Secular evolution in action: central values and radial trends in the stellar populations of boxy bulges

TL;DR

This study analyzes the stellar populations and metallicity gradients in the bulges of 28 edge-on disk galaxies, revealing similarities with early-type galaxies and effects of bar-driven secular evolution on metallicity distribution.

Contribution

It provides new insights into how secular evolution influences stellar populations and metallicity gradients in barred galaxy bulges compared to unbarred systems.

Findings

Central stellar populations in barred bulges resemble those in early-type galaxies.

Radial metallicity gradients are shallower in barred bulges and uncorrelated with velocity dispersion.

Secular evolution may affect stellar populations similarly to mergers or may be less influential in central regions.

Abstract

We determine central values and radial trends in the stellar populations of the bulges of a sample of 28 edge-on S0-Sb disk galaxies, 22 of which are boxy/peanut-shaped (and therefore barred). Our principal findings are the following. (1) At a given velocity dispersion, the central stellar populations of galaxies with boxy/peanut-shaped bulges are indistinguishable from those of early-type (elliptical and S0) galaxies. Either secular evolution affects stellar populations no differently to monolithic collapse or mergers, or secular evolution is not important in the central regions of these galaxies, despite the fact that they are barred. (2) The radial metallicity gradients of boxy/peanut-shaped bulges are uncorrelated with velocity dispersion and are, on average, shallower than those of unbarred early-type galaxies. This is qualitatively consistent with chemodynamical models of bar formation, in which radial inflow and outflow smears out pre-existing gradients.