[Paper Review] Starbursts in barred spiral galaxies. V. Morphological analysis of bars

S. Chapelon, T. Contini+1 more|arXiv (Cornell University)|Feb 11, 1999

Galaxies: Formation, Evolution, Phenomena3 citations

TL;DR

This study analyzes bar morphology in 125 barred spiral galaxies using CCD imaging to investigate how bar strength (quantified by axis ratio) correlates with morphological type, nuclear activity, and surface brightness. Key findings show that early-type barred galaxies (SBbc and earlier) uniformly host strong bars regardless of activity, while late-type normal galaxies exhibit weaker, shorter bars; active late-type galaxies, however, display both longer and stronger bars, suggesting distinct evolutionary pathways for early- and late-type bars.

ABSTRACT

We have measured the bar lengths and widths of 125 barred galaxies observed with CCDs. The dependence of bar strength (identified with bar axis ratio) on morphological type, nuclear activity, central and mid-bar surface brightness is investigated. The properties of the bars are best explained if the sample is divided into early- (< SBbc) and late-type galaxies, and into active (starburst, Seyfert or LINER) and normal galaxies. We find that galaxies with very long bars are mostly active and that normal late-type galaxies have a distinct behavior from the three other groups of galaxies. We confirm earlier findings that active late-type galaxies tend to have both stronger and longer bars than normal ones. An important result of this paper is that early-type galaxies do not share this behavior : they all tend to have strong bars, whether they are active or not. We also find correlations between bar strength and relative surface brightness in the middle and at the edge of the bar, which are not followed by normal late-type galaxies. These results are interpreted in the light of recent numerical simulations and paradigms about galaxy evolution. They suggest that normal late-type galaxies represent the first stage of galaxy evolution, and that bars in early- and late-type galaxies do not have the same properties because they have a different origin.

Motivation & Objective

• To investigate the relationship between bar strength and morphological type in barred spiral galaxies.
• To examine how nuclear activity (starburst, Seyfert, LINER) influences bar properties such as length and axis ratio.
• To explore correlations between bar strength and surface brightness at the bar's center, middle, and edge.
• To determine whether bar morphology differs significantly between active and normal galaxies across morphological types.
• To interpret the results in light of galaxy evolution models and numerical simulations.

Proposed method

• Measured bar lengths and widths from high-resolution CCD images of 125 barred spiral galaxies.
• Classified galaxies by morphological type (early-: SBbc and earlier; late-: later types) and nuclear activity (active vs. normal).
• Quantified bar strength using the bar axis ratio (minor-to-major axis), a standard proxy for bar prominence.
• Analyzed surface brightness profiles at the bar center, mid-bar, and bar edge to assess relative luminosity variations.
• Performed statistical comparisons between active and normal galaxies within early- and late-type subgroups.
• Integrated results with recent numerical simulations and galaxy evolution paradigms to interpret morphological differences.

Experimental results

Research questions

• RQ1 How does bar strength (axis ratio) vary with morphological type in barred spiral galaxies?
• RQ2 Do active galaxies (starburst, Seyfert, LINER) exhibit systematically longer or stronger bars than normal galaxies?
• RQ3 Is there a correlation between bar strength and surface brightness at different radial positions along the bar?
• RQ4 Do early-type and late-type barred galaxies follow different evolutionary pathways based on bar morphology?
• RQ5 What do the observed bar properties imply about the origin and evolution of bars in different galaxy types?

Key findings

• Early-type barred galaxies (SBbc and earlier) all exhibit strong bars, regardless of nuclear activity, indicating that bar strength is not significantly influenced by activity in these systems.
• Late-type normal galaxies have significantly weaker and shorter bars compared to active late-type galaxies, which display both longer and stronger bars.
• Active late-type galaxies consistently show stronger and longer bars than their normal counterparts, confirming earlier findings of enhanced bar strength in starburst or AGN-affected systems.
• Correlations between bar strength and mid-bar and edge surface brightness are present in early-type and active late-type galaxies but absent in normal late-type galaxies.
• The distinct behavior of normal late-type galaxies suggests they represent a different evolutionary stage compared to other barred systems.
• The results imply that bars in early- and late-type galaxies likely have different origins, with early-type bars being more stable and intrinsic to the bulge-dominated structure, while late-type bars may be more transient and influenced by ongoing star formation or nuclear activity.