Illuminating protogalaxies? The discovery of extended Lyman-α emission around a QSO at z=4.5 |
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Authors: | Andrew Bunker Joanna Smith Hyron Spinrad Daniel Stern Stephen Warren |
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Institution: | (1) Institute of Astronomy, University of Cambridge, Cambridge, CB3 0HA, UK;(2) Astronomy Department, University of California, Berkeley, USA;(3) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA;(4) Department of Physics, Imperial College, London, UK |
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Abstract: | We have discovered extended Lyman-α emission around a z=4.5 QSO in a deep long-slit spectrum with Keck/LRIS at moderate spectral resolution (R≈ 1000). The line emission extends 5 arcsec beyond the continuum of the QSO and is spatially asymmetric. This extended line
emission has a spectral extent of 1000km/s, much narrower in velocity spread than the broad Lyman-α from the QSO itself and
slightly offset in redshift. No evidence of continuum is seen for the extended emission line region, suggesting that this
recombination line is powered by reprocessed QSO Lyman continuum flux rather than by local star formation. This phenomenon
is rare in QSOs which are not radio loud, and this is the first time it has been observed at z>4. It seems likely that the QSO is illuminating the surrounding cold gas of the host galaxy, with the ionizing photons producing
Lyman-α fluorescence. As suggested by Haiman and Rees (2001), this `fuzz' around a distant quasar may place strong constraints
on galaxy formation and the extended distribution of cold, neutral gas.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | line: profiles formation techniques: spectroscopic galaxies: formation evolution quasars: emission lines high-redshift individual – PC0953+4749 |
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