Discovery of a color-selected quasar at z=5.50
ASTROPHYSICAL JOURNAL 533:2 (2000) L75-L78
Resolving the stellar populations in A z = 4 lensed galaxy
Astrophysical Journal 531:1 PART 1 (2000) 95-117
Abstract:
We present deep near-infrared Keck Near-Infrared Camera (NIRC) imaging of a recently discovered z = 4.04 galaxy. This is lensed by the rich foreground cluster Abell 2390 (z ≈ 0.23) into highly magnified arcs ″-5″ in length. Our H and K′ band NIRC imaging allows us to map the Balmer + 4000 Å break amplitude. In combination with high-quality archival Hubble Space Telescope (HST) WFPC2 data, we can spatially resolve stellar populations along the arcs. The WFPC2 images clearly reveal several bright knots, which correspond to sites of active star formation. However, there are considerable portions of the arcs that are significantly redder, consistent with being observed ≳ 100 Myr after star formation has ceased. Keck Low-Resolution Imaging Spectrograph (LRIS) long-slit spectroscopy along the arcs reveals that the Lyα emission is spatially offset by ≈1″ from the rest-UV continuum regions. We show that this line emission is most probably powered by star formation in neighboring H II regions and that the z = 4 system is unlikely to be an active galactic nucleus.The evolution of the stellar hosts of radio galaxies
Astronomical Journal 120:1 (2000) 68-79
Abstract:
We present new near-infrared images of z > 0.8 radio galaxies from the flux-limited 7C-III sample of radio sources for which we have recently obtained almost complete spectroscopic redshifts. The 7C objects have radio luminosities ≈20 times fainter than 3C radio galaxies at a given redshift. The absolute magnitudes of the underlying host galaxies and their scale sizes are only weakly dependent on radio luminosity. Radio galaxy hosts at z ∼ 2 are significantly brighter than the hosts of radio-quiet quasars at similar redshifts and the recent model AGN hosts of Kauffmann & Haehnelt. There is no evidence for strong evolution in scale size, which shows a large scatter at all redshifts. The hosts brighten significantly with redshift, consistent with the passive evolution of a stellar population that formed at z ≳ 3. This scenario is consistent with studies of host galaxy morphology and submillimeter continuum emission, both of which show strong evolution at z ≳ 2.5. The lack of a strong "redshift cutoff" in the radio luminosity function to z > 4 suggests that the formation epoch of the radio galaxy host population lasts ≳ 1 Gyr, from z ≳ 5 to z ∼ 3. We suggest these facts are best explained by models in which the most massive galaxies and their associated AGN form early because of high baryon densities in the centers of their dark matter haloes.A serendipitous search for high-redshift Lyα emission:: Two primeval galaxy candidates at z ≃ 3
ASTROPHYSICAL JOURNAL 537:1 (2000) 65-72
Limits on the star formation rates of z > 2 damped Lyα systems from Hα spectroscopy
Monthly Notices of the Royal Astronomical Society 309:4 (1999) 875-884