Authors: P. Ogle et al.
Link to the paper: arXiv:1009.4533
The authors examine a sample of 55 radio galaxies with z < 0.22 and find 31% percent of those to exhibit particularly strong mid-IR emission from warm H2 (T = 100 - 1500 K, with masses in this phase typically around some 108, up to 2 x 1010 solar masses), putting them in a newly (re)defined class of "molecular hydrogen emission galaxies" (MOHEGs). They argue that the jets in these sources may interact with the cold H2 in these galaxies and shock-heat it, resulting in the observed emission. They find that X-rays originating from the AGN are incapable of powering the H2 emission, but that cosmic rays may still be an alternative explanation if a cosmic ray pressure 25 times higher than thermal pressure is deemed to be reasonable.
The radio MOHEGs show only low to moderate star formation rates (< 3 solar masses per year) and much less 7.7 µm PAH emission then normal star forming galaxies with respect to the mid-IR continuum (a factor of 10 - 100 lower). The H2 luminosity does not show much correlation with radio power, but several sources in clusters with X-ray cavities indicate that the ratio between H2 luminosity and kinetic jet power may lie around 10-4 to some 10-3. Most (14 of 17) radio MOHEGs belong to close galaxy pairs, groups or cluster and the authors conjecture that this environment or past gas-rich mergers may deliver large quantities of gas to the galaxies.
The authors conclude that jet-driven outflows may be responsible for the emission, although the details are yet very unclear. The jet powers, however, would more than sufficient for this.
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