Andrew Bunker

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.

Abstract:

We report the discovery of a group of galaxies at redshift 2.38. We imaged ∼ 10% of a claimed supercluster of QSO absorption lines at z = 2.38. In this small field (2′ radius), we detect two Lyα-emitting galaxies. The discovery of two such galaxies in our tiny field supports Francis & Hewett's interpretation of the absorption-line supercluster as a high-redshift Great Wall. One of the Lyα galaxies lies 22″ from a background QSO and may be associated with a multicomponent Lyα absorption complex seen in the QSO spectrum. This galaxy has an extended (∼50 kpc), lumpy Lyα morphology surrounding a compact, IR-bright nucleus. The nucleus shows a pronounced break in its optical-UV colors at ∼4000 Å (rest frame), consistent with a stellar population of mass ∼7 × 10 M , an age of greater than 500 Myr, and little ongoing star formation. C iv emission is detected, which suggests that a concealed active galactic nucleus is present. The Lyα emission is redshifted by ∼490 km s with respect to the C IV emission, probably because of absorption. Extended Hα emission is also detected; the ratio of Lyα flux to Hα is abnormally low (∼0.7), probable evidence for extended dust. This galaxy is surrounded by a number of very red (B -K > 5 mag) objects, some of which have colors that suggest that they too are at z = 2.38. We hypothesize that this galaxy, its neighbors, and a surrounding lumpy gas cloud may be a giant elliptical galaxy in the process of bottom-up formation. © 1996. The American Astronomical Society. All rights reserved.