A Decade of Dark Energy: 1998 - 2008

The years 1998 to 2008 were very exciting years for cosmology. It was a pleasure to accept this invitation to describe my contributions to the development of our knowledge and understanding of the universe over the course of the past decade. Here, I begin by describing some of my work on radio galaxies as a modified standard yardstick and go on to describe model-independent studies of the accelerating universe and the properties of the dark energy. During the course of these studies, I came upon interesting ways to study the spin and other properties of supermassive black holes, some of which are briefly mentioned.Comment: Proceedings of the 2008 UCLA Conference "Dark Matter and Dark Energy in the Universe," submitted to AIP Conference Proceedings, 6 page

Black Hole Spin Properties of 130 AGN

Supermassive black holes may be described by their mass and spin. When supermassive black holes are active, the activity provides a probe of the state of the black hole system. The spin of a hole can be estimated when the black hole mass and beam power of the source are known for sources with powerful outflows. Seventy-five sources for which both the black hole mass and beam power could be obtained are identified and used to obtain estimates of black hole spins. The 75 supermassive black holes studied include 52 FRII radio galaxies and 23 FRII radio loud quasars with redshifts ranging from about zero to two. The new values are combined with those obtained previously for 19 FRII radio galaxies, 7 FRII radio loud quasars, and 29 radio sources associated with CD galaxies to form samples of 71 FRII radio galaxies, 30 FRII quasars, and a total sample of 130 spin values; all of the sources are associated with massive elliptical galaxies. The new values obtained are similar to those obtained earlier at similar redshift, and range from about 0.1 to 1 for FRII sources. The overall results are consistent with those obtained previously: the spins tend to decrease with decreasing redshift for the FRII sources studied. There is a hint that the range of values of black hole spin at a given redshift is larger for FRII quasars than for FRII radio galaxies. There is no indication of a strong correlation between supermassive black hole mass and spin for the supermassive black holes studied here. The relation between beam power and black hole mass is obtained and used as a diagnostic of the outflows and the dependence of the magnetic field strength on black hole mass.Comment: 12 pages, 12 figures, 5 table

Lateral Expansion of the Bridges of Cygnus A and other Powerful Radio Sources

Measurements of the width of the radio bridge at several locations along the bridge for each of four powerful extended radio sources are presented. Adopting a few simple assumptions, these measurements may be used to predict the radio surface brightness as a function of position across the radio bridge. The predicted and observed surface brightnesses across the bridges are compared and found to agree fairly well. The results are consistent with a simple picture in which the radio power and size of the radio lobe at the forward edge of the radio bridge are roughly time-independent for a given source, and the expansion of the bridge in the lateral direction is adiabatic. There is no indication that reacceleration or energy transport is important in the bridges of these sources. The rate of lateral expansion of the bridge just behind the radio lobe and hotspot in terms of the rate of forward propagation is compared with that predicted, and found to be in good agreement with the predicted value.Comment: 7 pages, uuencoded compressed postscript. To appear in the Proceding of the Cygnus A workshop, May 1-4, Green Bank, W

Empirical Determinations of Key Physical Parameters Related to Classical Double Radio Sources

Multi-frequency radio observations of the radio bridge of powerful classical double radio sources can be used to determine: the beam power of the jets emanating from the AGN; the total time the source will actively produce jets that power large-scale radio emission; the thermal pressure of the medium in the vicinity of the radio source; and the total mass, including dark matter, of the galaxy or cluster of galaxies traced by the ambient gas that surrounds the radio source. The theoretical constructs that allow a determination of each of these quantities using radio observations are presented and discussed. Empirical determinations of each of these quantities are obtained and analyzed. A sample of 14 radio galaxies and 8 radio loud quasars with redshifts between zero and two for which there is enough radio information to be able to determine the physical parameters listed above was studied in detail. (abridged)Comment: Submitted to ApJ, LaTex, 26 total pages of text which includes captions & two tables, plus 13 EPS figures & 1 tabl