John Cannon, Ph.D. 2004

Starbursts in Dwarf Galaxies: A Multiwavelength Case Study of NGC 625

by John Cannon

Under the supervision of Professor Evan Skillman


The results of a multiwavelength case study of the nearby dwarf starburst galaxy NGC 625 are presented. This low-mass galaxy hosts a massive starburst comparable in luminosity to 30 Doradus in the Large Magellanic Cloud; its proximity and high galactic latitude provide an ideal opportunity to investigate the starburst phenomenon and its impact on the ISM and IGM. We use Chandra, FUSE, HST, CTIO, ATCA, and VLA data to investigate the nature of the stellar population and multi-phase ISM. Our principal findings are summarized as follows: 1) Ground-based optical spectroscopy finds a prominent Wolf-Rayet (W-R) feature arising from the major starburst region, implying a brief burst duration (4-6 Myr); 2) A spatially resolved star formation history analysis using HST/WFPC2 data shows that the duration of the burst is actually much longer than the W-R features would imply (duration ≥ 50 Myr), and that the star formation has been widespread throughout the disk over this interval; 3) This extended starburst has input sufficient kinetic energy into the ISM to create a large-scale outflow; 4) HI observations from the ATCA show complex kinematics that are consistent with a minor-axis outflow of large amounts of neutral gas; 5) This outflow is verified by FUSE spectroscopy, where strong O VI coronal gas absorption is blueshifted with respect to the neutral and diffuse H2 absorption lines; 6) FUSE spectra also reveal an abundance offset between the neutral and nebular gas regions that may be a common component of the ISM of low-metallicity dwarf galaxies; 7) The ROSAT detection of diffuse soft x-ray emission is verified by new Chandra imaging of NGC 625; 8) VLA radio continuum data shows a thermal global spectral index and a mix of thermal and nonthermal indices for the individual major star formation regions, suggesting vigorous and (temporally and spatially) extended star formation throughout the disk. We interpret these results in the context of low-mass galaxy evolution and compare our results to those found for other well-studied dwarf starburst systems.