[Paper Review] Dynamics of blue compact galaxies, as revealed by their H$\\alpha$ velocity fields II. Mass models and the starburst triggering mechanism

Göran Östlin, P. Amram+4 more|arXiv (Cornell University)|Jun 11, 2001

Galaxies: Formation, Evolution, Phenomena73 references79 citations

TL;DR

This study analyzes Hα velocity fields and mass models of six luminous blue compact galaxies (BCGs) and two companions using Fabry-Perot interferometry and multiwavelength photometry. It finds that half the BCGs lack sufficient rotational support, suggesting dynamical disturbances or dark matter; combined morphology and kinematics point to dwarf galaxy mergers as the primary trigger for their starbursts.

ABSTRACT

The H$\\alpha$ velocity fields of a sample of six luminous blue compact galaxies (BCGs) and two companions have been obtained by observations with a scanning Fabry-Perot interferometer. The Fabry-Perot images, velocity fields and rotations curves have been presented in a previous paper (Paper I). In general, the velocity fields are irregular and often contain secondary dynamical components, but display overall rotation. The two companions have more regular velocity fields and rotation curves. In this article we analyse the velocity fields and dynamics together with the morphology of the studied BCGs, and present detailed mass models. In addition, we model the stellar mass content by means of multicolour surface photometry and spectral evolutionary synthesis analysis. By comparison of the masses of stars and those derived from the rotation curve, we show that about half of the galaxies cannot be supported by rotation alone. The morphology and dynamics of the BCGs suggest that the starburst activity in these galaxies are most likely triggered by mergers involving gas-rich dwarf galaxies and/or massive gas clouds.

Motivation & Objective

• To determine the dynamical mass distribution in luminous blue compact galaxies (BCGs) using Hα velocity fields.
• To assess the contribution of stellar populations and dark matter to the total mass budget in BCGs.
• To investigate the origin of starburst activity by analyzing kinematic and morphological signatures.
• To test whether rotation alone can support the observed velocity fields or if additional support (e.g., velocity dispersion or non-equilibrium dynamics) is required.
• To evaluate the role of interactions with gas-rich dwarf companions in triggering starbursts in BCGs.

Proposed method

• Obtained high-resolution Hα velocity fields using scanning Fabry-Perot interferometry at the ESO La Silla Observatory.
• Constructed rotation curves from the Hα velocity fields to infer dynamical mass distributions.
• Combined optical and near-infrared surface photometry with spectral energy distribution (SED) synthesis to model the stellar mass content.
• Built multi-component mass models including contributions from stars, gas, and dark matter halos.
• Used velocity dispersion measurements (σHα = 35–80 km/s) to assess non-rotational support in the gravitational potential.
• Analyzed galaxy morphologies down to faint isophotes to identify asymmetries and signs of interactions.

Experimental results

Research questions

• RQ1 Can the observed rotational velocities in BCGs be explained by rotational support alone, or is additional dynamical support required?
• RQ2 What is the relative contribution of young starburst populations versus older stellar populations to the total stellar mass and luminosity?
• RQ3 To what extent do dark matter halos contribute to the gravitational potential in these systems?
• RQ4 How do the kinematic and morphological properties of BCGs and their companions support or contradict merger-driven starburst models?
• RQ5 What is the role of gas-rich dwarf companions in triggering the observed starburst activity?

Key findings

• About half of the BCGs cannot be supported by rotation alone, as their observed rotational velocities are insufficient to balance gravitational collapse.
• The Hα velocity fields show large-scale peculiarities and secondary components, including counter-rotation, indicating dynamical disturbances.
• The stellar mass-to-light ratio (M/LV) for the integrated population (burst + old) is approximately 1, indicating that the old stellar population dominates the mass budget.
• The young starburst population contributes only 1–5% of the total stellar mass, despite dominating the optical luminosity.
• In two BCGs, there is direct evidence for dark matter within the extent of the Hα rotation curves, and in two others, marginal evidence is found.
• Morphological analysis reveals strong large-scale asymmetries in stars and gas, with clear signs of ongoing or recent interactions, supporting a merger-triggered origin for the starbursts.