The differences between mass- and light-derived structural parameters over time for MaNGA Elliptical galaxies

TL;DR

This study investigates how the structural parameters derived from stellar mass and light distributions in elliptical galaxies evolve over time, revealing that differences decrease as galaxies become passive and suggesting photometric effects influence perceived structural evolution.

Contribution

It provides a detailed comparison of mass- and light-derived galaxy structures over cosmic time, highlighting the impact of photometric changes on perceived galaxy evolution.

Findings

Mass-to-light ratios increase with look-back time, especially in more massive galaxies.

Mass and light distributions become more similar at later times as galaxies passively evolve.

Observed structural evolution may be partly due to photometric effects rather than intrinsic changes.

Abstract

We apply stellar population synthesis analysis to obtain spatially-resolved archaeological inferences for a large sample of "red and dead" Elliptical galaxies (Classical Ellipticals; CLEs) from the MaNGA/SDSS-IV DR15 survey. From their 2D stellar light and mass maps, we explore the differences between the radial mass and light distributions in the rest-frame bands $g,$ $r,$ and $i$ as functions of look-back time, $t_{\rm lb}$, or redshift, $z$. We characterize these differences through the ratios between the following mass- and light-derived global properties: sizes, concentrations, and effective surface densities. We find that the mass-to-light ratios of these properties change with $t_{\rm lb}$, more the more massive the galaxies are. The CLE galaxy archaeological progenitors are, on average, less compact, concentrated, and dense in light than in mass as $z$ decreases. However, at later times, when also the evolution of the progenitors becomes passive at all radii, there is an upturn in these trends and the differences between mass and light in compactness/concentration decrease towards $z\sim 0$. The trends in the ratios of mass to light sizes agree qualitatively with results from direct observations in galaxy surveys at different redshifts. We discuss the caveats and interpretations of our results, and speculate that the strong structural evolution found in some previous studies for early-type galaxies could be explained partially by photometric changes rather than by intrinsic structural changes.