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Session 21 - Galaxies and Clusters of Galaxies.
Oral session, Monday, June 10
We report observations on redshift z>4.5 objects identified in deep narrow-band Lyman \alpha imaging of the fields surrounding the quasars BR1202--0725 (z=4.695) and BR2237--0607 (z=4.558) and studied with followup spectroscopy with the LRIS spectrograph on Keck. Previous narrow-band imaging at the wavelength of redshifted Lyman \alpha for BR1202--0725 identified emission which coincides with the continuum light from a faint galaxy seen in Hubble Space Telescope (HST) WFPC2 images 2.6'' NW of the quasar, and pointing radially towards it (Hu, McMahon, amp; Egami 1996, Ap. J., 459, L53--L55). From high resolution tip-tilt imaging (FWHM 0.45'') of this system at the UH 2.2m telescope in the Lyman \alpha line, we identify a faint Lyman \alpha emission component coincident with a second fainter galaxy 3'' SW of the quasar, also pointing radially towards the quasar in the HST image. This second emission system near the quasar at z=4.7 is confirmed in multi-slit LRIS spectra taken on these objects with the Keck 10m telescope. CIV emission is not detected in these spectra.
For BR2237--0607 based on deep narrow-band Lyman \alpha imaging followed by spectroscopy using LRIS at Keck, we identify two Lyman \alpha emitting galaxies at z=4.55. In contrast to the BR1202--0725 emission-line objects, these galaxies have separations > 100'' (\sim 700 kpc) from the quasar, which is unlikely to have a significant role in exciting them. Observed equivalent widths for the Lyman \alpha line exceed 1000 Åin each case. While one of these objects is quite compact, and has no detectable continuum in a 1-hr I-band exposure at Keck, and thus might be an AGN, the second has a diffuse extended structure in both continuum and emission, and is probably a star-forming galaxy. Line fluxes are \sim5\times 10^-17 ergs cm^-2 s^-1.
Program listing for Monday