Polytropic transonic galactic outflows in a dark matter halo with a central black hole

Abstract

Polytropic transonic solutions of spherically symmetric and steady galactic winds in the gravitational potential of a dark matter halo (DMH) with a supermassive black hole (SMBH) are studied. The solutions are classified in terms of their topological features, and the gravitational potential of the SMBH adds a new branch to the transonic solutions generated by the gravity of the DMH. The topological types of the transonic solutions depend on the mass distribution, the amount of supplied energy, the polytropic index γ, and the slope α of the DMH mass distribution. When α becomes larger than a critical value α c , the transonic solution types change dramatically. Further, our model predicts that it is possible for a slowly accelerating outflow to exist, even in quiescent galaxies with small γ. This slowly accelerating outflow differs from those considered in many of the previous studies focusing on supersonic outflows in active star-forming galaxies. In addition, our model indicates that outflows in active star-forming galaxies have only one transonic point in the inner region (∼ 0.01 kpc). The locus of this transonic point does not strongly depend on γ. We apply the polytropic model incorporating mass flux supplied by stellar components to the Sombrero Galaxy, and conclude that it can reproduce the observed gas density and the temperature distribution well. This result differs significantly from the isothermal model, which requires an unrealistically large mass flux (Igarashi et al. 2014). Thus, we conclude that the polytropic model is more realistic than the isothermal model, and that the Sombrero Galaxy can have a slowly accelerating outflow.

Tidal disruption events can power the observed AGN in dwarf galaxies

“…In particular, one can obtain the typical outflow velocities and average velocities, pressures, as well as energy and momentum rates, which provide information on the expected observability of outflows, their escape from the galaxy and potential impact on star formation in the host. The expansion of outflows driven by wide-angle AGN winds and supernovae has been investigated extensively via 1D spherically symmetric numerical means (e.g., Sharma & Nath 2013;Zubovas & King 2016;Igarashi et al 2017;Dashyan et al 2018). In the Discussion section, I consider the possible effects of asymmetries in the gas distribution surrounding the black hole.…”

Galactic breeze origin for the Fermi bubbles emission

“…Beyond rc, for a positive numerator, a transonic outflow will accelerate while a subsonic outflow will decelerate. The behavior of a transonic outflow and its different solutions have been studied in a gravitational potential of a cold dark matter halo (Tsuchiya et al 2013;Igarashi et al 2014Igarashi et al , 2017.…”

A galactic breeze origin for the Fermi bubbles emission

“…Beyond rc, for a positive numerator, a transonic outflow will accelerate while a subsonic outflow will decelerate. The behavior of a transonic outflow and its different solutions have been studied in a gravitational potential of a cold dark matter halo (Tsuchiya et al 2013;Igarashi et al 2014Igarashi et al , 2017. Moreover a transonic outflow considerably reduces the ambient density whereas a subsonic outflow does not.…”