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A Giant Metrewave Radio Telescope/Chandra view of IRAS 09104+4109: a type 2 QSO in a cooling flow




IRAS 09104+4109 is a rare example of a dust enshrouded type 2 quasi-stellar object (QSO) in the centre of a cool-core galaxy cluster. Previous observations of this z = 0.44 system showed that, as well as powering the hyperluminous infrared emission of the cluster-central galaxy, the QSO is associated with a double-lobed radio source. However, the steep radio spectral index and misalignment between the jets and ionized optical emission suggested that the orientation of the QSO had recently changed. We use a combination of new, multiband Giant Metrewave Radio Telescope observations and archival radio data to confirm that the jets are no longer powered by the QSO, and estimate their age to be 120–160 Myr. This is in agreement with the ∼70–200 Myr age previously estimated for star formation in the galaxy. Previously unpublished Very Long Baseline Array data reveal a 200 pc scale double radio source in the galaxy core which is more closely aligned with the current QSO axis and may represent a more recent period of jet activity. These results suggest that the realignment of the QSO, the cessation of jet activity and the onset of rapid star formation may have been caused by a gas-rich galaxy merger. X-ray observations reveal a spiral structure in the intracluster medium (ICM) which suggests that the cluster is in the process of relaxation after a tidal encounter or merger with another system; such a merger could provide a mechanism for transporting a gas-rich galaxy into the cluster core without stripping its cold gas. A Chandra X-ray observation confirms the presence of cavities associated with the radio jets, and we estimate the energy required to inflate them to be ∼7.7 ×1060 erg. The mechanical power of the jets is sufficient to balance radiative cooling in the cluster, provided that they are efficiently coupled to the ICM. We find no evidence of direct radiative heating and conclude that the QSO either lacks the radiative luminosity to heat the ICM, or that it requires longer than 100–200 Myr to significantly impact its environment.