Stellar populations of the bulges of four spiral galaxies

TL;DR

This study measures stellar population properties in four spiral galaxy bulges, revealing insights into their formation processes through spectral analysis and gradients, with some bulges showing signs of external material accretion.

Contribution

It provides new measurements of line strength indices and stellar population gradients for four spiral galaxy bulges, including detailed analysis of their formation clues.

Findings

Negative metallicity gradients suggest dissipative collapse.

Shallow age and alpha/Fe gradients imply merging influences.

One bulge shows peculiar properties indicating external material capture.

Abstract

Key information to understand the formation and evolution of disk galaxies are imprinted in the stellar populations of their bulges. This paper has the purpose to make available new measurements of the stellar population properties of the bulges of four spiral galaxies. Both the central values and radial profiles of the line strength of some of the most common Lick indices are measured along the major- and minor- axis of the bulge-dominated region of the sample galaxies. The corresponding age, metallicity, and {\alpha}/Fe ratio are derived by using the simple stellar population synthesis model predictions. The central values and the gradients of the stellar population properties of ESO-LV1890070, ESO-LV4460170, and ESO-LV 5140100 are consistent with previous findings for bulges of spiral galaxies. On the contrary, the bulge of ESO-LV 4500200 shows peculiar chemical properties possibly due to the presence of a central kinematically-decoupled component. The negative metallicity gradient found in our bulges sample indicates a relevant role for the dissipative collapse in bulge formation. However, the shallow gradients found for the age and {\alpha}/Fe ratio suggests that merging can not be completely ruled out for the sample bulges. This is confirmed by the properties of ESO-LV 4500200 which can hardly be explained without invoking the capture of external material.