Space Grant Consortium - University of Wisconsin - Green Bay

and then can spiral in to the black hole. This accretion disk feeds the black hole and increases its
mass and once the black hole has accreted enough mass the AGN is triggered 'on'. The turning
on of the AGN sends out highly collimated beams of particles, accelerating to relativistic velocities
along magnetic field lines. These structures are called jets. The exact physics of how the AGN is
triggered, and the black hole transitions from dormant to active, are not quite clear and this is an
active area of study in astrophysics. For example, it remains unclear as to whether or not an AGN
turns on only once in it's lifetime, or whether it has a duty cyele where it turns on and off several
times. Also, although every galaxy has a black hole at the center, very few of them are actually
active. This may be simply because not all galaxies can have an AGN, or because the AGN in a
particular galaxy may be in a dormant phase of it's duty cycle.
It is through the interaction of the jet with the IGM that the AGN is believed to heat the IGM.
The exact method of energy transfer between the relativistic particles of the jet and the cool IGM
is not known exactly, but it is probable that the turbulent mixing resulting from the jet running in
to the surrounding medium is what heats the IGM gas.
What we have done is to consider the lowest mass group in our study at 10 13 Mev. Assuming
that the group virialized and began to cool llGyr ago, we allow it to cool for one cooling time
which for such a group is 4Gyr. During this time, the potential AGN host galaxy has enough time
to accrete a significant amount of mass on it's central black hole. We assume the AGN turns on
after one cooling time and remains active for 2 x 10 6 years, imparting lkeV of energy per particle
in the group. With this additional energy, the temperature - and therefore the cooling time - of
the group is increased. Figure 4 outlines the evolution of such a group, and it is evident from the
cooling times and temperatures that if the group evolves in this way then the temperature after
cooling to the present day is consistent with those of observed hot groups.
2.4. Emissivity & Luminosity
We performed another consistency check by calculating the peak luminosity of a group, given
the present day temperature. We used equations 6 & 7 to calculate the emissivity and luminosity
as a function of frequency. The frequency we used to calculate these was the peak frequency found
using Wien's Law, Amax 0.0029jT m·K.
Pavg = Eff
6.8e ­ 38Z 2 ngff -1 -3 -1
TO.5 e hvjkT ergss em Hz (6)
L (4j3)1T R3P avg (7)
The peak frequency came out in the soft x-rays, which is expected. The actual luminosities we
calculated were on the order of Lx = 2 X 10 16 W H z-l which is significantly lower than the observed
10 40 W H z-l of Croston et al 2005. But this is also consistent with our expectations in that we
did not include metallicity, and the most effective way of cooling and most prominent source of
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