J2233-606 narrow band
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J2233-606 (narrow band)

May 16, 2005
A search for Lyman-alpha companions to the radio-weak quasar J2233-606 in the Hubble Deep Field South (HDF-S) was conducted during the VLT UT1 SV programme in a small field of 1.2 x 1.3 arcmin2, centered on the quasar. Candidate Lyman-alpha companions were identified by subtracting a broad-band B (blue) image, that traces the galaxy stellar populations, from a narrow-band image, spectrally centered on the redshifted, narrow Lyman-alpha emission line of the quasar (z = 2.2).

Three Lyman-alpha candidate companions were discovered at angular distances of 15 to 23 arcsec, or 200 to 300 kpc (650,000 to 1,000,000 light-years) at the distance corresponding to the quasar redshift. The emission lines are very strong, relative to the continuum emission of the galaxies - this could be a consequence of the strong ionizing radiation field of the quasar. These companions to the quasar may trace a large-scale structure which would extend over larger distances beyond the observed, small field.

Even more striking is the presence of a very extended nebulosity whose size (120 kpc x 160 kpc) and Lyman-alpha luminosity (3 x 1044 erg/cm2/s) are among the largest observed around radio galaxies and radio-loud quasars, but rarely seen around a radio-weak quasar. Tidal interaction between the northern, very nearby companion and the quasar is clearly present: the companion is embedded in the quasar nebulosity, most of its gas has been stripped and lies in a tail westwards of the galaxy.

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