Other
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt.........6z&link_type=abstract
Thesis (PhD). THE JOHNS HOPKINS UNIVERSITY, Source DAI-B 64/02, p. 767, Aug 2003, 167 pages.
Other
2
Scientific paper
In this thesis I use data from the Hubble Space Telescope to address several outstanding issues in the study of z ≈ 1 powerful radio sources and their host galaxies. I use NICMOS images to show that the stellar hosts are elliptical galaxies with r1/4 law light profiles. I derive both the effective radius and surface brightness by fitting surface-brightness models. I find that their sizes are similar to those of local radio hosts and are in general larger than other local galaxies. The derived galaxy luminosities lie at the bright end of luminosity functions constructed at similar red-shifts. Overall, our host results are consistent with these galaxies having formed the bulk of their stars at redshifts greater than z ≳ 2. I use the NICMOS data in conjunction with images from WFPC2 to measure optical-infrared colors for the aligned component. These colors are generally quite blue. Comparison to template spectral energy distributions (SEDs) show that only young stars can match the bluest aligned light. In addition, WFPC2 imaging polarimetry confirms that light from the active nucleus is scattered into the line-of-sight by either dust or electrons. Two of the four galaxies studied show high overall polarizations with a large degree of circular symmetry. Deconstruction of the galactic SEDs, suggests that while the same mechanisms are responsible for the alignment effect in all the galaxies, their proportions may vary considerably from source-to-source. If young stars are responsible for some of the alignment, the necessary stellar masses are insignificant compared to that of the old population seen in the near-infrared images. Together, these results suggest that these radio galaxies are not exceptionally strange sources. In fact, along with the observed relation between black-hole and bulge masses in the local Universe, my research implies that these z ≈ 1 sources may simply be caught in an active phase through which all galaxies pass.
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