The morphology, environment and interstellar medium of early-type galaxies as a means for studying the evolution of galaxies outside of clusters

Abstract

The main goal of this thesis is to study the properties of isolated early-type galaxies with the hope of learning about their formation and evolution. With this goal in mind, B and I optical, and Ks near infrared images of 4 different samples of early-type galaxies in contrasting galactic density environments have been secured with the Steward Observatory 90 inch and 61 inch telescopes. The 4 early-type galaxy samples consist of: a sample extracted from the Catalog of Isolated Galaxies of Karachentseva, a sample of isolated galaxies previously studied by Fasano and Bonoli, a sample of galaxies from the Hickson Compact Groups Catalog, and a sample of galaxies with detected ISM's. This data set is used to examine whether differences in the galactic environment are related to differences in key properties of early-type galaxies. Multi-color surface photometry analysis is performed on the 4 samples, and the results are used in several contexts. For most of the galaxies in the Karachentseva sample surface photometry is reported for the first time. Likewise, Ks data for most of the objects in this thesis have never been reported. The light profile of the galaxies are fitted with Sersic profile functions. In agreement with other investigations, it is found that the Sersic parameter, n is primarily dependent on the galaxy size, and does not seem to be strongly dependent on properties such as environment or ISM content. The (B - I) color index, ellipticity, position angle, and third and fourth-order Fourier coefficients are derived from the surface photometry. It is confirmed that the third-order coefficients signal the presence of dust, and that the coefficient of the cos(4θ) gives structural information of the galaxies. Furthermore, the subtraction of model ellipticals has revealed peculiarities in the morphology, such as disks, spiral arms, dust lanes, multiple nuclei, etc. The largest and most relevant sample in this investigation consists of 39 galaxies, and it contains ∼25% of the galaxies classified as ellipticals in the Karachentseva catalog. Only approximately one half of the galaxies classified as ellipticals in that catalog appear to be correctly classified, a result which may imply a reduction of the percentage of ellipticals in the Karachentseva catalog to ∼6% of the total population of Isolated Galaxies. A significant number of merger candidates has also been found among the isolated galaxies. It is argued that the fraction of merger candidates to isolated ellipticals can be used to constrain models for the evolution of compact groups into isolated galaxies. The results of CO(1-0) millimetric wavelength observations taken at the NRAO 12 M telescope, as well as submillimeter continuum emission from dust at the SMT are also presented.