Molecular hydrogen in the cooling flow cluster Abell 1795

Abstract

A cooling flow forms in a galaxy cluster when the internal pressure of the gas drops below the gravitational potential of the cluster due to the cooling of the X-ray gas in the Inter-Cluster Medium (ICM). The cooling flow hypothesis is that the cooling X-ray gas condenses into clouds of molecular hydrogen and perhaps forms stars.

This thesis explores the above picture and is presented in two parts. First, we assemble cooling flow clusters and their X-ray properties in a study of alignments of the X-ray properties and optical emission. Second, we use that information to help pick the best cooling flow cluster in which to image the 2.12 μm v = (1-0) S(1) emission line of molecular hydrogen. We choose Abell 1795 (redshift of z = 0.06) as (1) it can be imaged within our time constraints of one night on the Canada-France-Hawaii Telescope's infrared camera (CFHT-IR); (2) the line flux has previously been determined; (3) high resolution Chandra X-ray data is available; and (4) this cluster is well studied at other wavelengths.

We find the morphology of the molecular hydrogen emission in the Central Dominant Galaxy (CDG) of Abell 1795 to be condensed and compare this image to that of the CDG in other wavebands. We conclude that the molecular hydrogen is not a direct result of the cooling flow, rather it is cooler gas that has been reheated by an Active Galactic Nucleus (AGN), or hot stars in the center of the galaxy.

We also, for the first time, detect molecular hydrogen emission from galaxies neighboring the CDG. We discuss what implications these observations have for the current cooling flow theory.