Study of stellar populations in the bulges of barred galaxies

Abstract

Aims. We wish to determine the influence of bars on the building of galaxy bulges through analysis of ages and metallicities derived from stellar absorption line-strength indices. Methods. Long-slit spectroscopy was obtained for a sample of 20 early-type barred galaxies. Line-strength indices were measured and used to derive age and metallicity gradients in the bulge region by comparing them with stellar population models. The same analysis was carried out with similar data for unbarred galaxies taken from the literature. Results. The bulges of barred galaxies seem to be more metal rich, at a given velocity dispersion (σ), than the bulges of unbarred galaxies, as measured by a few metallicity sensitive indices. There are indications that the ratio of relative abundance of alpha elements with respect to iron, [E/Fe], derived for the bulges of barred galaxies tend to lie above the values of the unbarred galaxies at a given σ. The metallicity gradients for the majority of the bulges are negative so less metal-rich towards the end of the bulge. The gradient values show a large scatter for galaxies with σ below 150 km s −1 . The age distribution is related to the presence of a bulge substructure, such as a nuclear ring or an inner disk. The metallicity of both the bulge and the bar are very well correlated, indicating a close link between the enrichment histories of both components. Conclusions. Bulges of barred early type galaxies might have experienced a different chemical enrichment than do the bulges of unbarred galaxies of the same morphological type, the same central velocity dispersion, and low inclination angles. The hinted stellar populations differences separating the bulges of barred and unbarred galaxies and the strong link between the metallicity of the bulge and the presence of a bar points to scenarios where they both form simultaneously in processes that lead to rapid and massive episodes of star formation, possibly linked to the bar formation. To confirm and generalise the results found here, it would be useful to extend the data set to a larger number of unbarred galaxies and a wider range of morphological types

The impact of gas inflows on star formation rates and metallicities in barred galaxies

“…In contrast to the observations, simulations predict that star formation should lead to higher central abundances (Friedli et al 1994; Friedli & Benz 1995). High stellar metallicities in the bulges of barred galaxies have recently been reported by Perez & Sanchez‐Blazquez (2011), but similar enhancements in the gas‐phase abundances have not been convincingly demonstrated.…”

Constraining the formation of inner bars: photometry, kinematics and stellar populations in NGC 357★

“…For this reason, these works focus only on the main bar and they do not account for the inner bar. This is the case in the set of papers by Pérez et al (2007, 2009), Pérez & Sánchez‐Blázquez (2011) and Sánchez‐Blázquez et al (2011), who study the stellar populations of bars and bulges. They find positive, negative and even null metallicity gradients along the bars independently of the age distribution.…”

Star formation history of barred disc galaxies

“…One of our main goals is to understand the influence of bars on the evolution of these systems, for which, in a forthcoming paper, we will compare with analogous non‐barred galaxies. This study is complemented by that of the stellar populations in galaxy bars and their bulges (Pérez, Sánchez‐Blázquez & Zurita 2007; Pérez, Sánchez‐Blázquez & Zurita 2009; Pérez & Sánchez‐Blázquez 2011). In this paper, we present a pilot study using data from four galaxies.…”