Full spectrum fitting with photometry in ppxf: stellar population versus dynamical masses, non-parametric star formation history and metallicity for 3200 LEGA-C galaxies at redshift z ≈ 0.8

I introduce some improvements to the ppxf method, which measures the stellar and gas kinematics, star formation history (SFH) and chemical composition of galaxies. I describe the new optimization algorithm that ppxf uses and the changes I made to fit both spectra and photometry simultaneously. I apply the updated ppxf method to a sample of 3200 galaxies at redshift 0.6 < z < 1 (median z = 0.76, stellar mass M-circle dot), using spectroscopy from the LEGA-C survey (DR3) and 28-bands photometry from two different sources. I compare the masses from new JAM dynamical models with the ppxf stellar population M-* and show the latter are more reliable than previous estimates. I use three different stellar population synthesis (SPS) models in ppxf and both photometric sources. I confirm the main trend of the galaxies' global ages and metallicity [M/H] with stellar velocity dispersion sigma (*) (or central density), but I also find that [M/H] depends on age at fixed sigma (*). The SFHs reveal a sharp transition from star formation to quenching for galaxies with (), or average mass density within 1 kpc (), or with , or with Sersic index (). However, the transition is smoother as a function of M-*. These results are consistent for two SPS models and both photometric sources, but they differ significantly from the third SPS model, which demonstrates the importance of comparing model assumptions.

Automated summary

This study introduces improvements to the ppxf method in measuring the kinematics, star formation history, and chemical composition of galaxies. The updated ppxf method shows more reliable estimates for stellar population mass and reveals relationships between galaxy age, metallicity, and stellar velocity dispersion. The comparison with different model assumptions demonstrates the importance of model comparisons in interpreting the results.