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Constraining the dynamical importance of hot gas and radiation pressure in quasar outflows using emission line ratios | | Jonathan Stern
; Claude-Andre Faucher-Giguere
; Nadia L. Zakamska
; Joseph F. Hennawi
; | | Date: |
Mon, 26 Oct 2015 21:21:48 GMT (1867kb,D) | | Abstract: | Quasar feedback models often predict an expanding hot gas bubble which drives
a galaxy-scale outflow. In many circumstances the hot gas is predicted to
radiate inefficiently, making the hot bubble hard to observe directly. We
present an indirect method to detect the presence of a hot bubble using
hydrostatic photoionization models of the cold (10^4 K) line-emitting gas.
These models assume that the cold gas is in pressure equilibrium with either
the hot gas pressure or with the radiation pressure, whichever is larger. We
compare our models with observations of the broad line region (BLR), the inner
face of the dusty torus, the narrow line region (NLR), and the extended NLR,
and thus constrain the hot gas pressure over a dynamical range of 10^5 in
radius, from 0.1 pc to 10 kpc. We find that the emission line ratios observed
in the average quasar spectrum are consistent with radiation-pressure-dominated
models on all scales. On scales <40 pc a dynamically significant hot gas
pressure is ruled out for an average quasar spectrum, while on larger scales
the hot gas pressure cannot exceed six times the local radiation pressure. In
individual quasars, ~25% of the objects exhibit narrow line ratios that are
inconsistent with radiation-pressure-dominated models by a factor of ~2, though
in these objects the hot gas pressure is also unlikely to exceed the radiation
pressure by an order of magnitude or more. The upper limits we derive on the
hot gas pressure imply that the instantaneous gas pressure force acting on
galaxy-scale outflows falls short of the time-averaged force needed to explain
the large momentum fluxes dot{p} >> L_AGN/c inferred for galaxy-scale outflows
in luminous quasars. This apparent discrepancy can be reconciled if the optical
quasars observed today previously experienced a buried, fully-obscured phase,
(abridged) | | Source: | arXiv, 1510.7690 | | Services: | Forum | Review | PDF | Favorites | |
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