[Paper Review] Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby objects

Federico Lelli, Marc Verheijen+1 more|University of Groningen research database (University of Groningen / Centre for Information Technology)|Apr 24, 2014

Galaxies: Formation, Evolution, Phenomena114 references61 citations

TL;DR

This study analyzes the H I kinematics of 18 nearby starbursting dwarf galaxies using new and archival radio data, finding that despite intense recent star formation, these systems retain high baryonic and gas fractions—implying minimal gas ejection. On average, baryons make up at least 30% of the total mass, suggesting starburst feedback does not significantly disrupt the gravitational potential or expel gas from the halos.

ABSTRACT

We investigate the dynamics of starbursting dwarf galaxies, using both new and archival HI observations. We consider 18 nearby galaxies that have been resolved into single stars by HST observations, providing their star formation history and total stellar mass. We find that 9 objects have a regularly-rotating HI disk, 7 have a kinematically disturbed HI disk, and 2 show unsettled HI distributions. Two galaxies (NGC 5253 and UGC 6456) show a velocity gradient along the minor axis of the HI disk, that we interpret as strong radial motions. For galaxies with a regularly rotating disk we derive rotation curves, while for galaxies with a kinematically disturbed disk we estimate the rotation velocities in their outer parts. We derive baryonic fractions within about 3 optical scale lengths and find that, on average, baryons constitute at least 30$\%$ of the total mass. Despite the star formation having injected $\sim$10$^{56}$ ergs in the ISM in the last $\sim$500 Myr, these starbursting dwarfs have both baryonic and gas fractions similar to those of typical dwarf irregulars, suggesting that they did not eject a large amount of gas out of their potential wells.

Motivation & Objective

• To understand the dynamical response of starbursting dwarf galaxies to intense star formation, particularly regarding gas retention and mass budget.
• To determine whether strong star formation feedback leads to significant gas ejection or alters the baryonic and dark matter distribution.
• To assess the role of H I kinematics in constraining the mass distribution and baryonic fractions in these systems.
• To compare the observed H I kinematics and mass fractions with predictions from ΛCDM models involving feedback-driven evolution.
• To resolve the kinematic center and H I morphology to infer disk stability and potential external influences.

Proposed method

• Acquired new and archival H I 21 cm line data to map the neutral gas distribution and kinematics in 18 nearby starbursting dwarfs.
• Used H I velocity fields, position-velocity diagrams, and channel maps to classify H I kinematics as regularly rotating, disturbed, or unsettled.
• Fitted 3D disk models to derive kinematic centers, systemic velocities, position angles, and inclinations from H I data.
• Derived rotation curves for galaxies with regular H I disks and estimated outer rotation velocities for disturbed systems.
• Calculated stellar masses from resolved star formation histories (SFHs) using HST data and a Salpeter IMF, with gas recycling efficiency of 30%.
• Estimated molecular gas mass using a star-formation efficiency scaling relation assumed to be the same as in spirals.

Experimental results

Research questions

• RQ1 Do starbursting dwarf galaxies retain significant H I gas despite intense star formation, or is feedback efficient at ejecting gas?
• RQ2 What is the baryonic mass fraction within ~3 optical scale lengths, and how does it compare to typical dwarf irregulars?
• RQ3 How do the kinematics of H I gas (regular rotation vs. disturbances) correlate with the intensity and duration of star formation?
• RQ4 Is there evidence for strong radial motions in the H I disks, and what might drive them?
• RQ5 To what extent is dark matter required to explain the observed rotation curves, especially in systems with high star formation rates?

Key findings

• Nine of the 18 galaxies exhibit regularly rotating H I disks, seven show kinematically disturbed H I kinematics, and two have unsettled H I distributions.
• Two galaxies, NGC 5253 and UGC 6456, display velocity gradients along the minor axis, interpreted as strong radial motions in the H I disk.
• The average baryonic fraction within ~3 optical scale lengths is at least 30%, indicating that baryons constitute a substantial fraction of the total mass.
• Despite injecting ~10^56 ergs of energy into the ISM over the past ~500 Myr via star formation, the baryonic and gas fractions remain similar to those of typical dwarf irregulars.
• The lack of significant gas depletion suggests that starburst feedback in these systems does not efficiently eject gas from the gravitational potential well.
• The results imply that starburst feedback in these dwarfs is not strong enough to cause large-scale gas loss or alter the global mass budget significantly.