Query : 2017A&A...603A..69G

2017A&A...603A..69G - Astronomy and Astrophysics, volume 603A, 69-69 (2017/7-1)

Exponentially growing bubbles around early supermassive black holes.


Abstract (from CDS):

We address the as yet unexplored issue of outflows induced by exponentially growing power sources, focusing on early supermassive black holes (BHs). We assumed that these objects grow to 109M by z=6 by Eddington-limited accretion and convert 5% of their bolometric output into a wind. We first considered the case of energy-driven and momentum-driven outflows expanding in a region where the gas and total mass densities are uniform and equal to the average values in the Universe at z> 6. We derived analytic solutions for the evolution of the outflow: for an exponentially growing power with e-folding time tSal, we find that the late time expansion of the outflow radius is also exponential, with e-folding time of 5tSal and 4tSal in the energy-driven and momentum-driven limit, respectively. We then considered energy-driven outflows produced by quasi-stellar objects (QSOs) at the centre of early dark matter halos of different masses and powered by BHs growing from different seeds. We followed the evolution of the source power and of the gas and dark matter density profiles in the halos from the beginning of the accretion until z=6. The final bubble radius and velocity do not depend on the seed BH mass, but are instead smaller for larger halo masses. At z=6, bubble radii in the range 50-180kpc and velocities in the range 400-1000km/s are expected for QSOs hosted by halos in the mass range 3x1011-1013M. These radius and velocity scales compare well with those measured for the outflowing gas in the z=6.4 QSO SDSS J1148+5251. By the time the QSO is observed, we found that the total thermal energy injected within the bubble in the case of an energy-driven outflow is Eth∼5x1060erg. This is in excellent agreement with the value of Eth=(6.2±1.7)x1060erg measured through the detection of the thermal Sunyaev-Zeldovich effect around a large population of luminous QSOs at lower redshifts. This suggests that QSO outflows are closer to the energy-driven limit than to the momentum-driven limit. We investigated the stability of the expanding gas shell in the case of an energy-driven supersonic outflow propagating within a dark matter halo with Mh=3x1011M at z=6. We found that the shell is Rayleigh-Taylor unstable already at early times and, by means of a simple model, we investigated the fate of the fragments detaching from the shell. We found that these fragments should rapidly evaporate because of the extremely high temperature of the hot gas bubble if this does not cool. Since the only effective cooling mechanism for such a gas is inverse Compton by the cosmic microwave background (CMB) photons (IC-CMB), which is important only at z≥6, we speculate that such shell fragments may be observed only around high-z QSOs, where IC-CMB cooling of the bubble gas can prevent their evaporation.

Abstract Copyright: © ESO, 2017

Journal keyword(s): black hole physics - quasars: supermassive black holes - shock waves - galaxies: high-redshift - galaxies: high-redshift

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 IRAS 11119+3257 Sy1 11 14 38.8902542640 +32 41 33.483258276   19.22 17.96     ~ 130 1
2 SDSS J114816.64+525150.3 QSO 11 48 16.647 +52 51 50.31   25.73 25.04     ~ 422 0
3 Mrk 231 Sy1 12 56 14.2341182928 +56 52 25.238373852   14.68 13.84     ~ 1894 3
4 QSO B1725-142 QSO 17 28 19.7893499760 -14 15 55.854918288   14.69 14.03 13.7   ~ 269 0

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