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15-05-2009
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B2 0722+30: A classical radio source hosted by a disc galaxy

Submitter: Bjorn Emonts (ATNF)
Description: At low redshift, classical double-lobed radio sources are almost always hosted by early-type galaxies. Our group, including researchers at ASTRON (Raffaella Morganti and Tom Oosterloo), has found that the nearby radio galaxy B2 0722+30 belongs to a very select group of disc-dominated radio galaxies. Using the Very Large Array in New Mexico (HI imaging), the William Herschel Telescope at La Palma (optical spectroscopy) and the MDM 2.4-m Hiltner Telescope at Kitt Peak (deep optical imaging), we established that the radio galaxy B2 0722+30 is very unusual. This object, known to have a classical edge-darkened radio morphology with an optical AGN, is hosted by a late-type galaxy with a gaseous disc with ongoing star formation and a relatively high far-infrared luminosity.

The host galaxy B2 0722+30 is a relatively small late-type galaxy with only an average-mass bulge, indicating that the intrinsic black-hole mass is likely to be similar to that of 'normal' spirals. The most likely explanation for the existence of this radio source is related to gas-rich interactions with companion galaxies. Evidence for this is found in the large-scale distribution of the neutral hydrogen (HI) gas in the environment of B2 0722+30 (see Figure). Interestingly, the radio-jet axis is not aligned with the rotation axis of the disc, but along the direction of an HI bridge towards the peculiar galaxy pair MRK1201/UGC3841a. This offers the interesting possibility that an interaction with this pair may have cleared a path for the radio source to escape the host galaxy, possibly in combination with an induced precession of the accretion-disc/jet-axis in this direction.

Exploring rare examples of disc-dominated radio galaxies like B2 0722+30 may reveal vital clues as to what mechanisms can cause the onset of radio-loud AGN in nearby galaxies. This will provide valuable information for understanding the importance of AGN activity also at high redshift, for which recent studies suggest that disc-dominated radio galaxies may be much more common than in the nearby Universe.

This study is presented in a paper that is now in press in the Montly Notice of Royal Astronomical Society (Emonts B., Tadhunter C.N., Morganti R., Oosterloo T., Holt J., Brogt E., van Moorsel G. MNRAS in press, http://arxiv.org/abs/0904.3381).

FIGURE CAPTION: Contours of the total intensity map of the neutral hydrogen gas overlaid on to a deep optical B-band image of the environment of radio galaxy B2 0722+30 (left). Several galaxies of interest are marked A,B,C,D and are shown in more detail in a three-colour BVI representation on the right. The contours of the radio continuum in B2 0722+30 (galaxy 'A') are taken from Fanti et al. (1986)
Copyright: Emonts/ATNF
 
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