Hubble Space Telescope NICMOS Observations of Rest-Frame Optical Continuum and Hα+[N I] Emission In FSC 10214+4724

June 1999 • 1999ApJ...518..145E

Authors • Evans, A. S. • Scoville, N. Z. • Dinshaw, N. • Armus, L. • Soifer, B. T. • Neugebauer, G. • Rieke, M.

Abstract • High-resolution 1.10, 2.05, 2.12, and 2.15 μm imaging of the gravitationally lensed system FSC 10214+4724 are presented. These data extend Hubble Space Telescope (HST) observations of the lens system to redder wavelengths, thus providing the highest resolution images to date of the rest-frame optical and narrow-line (i.e., Hα+[N II]) regions of the background quasar. The length of the arc in the wide-band continuum images increases with increasing wavelength, and the Hα+[N II] emission has a length in between that of the 1.10 and 2.05 μm emission. The structure of the arc changes from having an eastern and western peak at 1.10 μm to having a single peak in the center at 2.05 μm. The changing structure and length of the arc can be understood in terms of a model in which the background quasar consists of a region of scattered active galactic nucleus (AGN) light that dominates at 1.10 μm (rest frame 3300 Å), surrounded by a more extended narrow-line region. An even more extended red stellar population would thus contribute light at 2.05 μm (rest frame 6200 Å). In addition, the Hα+[N II] emission has structural features similar to the 1.10 μm emission normalized by the (predominantly stellar) 2.05 μm emission, possibly confirming that the 1.10 μm emission is a superposition of the sources associated with the line emission (AGNs/massive stars) and the red stellar component that dominates the 2.05 μm emission. The counterimage of the lensed quasar is detected in the 1.10 and 2.05 μm images, and the rest frame 3300 and 6200 Å magnifications of the lensed quasar are calculated to be 50+/-11 and 25+/-6, respectively, which translates into a rest-frame optical luminosity for the quasar of ~6×10⁹ L_solar. These magnification values are lower than the previously measured magnification of ~100 at rest frame 2400 Å. If the dust in the primary lensing galaxy is not affecting the measurement of the counterimage flux at 2400 and 3300 Å, the magnification of the quasar appears to decrease with increasing wavelength. Flux measurements of the primary lensing galaxy fit the spectral energy distribution of an unevolving elliptical galaxy at a redshift of 0.9, consistent with previous determinations of the redshift.

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Lee Armus

Senior Scientist