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

ABSTRACT 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_ 3 10^10 M⊙), 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 σ* (or central density), but I also find that M/H depends on age at fixed σ*. The SFHs reveal a sharp transition from star formation to quenching for galaxies with (_ /km\, s^-1) 2. 3 (_ 200km\, s^-1), or average mass density within 1 kpc (₁^ JAM/M ₊₏₂^-₂) 9. 9 (₁^ JAM 7. 9 10⁹\, M \ ₊₏₂^-₂), or with M/H -0. 1, or with Sersic index n ₒ₄ₑ 0. 5 (n ₒ₄ₑ 3. 2). 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.