Molecular gas properties of the most isolated galaxies

Abstract

The AMIGA project: The role of nature vs. nurture for the properties and evolution of galaxies is still an open question. In order to find answers, it is crucial to have a well-selected sample of isolated galaxies as a baseline and comparison. We built, refined and analised such a sample in the project AMIGA ("Analysis of the Interstellar Medium of Isolated GAlaxies”, http://www.iaa.es/AMIGA.html). The sample is based on the Catalogue of Isolated Galaxies (CIG) by Karanchenseva (1978) and the database (containing optical magnitude, Hα, far-infrared, radio continuum, HI and CO) enables us to characterize the properties of the star formation and interstellar medium.

The CO data: We present CO data for 276 AMIGA galaxies, obtained to a large extent (189 galaxies) from own observations in addition to data from the literature. This sample enables us to characterize the molecular gas content of isolated galaxies.

Comparison to other wavelengths: We show the comparison of the total molecular gas mass to the blue luminosity and the atomic gas mass. The molecular gas mass and the blue luminosity show a good correlation which can serve as a baseline to define the extected molecular gas content in a galaxy in the absence of interaction. The atomic gas mass is higher than the molecular gas mass for all Hubble types, and the ratio of the molecular-to-atomic mass ratio decreases towards late Hubble type.