 years ago

Compared to EAGLE and TNG, the posteriors from ABC for SIMBA had the opposite correlation with SFR. In fact, the SIMBA posteriors reversed the SFR-to-color relation --- i.e. star-forming galaxies formed the red sequence in the optical color-magnitude diagram.

Here's what happens if we take SIMBA and run the dust model with the EAGLE posteriors. I've marked in red galaxies with high SSFR

This discrepancy seems to be driven by two factors:

Compared to other sims, SIMBA predict a large number of starburst galaxies, especially at low M*
SIMBA has a broader intrinsic (without dust) color distribution than the other simulations

changhoonhahn commented 3 years ago

I recently changed the dust model parameterization from SFR to SSFR (de247a663eba4ce7b87e6d030f70a814ce9adec7, see also #47). Even after the change in parameterization, the posterior for SIMBA reverses the relationship between SFR and color:

changhoonhahn commented 3 years ago

Here's an updated plot using the new SSFR parameterization: Once star-burst galaxies are removed, SIMBA run with EAGLE posteriors have very good agreement with SDSS observations.

changhoonhahn commented 3 years ago

Updates after new SFR=0 prescription*:

~~We continue to find the reversal of the SSFR to color relation for SIMBA.~~ Not sure what I was looking at but with the new SFR=0 prescription the SSFR to color relation is no longer reversed. However, we don't reproduce the color magnitude relation very well with SIMBA.
It again seems to be driven by the starburst population. Without the starburst galaxies, the dust model with TNG posteriors is able to better reproduce SDSS.

In order to reproduce the observed optical color-magnitude relation, SIMBA's starburst population requires high attenuation and steep slope, which contradicts the observed attenuation-slope relation

*in the new prescription SFR=0 galaxies are assigned SFR=SFR_min

changhoonhahn commented 3 years ago

New text added describing the discrepancy with SIMBA and how that's driven by the starburst population: https://github.com/IQcollaboratory/galpopFM/blob/abfa96ec5cbe9dfa842aa0b672a4bbe748264c8d/doc/paper/results.tex#L60