Galaxy formation and evolution

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 × 1010 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 differentstellar population synthesis(SPS) modelsin 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 SFHsreveal a sharp transition from star formation to quenching for galaxies with lg(σ∗/km s−1) 2.3 (σ∗ 200 km s−1), or average mass density within 1 kpc lg(JAM 1 /Mkpc−2) 9.9 (JAM 1 7.9 × 109 M kpc−2), or with [M/H] −0.1, or with Sersic index lg nSer 0.5 (nSer 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.

Abstract:

Rotation curves are the key observational manifestation of the dark matter distribution around late-type galaxies. In a halo model context, the precision of constraints on halo parameters is a complex function of properties of the measurements as well as properties of the galaxy itself. Forthcoming surveys will resolve rotation curves to varying degrees of precision, or measure their integrated effect in the HI linewidth. To ascertain the relative significance of the relevant quantities for constraining halo properties, we study the information on halo mass and concentration as quantified by the Kullback–Leibler divergence of the kinematics-informed posterior from the uninformative prior. We calculate this divergence as a function of the different types of spectroscopic observation, properties of the measurement, galaxy properties, and auxiliary observational data on the baryonic components. Using the SPARC (Spitzer Photometry & Accurate Rotation Curves) sample, we find that fits to the full rotation curve exhibit a large variation in information gain between galaxies, ranging from ~1 to ~11 bits. The variation is predominantly caused by the vast differences in the number of data points and the size of velocity uncertainties between the SPARC galaxies. We also study the relative importance of the minimum HI surface density probed and the size of velocity uncertainties on the constraining power on the inner halo density slope, finding the latter to be significantly more important. We spell out the implications of these results for the optimization of galaxy surveys aiming to constrain galaxies’ dark matter distributions, highlighting the need for precise velocity measurements.