Starbursts in Barred Spiral Galaxies. III. Definition of a homogeneous sample of Starburst Nucleus Galaxies

TL;DR

This study characterizes a homogeneous sample of Starburst Nucleus Galaxies using optical spectroscopy, revealing their properties, low contamination by Seyferts, and likely nitrogen enrichment from starburst activity, with implications for galaxy evolution.

Contribution

It defines a new homogeneous sample of SBNGs with detailed spectroscopic analysis, distinguishing them from other galaxy types and exploring their nuclear properties and starburst mechanisms.

Findings

82% of emission-line regions are starbursts

Low Seyfert contamination (9%)

Nitrogen excess likely due to starburst enrichment

Abstract

This paper presents optical long-slit spectroscopic observations of 105 barred Markarian IRAS galaxies. These observations are used to determine the spectral type of emission-line regions in the nucleus and along the bar of the galaxies, in order to define a homogeneous sample of Starburst Nucleus Galaxies (SBNGs). Our selection criteria have been very efficient for selecting star-forming galaxies, since our sample of 221 emission-line regions includes 82% nuclear or extranuclear starbursts. The contamination by Seyferts is low (9%). The remaining galaxies (9%) are objects with ambiguous classification (HII or LINER). The dust content and Halpha luminosity increase towards the nuclei of the galaxies. No significant variation of the electron density is found between nuclear and bar HII regions. However, the mean Halpha luminosity and electron density in the bar are higher than in typical disk HII regions. We investigate different mechanisms for explaining the excess of nitrogen emission observed in our starburst nuclei. There is no evidence for the presence of a weak hidden active galactic nucleus in our starburst galaxies. The cause of this excess is probably a selective enrichment of nitrogen in the nuclei of the galaxies, following a succession of short and intense bursts of star formation. Our sample of SBNGs, located at a mean redshift of 0.015, has moderate Halpha (10^41 erg/s) and far infrared (10^10 Lsun) luminosities. The types are distributed equally among early- and late-type giant spirals with a slight preference for Sbc/Sc types because of their barred morphology. The majority (62%) of SBNGs are isolated with no sign of gravitational interaction. In terms of distance, luminosity and level of interaction, SBNGs are intermediate between HII galaxies and luminous infrared galaxies.