Non-circular flows in HIghMass Galaxies in a Test of the Late Accretion Hypothesis

Abstract

This thesis investigates the late accretion hypothesis as an explanation for the unusual gas-richness of the HIghMass sample, a collection of 34 galaxies from the recently completed Arecibo Legacy Fast ALFA survey. Accretion is vital to galaxy evolution models as it explains several galaxy properties, including but not limited to the relatively constant metallicity distribution in disk galaxies as well as their extended star formation histories. As such, we search for the indirect signatures of accretion of extraplanar gas in H-alpha velocity fields of three HIghMass galaxies (UGC 7899, UGC 8475, and UGC 9037), obtained with the SITELLE Imaging Fourier Transform Spectrometer on the Canada-France-Hawaii Telescope. Only the data for UGC 7899 and UGC 9037 are amenable to a direct search of non-circular flows in their inner disk using the DiskFit algorithm. We applied rotation-only, bisymmetric, and radial flow models separately to UGC 7899 and UGC 9037, and a rotation-only model to UGC 8475. Using the kinematic data, and comparison with DiskFit runs on photometric images of each galaxy, we conclude that a bar-like model best describes the kinematics of UGC 7899, and that UGC 9037 exhibits radial flows in its inner disk. A radial flow model for UGC 9037 is consisted with previous results obtained at lower resolution from H I maps. Though this work further constrained the non-circular flows in the inner disk of two HIghMass galaxies, we find no direct evidence to support the late accretion hypothesis for the origin of their unusual gas-richness.