Patricia Marie Knezek

New Galaxies Discovered in the First Blind H I Survey of the Centaurus A Group

We have commenced a 21 cm survey of the entire southern sky (δ -13.0), low surface brightness dwarf galaxies with H I profile line-widths suggestive of dynamics dominated by dark matter. The new group members add approximately 6% to the H I mass of the group and 4% to its light. The H I mass function, derived from all the known group galaxies in the interval 107 M☉ < M < 109 M☉, has a faint-end slope of 1.30 ± 0.15, allowing us to rule out a slope of 1.7 at 95% confidence. Even if the number in the lowest mass bin is increased by 50%, the slope only increases to 1.45 ± 0.15.

The Identification of Quasars behind Elliptical Galaxies and Clusters of Galaxies

The detection of resonance absorption lines against known objects such as individual galaxies and clusters of galaxies is a powerful approach for studying the gas content of these systems. We describe an efficient method of identifying background quasars suitable for absorption-line studies. In this finding technique, we identify serendipitous X-ray sources, about one-eighth of which are suitably bright quasars at moderate redshift. We identify 16 new quasars and galaxies with active galactic nuclei (AGNs) and confirm five known quasars and AGNs, superposed behind elliptical galaxies and clusters of galaxies. We also present three QSO/AGN candidates with uncertain redshift identifications.

Optical Counterparts to Galaxies in the Cen A Group Discovered by HIPASS

We have completed a 21-cm survey of a 600 square degree region of the Centaurus A group of galaxies at a redshift of ~500 km s-1 as part of a larger survey of the entire southern sky. This group of galaxies was recently the subject of a separate and thorough optical survey (Cote et al. 1997), and thus presented an ideal comparison for us to test the survey performance. We have identified 10 new group members to add to the 21 already known in our survey area. Six of the new members are previously uncatalogued galaxies, while four were catalogued but assumed not to be group members. Including the seven known members outside of our survey area, this brings the total known number of Cen A members to 38. All of the new HI detections have optical counterparts, most being intrinsically very faint (M_B > -13.0), late-type low surface brightness dwarfs. Most of the new members have HI masses only a few times our survey limit of 10^7 M_sun at an assumed distance for the group of 3.5 Mpc, and are extremely gas-rich, with a median M_HI / L_B > 1. Our limiting HI sensitivity was actually slightly worse than the HI follow-up observations of the Cote et al. optical survey, yet we have already increased the known number of group members by 50% using an HI survey technique. While we have increased the known number of members by ~50%, these new members contribute < 4% to its light.

Morphology and Stellar Populations in the Gas-Rich, Giant LSBGs

An unexpected characteristic of low surface brightness galaxies (LSBGs) is that a significant number are massive and possess substantial amounts of atomic gas. We present preliminary results of an ongoing program to obtain BVRIJHK imaging, along with some nuclear spectroscopy, of a well-defined sample of LSBGs which are gas-rich and of similar size to giant, high surface brightness spiral galaxies (HSBGs). These LSBGs span the entire range of Hubble disk morphologies. While their disks are bluer, on average, than comparable HSBGs, the optical morphology of massive LSBGs indicates that many of these systems have undergone previous star formation episodes. They typically have long disk scale lengths, and range from

Evolutionary Status of Dwarf “Transition” Galaxies

M_B = -16 to -22 (H_0 = 75 km/s Mpc^{-1})

The Evolution of Extreme Gas Rich Galaxies

. About half of the LSBGs with bulges show evidence of nuclear activity, and

Constraints on Ultraviolet Absorption in Rich Clusters of Galaxies

\sim 30%

The Underlying Stellar Populations of Dwarf ``Transition'' Galaxies

have appear to be barred. These massive, gas-rich LSBGs apparently have varied, and often complex, evolutionary histories.