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Discovery of a bright quasar without a massive host galaxy


A quasar is thought to be powered by the infall of matter onto a supermassive black hole at the centre of a massive galaxy1,2. Because the optical luminosity of quasars exceeds that of their host galaxy, disentangling the two components can be difficult. This led in the 1990s to the controversial claim of the discovery of ‘naked’ quasars3,4,5,6,7. Since then, the connection between quasars and galaxies has been well established8. Here we report the discovery of a quasar lying at the edge of a gas cloud, whose size is comparable to that of a small galaxy, but whose spectrum shows no evidence for stars. The gas in the cloud is excited by the quasar itself. If a host galaxy is present, it is at least six times fainter than would normally be expected8,9 for such a bright quasar. The quasar is interacting dynamically with a neighbouring galaxy, whose gas might be feeding the black hole.

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Figure 1: HST images of the quasar and its immediate surroundings.
Figure 2: Two-dimensional VLT spectra of the quasar and neighbouring objects.
Figure 3: Spectra of the companion galaxy, quasar, and blob.
Figure 4: Intensity profile through the quasar position.
Figure 5: Upper limits on the host magnitudes.


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P.J. is on leave from GEPI. This work has been supported by the PPS Science Policy (Belgium), by PRODEX (ESA), and by the Swiss National Science Fundation. The observations were obtained with the ESO/VLT (Paranal, Chile) and with the NASA/ESA Hubble Space Telescope.

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Correspondence to Pierre Magain.

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Magain, P., Letawe, G., Courbin, F. et al. Discovery of a bright quasar without a massive host galaxy. Nature 437, 381–384 (2005).

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