High-resolution H i distributions and multi-wavelength analyses of magellanic spirals NGC4618 and NGC4625

Abstract

We present a detailed analysis of high-resolution H I observations of the Magellanic spiral galaxies NGC4618 and NGC4625. While the H I disk of NGC4625 is remarkably quiescent with a nearly uniform velocity dispersion and no evidence of H I holes, there is a dynamic interplay between star formation and the distribution of neutral hydrogen in NGC4618. We calculate the critical density for widespread star formation in each galaxy and find that star formation proceeds even where the surface density of the atomic gas is well below the critical density necessary for global star formation. There are strong spatial correlations in NGC4618 between UV emission, 1.4GHz radio continuum emission, and peaks in the H I column density. Despite the apparent overlap of the outer disks of the two galaxies, we find that they are kinematically distinct, indicating that NGC4618 and NGC4625 are not interacting. The structure of NGC4618 and, in particular, the nature of its outer ring are highly suggestive of an interaction, but the timing and nature of such an interaction remain unclear. © 2012. The American Astronomical Society. All rights reserved.