In-spiraling Clumps in Blue Compact Dwarf Galaxies

TL;DR

This paper proposes that giant star-forming clumps in dwarf irregular galaxies can lose angular momentum and spiral inward, forming a central concentration of stars and gas that resembles a bulge, with observational evidence supporting long-lived clumps.

Contribution

It introduces a mechanism for clump-driven angular momentum loss leading to bulge-like structures in dwarf galaxies, supported by observational data.

Findings

Giant clumps can have masses exceeding a few percent of the galaxy mass.

Clumps contain old stars, indicating they may be long-lived.

Central regions of BCDs resemble bulges with high disk height-to-length ratios.

Abstract

Giant star-formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the BCD phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.