Professor Andrew Bunker

Abstract:

We present Keck Low Resolution Imaging Spectrometer spectroscopy along with Near-Infrared Camera and Multiobject Spectrometer (NICMOS) F110W (∼J) and F160W (∼H) images of the galaxy HDF 4-473.0 in the Hubble Deep Field (HDF), with a detection of an emission line consistent with Lyα at a redshift of z = 5.60. Attention to this object as a high-redshift galaxy was first drawn by Lanzetta, Yahil, & Fernandez-Soto and appeared in their initial list of galaxies with redshifts estimated from the Wide Field Planetary Camera 2 (WFPC2) HDF photometry. It was selected by us for spectroscopic observation, along with others in the HDF, on the basis of the NICMOS F110W and F160W and WFPC2 photometry. ForH0 = 65 km s-1 Mpc-1 and q0 = 0.125, the use of simple evolutionary models along with the F814W (∼I), F110W, and F160W magnitudes allow us to estimate the star formation rate (∼13 M⊙ yr-1). The colors suggest a reddening of E(B - V) ∼ 0.06. The measured flux in the Lyα line is approximately 1.0 × 10-17 ergs cm-2 s-1, and the rest-frame equivalent width, correcting for the absorption caused by intervening H I, is ∼90 Å. The galaxy is compact and regular, but resolved, with an observed FWHM of ∼0″.44. Simple evolutionary models can accurately reproduce the colors, and these models predict the Lyα flux to within a factor of 2. Using this object as a template shifted to higher redshifts, we calculate the magnitudes through the F814W and two NICMOS passbands for galaxies at redshifts 6 < z < 10. © 1998. The American Astronomical Socicly. All rights reserved.

Abstract:

In a companion Letter, Jones et al. report the discovery of a cosmic microwave background decrement, indicative of a distant cluster with mass ∼1015 M⊙, toward the quasar pair PC 1643+4631A, B (z = 3.79, 3.83, separation 1980). To search for the cluster responsible, we have obtained R-, J-, and K-band images of the field and have also carried out optical spectroscopy of selected objects in it. No such cluster is evident in these images. Assuming that the cluster causing the decrement is similar to massive clusters already known, our magnitude limits imply that it must lie at about or beyond z = 1. This provides independent support for the X-ray-based distance argument of Jones et al. The cluster must gravitationally lens objects behind it; for a cluster z around 1-2, the Einstein ring radius for sources at z ≈ 3.8 is ∼100″. Simple modeling, producing simultaneously the Sunyaev-Zeldovich effect and the lensing, shows that the source positions of quasars A and B lie within 1100 of each other and may indeed be coincident. The two quasar spectra are found to be remarkably similar apart from their 1% redshift difference. Assuming that A and B are images of a single quasar, we present a possible explanation of this difference.