A Close Separation Double Quasar Lensed by a Gas-Rich Galaxy

Kavli Affiliate: Paul Schechter

| First 5 Authors: Michael D. Gregg, Lutz Wisotzki, Robert Becker, Jose Maza, Paul Schechter

| Summary:

In the course of a Cycle 8 snapshot survey, we have discovered that the
z=1.565 quasar HE 0512-3329 is a double with image separation 0.644", almost
certainly due to gravitational lensing. The two components differ in brightness
by only 0.4 magnitudes and a high signal-to-noise ground-based composite
optical spectrum shows no trace of any stellar features at zero redshift,
essentially ruling out the possibility that one of the two components is an
ordinary Galactic star. The optical spectrum shows strong absorption features
of MgII, MgI, FeII, FeI, and CaI, all at an identical intervening redshift of
z=0.9313, probably due to the lensing object. The strength of the MgII and the
presence of the other low ionization absorption features is strong evidence for
a damped Lyman alpha system, likely the disk of a spiral galaxy. Point spread
function fitting to remove the two quasar components from the STIS image leads
to a tentative detection of a third object which may be the nucleus of the
lensing galaxy. The brighter component is significantly redder than the
fainter, due to either differential extinction or microlensing.

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