Keck Spectroscopy of Objects with Lens-like Morphologies in the Hubble Deep Field

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  • 25 June 1996
Abstract
We present spectroscopy from the Keck telescope of three sets of objects in the Hubble Deep Field which have lens-like morphologies. In the case of J123641+621204, which is composed of four objects with similar colors and a mean separation of < 0.8 arcsec, we find at least two distinct components at redshifts of z=3.209 and z=3.220 which are separated by 0.5arcsec spatially. There are features suggestive of an AGN. The second case is J123652+621227, which has an arc-like feature offset by 1.8 arcsec to the southwest of a red elliptical-like galaxy, and a ``counterimage'' offset 1.4 arcsec on the opposite side. We find a single line at 5301 AA at the spatial position of the counterimage which by its colors is consistent with Lyman-alpha, hence z=3.36. There is no corresponding emission line at the position of the arc, and therefore this is likely not a lens. The third lensing candidate, J123656+621221, is a blue arc offset by 0.9 arcsec from a red, elliptical-like galaxy. Our spectroscopy does not clearly resolve the system spatially, complicating the interpretation of the spectrum. We discuss possible identifications of a number of absorption features and a very tentative detection of a pair of emission lines at 5650 AA and 5664 AA, and find that gravitational lensing remains a possibility in this case. We conclude that the frequency of strong gravitational lensing by galaxies in the HDF is very low. This result is inconsistent with the introduction of a cosmological constant to account for the large number of faint blue galaxies via a large volume element at high redshift, and tends to favor models in which very faint galaxies are at fairly modest redshifts.

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