1109.6593 (S. Hocuk et al.)
S. Hocuk, M. Spaans
The conditions that affect the formation of stars in radiatively and
mechanically active environments are quite different than the conditions that
apply to our local interstellar neighborhood. In such galactic environments, a
variety of feedback processes can play a significant role in shaping the
initial mass function (IMF). Here, we present a numerical study on the effects
of an accreting black hole and the influence of nearby massive stars to a
collapsing, 800 M_sun, molecular cloud at 10 pc distance from the black hole.
We parametrize and study radiative feedback effects of hard X-rays emanating
from the black hole broad line region, increased cosmic ray rates due to
supernovae in starbursts, and strong UV radiation produced by nearby massive
stars. We also investigate the importance of shear from the supermassive,
10^6-10^8 M_sun, black hole as the star-forming cloud orbits around it. We find
that thermal pressure from X-rays compresses the cloud, which induces a high
star formation rate early on, but reduces the overall star formation efficiency
to about 7% due to gas depletion by evaporation. We see that the turn-over mass
of the IMF increases up to a factor of 2.3, M_turn = 1-1.5 M_sun, for the model
with the highest X-ray flux (160 erg s^-1 cm^-2), while the high-mass slope of
the IMF becomes Gamma > -1. This results in more high mass stars and a
non-Salpeter initial mass function. Cosmic rays penetrate deeply into the cloud
and increase the gas temperature (50-200 K), which leads to a reduced formation
efficiency of low mass stars. High cosmic ray rates increase the average mass
of stars, thereby shifting the turn-over mass to higher values, i.e., up to
several solar masses. Due to this process, the onset of star formation is also
delayed. We conclude that the initial mass function inside active galaxies is
different than the one obtained from local environments.
View original:
http://arxiv.org/abs/1109.6593
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