Spatially resolved gas and stellar kinematics in compact starburst galaxies

Abstract

The kinematics of galaxies provide valuable insights in their physics and assembly history. Kinematics are governed not only by the gravitational potential, but also by merger events and stellar feedback processes such as stellar winds and supernova explosions. Aims. We aim at identifying what governs the kinematics in a sample of SDSS selected nearby starburst galaxies, by obtaining spatially resolved measurements of the gas and stellar kinematics. We obtain near-infrared integral field K-band spectroscopy with VLT/SINFONI of 15 compact starburst galaxies. We derive the integrated as well as spatially resolved stellar and gas kinematics. The stellar kinematics are derived from the CO absorption bands, and Pa$\alpha$ and Br$\gamma$ emission lines are used for the gas kinematics. Based on the integrated spectra we find that the majority of galaxies have gas and stellar velocity dispersion that are comparable. A spatially resolved comparison shows that the six galaxies that deviate show evidence for a bulge or stellar feedback. Two galaxies are identified as mergers based on their double peaked emission lines. In our sample, we find a negative correlation between the ratio of the rotational velocity over the velocity dispersion (vrot/$\sigma$) and the star formation rate surface density. We propose a scenario where the global kinematics of the galaxies are determined by gravitational instabilities that affect both the stars and gas. This process could be driven by mergers or accretion events. Effects of stellar feedback on the ionised gas are more localised and detected only in the spatially resolved analysis. The mass derived from the velocity dispersion provides a reliable mass even if the galaxy cannot be spatially resolved. The technique used in this paper is applicable to galaxies at low and high redshift with the next generation of infrared focussed telescopes (JWST, ELT).

26 pages, 31 figures. Accepted for publication in Astronomy and Astrophysics, corrected by language editor

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