Nearby early-type galaxies with ionized gas.I. Line-strength indices of the underlying stellar population

TL;DR

This study provides detailed spectral line-strength measurements of 50 nearby early-type galaxies with emission lines, aiming to analyze their stellar populations and compare with existing data, covering various environments and galaxy sub-classes.

Contribution

It presents a homogeneous set of line-strength indices for early-type galaxies with emission lines, including data reduction and correction procedures, expanding the spectral database for stellar population studies.

Findings

Measured 25 line-strength indices across 50 galaxies.

Corrected indices for emission contamination and transformed to Lick-IDS system.

Compared results with existing literature to validate data quality.

Abstract

With the aim of building a data-set of spectral properties of well studied early-type galaxies showing emission lines, we present intermediate resolution spectra of 50 galaxies in the nearby Universe. The sample, which covers several of the E and S0 morphological sub-classes, is biased toward objects that might be expected to have ongoing and recent star formation, at least in small amounts, because of the presence of the emission lines. The emission are expected to come from the combination of active galactic nuclei and star formation regions within the galaxies. Sample galaxies are located in environments corresponding to a broad range of local galaxy densities, although predominantly in low density environments. Our long-slit spectra cover the 3700 - 7250 A wavelength range with a spectral resolution of about 7.6 A at 5550 A. The specific aim of this paper, and our first step on the investigation, is to map the underlying galaxy stellar population by measuring, along the slit, positioned along the galaxy major axis, line--strength indices at several, homogeneous galacto-centric distances. For each object we extracted 7 luminosity weighted apertures corrected for the galaxy ellipticity and 4 gradients and we measured 25 line-strength indices. The paper introduces the sample, presents the observations, describes the data reduction procedures, the extraction of apertures and gradients, the determination and correction of the line--strength indices, the procedure adopted to transform them into the Lick-IDS System and the procedures adopted for the emission correction. We finally discuss the comparisons between our dataset and line-strength indices available in the literature.