Reddened QSOs

Reddened QSOs are systems with exceptionally red UV/optical continua, in contrast to the traditional population of UV/optically bright QSOs. In order to explore the properties of this population, we have built multi-wavelength Spectral Energy Distributions (SED; UV to far-IR and radio; see Figure on the left) for a sample of reddened QSOs selected in the 2MASS. Fitting templates to the observed SEDs is a powerful diagnostic of the nature of these sources. We find evidence for (i) moderate dust extinction (A_V~1-3), which is responsible for the red UV/optical continua (ii) star-formation activity in the host galaxy, which proceeds at a higher rate than in UV/optically bright QSOs of similar luminosity and (iii) a higher fraction of radio sources among reddened QSOs suggesting outflows.

The findings above are consistent with suggestions that reddened QSOs represent an early stage of the evolution of active supermassive black holes. In this picture AGN are born in a cocoon of dust and gas clouds, which eventually will be blown away by the energy output from the central engine. This allows the active supermassive black hole to shine unobscured for short period of time (UV/optically bright QSOs). This process will also terminate the star-formation in the nuclear regions of the host galaxy, as the gas, the raw material to form stars, is swept away. Reddened QSOs are systems shortly before or during the blow-out stage in the scenario above.

The figure on the left shows the template fits to the panchromatic SEDs of reddened QSOs, following the methodology developed by Rowan-Robinson et al. 2008.