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Quasars are extremely luminous sources powered by accretio n of gas onto a supermassive black hole in the nucleus of some galaxies. Most of the > 105 quasars identified in the literature have been identified in optical surveys through the "ultraviolet excess" (UVX) method. However, these samples are known to be incomplete and biased because of obsc uration and anisotropic radiation. To overcome some of these biases and search for candidate obs cured quasars, we matched radio sources from the FIRST 1.4 GHz survey with the 2MASS near-inf rared survey and selected objects with red optical-to-near-infrared colours. We follo wed up our candidates with optical and/or near-infrared spectroscopy and identified 119 dust-redden e quasars, defined as having at least one broad emission line in and a reddening of E(B−V)> 0.1. The sample spans a wide redshift range, 0.1< z< 3 and reaches a reddening, E(B−V) . 1.5. When corrected for extinction, red quasars are the most luminous objects at every redshift and t he fraction of red quasars increases with luminosity. The properties of red quasars suggest that they are revealing an evolutionary phase where the heavily obscured quasar is emerging from its dusty environment prior to becoming a "normal" blue quasar. We compute the fraction of qua sars that are in this red phase and determine that its duration is ∼ 20% as long as the unobscured quasars phase: a few million years.

The Reddest Quasars: A Transitional Phase in Quasar/Galaxy Co-Evolution